JPRS ID: 10536 TRANSLATION OPERATION OF SHIPBOARD HYDROACOUSTIC STATIONS BY V.A. POKROVSKIY AND G.A. SHCHEGLOV

• Document Type: CREST
• Collection: JPRS
• Document Number (FOIA) /ESDN (CREST): CIA-RDP82-00850R000500060049-7
• Release Decision: RIF
• Original Classification: U
• Document Page Count: 106
• Document Creation Date: November 1, 2016
• Sequence Number: 49
• Content Type: REPORTS

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JPRS L/ 10536
21 May 1982
Transiation
~ OPERATION OF
SHIPBOA~D HYDROACOUSTIC STA~TIONS
B~ ,
V.A. Pokrovski~ and G.A. Shcheglov
' Fg~~ FOREIGN BRO~DCAST INFORMATION SERVICE
~ FOR OFF[CIAL USE ONLY
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NOTE
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_ transmissions and broadcasts. Materials from foreign-language
sources are transla~ed; those from English-language sources
are transcribed or r~eprinted, with the ~riginal phrasing and
other characteristics retained.
Headlines, editorial reports, and material enclosed in brackets
- [J are supplied by JPRS. Processing indicators such as [Text]
or [Excerpt] in the first line of each item, or following the
last line of a brief, indicate how the original information was
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mation was summarized or extracted.
Unfamiliar names rendered phonetically or transliterated are
enclosed in pa~entheses. Words ~r names preceded by a ques-
tion mark and enclosed in parentheses were not clear in the
original but have been supplied as approprfate in context.
Other unattributed parenthetical notes within the body of an
item originate with the source. Times within ~tems are as
_ given by source.
The contents of this publication in no way represent the poli-
cies, views or at.ti~tudes of the U.S. Government.
COPYRIGHT LAWS AND REGULATIONS GOVERNING OWNERSHIP OF
MATERIALS REPRODUCED AEREIN REQUIRE THAT DISSEMINATION
OF THIS PUBLICATION BE RESTRICTED FOR OFFICIAL USE ONLY.
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JPRS L/10536
21 May 1982
OPERATION 0~ ~H~PBOARD HYDROACOUSTIC STATIONS ~
,
- Leningrad EKSPLU~T~TSTY,~ SUDO~VYKH GTDROARUSTICHESKIKH ST~iN~SIY in
Russian 1980 Cstgned to press 19 Sep 80) pp 3'4, 78-191
~List of syYUbols, seGt~:ons 2-5 of chapter 3, ~chapters 4-7, cc~nclusion,
references Qnd table of contents fram book "Operation of S~iipboard
- Hydroacoust3c Stations", by'~ladlen Anatol'yevich Pokrovskiy 95 ~p~,lser �
82 talibr ~Q
141 1.i16 of ~ 109 39 -F1
1J 12 a�.. I1 9 i I
quartz wa~ve mplif'~e� Y.modulation
+ g4 of f }tL~e 1Jfati ~7 e 69
.signal ~
o~~a~ep one .
PP Y
_ Fig. 3.3. Block diagram of "GV-1M" instrument: 1--~aster
oscillator; 2, 12--buffer stages; 3--electronic switch;
4--linear amplifier; 5--attenuator; 6, 11, 16--mixers; 7--
modulator; 8--monitoring voltmeter; 9--voltmeter display;
10~-amplifier; 13--crystal-controlled oscillator; 14--clock
multivibrator; 15--duration multivibrator
The oscillator of the instrument can operate in three modes: unmodulated
sine waves, amplitude modulation, and pulsed.
In all modes, the master oscillator in RC c~rcuit form generates sine-wave
signals with frequency that can be continuously tuned from 0.3 to 100 kHz
- in f ive sub-bands. Over narrow limits, the frequency of the master oscillator
5
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can be tuned by the "catibration" regulator. High precision of frequency set-
tin~ (0.12-0.25~6) is achieved by using a long spiral scale (up to 1.2 m) cali-
brated by a crystal-controlled oscillator.
