ELFIN III FINAL REPORT

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-05288A000100020001-9
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 119
• Document Creation Date: December 23, 2016
• Document Release Date: August 14, 2013
• Sequence Number: 1
• Publication Date: August 1, 1963
• Content Type: REPORT

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CONFIDE
NTIAL
DOCIJMNT NO.
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DATE: '42,45 si"L::_?? REVIEWER: 0371 _
CONFIDE\ RA
ELFIN III FINAL REPORT
1 August 1963
CONF DEHNT1AL
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El
a
I. INTRODUCTION AND SYSTEM CONCEPT
The purpose of the Elfin program is to develop electroplating
techniques for the passive integration of microwave field intensities.
The word Elfin itself is an acronym derived from electromagnetic-
field-integration. Elfin I was a program to investigate the feasibility
of developing electroplating cells hereafter called E-Cells, to inte-
grate DC currents at high sensitivity. In particular, a sensitivity
was specified such that the E-Cell would reproducibly measure an
electric charge with an accuracy of one-tenth microcoulomb. E-Cells
weresiemeJaped under the Elfin I ?ro ram which ha ensitivit
two orders of magnitude greater than the original goal. Currents
smaller than a millimicroampere can be integrated with E-Cells to
an accuracy of approximately 1 millimicrocoulomb.
The Elfin II was a program to develop an instrument to measure
microwave field intensities at hazardous levels. This program,
supported by the Navy, developed instruments which would provide
a digital readout of the integrated microwave energy over a thirty
second time interval. This phase of the program is continuing with
instruments currently being tested which provide acoustic warning
signals when the integrated power level exceeds certain specified
values.
The present report is the Final Report of the Elfin III program
which had as its goal the development of small passive integrators to
measure very low microwave field intensities. The range of field
intensities which are of importance for this program are in the
region of one-tenth to one-hundredth of a-microwatt per square centi-
meter. The goal of the Elfin III program was to produce such devices
and demonstrate the feasibility by means of field tests. A subsidiary
goal was to investigate the feasibility of determining the frequency
of the microwave field by noting the realtive signal integration using
antennas tuned to different wavelehgths.
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The goals of the Elfin III program have been substantially
met, as stated above, with devices having been constructed which will
measure microwave field intensities at distances from 1000 to 5000
feet from a radar antenna. Indication has also been obtained that the
frequency of the radar can be determined by these techniques to an
accuracy of approximatel 0-_?'. ''? . ? - ? - ion to
T.-6=e accumulated charge in the E-Cells has also been constructed
and tested under field conditions.
The Elfin device for measuring low intensity microwave fields
consists in its simplest form of an antenna, a diode, a switch and
an E-Cell for integrating the current generated by the diode. Some
improvement in sensitivity is added if a small capacitor is connected
in parallel across the diode when narrow pulses are to be integrated.
The feasibility tests of the Elfin devices have been completed and the
design sufficiently established that operational equipment can now be
constructed to operate with a high degree of reliability.
The remainder of the report is divided into several sections
and two Appendices. These sections describe tests performed on
diodes and E-Cells of different designs and the selection of components '
?for the final field tested equipment. A description of the field test
equipment is provided and instructions for using the various components.
The first Appendix contains a very brief summary of the large volume
of electrochemical research which went into the development of the
latest version of the E-Cell being used in the Elfin devices. The
second Appendix is a discussion of the application of E-Cells to timers
and is included because of its general qualitative discussion of E-Cell
characteristics and circuitry to be used with E-Cells. A reader not
familiar with many of the concepts associated with the E-Cells would
be advised to read this discussion of cell characteristics in Appendix
B before undertaking the remainder of this report.
2
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2, DIODE TESTS AND MICROWAVE EQUIPMENT
In addition to the E-Cell the device requires an antenna diode,
a capacitor, and a switch. Of these additional components the diode
is the most critical. For the sake of simplicity, it was decided to use
a microwave video diode which is enclosed in a small glass bead
with leads protruding from either end rather than the cartridge type
which has to be mounted in a special container coupled to coaxial
cable. By using the diode with leads extending from each side it
was necessary only to trim the leads to the proper length in order c?4 aital
that the diode could serve as a half-wave dipole antenna. Two wires
2
0
sodered to these leads at right angles serve as the DC pa h to the
E-Cell so that no microwave linkage is needed in the system elimina-
ting coaxial connections and waveguide.
Before a diode was chosen for this system, tests were con-
ducted on several potential diodes to find the one most suitable for
the application in mind. It had been found in previous work that at
very low current levels the E-Cell acts as a relatively large resistance
compared to its behavior at higher current levels. Since we would
be operating at low field intensities the current generated by the
diode would be relatively small and for that reason high sensitivity
E-Cells were developed. The increase in resistance of the E-Cell
at low current level also occurs for diodes for the same theoretical
principle., This can be seen in Figure 2. 1 which gives typical values
for open circuit voltage and short circuit current of the diode at
various power levels. It will be seen that the internal resistance of
the diode is approximately 15K at a power level of 1 microwatt
whereas it is less than 1K at a milliwatt? Since the high sensitivity
cells which were developed under the previous phase of the program
had a resistance at very low current levels of 1 megohm the diode resis-
tance becomes relatively unimportant and the current through the E-Cell
is determined primarily by the open circuit voltage of the diode.
Therefore, this is the factor which is considered in evaluating the
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MICRO-
AMPS
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relative merits of the diodes.
Before the glass diodes were tested, an experiment was set
up to measure the characteristics of a IN23C diode which is a capsule
mounted diode unsuitable for our application but useful in some lab-
oratory measurements. Its characteristics were found to be very
similar to those shown in Figure 2. 1 and will not be repeated here.
Figure 2.2 shows the microwave setup used for making these measure-
ments. The agreement with the data in Figure 2. 1 provided some
confidence that this means for making the open circuit voltage
measurements was relatively sound. A 5.6 gigacycle Klystron
was coupled by means of waveguide into a PRD variable attenuator
with an absorption type frequency meter coupled to the waveguide.
Beyond the attenuator was a waveguide section in which one quarter
of one percent of the energy in the waveguide was picked off and
coupled into a Bolorneter to monitor the output power of the Klystron.
The main portion of the power passed through a fixed attenuator to
reduce the power level sufficient for diode detection, The diode was
mounted in a section with a stub tuner which was tuned to provide
maximum voltage output from the diode at a fixed power level of the
Klystron. The current from the diode passed through a 1 megohm load
and a Hewlett-Packard microvolt ammeter.
The microwave equipment setup used for making the measure-
ments on the glass diodes was very similar to that shown for the IN23C
diode and is illustrated in Figure 2.3. In place of the fixed attenuator
and diode mount a 10 DB horn was mounted on the end of the waveguide.
The diodes were then tested by cutting their leads so that the length
of the diode would be resonant to the Klystron frequency, the length
being one-half the radiated wavelength. DC pickoff leads were then
sodered to the resonant diode leads in the manner that they would be
used in operation. However, rather than passing the current from
the diode through an E-Cell, it was passed in series through a 1
megohm load. The voltage acros.s the 1 megohm resistor was monitor-
ed by the same microvolt ammeter used before.
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F= 5.6 gc.
.KLYSTRON
POWER
SUPPLIES
PRD
VARIABLE
ATTENUATOR
PRD
FREQ
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PRD
WAVE GUIDE
PRD
BOLOMETER
HP 430 C
RF Power
Meter
IN23C DIODE CURRENT MEASUREMENTS
TEST SET-UP BLOCK DIAGRAM
Figure 2, 2
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MICRO-
AMMETER
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POWE.R,
Supplies
pRD
FREQ
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METER
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TEST SET-UP
Figure 2. 3
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MICRO
.Ammete
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Three diodes were chosen from those available in the literature
on the basis of their predicted performance for video operation at
the microwave frequency and power levels under consideration. The
results of these measurements on the MA 4123A, MA 4123, and IN833
diodes are shown in Figure 2.4. The Microwave Associates diode
MA,-44ed about a factor of two ?-n e other two
for 1 ?? . - e o'ff----1173(7---le that -wa
for our experimental equipment.
It will be noted from the data that the results for these diodes
are about an order of magnitude less than the voltage reported as
being typical in Figure 2.1. This is the result, however, of the fact
that the RF power given as the independent parameter in Figure
2. 4 is actually the total power being radiated from the 10 DB horn
?and is not the power intercepted by the diode, Although the diode
antenna combination was placed very close the to aperture of the
horn, the fact that it received only about one-tenth of the radiated
power is quite reasonable. Indeed external monitoring of the radiated
_ _
power with and without the diode in place showed no significant
difference.
2--
These voltage measurements were made with the Klystron
operating in the CW mode so that they do not reflect the peak vol-
tages which would be obtained for the same average power level if
a pulsed source were used. Such peak voltages would not be readily
measured at the lower levels with the microvolt ammeter because
of its long integrating time constant. It will be noted, however, that
the CW voltage generated by the diode at the 20 microwatt CW level
?is approximately 10 millivolts. An esti-nate of the spread of the
energy out of the 10 DB horn allows one to make an estimate of the
power density at the diode. 20 microwatts radiated power over
200 sq. cm, area yields a power density of approximately one-tenth
microwatt per square centimeter which is typical of the field intensi-
ties which will be foundin practice. Therefore, one should expect
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1000
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LDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
peak voltages out of the diode in excess of 10 millivolts. This is
important since pp.revious work with the E.-Cells indicated that voltages
below 10 millivolts are very ineffective fc_21:_pas_aing cur_r_ezzts--th.r-augh___
cefl This question will be examined in more detail in a later
section.
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LDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
3. TESTS ON B-CELLS
3, 1 INTRODUCTION
The first phase of the Elfin program was concerned with the
development of an electroplating integrator subsequently called the
E-Cell which would integrate currents as small as a tenth micro-
ampere and reproducibly measure charge to the order of one-tenth
microcoulomb. During the course of that program successive steps
were made in improving cell sensitivity so that ultimately currents
smaller than one millimicroampere could be integrated with charge
sensitivity of the order of one millimicrocoulomb, two orders of
magnitude beyond that which was required.
? However, the analysis of the application which indicated the
one-tenth microcoulomb sensitivity requirement assumed a cell re-
sistance which was somewhat lower than the actual cell resistance
encountered. It was also found that the more sensitive cells had
higher internal resistances so that their sensitivity was offset by
the fact that smaller currents would automatically be passed through
them when a constant voltage source was applied. More specifically,
c-11 resistance of 10 K was assu n the sensitivit analysis and
resistances of a
? ?
tive B-Cells at o
roxi
?
obtained in the sensi-
ere current level. There-
fore, the increased sensitivity of the cells nearl cam ensated for
the i cxn sensitivity requirement due to the lar gr cell resistance.
Nevertheless, with this consideration it still appeared practical to
meet the operational system requirements of integrating very small
microwave field intensities.
In addition to the large resistance problem with the high
sensitivity B-Cells, other problems were observed when the cells
were used in other than controlled laboratory operation. There were
periods in which the cell operation appeared quite erratic and a batch
of cells would not yield consistent results among the individual mem-
11
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jDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
bers. Furthermore, if silver were deposited on to one of the electrodes
and allowed to stand overnight the recovered silver was often not very
close in quantity to the original plated charge.
All of these characteristics indicated that much work would
need to be done to take the laboratory type cell and convert it into
a device which would be reliable under a variety of field operating
conditions. Many of the experiments which were done on the high
sensitivity B-Cells are summarized in the fo-llorwing- s-ections to illustrate
---------------
the problems which led to the eve 6-Pment of a cell af?s_am.e_w_hat_leS s
sensitivit ? eliabi an
stics
to the microwave diode. This neweak the DB-Cell, ?is described
in more detail in Section 4.
3.2 SENSITIVITY TESTS OF B-CELLS
Tests were made on B-Cells containing 0. IN Ag NO3 electo-
lyte. Several freshly prepared cells were tested for sensitivity to
low levels of applied voltage and current, revealing unexpected
characteristics. An attempt was made also to test several cells
that had been stored for approximately fifty days, but they could
not be made operational.
Voltage and current for the cells were supplied by the labora-
tory cell testing unit. Continuous measurements were made with two
Hewlett-Packard Model 425A DC microvolt ammeters, one mea-
suring the current and the other the voltage. The outputs of these
meters were used to operate a Sanborn Dual Channel DC amplifier-
recorder. This unit provided a continuous plot of the voltage and
current versus time.
