BASIC RESEARCH IN PRECISE MEASUREMENT APPENDIX C FINAL REPORT FOR TASK 3 - FILM STABILITY ON MEASURING DEVICES

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80T00703A000100080001-3
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 10
• Document Creation Date: December 28, 2016
• Document Release Date: April 21, 2001
• Sequence Number: 1
• Content Type: REPORT

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FR 71-1410
APPENDIX C
BASIC RESEARCH IN PRECISE MEASUREMENT
FLNAL REPORT
FOR
TASK 3- FILM STABILITY ON MEASURING DEVICES
]?repared by
Raytheon Company
Equipment Division
Autometric Operation
4217 'Wheeler Avenue
Alexandria, Virginia
Declass Review by NIMA / DoD
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ABSTRACT
A Gilliland Measuring; Engine hats been modified to allow
experimental measurements to be made on the relationship between
the radient energy incident on a photographic film and the air flow
rate required tb cool the film sufficiently for precise measurement.
This report describes the test set up and presents the experimental
results.
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TABLE OF CONTENTS
Section Title
Page
1 INTRODUCTION ....................>..... 1
2 QUANTITATIVE TEST P1~OGRAM ............. 1
3 RECOMMENDATION ........................ 6
LIST OF ILLUSTRATIONS
Figure
Title .
page
1
Gilliland Lens System ...........>.....
2
~+
2
Calorimeter Test Setup ..........>.....
4
3
Film Stability Test Setup .............
5
4
Minimum Cooling vs. Heat Input ........
7
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1. INTRODUCTION
In principle, there are many forces which can act on a piece
of photographic film in a measuring instru~ent to cause distortions and,
therefore,measurement errors. Iu practicey a good many of these poten-
tial sources of error are reduced to negligible quantities by good
instrument design and proper area environmental control. Film stretch
caused by excessive tension in film transports is generally controlled
by good transport design or eliminated entirely by the use of cut film
or chips. Humidity control of the mensurakion area is generally con-
sidered a necessity and is therefore provided.
The major problem which cannot be eliminated by design is the
heating effect caused by absorption of the viewing light which passes
through the film. This problem is a rathet small one in instruments
designed solely fo'r manual measurements at, low to medium magnifications.
It becomes a major problem in instruments tahich are designed for high
magnification and/or image correlation using image disectors, In this
latter case, the light intensity may not only be quite high, but might
also be variable as a function of magnific~.tion. In addition, the amount
of energy which is absorbed in the emulsion. and converted into heat is
a function of the film density, and is/ the;refore,a variable.
To put the problem in some perspective, it should be noted that
the lamps in manual instrument s, such as thle Mann engine,are usually rated
at one to five watts. After accounting for light losses in the condenser
system, lamp efficiencies, and removal of ''the infra-red components by
filtering, the actual amount of light power impinging on the film is prob-
ably in the milliwatt range. In contrast to this, measuring projector
systems and systems employing image correlation and viewing frequently
use arc lamps rated between 400 watts and '4 kilowatts, With these lamps
it is possible to have several watts of .li;ght energy impinging on the'
film, even after great care has been taken to remove all the IR components,
If this energy is focused onto a small area, the energy density can
quickly become high. enough to completely destroy the film unless measures
are taken to remove the heat.
2. QUANTITATIVE TEST PROGRAM
In order to obtain some quantitative data, a series of tests
was run using the Gilliland measuring pro~ector. This instrument is
equipped with a 1000 watt mercury arc lamp. Figure 1 is a schematic
diagram of the lamp -condenser assembly showing the major components.
The arc lamp is operated inside a double wall cylinder which contains a
mineral oil coolant. The mineral oil is quite transparent in the visible
but strongly absorbs ultra-violet and infra-red energy. The condenser
lenses collect the light energy and concentrate it in a circular area
on the film platen which normally has a diameter of about two inches.
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COOLANT
ARC LAMP
CONDENSER LENSES
~-REFLECTOR
PROJECTION LENS?
GIL.LILAND F LENS SYSTEM
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Calculations as to lamp efficiencies, optical efficiencies,
and losses are very difficult to perform with any high degree of accuracy.
In addition, lamp output tends to vary as a function of time as the
lamp ages.