The one-volt potentiometer to which waveforms are sent from the master oscii-
lator output is used to set a voltage of 1 V across the output divider. The
voltage setting is monitored by a VTVM that should have the pointer set at
the 1 V mark. .
The oscillator has two outputs: "1 volt" from which the volzage set on the
voltmeter scale is taken, and "uV" from which a voltage is taken zhat is con-
tinuously variable from 1 �V to 0.1 V. The impedance of the "uV" output is
10 S2 on all stages of the divider except the last (X10 000).
The pulse oscillator is connected by the pulser switch and shapes square pulses
with durations of 2.5n 5, 10 and 20 ms with recurrence rate of 1 s.
The amplitude modulator is connected by the modulator switch, and provides
continuously variable modulation up to 80Y for a sine-wave signal on constant
- frequency of 400 Hz. In the M% position of the modulator selector, the VTVM
is connected to the modulator output for checking percentage modulation. A
high-frequency filter suppresses the audio frequency of the operating modu-
lator.
The output divider and VTVM of the device can be used to get a calibrated
voltage from an external source that does not have its own voltage divi?er.
To do this, the signal toggle switch kills the power from all units of the
device except the VTVM. Voltage from the external source is fed to the "one
volt" 3ack, its magnitude is displayed on the 1 V scale of the voltmeter,
and the required output voltage is taken from the uV plug.
The wave meter of the device is connected by the calibration selector, and
operates in two modes "cal." and "w.m."
In the "w.m" mode, the waveme~ter measures the frequ.~ncy of the signal from
an external source connected to the "w.m" input. Ztao signals--from the ex-
ternal source and from the master oscillator--are sent simultaneously to the
wave meter mixer. A low-frequency filter isolates ::he difference frequency
of the signals--the beat frequency--and the difference signal after amplifica-
- tion is sent to a telephone and through a detector to an electric eye cathode-
ray tuning indicator tube (6Ye55). The master oscillator is tiined until "zero"
beats are achieved on both indicators, corresponding to the difference fre-
quency. At this point, the earphones give minimum loudness, and the "pupil"
of the electric eye is opened to the maximum. The value of the measured fre-
quency is taken from the frequency scale of the master oscillator. Sensitiv-
ity with respect to the wave meter input is 0.5 V, and it can be reduced by
the "amplif." regulator.
The ~cale of the master oscillator is calibrated in the "cal." mode. This
involves establishing exact correspondence between the scale reading and the
actual frequency of the master oscillator. In this mode, a crystal-controlled
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oscillator with resonant frequency of 5 icHz is connected to the mixer input
instead of the external source. The voltage of the crystal-controlled oscil-~
lator is purposely limited, and the frequency spectrum contains a large niunber
of harmonics that are multi~les of 5 kHz; therefore zero beats are observed
at corresponding points of the master oscillator scale. Less pronounced zero
beats can be observed on frequencies or the master oscillator that ~re multi-
ples of 2.5 kHz as well, which is attributed to the presence of second harmon-
ics of the fundamental frequency in the voltage of the master oscillator.
For example, for a scale point of 12.5 kHz, zero beats can be observed between
the second harmonic of the 12.5 kHz frequency and the fourth harmonic of the
~uartz crystal.
For calibration, a scale value is taken that is a multiple of 5 kHz in rhe
band in which the measurements will be made, and the "calibration" control
is used to set the frequency of the master oscillator to give zero beats,
which will indicate exact correspondence of frequency to the value of the
scale.
The "GV" instrument differs from the "GV-1M" in scale design and calibra-
tion procedure. In calibrating this instrument, zero beats are first ob~ained
near a scale point that is a multiple of 5 kHz, after which the cursor of
the scale is brc+ught to this point.