Stored Cells
Measurements were made on five cells which had been stored
for a period of approximately fifty days, An open-circuit voltage
(E0) of 100 millivolts and a short-circuit current (Is) of 1.0 microamps
12
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uDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
were used as the power source. The results for each cell were the
same: as the silver deposit was transferred successively from one
electrode to the other, the amount transferred consistently diminish-
ed with each transfer until finally no measurable current flowed
through the cell. The applied voltage was then varied from 10 my
to 500 my, but no appreciable current could be detected.
Cell B-34
This cell was freshly prepared on 29 January, 1963, and tested
on 31 January, 1963. The conduction values of current (I) and
voltage (E) were obtained from the Sanborn Recorder plots for given
values of E and Is.* R is the conduction resistance of the cell cal-
culated from the average values of E and I for each transfer (a
transfer is defined as the time interval during which silver is trans-
ferred from one electrode to the other). In cases where E and I
changed significantly during successive transfers for a given value
of E0' the maximum and minimum averages were recorded. Figure
3.1 is a plot of conduction resistance versus E0 using the data obtained.
The various effects resulting from the tests are discussed in
the following paragraphs. In all cases, measurements with E0 less
than 100 my were begun with approximately half the total silver deposit
on each electrode.
a. In the first series of runs (a run consists of measure-
ments at a given E0) it was found that when E0 was reduced from
100 my to 1 my and then increased, no measurable results were ob-
tained until E0 became 30 my. However, when E0 was decreased
following the 30 my run, significant measurements were obtained
down to 10 my. At this point the series was concluded.
b. In the second series of runs on this cell readings at
20 my and above were found to be consistent with the first series
E0 - -
of data. Below 20 my, it was found that by preceding each run with
a run at 100 my, significant result's were obtained for the smaller
Open'circuit voltage and short circuit current.
13
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
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14
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uDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
values of E0? If E0 was decreased directly to successively smaller
values, either no cell current could be measured or it would decrease
from a measurable value to insignficance after two or three transfers
of a run.
c. Another effect noted was a change in the total charge
being transferred with different runs at E0 = 100 my. The charge
transferred in the initial run of the first series, E0= 100 my, shall
be taken as 100% charge transfer for purposes of discussion. Sub-
sequent runs at E0 = 100 my (all in the second series) yielded charge
transfers of 95%, 78%, 90%, 78%, 79%, and 65%, respectively.
Preceding the run yielding 65%, a run was made with E0 = 500 my
(prior to this run, E0 was never greater than 100 my), The 500 my
run gave 82%, 79%, and 75% values in three successive charge
transfers. Then E0 was returned to 100 my and the last run was
made, giving three successive transfer values of 68%, 65%, and 63%;
i. e., after 500 my was applied to the cell, the total charge transfer
consistently decreased with subsequent transfers. No data was ob-
tained for total charge transfers with E0 less than 100 my. Figure
3.2 compares a transfer of the initial run at 100 my to the first trans-
fer of the final 100 my run.
d. A study of the Sanborn plots of current versus time reveal-
ed that after some of the runs with E0 other than 100 my, the initial
transfer that occurred when E0 was again made 100 my had a "tail";
e., towards the end of the transfer the current dropped sharply
to about 70-80% of its peak value and continued at this level for a
period of time. This effect was most pronounced after the success-
ful 1.0 my run. In the 100 my run which followed, the tail appeared
in four successive transfers, and in fact, appeared to increase with
each transfer. In the third transfer of this run, the tail accounted
for about 15% of the total charge. Figures3. 3 and 3,4 illustrate this
effect for 100 my runs which followed runs at 1.0 my, 10 my, and
Current is on the left and voltage on the right. Time
runs from bottom to top at one millimeter per second.
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
Figure 3. 2 16
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
Figure 3. 3
1
17
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1
Figure 3. 4
18
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
LI
ill
30 my. These should be compared with the initial transfer of Figure
3, 2. Note also in Figure 3. 2 the tail on the transfer which followed
the 500 mv run.
e. . AtE0 - 1 my and less, the conduction resistance
-
of the cell was found to consistently increase within a run. That is,
the transfer current decreased and the transfer voltage increased
with successive transfers for a given value of E0. For values of
E0 between 10 my and 100 my, this effect could not be determined
due to an insufficient number of transfers per run. At E0 = 100 my,
the conduction reistance appeared to decrease slightly with successive
transfers, but this is believed due to a "dip" effect discussed in the
next paragraph. However, the aggregate of runs at E0 = 100 my
showed a trend of increasing conduction resistance with each run
until the 500 mv run was made. In the 100 my run which followed
the latter, the conduction resistance was less than in any of the previous
100 my runs, while at the same time, it increased slightly with
successive transfers. Figures 3. 5 and 3.6 show the trend of increas-
ing resistance at E0 = 10 mv (note: the current scale has been
decreased in Figure 3. 6).
f. When the initial condition of the cell consisted of part
of the silver deposited on each electrode, a "dip" phenomena occurred
after the silver was transferred completely to one electrode. To
illustrate this effect, assume one-fourth of the silver is on the right
electrode and three-fourths on the left electrode. The first transfer,
say from right to left, deposits the fourth of silver from the right
onto the left electrode. Then a total transfer is made from left to
right. As the point at which the original condition existed (1/4 R -3/4L)
is reached during the transfer, the conduction resistance increases
approximately 10-20% and then returns to its previous value of the
transfer, forming a "dip" in the current and voltage time plots.
Subsequent transfers are then normal (no "dip"), with a slightly
lower value of conduction resistarice. Total transfers were made .
with the above initial conditions only at 100 mv,. and the effect was
19
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uDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
... : ..... .
===.=
-
;.:
........
.? :
-? ?IiiiL
*: ' ?
Figure 3. 5
;.:
I :
:.?
:::: ?
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,
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
?
0000 000
00000000000
0_._,
00 . mm 00
0 01111 26"-6011
0
0000000 000000000
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ri
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:
Figure 3.6 21
Declassified. in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
U.
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-7
observed in every case. It occurred with various initial distributions
of silver deposit and appeared independent of whether the first
transfer was made right to left or left to right. Figure 3.7 is a plot
of the "dip" effect.
Cell B-35
This cell was freshly prepared on 29 January, 1963, and
used for some preliminary test on 30 January. The measurements
of this report were made on 31 January, at which time the cell displayed
a pronounced effect of consistently decreasing the total amount of
silver transferred, whatever value of E0 was applied. Taking the
initial transfer of the first run at 100 my as 100%, the last transfer
of the fourth run (also at 100 my) was found to have decreased to
30% of the initial, value. Total transfers were not made at values of
E0 less than 100 my.
Readings were obtained with this cell down to E0 = 10 my,
where E0 was decreased directly to this value from 50 my. The
procedure used with cell B-34 of returning to 100 my before proceeding
to small values of E0 was not used with this cell, and readings were
not obtained at 1.0 my, the next run attempted after 10 my.
Figure 3. 8 is a graph of conduction resistance versus E0
for the cell, obtained from the data. The single value of R plotted
for E0 = 10 my is assumed questionable, based on information obtained
from cell B-34.
Conclusions
To summarize the effects discussed above:
a. When E0 was initially decreased from 100 my to 1 my,
and then increased to 5 my, 10 my and 20 my, negligible current flowed
at any of the values below 100 my. At 30 my satisfactory results were
obtained; E0 was then decreased to 20 my and 10 my with positive
results.
b. Below 20 my, when E0 was returned to 100 my before
22
Li
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
?
Declassified in Part - Sanitized Copy Approved for Re ease 2013/08/14: CIA-RDP78-05288A000100020001-9
i??:
?':
_..1:1::
ealH7[7Z
Figure 3. 7
23
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!Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
10
9
6
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Figure 3. 8
5 6 7 8 8110 0
2 3 4 5 6 7 816 Ofb
24
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
bDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
Li
.11?-?-?
Li
r?
L-1
fl
LJ
going to each of the smaller values, performance was greatly im-
proved over the results obtained when E0 was decreased directly to
the smaller values.
c. Total charge transfer decreased with subsequent
runs at 100 my. After 500 my was applied, successive transfers
consistently decreased in amount of charge.
d. "Tails" occurred on 100 my total transfers after some
runs at other values of E0, This was very pronounced after the 1.0
my run.
e. Below 10 my, the conduction resistance of successive
transfers consistently increased within a run.
f. "Dips" occurred in transfers at 100 my when the silver
deposit was initially on both electrodes.
The results indicate inconsistent operation of the cells may be
expected below 30 my. While some of the difficulties encountered
at low voltages might be overcome by operational techniques, the
effect of increasing conduction resistance with time would seem a
difficult problem to solve in this manner. In addition, no information
was obtained concerning the effects of prolonged time intervals
between transfers.
3,3 B-CELL R. F. POWER MEASUREMENTS
A freshly prepared cell, B-35, was tested for response to
a microwave power source. The R. F. power, at a frequency of
5. 6 kmc, was detected with a IN23C crystal diode in a PRD microwave
detector. Figure 3.9 is a block diagram of the test setup.
The general procedure was to first transfer all the silver
of the cell to one electrode, then transfer approximately half back
to the other electrode, the exact amount being determined from the
Sanborn current time plot. The laboratory test unit was then dis-
connected and the cell connected to the diode. The R. F. power was
then turned to the desired power level (by, changing the attenuator
25
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14 : CIA-RDP78-05288A000100020001-9
E:=1 C3 =1
Klystron
PRD
Variable
Attenuator
PRD
Frequency
Meter
PRD
Wave
Guide
PRD
Bolometer
HP430C
RF
Power
Meter
Fixed
Attenuator
PRD
IN23C
Diode
Detector
Figure 3. a RF Power Measurements With
B-Cells Test Set-Up.
- -1
Micro
1.
1Am
_
_m_e_ter
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Sanborn
Recorder
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
U
setting) for the specified exposure time. The last step was to
reconnect the lab test unit and transfer the remaining silver back to
the original electrode. The amount of this final transfer was determined.
from the Sanborn current time plot. In all runs with the lab test unit,
the open circuit voltage E0 was 100 my and the short circuit current
Is was 1.0 microamps.
The difference between the transfers before and after the R. F
was applied to the cell is the amount of charge deposited by the R. F.
diode current. Thus, the diode current may be calculated.
The first set of measurements was obtained using a micro-
ammeter with a 10 KO internal resistance in series with the cell
and diode. The data is given in Table 3, 1. Due to the experimental
procedure used, there was a possible error of +20% in the exposure
time. Thus, the current calculated from the charge transfer is
in agreement with the measured current through the cell. These
measurements were made only at the relatively high current levels
shown in the table to establish the correct operation of the cell at
a level known previously to give good response.
The second set of measurements, Table 3.2 was then made
to determine the cell's response to low R. F. power levels. The
ammeter was removed from the circuit and the cell connected directly
across the diode. The R. F. power input to the diode detector was
measured and the cell current calculated from the resulting charge
transfer.
Multiple readings were taken at power levels of 16.9 mw,
15.0 mw, and 13,4 mw at various exposure times. It can be seen
from the table that consistent results were not obtained in this region.
This might be due in part to the procedure used in setting the R. F.
power level for each run. The attenuator was varied from maximum
attenuation to the desired reading at the beginning of the run and re-
turned to maximum attenuation at the end, This allowed considerable
error in the exposure time and the attenuator dial setting. The error in
the attenuator setting is estimated at -- 0. 5 db. However, previous
27
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
Li
TABLE 3.1
R. F. MEASUREMENTS -- CELL B-35
Run
Measured
Exposure
Calculated
%
Number
Diode Current
Time,_
Diode Current
Error
(amps)
(sec) 2-20%
From Cell
(p.amps)
1.
1.0 pa
15 sec
1.13 p.a
+13%
2.
1.0 p.a.
15 sec
1.10 p.a
+10%
3.
1.0 p.a
15 sec
1.23 p.a
+23%
4.
1.0 p.a
15 sec
1.04 p.a
+ 4%
5,
0.50 [la
15 sec
0.51 p.a
+ 2%
28
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ci
II
ii
Ii
Table 3.2
RF Measurements - Cell No. 35
(Measured RF Power)
Run
No.
RF RF Diode Exposure RF Diod
Power E0 Time Current
(p.watts) (millivolts) (s ec) + 3 sec. (p,amps)
134 p.w 270 my 15 sec. 1.23 p.a
86
53.5
200
140
15
15
1.0
0.37
??
33.6
90
30
0.13
5,
13.4
42
60
0.050
6.
13.4
42
120
0.017
7.
21.2
63
120
0.14
8.
13.4
42
180
9.
16.9
50
120
0.16
10.
16.9
50
60
0.099
11.
15.0
46
120
0.054
12.
15.0
46
180
0.038
13.
13.4
42
300
0.056
14.