In order to overcome these difficulties, it was decided to cali-
brate the illumination system by actually measuring the incident energy
at the film plane. Figure 2 shows the test setup which was used, In.
order to simulate the conditions of some of the newer instruments, addi-
tional condenser lenses were added to concentrate the light onto a
smaller area. The net result was that the energy was concentrated into
a spot with a 0.75 inch diameter at the film plane. The total energy
was measured by use of a calorimeter in w'~hich the temperature rise in
a measured quantity of blackened mineral oil was measured as a function
of time. Neutral density filters were placed in the light path, so that
several values of .energy density at the film plane could be obtained.
Table 1 shows the light power obtained far the various filters.
Filter Light Power - Watts
p 8.48
0.1 5.85
0,2 4.46
0.3 3.57
0.4 2.23
0.5 1.80
The fact that the me~~sured attenuation through the filters does
not quite match the theoretical is probably due to reflection losses at
the glass-air surfaces of the :Filters. phis merely demonstrates once
again the necessity of making direct measurements at the film plane.
With the illumination system calibrated, the film stability
tests were set up as shown in :Figure 3. .,The test film strip was produced
by contact printing from a glass grid plate onto film supplied by the
customer. The resulting film strip had Clear lines on a black background
(b = 2.0). The Gilliland measuring engine was used to detect any appre-
ciable expansion of the film by successively measuring the distance between
two grid intersections as the rate of copl.ing air flow was varied. Air
flow variation was achieved by varying a~:r supply pressure, or nozzle
orifice size, or a combination of both. Since the pressure ratio across
the orifice always exceeded the critical pressure ratio, the air flow
through the orifice was always at the acoustic velocity, and this permits
a rather straightforward calculation of 'the weight flow rate. By varying
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BLACKENED MINERAL OIL ( 14Occ)
THERMOMETER
GLASS PLATEN
CALORIMETER TEST SETUP
FIGUF~E 2
-4-
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FILM STABILITY TEST SETUP
FIG RE 3
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AIR SUPPLY
STEEL WEIGHTS
GLASS
GLASS PLATEN
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the flow rate from a maximum down. to the point where a fi:Lm expansion could
be detected, the minimum acceptable flow rate for each heating condition
was determined,
Flow through a "choked" orifice can be determined from the equa~
n~
G = R C-~_i) k=1
~-i
G = flow rate in ~~/sec
g = 32.2 ft/sect
R = gas constant -- 53.3
k = adiabatic coefficif>_nt - 1.4 $or air
A2 = orifice area - ft2
pl = upstream pressure -- ~~/f t2
T1 = upstream temperature -?R
G = 0.532 AzPi
For the air supply equipment set up for these tests, the entire
process can be considered adiabatic, sincelthe air supply storage tank
was not sufficiently large to allow any appreciable heat transfer. Thus,
the upstream temperature was calculated under the assumption of adiabatic
compression to the pressure pl. Flow rate were then calculated from the
known orifice areas and pressures. Figure',4 is a plot showing the minimum
flow rate for acceptable cooling versus the heat input. It is interesting
to note that there is a breaklin. the curve'at about 2 standard cubic feet
per minute and 5 watts per square inch, indicating more efficient cooling
at the higher air velocities. Above this''~break point, there is a linear
relationship between the cooling flow rate and the heat input. This should
allow for a reasonable amount of: extrapolation to higher heat inputs in the
new instruments. This linear relationship also agrees with heat transfer
theory for turbulent flow, which predicts 'a heat transfer coefficient linearly
related to the fluid velocity.
3. RECOMMENDATION
In using these experimental data for instrument design, one
should remember that the curve of figure 4 represents the minimum allowable
cooling for safe operation in the measuring engine. A prudent designer
would probably include a safety factor of 1.5 to 2.0 in his equipment.
Another important point to be considered in cooling system design
is that the temperature of the air as it Strikes the film should be very
near the room ambient temperature. This mill prevent sub--cooling in the
case wh~~e ~~ flow ate is greeter than Chat actually required.
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x10 3
S.S T
ACCEPTABLE
ZONE
UNACCEPTABLE
ZONE
0
5 10 15 2
25
0
HEAT INPUT-WATTS PER SQUARE INCH
MINIMUM COOLING VS. HEAT INPUT
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FIGURE 4