17 17 ~ s,i
wide band 5~
~nar ow band ~
5~ 17 -~1 a ~if 41,47 5960
1 2 IWr-~ I 4 5 6 ~utput ,
L 3 ~ 29 ,~s coarse
~ ~m l,tifierk~ f ine
88 ignition ~ n~u gy power
~ of f 76 lir~~93
~ 8 7
Fig. 3.4. Block diagram of "ShGU" instrument: 1--noise
generator; 2, 4, 5, 6--amplif iers; 3--bandpass f_ilter;
7, 8--power supplies
The "ShGU" noise-generator amplif ier (Fig. 3.4) shapes a sound field
in water jointly with an emitter incorporated into the device. Besides, the
instrument can be used as a powpr amplif ier for any electric signals in the
frequency range from 0.5 to 100 kHz.
- The instrument can be used in three modes: wide band, narrow band and ampli-
Pier.
In the first and second modes, the master noise generator b ased on a thyratron
generates noise voltage in the band of frequencies from 0.5 to 100 kHz. The
thyratron f ires upon pressing the "ignition" switch. After preampl~fication,
the noise signal is fed either directly to the next stage ("wide band" mode)
or to the interchangeable banclpass filter ("narrow band" mode) that limits
the frequency spectrum of the noise. An inverse-phase stage enables continuous
\
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control of signal power, a built-in VTVM with two measurement ranges being
used to monitor the voltage sent to the emitter.
In the "amplifier" mode, the master oscillator is disconnected and an exteraal
signal source can be connected to the input jacks. pfter power amplification,
this signal can be sent to the emitter and simultaneously taken from the out~
put jacks. If the emitter is not connected, the power amplifi~r can be dis-
connected from work by a contact block in an output coaxial plug to protect
the output tubes froffi the open-circuit state.
In addition to the emitter with stand, the instrument is equipped with a ser
of eight interchangeable bandpass filters and a boom for holding the emitter.
The documentation furnished with the instrument includes curves for the mutual
dependence of output voltage, sound pressure and distance.
The emitter of the instrument is a tubular magnetostriction transducer made
of a tube of Nicosi alloy accommodating a permanent rectangular magnet with
winding having 15 turns of wire with cross section of 0.55 mm. The resonant
frequency of the transducer lies in a range of 25-35 kHz.
~ 84~ B4E ~
KS K7
i tel~phone - wave ~neter - 2.
1
'frequencies 81� K~
coars~Rf � 3
fine R4 � B4A
K2 R7 K~ B6A K6
. synchr~uls~ 4 5 R7 6 ,iB ~ V
. ~;OB �
frequency, i~~ ~{R5 � outpu t; �R13 B4
83 � ByB regul . 8 . BS ~ave meter
O
duratxon, ms ~RS � _ ~e
KJ L . K4 ~[l~ ~e l
~o g _ -no se Z
output
B41X
filter supply
(onlq in position 30B)
Fig. 3.5. Block diagram of "Generator" device: 1--mixer;
2--frequency meter; 3--audio-frequency oscillator; 4--pulser;
5--electronic switch; 6--buffer stage; 7--voltmeter circuit;
8--attenuator; 9--amplifier
The "Generator" oscillator-frequency meter (Fig. 3.5) produces standard
~ cw sine-wave and noise signals as well as pulse signals with audio filler.
The built-in frequency meter measures the instantanaous frequency of the master
oscillator and the frequency of signals of external sources.
The technical data of the "Generator" are similar to those of the "GV-1M".
The difference is the great expansion of capabilities of the pulse generator
and increase3 prec~sion of frequency readout.
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The instrument can be used in five modes: "wave meter", "tone", "pulse",
"noise 1" and "noise 2".
In the "tone" mode, sine-wave voltage from the master oscillator (audio-
frequency oscillator K1) is fed from selector B4 through a plate to the fre-
quency me t e r t ha t a c t�s a s an electronic f our-digit scale of the oscil-
lator, and through a plate of the same selector to the "output regulator"
- (R7) that sets a voltage of 1 V on the output attenuator. The voltage setting
is monitored by a voltmeter on the 3B [3-volt] scale. The attenuator design
is analogous to the "GV-1M" instrument; a standard signal is taken off from
~ the "uV" coaxial output.