13.4
42
180
0.0067
(Calculated
? from
Cell read-out)
29
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
work a. s shown them to be inconsistent at applied
voltage levels below 50 my, which corresponds in this case to power
levels below 20 microwatts.
3.4 B-CELL FIELD TESTS
Five high sensitivity B-Cells were prepared for field test-
ings. These were cells B-27, B-29, B-32, B-33, and B-34. The cells
had been prepared in the manner of previous laboratory experiments
and filled with one-tenth normal silver nitrate solution. The cells
were each charged with approximately 20 microampere seconds of
silver on each electrode. Then the cells were sealed with Teflon
tape. The current source in the field was an S-band antenna, a tunable
crystal diode mount containing a IN23C diode, and external leads to
which the B-Cells were attached. The tests were conducted at the
Los Angeles International Airport Radar Facility. A sketch of the
facility is shown in Figure 3.10. A low sensitivity microwave radia-
tion monitor using A-Cells rather than the high sensitivity B-Cells,
was also taken along on the test. This instrument gave integrated
reading at Positions 1 and 2 shown in the figure. No reading was
obtained in Position 3. The B-Cells were all exposed one hundred
feet from the antenna at Position 4, as shown in the figure. They
were exposed for a range of time intervals from a few seconds up
to several minutes. Figure 3.11 is a Xerox reproduction of a
photograph showing an exposure taking place. The antenna diode
and cell combination was hand held for all the exposures.
The airport radar radiates at a frequency approximately
2900 megacycles with pulses 1 microsecond wide and a pulse
repetition frequency of approximately. 1000 pulses per second. The
antenna gain was given to be 34db with a 1 1/2? beam width in the
azimuth. The maximum of the beam is tilted approximately 3?
above the horizontal. The average power of the antenna was given to
be approximately 290 watts with a' peak power close to.500 kilowatts.
The antenna rotates once every twelve seconds.
30
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88th Street
[ Declassified in Part- Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9 1 C---1 LI -
RESIDENTIAL AREA
Fence
Gate
5'x5' tSteel
Tower
Car
Radar
Shack -
0
Steel
Platform
Radar
-?1
? LAX FAA SEARCH RADAR FACILITY
? Figure 3. 10
Circled numbers indicate
locations of rf measure-
ments.
Approximate scale -
1/41! , = 10'
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uDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
Figure 3. 11
32
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
The B-Cells were rged with silver in the lab prior to
being taken to the radar si-gh-t?and were brought back to the lab for
discharge and determination of the integrated current. Figures
3.12 and 3.13, respectively, show the charge process and the dis-
charge record for cell B-29. These are the current-time and voltage-
time plots taken with the Sanborn recorder. In Figure 3.12 it will
be noticed that the silver was put upon the right electrode and then
integrated from right to left, from left to right again, and then appro-
ximately half the silver from right to left. When the cell was brought
back to the laboratory, the plating from right to left was continued
and then re-cycled from left to right, then right to left.
It will be noticed on this particular cell that the sum of the
integrals before and after the radar exposure is very, close within
the experimental error to the total integral of charge put on the electrode.
In other words, no de of silver occurred during
expia_s_i___Ire at the radar sight_ The "dip" effect will be noticed during
the plating period shown in the center of Figure 3.,13. The result
for cell B-29 is typical of the results for all five cells and in no case
was a detectable amount of plating measured during this field test.
Previous results and subsequent analysis in the laboratory
with the cells using a laboratory source which closely simulated the
airport radar revealed that the cell resistance at low power levels
was too large and its integration of narrow pulses too poor to have
produced measurable results under the operational situation describ-
ed for the test. The results of this test and other laboratory investiga-
tions, some of which are described above, suggested strongly that
another cell be built which would have characteristics which better
matched the video diodes being used and the field intensities which
it would be necessary to measure.
This test also indicated that it would be desireable to have
equipment in the field which could provide readout for the cells in
order to save considerable amount of time in transportation between
the radar sight and the laboratory. Laboratory tests also indicated
33
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LiDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
FigureU.
U.
U.
3. 12
34
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
m
m
Figure 3. 13
35
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
that it would be advisable to have a reflector behind the antenna to
eliminate the effects of interference behind the antenna. Imple-
mentation of these recommendations is described in the following
sections.
1
36
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
U.
4. DB-CELL TESTS
4.1 DB-CELL DEVELOPMENT
Concurrent with the microwave experimentation both in the
lab and in the field on B-Cells and diodes and their combination,
work was performed in the
of somewhat less sensitivity than the B-Cell but with
resistance and more stable behavior. These experiments resulted
? e e
evelo
in the cell which is desi nated
? - I!
,7zize and shape, and B is to icte the hi h sensitivity of the B-
cells.
The construction and preparation of the B-Cells is described
in the final report of Phase I of the Elfin program. These cells used
three mil platinum electrodes which were rather fragile. The DB-
Cell, on the other hand, uses ten mil platinum electrodes which are
clipped short near the glass base bonding the electrodes into the cell.
The electrode area is consequently not so small as for the B-Cells
and the sensitivity is therefore somewhat less. However, the cell
r_
does have a lower resistance and higher internal ca acitance. This
inter
ids the integration of nar
microwave source.
The DB-Cell has three electrodes which extend from the bottom
of the cell in contrast to the two electrodes of the B-Cell which extend
in opposite directions. The construction of the DB-Cell allows it to be
mounted on a standard TO-5 transistor header, sealed and encapsulated
to provide better handling capability in the field.
Improvements in electrolytes and cleaning techniques also resulted
from the laboratory work. e which finally used in
successful field tests contained an electrolyte of silversulfate dissolved
This electrolyte in addition to having low resistance
and a high degree of reproducibility also has the advantage of having
a very low freezing point which will'allow operation in very cold climates.
The freezing point varied from one mixture to another but was generally
37
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
Li

0
in the region of -40?F.
Figure 4.1 illustrates one of the test curves for a DB-Cell
using a silversulfate electrolyte. The figure provides a plot of the
voltage across the cell as a function of the DC current through the
cell. The resulting curves then give an indication of the cell resistance
at various operating current levels. These resistances are noted
on the graph at various points where they were calculated. It will
also be noted that the cell performs reproducibly at voltage
than 10 millivo ts across the cell. This factor aids considerably in
the integration of small microwave field intensities.
4.2 RF LAB TESTS
Numerous laboratory tests with the DB-Cells were made
with a microwave power source radiating in the C-band at approximately
5. 6 kilomegacycles. These tests were made on a set-up similar to
that described for the diode tests in Section 2. Figure 2.3 is a de-
scription of the DB-Cell tests where the load used was either a
resistor or a DB-Cell being investigated.
Typical of the results of these tests is the data, plotted in
Figure 4. Z. In this test a Microwave Associates diode 4123A was
mounted in front of a copper reflector, a half microfarad capacitor
was connected across the leads from the diode to improve the
integration of the pulses from the microwave source. One micro-
? second pulses at a repetition rate of 1000 cycles per second were
used in most of the tests. A 10,000 ohm resistor was used in place
of the cell for the initial measurements to determine the response
of the diode and to provide a reference at the power level being used.
The voltage and current through this resistor is shown on the curves
marked with the load resistance indicated. The fact that the load
resistance varies from 11K to 20K to 110K is result of the fact that
the resistance of the microammeter changes on different scales
and the load resistance shown is the combined resistance of the load
resistor and the internal impedance of the microarnmeter.
38
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
I Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
:me
rillillErdrderigliqri;?
km:s
1..-
?I: ? --
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ivr
I. 3O1III
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P:llPffllliillbIP:ll
JjiffIllffIll
thinlIIIIMEDIP" DAME ..111MEMBINE
am;
eafilrhis- LErlur alPFAMPIEMBILL
:AMU riltirdiERMIIME
-ELIMPFATIMillh9llllllOIIIIIUI
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RIEF-311 hEITAIMPHrills- Iff011,Thth WPMiIi
risiNLIMPLIERElligh wr:s" ,4115
di
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
o
The current through the cell is plotted in a set of eight points
lying between the current and voltage curves for the load resistance.
Results indicate that the cell has an operating resistance in the 1
microampere region of the order of 20,000 ohms. This compares
with the diode resistance of approximately 5 to 10,000 ohms in the
same current region. Experiments indicated that the cell could
integrate nearly as well without the one-half microfarad capacitance
being used in parallel as with it. However, since small capacitors
of one-half microfarad value were available and did improve some-
what the response of the cell, it was decided to use these in the field
tests and in the resulting equipment being delivered.
In addition to the current measuring experiments such as the
one described in Figure 4.2,charge integration using the microwave
equipment was also investigated and performed satisfactorily and
consistent with the laboratory measurements using a DC source rather
than microwave generated pulses.
Laboratory tests were also performed to determine whether or
not varying the antenna size could be used to give a reliable indication
of the radiating frequency. It was not expected that very good results
would be obtained in such laboratory tests because of the near field
effects-and the scattering and interference effects of the various
objects in the laboratory. That is to say, a good test range was not
available for these laboratory tests. However, the results were
nevertheless encouraging and evidence was developed that showed
some indication of source field frequency could be obtained by com-
paring measurements with antennas resonant to different wavelengths.
One such set of data is shown in Figure 4.3 where antennas of
length 2.8 cm. , 4 cm. , 5 cm. , and 6 cm. , were utilized and a plot
of readback time at 1 microampere versus exposure time to the source
in minutes was made for the different antennas. The source was the
same C-band Klystron used in other tests having a frequency of 5. 6
kilomegacycles. The resonant antenna length for this frequency
would be approximately 2. 8 cm. for a half wavelength dipole. The
41
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
11111 11.1 I Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9 ME 111111
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6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
jDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
a
results of Figure 4.3 indicate, however, that the 4 cm. antenna length
provided somewhat better response than that at 2.8 cm. However,
the 5 cm. wavelength is reduced considerably in sensitivity. The
measurements with the 6 cm. antenna were very erratic resulting
in considerable scatter in the data suggesting sharp interference
patterns with the radiating horn. As will be indicated, the field test
measurements,where no interference effects are possible, provided
much more consistent data and data more readily interpreted.
The results of these various laboratory experiments indicated
that the DB-Cells in combination with diodes did provide a sensitivity
which was sufficient to yield results in our field tests against the
airport radar. These field tests will be described in the following
section.
4.3 DB-CELL MICROWAVE FIELD TESTS
Prior to performing the field tests with the DB-Cells it was
decided to construct portable equipment which could be taken into the
field to allow on-site measurements of the accumulated charge in the
E-Cell. This equipment consists of two items described in more detail
in Section 5 below. The first of these items is a battery-operated
microarnmeter which provides a full-scale indication of current as low
as 100th of a microampere (one-hundredth of a microampere). The
scales most commonly used, however, were 1/10 microampere and
1 microampere full scale. The second item is a battery-powered
constant source with currents generated at 1/10 microampere, 1
microampere and 10 microamperes. Various switching mechanisms
are provided with the source for reversing the direction of current,
for adding a capacitor in parallel with the cell, and switches for
connecting the cell to an antenna diode combination or to the constant
current source for readout. Both instruments were checked repeatedly
in the laboratory and used for some of the laboratory measurements
described in earlier sections.
The field tests were performed at the site described above in
Section 3.3, and were conducted in the following manner. A range
43
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
II
11.1
from the radar antenna was chosen and the distance measured off
with a one-hundred foot tape to provide an accuracy of sight location
of approximately a few feet error. Measurements were taken primarily
a.1. distances of 200 feet and 1000 feet from the radar antem.- Measure-
ments taken at intermediate points checked well with the measurements
at fh-e-s-elo"- locations. _13?g3.a. ges be ond 1000 feet were not practical
because of the terrain and difficulties in estimatin? t e distances
properly. The results obtained at a 1000 feet with the radar of
290?w-a-": ct s average power in ica e t at distances out to 5000 feet
wauld_b_e_p.e.rie-ctly--p-r--ar-tical_w_ith radars of somewhat higher average
power. Furthermore, estimates of the field strength from the DC
current microwave measurements and comparison with laboratory
measurements indicate that (as would be expected from antenna beam
pattern) our measurements were below the maximum of the main beam
by a factor of 10 in power. The use of the equipment on a hill which
is swept by the main beam would provide even greater average currents
than those obtained.
Once a site had been established and its range to the antenna
measured, a non-metallic table was set up and equipment placed on
it. A diode antenna placed in front of a reflecting plate was erected
on top of the switching box which contained the constant current source.
The cell was plugged into a TO-5 socket on the switching box and connections
were made to the microammeter.
Prior to integration with the microwave antenna, current would
be passed through the cell first in one direction and then in the other,
several times, to insure that the cell was in proper working order
and to insure that the appropriate electrode was bare of silver.