The circuitry of the instrument includes a final amplifier (K4) for power
- amplification of the signal and transmission to an emitter connected to the
output ~ack. Supply to the final stage is fed through switch B6A only in
the 30B [30-volt] position. 'Phe voltage supplied to the emitter is simul-
taneously monitored in this case.
- In the "pulse" mode, voltage from the output of the audio-frequency oscillator
is fed to the "output regulator" through a switching circuit controlled by
the pulse generator. The pulse generator includes an auxiliary "synchropulse"
output for synchronizing instruments (oscilloscope and selector) connected
_ in the channel of the measurement hydrophone. ~
In the "noise 1" and "noise 2" modes, a noise generator is connected to the
output regulator instead of the audio-frequency oscillator, the frequency
, meter an~ pulse generator are not used, and the other circuits remain unchanged.
In the "noise 1" mode, the signal from the output of the noise generator is
fed directly to the output regulator, i. e. in a wide frequency band; in the
"noise 2" mode it is fed via a bandpass filter formed in the "filter block"
device (see �3.3). The f ilter block is connected to the "filter" plug on
the rear panel of the instrument.
The "wave meter" mode is used for rough measurement of the frequency of cw
and pulse signals from external sources by a zero-beam method, and for exact
measurement of the frequency of cw signals by a digital frequency meter.
To realize the zero-beat method, mixer K5 is provided to which signals are
sent from the output of the audio-frec~uency oscillator and from the "wave
meter" plug from an external source (through the output regulator in the
"wave meter" mode, and directly in the "pulse" mode). Headphones are used
for detecting zero beats by ear.
~ The digital frequency meter (Fig. 3.6) of the instrument is used to mea-
. sure the frequency of cw sinusoidal signals of an external source and of the
master oscillator. The instrument uses the method of counting the number
, of voltage periods of the frequency being measured in a standard time interval.
The time-mark generator is a crystal-controlled oscillator with resonant fre-
quency of 10 kHz. The frequency meter has three measurement ranges: x0.1,
xl and x10, for which the measurement times are 10 s, 1 s and 0.1 s respectively.
9 .
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,
~
a � . . _ . .
~--------T------ ,b ~~t~ , ~o - . ~
+ ~okHz i~J ; ~ao ms ~de1a ~ ~
~ � B1B ~ n dis la ~ ,
. . . ~ I~ ~
counter 4 ~ ~ , ~ ti ~ ~
on ~Y ' re e t .
~ o ~ �
from ~ diagrams for scale x0.1
.E4E ~ 9 8 5 1 t U(t)
1 or. 0:1. s
; IV l1/ ~ ~ J ~ 1os
i ~ llo I
10 i 6~a 3 ! p' t, ~ ; t
KB-10 ; . 10 �8 ( N ~ ~ .
~ ~ S S 'i
~ v ~ I Y . coun , ~ ,
- ~ ~ � . ~ reset
control unit ~ diagram's for scales
~(1 and x10
Fig. 3.6. Digital frequency meter: a--block diagram; b--
voltage diagrams; 1--crystal-controlled osc311ator; 2, 3--
frequency dividers; 4--delay multivibrator; 5--coincidence
circuit No 1; 6--preparatory flip-flop; 7--reset multi-
_ vibrator; 8--controlling flip-flop; 9--coincidence circuit
No 2; 10--decade counter
The integer part of the n~nber is segarated from the fractional part by a
decimal pointi with position that depends on the selected measurement range.
On the x0.1 measurement range, the frequency of the crystal-controlled oscil-
lator is divided by 105, and pulses with interval of 10 s go to the prepara-
tory flip-flop and delay multivibrator (diagram I and Ia). The preparatory
flip-flop is flipped (diagram III) and a negative differential triggers the
reset multivibrator that pulses the four-digit counter to zero (diagram V).
At the same time, the preparatory flip-flop sends an 'enabling potenti~l of
negative polarity to one of the inputs of coincidence gate 5. The delay multi-
vibrator delays the time-mark pulse by 100 us, which is necessary for resetting
the circuit to zero. The delayed negative pulse (diagram II) flips the con-
trolling flip-f lop for 10 s, i. e. until arrival of the next delayed pulse
(diagram V). The negative enabling pulse of the controlling flip-flop is
fed to coincidence gate 9, and the "counter on" light is simultaneously lit. .
The signal being measured goes continuously to the second input of coincidence
gate 9, and for 10 s passes through the open coincidence gate to the counter.
The second delayed pulse of the time~mark generator returns the controlling
flip-flop to the initial state, coin~_.i~:~ce gate 9 is blocked, counting stops
and the light is extinguished. At the sauie time, a positive differential ~
~of the controlling flip-flop pulse through the second input returns the prepa-
ratory flip-f lop to the initial state (the preparatory flip-flop does not react
to the second positive pulse of the time~mark generator). The measurement .
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result is fixed on the counter before arrival of the third pulse of the time-
mark generator (display time). With arrival of the third pulse of the time-
mark generator the process is repeated. Thus the total working cycle on the
"x0.1" scale is 20 s.
(hi the "xl" and "x10" scales, the preparratory flip-flop also enables operation
, oi coincidence gate S within 10 s, but since the controlling flip-flop is
' flipped only for the time between delayed pulses of the time-mark generator,
the counter is on for 1 s or 0.1 s respectively. Thus in these ranges the
- total working cycle is 10 s.
� D2 K?
i.nput ~ fine gain ~ 4 v
~ control R6 m .
i . RI ~ K 1 � R4 RS
~
~ 1 2 ,t output
� ~'3 coarse � output
impedance, i~
: .
1
Fig. 3.7. Block diagram of "Power amplifier" set: 1--
emitter follower; 2--preamplifier; 3--f inal amplifier; 4--
voltmeter circuit
' The "Power amplif ier" set (Fig. 3.7) amplifies signals sent to its input
and sets up the sound field in water ~ointly with the emitters that are part
of the device.
Gain is controlled by the "coarse" and "fine" gain potentiometers. The load
of the final amplifier is an output *ransformer with tapped secondary for
matching the output of the amplifier to the load. The number of tur.ns is
determir_ed by the setting of the "output impedance, SZ" selector. The voltage
at the output of the set is monitored by a built-in voltmeter with two mea-
- surement scales. .
�3.3. Sound pressure meters
Measurement of sound pressure is the most typical task in hydroacoustic mea-
surements. The measurements are based on converting sound pressure to elec-
tric voltage by an instrwnent hydrophone (see �3.1). The sensitivity of in-
strument hydrophones is relatively low from unizs to tens of uV/dyne/cm2
and therefore direct measurement of the emf at the hydrophone output is prac-
tically impossible. Instrument a~pplifiers (i. e. amplifiers with gain exactly
determined uhroughout the frequency band) are used to amplify the emf developed
by the hydrophone. An rms AC voltmeter is generally used for display.
The sound pressure p is defined as
P k~l~. ~3.3)
where u is amplifier output voltage measured by the voltmeter, k is amplifiz~
gain, and ~li~ is the sensitivity of the hydrophone.
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J If k and ~1~ are deCermined beforehand, the voltmeter scale can be graduated
in units of sound pressure measurement.
The devices assembled into the block diagram corresponding to Fig. 3.7 have
been given the name of "sound pressure meters."
The principal technical characteristics of sound pressure aaeters are: fre-
quency response, amplif ier input impedance, level of electrical set noises,
gain, dynamic range, coefficient of nonlinear distortions.
The nonuniformity of the frequency response of sound pressure meters should
not exceed 1-2 dB over the entier. working frequency band. The shape of the
frequency response curve is determined primarily by the propertiee of the
hydrophone used in the sound pressure meter. The hydrophone can be treated
as a voltage generator that has a certain internal impedance zint and that
~ develops an emf E. The input im~:edance of the amplifier zin is the load im- .
pedance of the hydrophone. ~mpedances zint and zin must be matched on the
basis of conditions of ensuring a s~ufficiently unifo~~m frequency response
and maximizing the ratio of signal voltage to the voltage of noises at the
amplifier input.