The switch containing the capacitor circuit would then be
closed in order that a 1/2 microfarz..d capacitance would be connected
in parallel across the cell. The cell would be disconnected from the
constant current source and connected to the diode antenna with proper
polarity. A switch would be thrown closing the circuit at the same
time a hand-held stopwatch is started. The diode antenna and reflector
44
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
11.]
plate had been pointed toward the radar antenna visually in order to
give the maximum current through the diode and cell.
At the end of the prescribed integration time which would
be of the order of one to five minutes, the switch would be thrown
opening the circuit. The cell would then be switched over to the
constant current source and the stopwatch rezeroed. When the switch
was closed, closing this circuit with the polarity such that the cell
would be deplated of the charge accumulated during the integration
of the microwave produced currents, the stopwatch would be started
and the microSiammeter would be watched to be sure that a constant
current of 1/10 microampere or 1 microampere flowed through the
cell.
Near the end of the deplating cycle the pointer of the micro-
ammeter would begin to drop below the constant current value. When
it passed half scale, the stopwatch would be stopped and the time
interval noted. The charge accumulated by the cell would then be
recorded as the product of the time interval of the stopwatch and the
value of constant current through the cell. The cell would then be
reconnected to the diode antenna and a new exposure made with the
same or somewhat different exposure time.
In general, it is found that the accumulated charge is linearly
proportional to the exposure time as would be expected. However,
for very short exposures of thirty seconds or less, the rotational
rate of the antenna (once every 12 seconds) would introduce scatter
in the data if a proportionate number of rotations were not included
in the time interval.
Figure 4.4. is a graph of results typical of this kind of field
test but in which several different antenna lengths were used. This
particular data shows the results for four antennas varying in length
from 4 cm. to 7 cm.; the 6 cm. antenna providing the largest
average current through the cell.
It will be noticed that the extrapolated lines do not pass through
the origin of the graph and apparently yield a finite charge through the
45
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
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........ ,.11,.: e .... . -I-. ..q ILILIMILIC -11111274
..F.LI-mewiedigabliu.. 1::::rmaj :hits ...,Hisi: .
anamillananalusawai-22::.u::. . : an ? um _ ?51.:i???1:-.4:12iO4,
:::: ?::::::::-
.P. HilipmrdioRmowsion Infariquill Epoff,
-n ? ? . m u marnamal..: a.p NSERIEWHEriil
INtraira.
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raw :s-l-tv cow .2 'FL. ? ra a..
:t4E112 IMIRMINIMIElliklliPui Jip qi-rif qatrallEP Wm - ?111:111-TINESP
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-mom xalim :pp
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MINI 6-1-000Z0001-000V88Z90-8LdC1I-V10 171,/80/?1,0Z eseelel -104 15eAaidd \9; AC100 13.8i1P6S u! pawssepaa MINI Nil
0
17
Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
cell with zero exposure time. This is due primarily to the capacitance
effect of the cell and the parallel capacitor across the cell. With no
silver on the anode of the cell, current will still surge through the
circuit due to the charging of the parallel capacitances. This effect
varies from one cell to another and represents a zero point error
in the system technique.
The range at which the data of Figure 4.4 was taken is 200 feet,
however, equally reproducible data was obtained out to greater distances
as we will see in the next figure. Since the radar frequency is 2900
megacycles, one would expect that the 5 cm. antenna would generate
larger currents than the 6 or 7 cm., because of its resonance. How-
ever, the use of a reflecting plate and the thin wire of the diode leads
which were used as the antenna members will distort somewhat the
expected resonant length. This would account for the fact that the
antenna of 6 cm. length was apparently more nearly resonant than
the 5 cm. antenna. The results of this experiment indicate that a set
of antennas of varying length, when properly calibrated against sources
of different frequency, will yield a fair indication of the source frequency
? being measured. The results of Figure 4.4 suggest that frequency
could be determined to approximately 10 or 20% with little difficulty.
Figure 4.5 indicates the kind of result which can be obtained
at 1000 feet from the 2.90 watt radar. The data is very consistent
within the accuracy of measurement of the time interval over a
range of exposure times from 6 minutes down to 10 or 15 seconds.
Most of the data was taken by deplating the cell at a constant current
of 1 microampere. However, 'for the very short exposure times when
a very small charge was accumulated, greater accuracy was obtained
by using a 1/10 microampere deplating current which allowed longer?,
time intervals for the same accumulated charge.
It should be noted that a 15 second exposure encompasses only
one sweep of the radar beam and this accumulated charge was readily
measured at the range of 1000 feet with an entirely passive system.
The results of these experiments indicate that the equipment as
47
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NEI NE I Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9 Nom --INN IN
1:11j:UAF F'EjL. ittCL73 CO: UA DL in IJ .1 A
d.t4 4-pi14:1
?r-"til t:Thalt
t- -:11-1. 4211. ri -lilt 411-L11V rj
fit 11 .
!At; 4_4
414 -P-
tfft
- ,,
t? t
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LDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
designed can meet the original requirements of making passive
measurements of radar power and frequency, at ranges from 1000
feet to 5000 feet. In addition to the cell-antenna-diode combination,
very little equipment is required. Only a small microarnmeter, a
constant current source, and a stopwatch is necessary to read the
accumulated charge in the cell.
13
U.
49
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Li
1:1
5, EQUIPMENT OPERATION
The final equipment consists of three different items:? one
a microammeter, two a constant current source and switching
network, and three the diode-antenna-cell combination package.
The use of each of these equipments will be described below.
The microammeter is a battery operated device with capa-
bility of measuring currents below 10-8 amperes. The front face
of the instrument contains three switches, an input and output jack,
and a dial for indicating current. There is also an opening in the
front face which allows access to a trimming potentiometer for
zeroing and calibration. One switch is simply the battery switch
which turns the circuit on and off. Another switch reverses the
meter polarity. The third switch is a multiple position switch
which can change the scales from one current range to another by
factors of ten. The instrument presently indicates scales of lila,
1/10 p.a, and 1/100 p.a, however, a change has been made through
the internal circuit so that each of these scales should be increased
by a factor of ten as the circuit is presently constituted. When in
doubt about the scale ranges of the microammeter it can be checked
against the constant current source, the operation of which is indicated
below. The input jack provides the connection for the current to be
measured and the output j_ack is the output of the DC amplifier which
constitutes the principle circuit of the microammeter_ This allows
external monitoring of the current through the microammeter. j
The circuit of the device is shown in Figure 5.1 and it will
be found that the input impedance of the microammeter is 1000 ohms
on the 1 ia scale. The instrument is powered by four Mercury cells
type TR-136-R. The device should be checked periodically against
the constant current source to be sure that the batteries in both the
microammeter and current source are working properly, The
principle component of the microammeter is a Philbrick No. 6547
_
DC amplifier which is a solid state device of hi h reliability. The
output meter is simply a standard 100 microampere full-scale meter
50
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1-11 Declassified in Part- Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9 171 1=11
+15V
4 EACH
TR-136--R
CELLS
_
;IN ?I5V
i 1
POWER
0.1 0.1
50V 50V
CASE
COM
4
5
+15
TRIAX
INPUT
1.0
MFD
IK
-6
10A
-7
104
-8
104
-9
10A
10-40AA-0
10K
YE
1D?W%-------o
0.IM
(1.0?MA----o
1M
-15 IN- 01N+
3 ? 2 1
NC NC
6 ? 7 ? 8
OUT
CHASSIS
GRD ?2.."
(SINGLE PT.)
METER
POLARITY
SW.
100
MA FS.
(500.11)
. PH1LBRICK
P2 NO. 6547
R 2
BLUE I M RD.
12
;. +100
100 UU F. (10 MV. F. S.)
10M -10
43--M/11.---0 104
100 M
45---MAr--0104
1K M -12
ce?ANY--ro 10 A
0 OPEN
R
10K
AAA".
INPUT
SHUNT
RES. SEL.
BLK.
COM
Microammeter
Figure 5.1
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ijDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
which will read both positive and negative currents, zero being
indicated at the center of the scale.
Prior to using the instrument, the input connection should
be shorted and the zero on the instrument adjusted after sufficient
time for the instrument to achieve equilibrium has been allowed.
This zero adjustment is made through the top of the case through
the appropriate aperture with a small screwdriver, preferably
non-metallic. Once the instrument is zeroed its calibration can
be checked against a standard current source. In field operation
the output jack is never used and the current is read directly from
the meter face.
The second item is the constant current source which con-
,-
tains a TO5 transistor socket into which the cell is mounted.
There is an on-,off switch for controlling the current from the in-
ternal battery, a switch marked left-right and right-left which
indicates the direction of current through the cell mounted in the
transistor socket. The center electrode of the cell is not activated
in this circuit when it is plugged into the socket in a proper fashion.
When the switch is in the left-right position it indicates that the left
electrode of the cell is positive and the right is negative so that
silver, therefore, moves through the cell from the left to the right
electrode. The right electrode is that electrode nearest the little
metal tab which radiates from the base of the transistor header.
There are three toggle switches mounted on the face of the instru-
ment, one which is a shorting switch for the purpose of zeroing the
microammeter, another is a switch marked DC and Pulses which
when in the pulse position adds a half microfa,rad capacitor in
parallel across the cell terminals. The third toggle switch is
marked Readback / RF and determines whether the box is being
used as a constant current source in the Readback position for the
depla.ting of the cell or used in the RF position to connect the cell
across a diode externally connected to the red and black wires
extending from the instrument. The switch labelled Z-function
52
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0
0
provides three values of constant current which are set by the
voltage of the Mercury cells inside the instrument and large cali-
brated resistors in series with the cell. A jack is provided for
connection to the microammeter so that the current through the
cell can be monitored. When the microammeter is not connected
it is necessary to have the toggle above this jack in the short
position to provide a complete pc path through the cell. The circuit
for the field test unit is shown in Figure 5, 2.
In using the field test unit and microammeter to check the
operation of a cell in the field the following procedure is used.
The cell is plugged in to the socket and the switch is thrown to the
Readback position; the microammeter is connected and the shorting
switch on the test unit is thrown. The power switches are turned
on and the microammeter is zeroed. The constant current source
is turned on and the Z-function switch is set to the appropriate
scale for the rnicroammeter. The left-right and right-left switches
are thrown to check the constant current through the microammeter
for calibration purposes. The shorting switch is then opened and it
is noted whether or not current flows through the cell . The polarity
is then reversed and it is again noted whether or not the current is
flowing through the cell. Once it has been determined that one
electrode, either the left or right, is bare and there is silver on
the other electrode in sufficient amount to perform a test, this
silver is transferred to that electrode which will be connected in
the right polarity to the diode for transfer to the bare electrode.
If pulses are to be integrated the appropriate switch is thrown.
The shorting switch is closed and the internal readback power is
opened. The cell and diode are now ready to integrate microwave
current. This is initiated by throwing the readback switch to RF
for ..:c.priate time interval. At the end of that time interval
the switch is replaced to the readback position and the shorting
switch is opened connecting the microammeter in series with the
cell. The polarity switch is put in the proper position for replating
53
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17A, I-1 I Declassified in Part- Sanitized Copy Approved for Release 2013/08/14 : CIA-RDP78-05288A000100020001-9 1:73
UA
METER
SWI READBACK
R32
220K
R33
2.2M
VS,Ae
OPEN
SHORT
5UF PULSES
ANT;
R part of the
run but no diffusion current for the reverse part. Considering that
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in this case, L is a 20 mil silver wire, 58 mm long and R a 20 mil
gold wire 5 mm long, it is seen that the difference in effective areas
of L and R are much greater than between C and R in DB 1 (Example 32).
Because of this and in line with the considerations applying to DB 1,
it is evident that the relative difference between the forward and reverse
currents should, theoretically, be greater and this is borne out by
the curves in Chart 56.
_f
15
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LIDeclassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
a
C.
IV
Ag2 SO4 - H2 SO4 - H2 0 ELECTROLYTES AND THE
t'
EFFECTIVE RESISTANCE OF CELLS
The original purpose in selecting these electrolytes was that
sulfuric acid of certain density ranges does not freeze above -40?F
(-40?C). See Table IV. Sulfuric acid of 1.250 density freezes at
-61?F (-52?C). However,' the disadvantage of this density acid is
that the solubility of Ag2 SO4 in it is less than in water (Table III).
In 1.300 density, H2 SO4 (freezing point -95?F (-70?C) at the minimum
solubility (Table III), the solubility of Ag2 SO4 is still less. As
this acid contains 40% H2 SO4, it is seen from Table III that the
solubility of Ag2 SO4 does not begin to increase until a somewhat
higher density acid is reached. At this point, however, the freezing
point is higher. Enough work has not been done yet in the investigation
of Ag2 SO4 - H2 SO4 - H2 0 electrolytes to determine the optimum
composition consistent with the best current level, sharpness of
cut-off and effective resistance. The higher the silver ion concentration,
the lower the effective resistance, other things being equal. The
effective resistance is given by the equation:
aan
RT ?
?rr - ITx n -a---
E an ca + Rc ca
c
Re + Rc = +R (26)
The higher the Ag2 SO4 concentration, the lower the value of
an - Trca) and Rc (Reference 3, p. 438). See Graphs 9 and 10.
The silver sulfate concentration, however, should not be so near the
saturation point that Ag2 SO4 separates out on the anode at the current
used in operating the cell as discussed in Section II. The curves shown
in Graphs 1 and 2, Examples 30 and 31, where Ea is plotted vs i
illustrate the large variation between two DB cells containing the same
electrolyte.
Example 19, Chart 29, for,DB3 containing 0.050 M Ag2SO4
in 1.610 H2 SO4' illustrates a case where there was too long a time
16
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interval between the filling and sealing of a cell. During this time
the electrolyte absorbed moisture from the atmosphere as strong
sulfuric acid solutions are noted for their hygroscopic properties.
This brought the solubility of the silver sulfate nearer the saturation
point (Table III), thus resulting in the precipitation of some silver
sulfate on the electrodes of DB3 when they were anodes. The silver
sulfate thus formed prevented the complete deplating of the anodes
in each successive run, thus accounting for the rapid loss in areas.
The discussion in the latter part of Section II covers this effect
more fully.
17
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V
PROGRESSIVE INCREASE IN AREAS IN CURRENT-TIME
CURVES DURING TRANSFER OF SILVER
BETWEEN ELECTRODES
In Chart 41, Example 24, for DB 22 (gold-plated electrodes)
containing 0.10 N Ag NO3, there is a gradual increase in areas with
relatively high residual currents. It is thought that during the tail part
of each current-time curve, when only the residual current is present,
silver is plated onto the cathode from the solution rather than from the
anode. During maximum values of the current, the anodic reaction,
which is a dissolution of silver from the anode:
Ag _Ag++ e (27)
and the cathodic reattion, which is the deposition of silver ions on
the cathode
e + Ag + Ag (28)
occur concurrently with no other reactions taking place but during
the flow of the residual current,
2 H20 2+ 4 H+ + 4 e
?(29) ,
is thought to be the anodic reaction which results in the iiroduction -
of oxygen at the anode with a simultaneous_ creas -he solution
while
e + Ag + Ag
still remains the cathodic reaction.
(30)
The occurrence of reaction (29) causes iran to rise with the
resultant increase in the back emf and decrease in the current. After
many runs it is seen that the total quantity of silver ions in the electrolyte
will decrease, causing a progressive increase in current-time areas.
When comparing the curves in Chart 41 with their high residual
currents and angular cut-offs to the curves in Charts 42 and 43 for
18
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the same cell, it is observed that in the latter the areas are constant,
the residual currents zero and the cut-offs less' angular. It is difficult
to define in Chart 41 just where reaction (27) stops and reaction (29)
begins.
In Chart 40, Example 23 for DB 6 containing 0.050 M Ag2 SO4
in 1.610 H2 SO4' there is a slight progressive increase in areas
but with no residual currents. The cut-offs are, however, quite angular
which apparently favors the possibility of reaction (29) setting in
before the current reaches zero, thus causing a gradual increase in
areas and in total silver deposited.
In cycling experiments it is important, therefore to consider
U1_9_5_4- ? -..t-off ortion of the current-time curve as well as
? the absence of residual currents in or er o o tain constant time
intervals for each half-cycle.
19
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LI
VI
ANODIC OXIDATION OF PLATINUM AND GOLD
The formation of films of platranous or platinic oxides on Pt
electrodes under sufficiently oxidizing potentials and their reduction
under appropriate conditions was claimed in the paper of Kolthoff
and Tanaka, (Reference 8). In their work, non-oxidizing and non-
reducing electrolytes were employed so that the observed effects
were entirely due to the potential applied to the Pt electrode. The
work of Ross and Shain (Reference 9) showed that if the oxidation
potential of .a solution of an oxidizing agent is less than that of the
Pt (OH)2 - Pt couple (+0.98 volts) a constant potential is quickly ?
attained for an oxide-free Pt electrode immersed in the solution.
The work of Anson and Lingane (Reference 10) proved the existence
of oxides of Pt by spectrophotometric analysis of Pt electrodes
previously subjected to anodic polarization in sulfuric and perchloric
acid. The work of Baumann and Shain (Reference 11) showed that
oxidation of gold takes place when a sufficiently high electrode potential
is applied. They state that gold is more resistant to oxidation than
platinum when complexing anions such as Cl- are absent.
The following equations show that the acidity of the electrolyte
influences the value of the potential required to oxidize an oxide-
free platinum or gold electrode.
2 H20+ Pt= Pt (OH)2 + 2 H+ + 2 e .(31)
o = 0. 98 volt (Reference 12, p. 343)
Pt
RT2
7T pt 0 =
Pt 2F 'n a H+
For a solution of p H = 6. 7 as 0.10 N Ag NO3,
-6. 7
O. 98 + O. 059 log 10
Irpt = 0. 58 VOlt
:(3Z)
20
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Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9
H
r'n
t_.11
3 H20.+ Au= Au (OH)3 + 3 1-1+ +3 e
Tro = 1.45 volt (Reference 12, p. 344)
RT 3
Tr =
Au TrAu + n a H4.
3F
For a solution of p H = 6.7 as 0.10 N Ag NO3,
Au .
Tr = 1. 45 + O. 059 log 10-6 7 = 1.05 volt.
(33)
?(34)
Considering that the mean activity co-efficient of the stronger
sulfuric acid solutions, such as used in our cells, is unknown, the value
of auf. cannot even be approximated for these electrolytes and as a
result Tr Pt and 7r cannot be calculated. However, for two cells, one
Au
with Pt and the other with Au electrodes and each containing the same
Ag2 SO4 - H2 SO4 - I-120 electrolyte (31-A - ir) is merely the differ-
ence
of Equations (34) and (32) where the second terms in each
equation cancel out. This difference is 1.45 - 0. 98 or 0.47 volt.
If decomposition voltage curves are run for these cells the difference
of the potentials at the two maxima should give the same value. These
maxima, can be defined as the maximum currents observed before
the decomposition voltages are reached. The decomposition voltage
is the voltage at the point where the curve takes its final upward
swing. It is, in any case, not an exact value. Maxima can be
observed in Graph 4 for DB 16 with platinum electrodes (Example 33)
and in Graph 5 for Ag Au Bottle Cell No. lb with gold electrodes
(Example 34). It is unfortunate that these two cells did not contain
the same strength electrolytes, however, the difference in their
maxima (1.00 volt - 0.72 volt) or 0.28 volt at least furnishes
qualitative proof for the formation of oxides of platinum and gold
at the potentials existing at these maxima. Ag Au Bottle Cells
No. 2 and No. 3 (Examples 35 and 36) also show maxima for the
decomposition voltage curves shown in Graphs 6 and 8.
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In Table V a comparison between the currents at the maxima
and the lengths of the gold electrodes in the three bottle cells discussed
is given. It is to.be noted that any oxides originally present on the
gold electrodes of these cells were reduced by the preliminary cathodiza-
tions. In the case of DB 16, the preliminary cathodization removed any
Pt oxides on its electrodes. Table V shows a rough proportionality
between electrode areas and currents at the maxima which, of course,
indicates that higher currents are necessary for the oxidation of
larger areas of gold.
As shown by the above theoretical discussion and the four
graphs mentioned, the use of gold electrodes permits a higher cut-
off voltage than with platinum before oxidation of the anode occurs,
assuming the same electrolyte is used in each case. This is equall
true for cells containing acid or neutral electrolytes and is shown
by the fact that the value of ( TrAu - TrPt ) is independent of p H.
Early work with B cells has demonstrated that a preliminary
cathodization of the Pt electrodes (which were not gold plated later)
usually resulted in better curves in initial tests. During the continued
testing of these cells at various cut-off voltages, it is entirely possible
that some or all of the voltages employed have been high enough to cause
a gradual oxidation of the electrodes during each successive cut-off.
It is not understood why these cells after continued use or most cells
with uncathodized electrodes gave poor performances. , The fact that
cplated electrodes containing both 0.10 N 'Ag NO3 and
sulfuric acid electrolytes have given constant areas for current-time.'
curves when transferring silver back and forth between two electrodes
attributed not to the elimination of crevices in the electrode-
,
t_-glass seals but also to the fact that the gold electrodes remained
oxide-free. There is no cell with Pt electrodes containing 0.10 N Ag NO3
on reco
_
?
?d
t areas for current-time curves. Of
the many cells of this type tested it seems reasonable to assume that
at least a few must have had perfect Pt-to-glass seals. On the
other hand, practicall all the cells with old plated platinum electrodes
containing 0.10 N Ag NO3 have given constant areas.
22
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1=1 r Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9 =1.
TABLE I
? SILVER SULFATE - SULFURIC ACID - WATER ELECTROLYTES
Molarity
of
Ag2 SO4
Weight
. o/o
Ag2 SO4
Density
of
H2 SO4
Molarity I
. of ?
H2SO4
Weight
0/0
I-1-2 SO4
Freezing
Point
(Approx. )
0.005
0.124
1.250
4.34
34.0
-52C (-61F)
0.010
0.249
1.250
4.34-
34.0
-52C (-61F)
0.015
0.373
1.250
- 4. 34
34.0
-52C (-61 F)
0.020
0,496
1.250
4.34
34.0
-52C (-61F)
0.015
0.423
1.102
1.685
15.0
-7. 7C (+18 F)
.0,015
0.403
1.155
2.f93
22.0
-15C (+ 5F)
0.015
0.388
1.202
_
3,430
28.0
-27C(-17F)
0.015
0.298
1.520
9.60
62.0
-30C (-20F)
0.025
0.510
1.520
9.60
62.0
-30C (-20F)
0.050
0.958
1.0610
11.48
70.0
Indeterminate
0.32
5.47
1.727
14. 10
80.0
-10C (+14F)
(
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LI
TABLE III
The System Silver Sulfate-Sulfuric Acid-Water at 250
(Simons and Ricci, 1946a)
Gms.
Ag2S 04
per 100
gms. sat.
sol.
Gms.
H2504
per 100
gms. sat.
sol.
Solid Phase
Gms. Gms.
Ag2SO4 H2SO4
per 100 per 100
gms. sat. gms.sa.t.
sol. sol.
Solid Phase
0.833
.990
.946
.618
.411
.400
.632
.831
1.897
2.273
2.84
2.94
3.89
4.06
4.50
4. 74
5.50
5.63
6.57
6.55
6.61
6.59
6.52
Av6. 57
6.18
6.23
6.32
6. 32
6.27
Av6. 26
0.0
4.75
.11.34
21.13
38.12
54.30
62.15
64.97
70.86
71.87
72.60
72.68
.73.66
73.78
74.03
74.26
74.26
74.19
74.21
74.47
74.25
74.31
74.5
74.35
74.30
74.08
74.31
73. 95
74.07
74. 14
-
Ag SO
4, 4
II
II
II
II
II
It
It
TI
It
IT
TI
Ag4S, 04 +13- Ag HS 04
It
TI
TI
Ag2SO4 +13-AgHSO4
.11
11
6.58 74.95 13- Ag HS 0
? 4
6.54 75.13
II
6.57 75.93
II
7.14 77.9
It
7. 97 79. 73
II
9.13 80.78
IT
9.42 80.92
II
10.85 81.27.
IT
11.39 81.21
II
12. 70 80. 89
11
13.58 .80.57
5.58 75.43 a- Ag HS 04
4.94 76.78
It
4.34 80.27
II
4.51 81.59
4.79 82.22
II
6.13 82.68.
?11
7.94 83.01
It
12.81 81.62
*19.45 77. 86 a or 13-AgHSO4(?)
*19.82 77.64 ?
II
*20.81 76.98
I11
*21.01 76.41
II
*21.45 76.32
It
*21.50 .76.55
It
*21.82 76,17
*Solubility curves of a and 3-
AgHSO4 indistinguishably close.
William F. Linke, Solubilities of Inorganic and Metal Organic Compounds,
Originated by Atherton Seidell, Ph. D., Vol. I, Fourth Edition, A-IR,
D. Van Nostrand Company, Inc., 1958, p. 132.
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TABLE II
Viscosity of Sulfuric Acid Solutions
Temperature
Viscosity in Centipoises
?C
oF
10%
20% ,-
30%
40%
50%
30
86
0.976
1.225
1.596
2.163
3.07
25
77
1.091
1.371
1.784 ?.