The maximum power presented by the generator to the load is ensured by satis-
fying the equality zint - Zin� It can be shown [Ref. 51] that for piezoelectric
sensors working outside of resonance, Zint= 1/wCp, i. e. the internal impec.ance
of such hydrophones depends on frequency, and the coa~',ition of optir.ium energy
matching cannot be met for a wide frequency band.
From Fig. 3.8 we can see that ~
Ezin (3.4)
uin r Zin+ Zint ~
Expression (3.4) implies that to reduce the influence of zint on the voltage
across the load it is necessary to satisfy the condition
Zin~Zint� (3.5)
In this case, the voltage across the load will be close to the emf developed
by the hydrophone under no-load conditions.
It can be shown that satisfaction of condition (3.5) reduces thermal noises
in the circuit including the hydrophone and the amplifier input. The level
of electrical set noises of the amplifier normalized to the input should not ~
exceed a few microvolts.
The internal impedance of spherical piezoceramic receivers usually does not
exceed a few hundred ohms, and condition (3.5) is easily satisfied for these.
. It may be difficult to match high-frequency hydrophones because of the in-
creased internal capacitive reactance for small-sized spheres.
Condition (3.5) may be violated when the connecting cable between hydropllone
and amplifier is very long (more than 50 m) as a consequence of the shunting
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action of the distributed capacitance of the cable. Therefore in deep-water
- measurements preamplifiers are used that are combined with the hydrophone
and power supply in a unified sealed enclosure. The preamplifier also compen-
sates for s~gnal attenuation in the cable and increases the signal level with
r~epect to possible electrical. pickups on the cable route. io reduce the
level of acoustic interference of external sources during measurements, band-
pass filters are used that are included in the instrument amplifier circuit.
- The passband of the filters is selected on the basis of the condition of un-
distorted transmission of a signal that has a finite spectrum. For example,
for undistorted transmission of a pulse signal of duration T the passband
of the amplifier may be selected from the condition Of = 1.5T.
The gain of the instrument amplifier must be exactly defined throughout the
worl~ing frequency band since it is only in this case that the scale of the
instrument can be calibrated in sound pressure units in accordance with formula
(3,�3). Therefore the gain is adjusted by calibrated attenuators and provision
is made in the sound pressure meter circuit for calibrating the amplifier
to compensate for variation of gain due to aging of components, influence
of external conditions and the like. Calibration is done with the hydrophone
connected to the amplifier input.
The dynamic range of the amplifier determines the range of input signals that
_ can be transmitted without distortion to ti~e display. The dynamic range of
- the amplifier that is part of the sound pressure meter must not be less than
the dynamic range of the hydrophone, i. e. as wide as 120-140 dB. The dynamic
bandwidth is determined mainly by the properties uf the amplif ier input stage
in which sufficient gain reserve must be ensured at minimum interference level.
Deviations of the amplitude response frou~ linear within the dynamic range
give rise to nonlinear signal distortions. These are evaluated by the coef-
ficient of nonlinear distortions
Yu2 u3 -f- . . .
kH~ N = � iW~
ui
where ul. u2, u3,... are the effective values of the f'irst, second, third,
etc. harmonics of the signal being studied. The coefficient of nonlinear
distortions of sound pressure meters must not exceed 1-2%.
electronic voltmeters incorporated into the instrument amplifier are used
as the displays in sound pressure meters. The voltmeter circuit must provide
capabilities for measuring voltages of both sine-wave and noise processes.
This requirement is met by rms voltmeters with readings corresponding to the
_ effective value of the measured voltage regardless of waveshape.
Pulsed sound pressures are usually measured by an electronic oscilloscope
connected to a special output of the instrument amplifier.
- "IZD" [sound pressure meter] and "Voltmeter" sets are most extensively used
- in practical operation of hydroacoustic facilities.
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~
;
C1t8I~ !
meas. ,
1 wiae 5 recor er ~
f2 28
nge 2~ar 4Q~ 45 6e B~e:
el '
1 2 3 4 ' ~ d ' I~
. ca~~3brate ~s~band cha t
110 ~se 36 SD 7Q fOtl 1f2
8e 12 10 9 A
S .