2.409
3.40
20
68
1.228
1.545
2. 006
2. 70
3. 79
10
50
1.595
2. 010
2. 600
3.48
4. 86
0
32
2. 160
2.710
.3.520
4.70
6.52
-10
14
3.820
4.950
6.60
9. 15
-20
- 4
7.490
9.89
13.60
-30
-22
12.200
16.00
21.70
-40
-40
28.80
....
- 50
-58
59.50
....
G. W. Vinal and D. N. Craig, The Viscosity of Sulfuric Acid Solutions Used For Battery
Electrolytes, Bureau of Standards, J. Research, 10,781 (1933), Storage Batteries, Fourth
Edition, John Wiley and Sons, Inc. , 1955, p. 119.
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TABLE IV
Freezing Points of Solutions of Pure Sulfuric Acid
Specific
Gravity
at 15?C
Freezing Points
Specific
Gravity
at 15?C
Freezing Points
Centigrade
- Fahrenheit
Centigrade
Fahrenheit
1.000
0
+ 32
1.450
-29
-20
1.050'-
- 3.3
+26
1.500
-29
-20
1.100
- 7.7
+18
1.550
-38
-36
1.150
- 15
+ -c
..,
1.600
*
1.200
- 27
- \17
1.650
*
*
1.250
- 52
- 61
1.700
-14
+ 6
1.3-00
- 70
- 95
1.750
+5
+40
1.350
- 49
- 56
1.800
+ 6
+42
1.400
- 36
- 33
1.835
-34
-29
*
Freezing Points Indeterminate
G. W. Vinal, Storage Batteries, Fourth Edition, John Wiley and Sons, Inc., 1955, p. 111.
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TABLE V
Comparison of currents observed at maxima in decomposition voltage
curves with lengths of gold electrodes.
Example
Bottle Cell
Graph
R (Au)
Current at
Maximum
34
. Ag Au No. lb
5
5 mm
0.6 p. a
35
.Ag Au No. 2
6
13 mm
1. 2 ? a
36
Ag Au No. 3
8
58 mm
5. 0 ? a
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10
LIST OF REFERENCES
1. Frank H. MacDougall, Physical Chemistry, Third Edition,
The Macmillan Company, 1952.
2. Elfin I, Final Report, C25-7, July 25, 1962.
3. Samuel Glasstone, An Introduction to Electro-Chemistry,
D. Van Nostrand Company, 1942.
4. ? I. M. Kolthoff and James J. Lingane, Polarography, Second
Edition, Vol. I, Interscience Publishers, Inc., 1952.
5. Handbook of Chemistry and Physics, 38th Edition.
? 6. William F. Linke, Solubilities, Vol. I, Fourth Edition,
D. Van Nostrand Company, Inc., 1958.
7. William Blum and George B. Hogaboom, Principles of
Electroplating and Electroforming, Third Edition, McGraw-
Hill Book Company, 1949.
8. I. M. Kolthoff and N. Tanaka, Analytical Chemistry, 26, 632,
1954.
? 9. J. W. Ross and I. Shain, Analytical Chemistry, 28, 548, 1956.
10. F. C. Anson and J. J. Lingane, Journal of American Chemistry
Society, 79,4901, 1957.
11. Frederic Baumann and Irving ShaM, Analytical Chemistry,
' 29,303, 1957.
12. Wendell M. Latimer, Oxidation States of the Elements and ?
Their Potentials in Aqueous Solutions, Second Edition,
Prentice-Hall, Inc., 1952.
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a
a
APPENDIX
ELECTRO-CHEMICAL TIMER
INTRODUCTION
If silver is removed from a platinum electrode and deposited
onto a second electrode by means of an electroplating process at constant
current, it will be found that the voltage across the electrolytic cell
remains constant for the time interval during which most of the silver
is removed from the electrode and increases abruptly at the end of the
process. If the current is constant, there is an exact relationship
between the amount of silver on the anode and the time required to
remove it, provided that the voltage across the cell does not exceed
a given value. The rise in voltage across the cell at the end of the
process is of the order of one volt or less. This is a convenient change
for? s a e ?evices such as transistor and silicon controlled
rectifiers. Using this technique it is possible to build a very precise
timer with a minimum of components, occupying a very small volume
and providing timing intervals of accuracy of the order of a tenth of
a percent. Such a timer is shown in Figure 1 and 2 and its circuit in
Figure 3. This timer when combined with a battery of a few volts will
fire a squib or flash bulb after a time interval which can range from a
few seconds to several months.
has been engaged for the past
two years in the development of electroplating cells (E-cells, hereafter)
for application to timers, integrators, and computer logic functions.
The company has available many items of equipment used for assembly,
preparation and test o the E-cells. Precision equipment for charging
the cells and setting precise time intervals also exist. In brief, it
will be noted that the electro-chemical laboratory of
has developed E-cells with sharp cutoff when the
50X1
5OX1'
50X1
silvr is removed at a rate of only one millimicroampere (10-9 amperes)
current dlr.? ? .1 current through the cell after
------- ?
the end point is as small as 10 pico, amperes (10-11 amperes).
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LI
LI
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SCR
_-r-
E- Cell
Disarm
Switch
Figure 3
Basic SCR Circuit
3
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11
a
Timing cells have been built and operated in timers several
hundred times with a typical accuracy of . 2 of one per cent in the timing
interval at ambient temperatures. Equipment has been developed around
the cell to integrate microwave energy to an accuracy of better than one ?
db whether or not the source is pulsed or constant. The sensitive cells
can be connected directly to a variety of transducers without intervening
afrip-lification, such as photovoltaic devices, micro hones, and antenna--
dii5a-e-C-orinations. The integrated field intensities can be read immedi-
at-ely by plugging the cell which is mounted on a standard TO-5 transistor
header into a hand-held instrument which deplates the accumulated silver.
The discussion below considers both the basic operation of E-cells
and the application of appropriate solid state circuitry to the E-cells to
perform the timing function. Most of the information presented below
has never appeared in open literature and is primarily the result of
intensive activity in electro-chemistry at
over the past two years.
E-CELL PRINCIPLES AND OPERATING CHARACTERISTICS
Electro-Chemical Principles
This section will not discuss the well-known principles of
elect ro-chemistry which can be found in many of the excellent texts
such as those by Glasstone and Kortum-Bockris. Such texts discuss
.the basic properties of electrolytes and their conductivity as well as
the concepts of electrode potential, over potential, polarization, and
reference electrodes.
Instead we will concentrate specifically on those features
which are most directly related to the use of an E-cell in a timer.
The features of interest involve properties of the electrolyte, of
the interface between the electrolyte and the electrodes, the electrode.
itself, and the crystallization of the silver, or other plated material on
the electrode. Our discussion will consider primarily the plating of
silver onto platinum electrodes, although nearly all the considerations
apply equally as well to other combinations. The operation of gold
electrodes has been found to be very slightly different from that of
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platinum electrodes and materials such as copper and nickel have been
plated with much the same success as silver. However, experience has
shown that there is good reason for using silver on platinum and con -
sequently, this will occupy our attention primarily.
The choice of an electrolyte involves many considerations. Its
resistance should be small in order that it will not interfere severely
with the regulation of the current source. It should be reasonably stable
so that voltages applied to the electrolyte after the silver has been removed
from the anode will not trigger other reactions which will introduce errors
in the time interval; and finally its temperature characteristics should be
such that the electrolyte does not freeze at the low end of its operating
and storage range nor change chemically at the high end by means of
hydrolysis or other chemical reactions.
It is well known that the resistance of an electrolyte generally
decreases as the concentration of the salt in the electrolyte increases.
The salt concentration cannot be made too high however, because at
very low temperatures the solution can become supersaturated and
salt crystals would precipitate interrupting the flow of current to
the electrode. Also, very high concentration of the electrolyte can
effect the crystal structure of the silver being deposited on the electrode
and provide crystals which do not adhere properly to the electrode surface.
The resistance can be lowered best by keeping the cells small
and the electrodes reasonably close together,but not too close that silver
crystals can provide an electronic short between the electrodes. The
electrode area can also be increased to lower the resistance, but
this increase degrades the low current characteristics of the cell as
will be discussed below. _ Exp_Qrience indicates that electrolyte concen-
_
trAtio the region of . 1 normal to 1 normal is sufficient to provide
ohmscellswi-t-&s.is.t.nce of a few hundred or ? less.
--Silver nitrate thoughnly used, is unsatisfactory for most
E-cell applications where accuracy, stability and many c cles
operation are required. The reason is that the nitrate ion itself is
n52.t..A very
water. If the voltage across a cell with a bare platinum anode is
5
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rl
L.
'71
La
allowed to rise over . 7 of a volt this process takes place spontaneously
and not only provides a current when the cell should be nonconducting,
but also causes chemical reactions which seriously degrade the surface
of the electrode so that later operation is found to be very erratic.
In order to use semiconductor switches in conjunction with the
E-cell, such as the use of a silicon controlled rectifier, it is desirable
to have voltage changes across the cell of . 8 of a volt or larger for reliable
operation. Several such electrolytes are available. One, which is
a mixture of silver cyanide and potassium cyanide, allows one volt to
be put across the cell without detrimental effects. This is due to
the stability of the cyanide ion and the fact that the silver ion is more
tightly bound in solution by the cyanide complex formation, Ag (CN)2 .
If a potential less than one volt is placed across two platinum
electrodes inserted in an electrolyte most of the voltage drop will occur
across electrode-electrolyte interface which is only a few atomic diameters
thick. This interface behaves like the parallel plates of a capacitor with
negative charges on the cathode being opposed by positive silver ions
in the electrolyte. At the other electrode, positive charges hold the
negative ions in an array very close to the electrode surface. The
result is exactly analogous to the polarization of a dielectric in a
parallel plate capacitor; and indeed, electrolytic capacitances are
used for this purpose. It is found that with platinum electrodes and
silver concentrations of approximately one normal, the capacitance
of the interface is approximately 20 microfarads per square centimeter
of electrode area. For very rough, uneven electrodes the true surface
area must be used rather than the geometric envelope. This capacitance
effect is very important in many applications where sharp cutoff times
are required or where the integration of very small quantities of
charge is under consideration.
A further contribution of the interface is its effect on the over-
all resistance of the cell during conduction of silver from one electrode
to another. It will be found that as the current is decreased through a
given cell that the resistance begins increasing rather abruptly at a
certain low current level depending upon the electrode area. If one
6
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fl
fl
looks at a plot of the potential across the cell as a function of the current
passing through it, instead of obtaining a straight line through the origin,
the potential varies as log (1 + i/i0) plus the resistive drop of the
electrolyte. At very low current levels, this potential drop across the
interface becomes more important than the resistive drop of the electrolyte.
Perhaps the most important phenomenon controlling the appli-
cation of E-cells to timers and sensitive integrators are the crystallization
effects of the silver on the platinum electrodes. Both platinum and silver
have the same cubical crystal structure with approximately the same
lattice constant. Consequently, when silver plates onto a platinum
electrode, the silver crystal structure tends to be an extension of the
platinum crystals and the bonding at the interface is very good. How-
ever, the points where the silver crystals form and the nature of the
crystals themselves varies considerably with different operating
conditions and chemical composition of the electrolyte.
For example, if the current density is too large for a given
electrolyte concentration, treeing of the crystals will occur. This
results from the fact that the silver ions in the solution very near the
electrode are quickly depleted. The extremities of the silver crystals
formed which reach out into the more concentrated portions of the
electrolyte are favored in crystal formation. The result is that long
spindly crystals are created which adhere at only one point to the platinum
electrodes and are easily broken loose by shock and vibration.
A comparable but not so serious effect occurs when very pure
silver nitrate solutions and solutions of other simple silver salts are
used as electrolytes. It is then observed that the crystal deposit tends
to be in the form of a few large cubical crystals rather than a lot of
small crystals closely bound to the electrode. This has two effects.
When large crystals are formed, the ratio of the surface area of con-
tact to the electrode to the total mass of the crystal is small so that
the crystals are more subject to shock and vibration.
A purely electrical effect is important also. As the silver is
deplated from the electrode, then the resistance of the electrode-
electrolyte interface is proportional to the area of the silver crystals
7
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0
exposed to the electrolyte. As the crystals get smaller and smaller,
this area decreases and the resistance at the end point of the deplating
process rises rather sharply. However, when only a few large crystals
are being removed from the anode, then the change in resistance at the
end point is much more gradual, since the surface area exposed to the
electrolyte is relatively small to begin with. For timer applications,
this results in what is known as a long cutoff time.
Perhaps of most interest from a theoretical point of view are
the recrystallization effects of the silver on a platinum electrode.
Regardless of how it is formed, a microscopic examination of the
platinum electrode will reveal a surface of very rugged structure.
Platinum wire is typically polycrystalline and the surface contains
many edges and corners and similar discontinuities at edges and
vertexes of crystals. As the silver is deposited the crystals form
preferentially on those points of the platinum crystal which reach into
the silver solution for
of the Silver ion
electric field intensit
two reasons. As mentioned above the concentration
crystal structure first
which are
and more importantly, the
is eater at these points. Consequently, the
formed appears as small cubical crystals_,
s and ed?e-f the platinum crystals.
Thermal. agitation and transfer of silver, ions back and forth
across the boundary cause these crystals to diffuse and migrate away
from the edges into the crevices of the platinum crystals where the
silver is more tightly bound. If this electrode is made an anode instead
of a cathode, then it will be found that the energy to remove this silver
is somewhat greater as time progresses than if it were deplated immediately.
If a large amount of silver is deposited then the silver rearranges itself
into more compact forms of lower potential energy. If the silver is
allowed to stand for awhile before it is deplated, the voltage required
to initiate deplating is somewhat higher than if the deplating were to
take place immediately after deposition. Once the deplating has started
and the crystal structure is broken into, the voltage required to continue
the process returns to the normal Yalue. These effects in one way or
another influence the accuracy, and reproducibility of electroplating cells
used for timer application.
?
8
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Operating Characteristics
Only the more important operating characteristics will be
considered here. The most important of these are the cell resistance
characteristics, the recovery and reproducibility and finally, the
accuracy and sharpness of the cutoff time. The resistance of a cell
at various current levels and three different temperatures can be
inferred from Figure 4 in which the voltage across the cell is plotted
versus the current through the cell during its conduction mode. The
extrapolated curves do not pass through the origin because of the inter-
face voltage drop which was described above. If data for very small
current values is taken, it will be found as illustrated in Figure 5 that
the curves actually do go through the origin. Figure 6 shows a similar
curve for a cell of higher sensitivity.
In our early work On the investigation of electroplating cells
for timer and integrator applications, it was found that if a given
quantity of silver were plated on one electrode and then transferred
back and forth between electrodes and the current time relationship
recorded, that there was an apparent decrease in the total quantity
of silver being transferred. The smaller the amount of silver involved,
the more rapid the percentage decrease during each cycle. This lack of
reproducibility was found to be due to a number of factors, the first
of which was inadequate chemical purity. This would seem like an
obvious consideration, however, it should be pointed out that the
degree of impurity is extremely important. Current passing through
a cell at a 100 microampere rate is transferring silver from one
electrode to another at only 1/10th of a microgram per second. Conse-
quently, a few micrograms of the wrong impurity can alter the total
amount of silver being transferred by many seconds.
Once adequate purity was obtained, it was found that there was
still a variation reliability depending upon the condition of the electrode
surface. Through many months of trial and error., it was found that
the electrode surface could be properly prepared by going through several
stages of treatment which had the effect of smoothing the surface and
removing monomolecular layers of platinum oxide.
9
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I-1 =3 Declassified in Part - Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9 i=1 in?J
Cell Resistance Characteristic
160 ?
140 _
120
100
80
60
40
20 _
0
Cell A29
Electrolyte K-2
20
40
60
80 100
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fl
Lj
r-
Cell Resistance Characteristic
16, 500
I l
10 20 30 40 50 60 70 80
i(pa)
Figure 5
11
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ti
C--J 0 76-e-classified in Part- Sanitized Copy Approved for Release 2013/08/14: CIA-RDP78-05288A000100020001-9 LJ EIIJ_j
Cell Resistance Characteristic
16
14
0 O. 1 0.2 0.3
0.4 0.5 0,6 0.7
Figure 6
O. 8
0. 9
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When both chemical purity and surface preparation were
accomplished, it was then found that the degree of recovery of silver
between cycles was a function of the maximum voltage that was used
to remove silver from the anode. In line with our discussion above
on crystallization effects, it was found that if too small a voltage
were used, then the silver deposited in the platinum crevices was
removed only very slowly because of the time required for the silver
to diffuse to the edges of the platinum crystals. If the cycle was
reversed before this slow diffusion effect took place then a certain
amount of silver remained behind in the crevices. As many cycles
were performed this silver in the crevices built up to a level which
was very difficult to recover. On the other hand, if the voltage
across the cell were made too large then side chemical reactions
due to impurities which were not removable from the electrolyte
would take place causing current to flow giving the appearance of
a larger amount of silver on the electrodes. With any particular
electrolyte and cell configuration, it is necessary to find the proper
operating voltages in order that accurate recovery can be obtained.
This is illustrated in Figure 7. In this figure a cell was cycled
back and forth every minute for several days. During the first two
days, the voltage was set at a level which caused a slight increase
in the current time product during each cycle and a gradual lengthening
of the time to deplate the silver at a fixed current level was observed.
The voltage was then reduced across the cell to a level which had been
found favorable under previous operating conditions and the current
time product remained constant within the accuracy of the measure-
ment for a time interval of six days or several thousand cycles. An
examination of the cell's characteristics after many thousand cycles
of operation at the proper volt age showed that they did not change or
perhaps improve/slightly; the resistance being somewhat lower and
the cutoff time being somewhat shorter than when the test was started.
The accuracy of a timer insofar as the E-cell characteristics are
concerned involves the reproducibility descr d in the paragraph above,
the variation of the cell resistance insofar as it effects the current source
13
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7
..??????
Lz)
4,7
fl
28 ?
24
2Q.
Jan 23
150 mv
Life Cycle Test
Cell Ay
Electrolyte K7
Jan 29
4
6
Thousands of Cycles
Figure 7
14
10
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1.1
which is deplating the cell, and the sharpness of reproducibility of the
cutoff time or more accurately, the rate of change of resistance at the
end of the plating cycle. The cutoff time was described as being a
function of the rate at which the crystal surface area changed near
the end of the plating process. It is also related to the total number
of crystal centers formed on the electrode and the extent to which the
platinum electrode has been covered with silver.* Since a larger
amount of silver initially slated onto the electrode resul A a lar
er
percentage of the crevices between the platinum crystals being filled-,
it is observed as expected that the cutoff ti
econds tends to be -
longer,the longer the total time required to de late the silver from
tR.e electrode.
1.,xperience indicates that the time required for the voltage
across the cell at the end of the deplating process to rise from about
20% of its maximum value to 80% of its maximum value is approximately
equal to 1% of the total deplating time, and its reproducibility under
normal conditions allows one to set a threshold which is crossed with
an accuracy of approximately one-tenth of a percent of the total time.
More accurate cutoff times than this are not required for most programs.
However, in other work being undertaken by
techniques to improve this cutoff time are being investigated.
It will be important here only to investigate and control the variation
in the cutoff time as it is affected by various environmental changes.
E- CELL CONSTRUCTION, PREPARATION, AND TESTING
Cells of various sizes and configuration have been constructed
of glass, plastics and other materials; electrodes of platinum, gold
and gold plating on other metals have also been investigated. After
several months of experimentation to develop a cell which is easily
constructed, durable and highly reliable, a design has been achieved
For short time applications, the capacitance of the electrode-
electrolyte interface is also important.
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which fits very well the requirement of the present proposal. This design
is illustrated in Figure 8. It consists of a small glass envelope with
'three electrodes of 10 mil platinum wire which extend from the cell at
the bottom and are soldered or welded to a standard TO-5 transistor
header.
Once the cell has been filled and the center electrode charged
with silver, it is sealed at the top by ,a variety of techniques depending
on the environmental requirements of the cell. Most frequently the
cell is capped with an epoxy sealer or an inert silicone rubber seal.
Special techniques have been developed to protect the electrolyte from
any contamination of the sealing material. The cell envelope is
fixed firmly to the header by an epoxy cement and the entire unit is
potted in silicone rubber inside a cylindrical container providing
shock resistance and durability under extreme environmental conditions.
Other techniques for cell construction oriented toward mass
production are presently under development and these techniques will
be applicable to the present problem if such large production is required.
The material cost for the cell described above are less than $1. 00,
and the cost of the cell as described in production quantities should
not be excessive although such a costing has not been accomplished
at present.
Cells are presently prepared in batches of 20 and go through
numerous steps before the device is finished. (The cell envelopes
are presently prepared by hand but in very large quantities are easily
manufactured by machine). The envelopes are cleaned and the
electrodes are treated with a series of chemicals to prepare the
surface. The. electrodes aie cathodized to remove any traces of
oxides and filled with an electrolyte designeCh specifically for the
application under consideration. The cells are charged with silver
in groups and the current is controlled carefully by a constant current
source and is cut off automatically at the proper time.
Once the cells are sealed, they are put through a variety of
tests which determine their operational characteristics and compare
them to previously determined specifications. Temperature cycling
o16
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^1.
In
^
ii
Figure 8
E-C ell Configuration
3 I,
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and renewed testing is performed as required by the application. The
tests are designed to determine reproducibility of charge and discharge,
current time product, resistance at two different current levels, and
to measure the speed and constancy of the cutoff time. In some cases,
additional tests are added which are oriented toward the specific
application.
ASSOCIATED ELECTRONICS,.E-CELL TIMER
The electronic circuitry to complete the timing and actuation
function established by the electrolytic cell must be inherently a simple,
rugged and reliable as the E-cell itself. In addition, it must provide
an operational system to utilize the E-cell in its most optimum form.
has developed in various programs many
. techniques and circuits which permit optimum operation of the cell,
yet maximize the reliability of the electronics itself.
Basic Circuit Considerations
Since E-cells can be made which operate reliably over a
current range from as small as a millimicroampere to well over
several amps, some flexibility is available to the circuit designer.
Considerations of size and battery life dictate that as low a current
as convenient be utilized in the cell. In order that simple and reliable
solid state circuit components can be used, the cell currents are
usually chosen in the range of one to one hundred microamperes.
For reliable operation a voltage chang_e_a.cross the cell at the end
of the plating process, greater than . 8 of a volt is desirable. This
eliminates the use of silver nitrate as an electrolyte in the cell, but
ctrol tes to be used successfully.
The circuit should be designed so the resistance variation ?
of the cell with temperature does not seriously influence the current
source. In practice it is found that the largest contribution to the
error of a timer is in the lack of constancy of the current source.
When great accuracy is required, special attention to the design of
a constant current source will yield excellent results.
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In addition to the obvious requirements of simplicity, reliability,
long-shelf life and low-power consumption, it is valuable to design a
circuit which can be used with the cell repeatedly for non-destructive
testing. Lack of experience with E-cell characteristics often results
in the design of circuits which lead to voltages greater than one volt
being applied across the cell at the end of its plating period. Excessively
high voltages will usually destroy the operating characteristics of the
cell as the result of oxidation of the electrodes and excessive precipitation
of silver compounds.
Circuit Designs
The solid state circuits which have been used most frequently
with E-cells for timer applications fall into three classifications:
1. Transistor circuits.
2. Silicon-controlled rectifier circuits.
3. Uni-junction (or four layer diode) and SCR combination
circuits.
The advantage of the transistor circuitry is that transistors are relatively
inexpensive and provide simple operating circuits. On the other hand,
these circuits are less stable under temperature variation and require
a fixed relationship between the cell deplating current and the load
current so that when large load currents are required, fairly large
deplating currents may be necessary, raising the energy requirements
for the circuit during long-time operation.
On the other hand, an SCR circuit requires a given minimum
current change at the cell to trigger its operation and very large
currents are passed through the load once the SCR has been fired.
The SCR circuits have proven to be highly reliable and require relatively
low power consumption, but there is at present a slightly larger cost
for the SCR component.
The uni-junttion SCR combination circuits have the advantage
that they can be triggered with very small currents as low as 1/10
microampere and still provide large current surges through the load
as is characteristic of SCR operation. This low current through the
E-cell which results in lower power consumption and longer operational
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U
U.
lifetime in most cases will be offset by the factor of decreased
reliability due to the doubling of the number of components. Further-
more, the 20 to 50 microampere operation of the SCR circuits is already
sufficiently small that at this current drain most batteries last out their
shelf life.
Some basic circuits will be presented which indicate operational
principles with the E-cell. These circuits are generic in nature and
would be adapted to specific applications. Figure 9 shows the fundamental
diagram for the operation of the electrolytic cell as a current-time
integrator. In this circuit it is assumed that the electrolytic cell has
at its anode, an amount of plating material proportional to a current-
time integral corresponding to a several hour timing period. A series
resistor R ' which is many times larger in impedance than the electro-
1
lytic cell during the condu.cting state is placed in series with the cell
and the combination placed across the battery supply. Resistor R2
shown in dotted lines may be placed in parallel with the electrolytic
cell in order to limit the volra-g?e?rise across the electrolytic cell to
a safe is determined by the Tr-O-1t-w1Tre'h
disassociation of the electrolyte takes place. It is to be noted that
resistor R2 is not necessary for the operation of the cell. If the device
were to be used in an application wherein it is self destroying upon
actuation, the need for resistor R2 would be non-existent.
The graphs of Figure 10 describe the operation of the circuit
in Figure 9. Assuming the electrolytic cell has silver on the anode,
the voltage across the cell when the circuit is activated will be as
indicated in Figure 10a, relatively low. The electrolytic cell conducts
at a current which is determined by Resister R1. Thus when a current-
time integral exhausts the silver on the anode, the electrolytic cell
no longer conducts effectively. The voltage abruptly rises to a value
limited by resistor R2 and the current through the cell abruptly drops
to almost zero. It is this voltage transition which is used to obtain a
contact closure.
The basic operation described in Figure 9 can now be implemented
with the addition of one transistor and a load resistor to obtain conduction
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t-1
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Figure 10 A
Voltage
Figure 9
E-Cell Deplating Circuit
Approx.
0. 7 to 1. 0 V.
to
1
Figure 10 B
Current
Figure 10
E- Cell Voltage/ Current- Time Relationships
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Li
through a load upon the transition of the E-cell from its conducting to
its non-conducting state. Figure 11 shows such an example of a simple
circuit. During the time delay period the electrolytic cell is a low
impedance and has a very low voltage drop across it. Consequently,
transistor Q1 is in a non-conductive state. When the current-time
integral has been completed through the electrolytic cell by the passage
of current i the cell abruptly becomes an open circuit with the
resultant rise in base voltage to the emitter voltage of Q1. This rise
results in Q1 conducting heavily and hence providing the equivalent of
a contact closure.
Figure 12 shows a more reliable circuit capable of taking
advantage of the fact that the electrolytic cell is a switching device.
This circuit replaces the analog control device Q1 with a much more
appropriate device, a silicon controlled rectifier Q. The advantage
here is that the SCR has a relatively predictable and stable firing
potential. The operation of the circuit is such that when the electrolytic
cell is conducting, the gate electrode of the SCR is operating at very
close to, zero potential. This prevents the SCR from firing. However,
with the addition of 0. 8 volt when the electrolytic cell ceases deplating,
the SCR gate electrode is raised above the threshold, guaranteeing firing
of the SCR under wide temperature conditions. A further advantage of
this circuit is that the current carrying capability of the SCR is not a
function of the gate current. As a result, the deplating current at
which the electrolytic cell is operated is independent of the ultimate
load current. This feature will be particularly advantageous for power
consumption. As shown in Figure 12 the circuit is so arranged for use
with a squib, such that capacitor C1 becomes charged very slowly
through R4 during the deplating phase. When the cell has deplated
and the SCR has fired, the energy to operate the squib is derived
from the storage capacitor. Although a squib type operation is shown
in the diagram, the same type circuit can be used without resistor R4
or the large capacitor C1 if the cathode of the SCR is tied directly to
B+. In this way, direct contact cldsure is obtained with B+ and up to
several amperes can be carried through the contacts. This circuit
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Li
Figure 11
Basic Transistor Circuit
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11
Li
"Disarm
Switch
Figure 12
Basic SCR Circuit
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fl
1-11
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has a further advantage over the previous one in that the load device
or squib is now tied to the ground side of the circuit and in much better
position for fail-safe features.
An additional feature that can be supplied in such a circuit, is
that of providing absolute disarming. This is provided by the insertion
of a switch from the SCR gate to ground.
An equipment utilizing an electrolytic cell timer of the type shown 50X1
in Figure 12 has been developed and is shown in photograph Figure 1.
Figure 2 shows a close-up view of the electrolytic cell timer. The actual
circuitry of this device occupies approximately 1 cubic centimeter.
timer was developed several months ago by
and has operated many hundreds of times since then with an accuracy of
approximately 1%;
Another circuit shown in Figure 13, though more complex, ha.s
several advants.ges that r...ay be unique. These advantages are particu-
larly useful in timers that are used for extremely long time delays and
conservation of power is one of the prime requirements. Since the elec-
trolytic cell can operate at extremely low values of current, much less
than 1 microampere, it would be desirable in some cases to take advan-
tage of this unique property. The circuit of Figure 13 does just this.
This device is very similar to that shown in Figure 12 except that a uni-
junction or four layer diode device is used as a trigger circuit prior to
the silicon controlled rectifier. If the electrolytic cell divider circuit
is operating at 1/10th microampere, it could not establish a sufficient
signal to drive the SCR; hence, the four layer diode or uni-j unction stage
is used ahead of it.
This type of circuit has been developed at
This
where operation down to very low, values has been obtained
with reliable operation.
General Operational Performance
Requirements of this program outline three specific areas of opera-
tional performance in addition to the more general requirements of
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E-Cell
Figure 13
Basic Uni-Junction --SCR Circuit
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environment. These specific areas are (1) time-delay accuracy (2)
operating and storage temperat
range and (3) long shelf life.
The fundamental accuracy of the time delay is a function of
several independent parameters. First and dominant is the require-
ment that the electrolytic cell be deplated at a fixed current. The
quantity stored by the electrolytic cell is charged. The time interval
is known only to the accuracy that the deplating current is known,
It can be assumed that any battery will vary in potential with tempera-
ture and discharge. Therefore, it is obvious that a voltage regulating
function may have to be included in the timer circuit if such a regulated
source is not available to the timer from other accessory equipment.
The required regulating function has been solved in other E-cell
timer developments by the use of a zener diode to provide regulation.
Recent zener diodes requiring only a few hundred microamperes to
achieve operation in their stable region, are very satisfactory for the
task without adding serious power drain.
It would be desirable to operate the zener diode at a zener po-
tential of 5..1 volts. In this range the maximum temperature stability
inherent in the diode without compensating circuitry is obtained; how-
ever, the voltage is greater than required by the rest of the circuitry.
With simple compensating forward drop diodes a stable zener reference
can be made for any practical operating potential. In any event, a
simple, reliable and proven technique exists to reduce the variation
of deplating current to less than one per cent and hence an inaccuracy
error of less than 1%. With more exotic, though readily available,
zener diodes the error due to deplating current inaccuracy could be
reduced to as low as 0.1% or less assuming, of course, the proper
selection of the series resistor.
Variation in E-cell impedance versus temperature and possibly
storage time can also affect the deplating current. However, as indi-
cated earlier, the
electrolytic cell is a much lower impedance 50X1
than the resistor placed in series with it. For example, if the deplating
current is operated from a 2-1/2 volt reference source the series
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resistor might well be 50 to 100 K. Since the cell impedance is approxi-
matejy. - 1 K ese c r ent levels the cell impeda?nce cou vary over a
rang ? 2 to 1 and still not affect the deplating cur ? than
one ?
As pointed out earlier the very nature of the E-cell virtually 50X1
eliminates the contributions of inaccuracy, from the associated electronic
circuitry because the cell in itself is almost a bi-stable element requiring
the electronics only to detect an abrupt large signal change. Hence,
small drifts in the firing potential of an SCR for example is inconse-
quential. This advantage is not present in some other electrolytic de-
vices where the elapsed time is measured by a slow, small variation
in potential drop across the cell. The basic characteristics of the timer
for variations with temperature are basically those of the E-cell and
are discussed earlier in this discussion. The associated circuitry con-
templated is based upon silicon semiconductor devices such that the
ability to obtain reliable operation of these elements over a range of
-25oF to +160o F is common engineering practice. Similarly the one
year shelf life required and 10 year life desired are achievable with the
same simple associated electronic components.
MANUFACTURING DESIGN, FABRICATION, AND ENVIRONMENTAL TEST
Manufacturing Design
The mechanical design of the electrolytic timer will most likely
take the form of a printed circuit or welded module device which can be
epoxy cast or foamed as required. All the solid state components to be
used in the device will be of conventional high reliability type such that
they can be packaged in a convenient and compact form. The electro-
lytic cell has been described previously and will operate in any position.
The general performance of small glass components have proven their
high quality and reliability from a mechanical standpoint in such applica-
tions as diodes and capacitors. During the course of the PHASE A effort,
*
The temperature coefficient of resistance for the E-cell is
negative and compensates partially the positive coefficient
of most resistors.
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J
environmental tests will be performed on both the electrolytic cell and
other critical individual components to ensure a conservative high re-
liability design.
As a general practice in developments of this nature,
performs both a reliability study of all
parts and develops a plot of operational loci versus loci of specified
limits for each component. In the case of the reliability study, data
accumulated by the individual component manufacturers can be used
in addition to standard referenced data, such as the Diamond Ordnance
Fuze Laboratories Reliability Engineering Notes.
Functional Testing
The development of an electrolytic timer which requires many
hours to perform functional tests, places some interesting demands on
the testing techniques employed to reduce test time. In addition, some
provisions must be made for resetting the electrolytic cell after each
use. Fortunately, these problems have already been encountered by
and such test equipment is being
constructed.
The problem of simulated testing of the timer over short periods
of time to determine the general operability of the unit can be readily
handled by the use of a 3 electrode cell.*
The source electrode has plated on it, at the factory, a quantity
of plating metal proportional to the current-time integral necessary for
the operational timing period. The working electrode is a noble metal
electrode containing no plated material. The test electrode is the third
electrode which contains only a small sample of plated material, for
example, a sufficient amount for 5 or 10 minutes timing at the current
rate being used in the timer. All 3 terminals of the electrolytic cell
are brought out of the timer device and appropriate connection is made
through external circuitry. Hence, in the actual application device the
*
The third electrode also provides a means of resetting the
timing intervals.
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test electrode is not hooked up at all and the source electrode is tied to
ground through an external connection and the working electrode is tied
to the series resistor which determines plating current in the timer.
During a test operation, the timer is mounted on a test fixture
which has a switch to determine whether the source electrode or the
test electrode will be tied in series with the series resistor deter-
mining deplating current. Hence, after a particular environmental
test, if it is desired to ascertain the functional operability of the unit,
the test electrode and the working electrode can be tied into the circuit.
In this way the electrolytic timer goes through a time function deter-
mined by the plating material originally established on the test electrode.
This might be only several minutes; hence, the total operation of the
circuit can be ascertained without erasing or destroying the current-
time integral memorized on the source electrode.
After the operational test has been completed, the working
electrode and test electrode are disconnected by a switch on the test
equipment from the other timer circuitry and instead connected to a
plating circuit of opposite.polarity to that used in the timer, such that
the plated material which is now on the working electrode, is returned
to the test electrode, so that the device will be ready for retest at a
later time. In addition, if it is necessary to ascertain whether the source
electrode is still in operating condition a further test can be made by
tieing the source electrode and working electrode to the electrolytic
timer and operating this for 2 to 3 minutes. If under this condition no
actuation of the electronics occurs and current of the specified quantity
does flow through the cell, it can be assumed by such a test that the
electrolytic cell is still in operating condition and the electronics have
demonstrated their ability to perform the contact closure. These various
short tests described here contribute to the complexity of the timer only
by the addition of one contact on the connector of the unit. No internal
components are added to provide for this type of testing capability. All
such extra components are included only in the test apparatus.
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When actual operational tests are performed utilizing the source
electrode and the full timing period of the device, the timer can be re-
set by use of the test apparatus to replate the source electrode from
the working electrode in a similar manner as discussed above in re-
setting the test electrode. Here again, the resetting time can be re-
duced from the several hours required for the deplating function. This
is accomplished by the use of a higher current determined by a resistor
placed in the test apparatus to deplate the cell. In some designs it
is found that resetting of the electrolytic cell can be accomplished as
fast as 1/100th of the deplating time. In most timers, effort is made
to include as fast a resetting time as practical.
CONCLUSIONS
The experience of in electro- 50X1
lytic timers closely matches many timer requirements. Timers have
been built with high reliability, accuracy, reproducibility, and wide
environmental stability. It remains for any specific application to
build a timer which incorporates all the appropriate requirements in
one device and test it thoroughly.
The extensive experience with E-cells and related circuits
summa.rized in the Technical Discussion evidences a variety and
subtlety of phenomena unsuspected by those with little experience
in the field. This accumulated knowledge of a basic and fundamental
nature provides an excellent foundation for undertaking further de-.
velopment.
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