~i ~ ' 6'J ~
meas. . e � outpu~ � set
range ,
15 - .L~buttong
~ ~cale"saPt}dlYhet."
. mqde8
Fig. 3.8. Block diagram of "IZD" set: 1--hydrophone; 2,
4, 7, 12, 13--amplifiers; 3, 14--attenuators; 5, 6--filters;
8--cathode follower; 9> 10, 11--voltmeter circuit; 15--cali-
bration oscillator
The " IZD" set (Fig. 3.8) is used for measuring both continuous and pulsed
sound pressures. This set includes a spherical hydrophone, instrument ampli-
f ier and VTVM unified into a single instrument, and eight interchangeable
bandpass filters.
The first amplification stage is based on a tube with high transconductance,
providing a dynamic range of up to 120 dB. The lower limit of ineasurable
- sound pressure is 1 dyne/cm2. A step'attenuator provides signal attenuation
by 120 dB in 10 dB steps.
The frequency response curve of the amplifier is shaped by interchangeable
bandpass filters that are connected in a break in the signal circuit in the
"narrow" mode. In the "wide" mode the amplif ier passes a wide frequency band
that is limited on the low side (300 Hz) by high-frequency filter~. The ampli-
fier circuit includes two special outputs for connecting a chart recorder,
an oscilloscope or other instruments. The signal goes to these outputs through
cathode followers; the level of the signal sent to the chart recorder is ad-
~ustable.
- The voltmeter circuit includes a diode rectif ier, an integrating circuit and
a measurement bridge with meter indieator connect~d in one of the diagnnals.
The voltmeter characteristics are determined by the values of the components
that make up the integrating circuit; the combination of components can be
. varied by switching the instrument to the different We9aur~ment modes: "pulse",
"noise" and "tone". The amplitude of ,~ingly recurring sound pressure pulses
can be measured in the "pulse" mode. In this mode, a storage capacitor is
nearly 3nstantaneously charged through the voltmeter rectifier, and the voltage
14
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. acro~ss the capacit is measured by the voltmeter. After each measurement,
the capacitor must be discharged by pressing the zeroing button. In the ab-
sence of a signal, the measurement bridge is balanced by the "zero set" con-
tro~.
The display scale is graduated in dynes/cm2 and dB. The zero level of the
(logarithmic) scale is taken as a sound pressure of 1 dyne/cm2. The instru-
ment readings taken from the logarithmic scale are sumaned with the "meas.
range" index of the step attenuator. Due to considerable nonuniformity of
the "IZD" frequency response, the readout rssults must be corrected by a cali-
bration curve given in the instructions for the instrument. The calibration
curve is plotted with the hydrophone connected, and therefore no other hydro-
phone can be used than the one included with the set.
The gain of the "IZD" amplifier is 100 (40 dB). To compensate for the change
in gain resulting from aging of components, changing tubes and so on, provision
is made for calibrating the instriunent by a special heterodyne. In the "het."
_ mode a calibration signal is sent directly to the voltmeter, where it is mea-
sured. In the "cal." mode, a signal from the heterodyne goes to the amplifier
input through the connected hydrophone. The position of the 40 dB attenuator
corresponds to gain of unity, and the readings of the instrimment in the "het."
, and "cal." modes should coincide. Otherwise, the amplification of the set
must be ad~usted by the calibrate control until the readings in both modes
agree exactly. '
In contrast to the "IZD", the "Voltmeter" set can be used as a sound pres-
sure meter, rms AC voltmeter and instrument amplifier. In addition to the
~ measuring instrument, the "Voltmeter" device includes a set of three spherical
hydrophones for measurement in different frequency bands.
~ r------_..~,
output i ~
filter ~ 7 ~
- ~ ~ ~ K4 . ~ .
input K1 A1 �B4 K2 i ~ ~ K5 ,
KC1 ~ 2 � B 6 3 y ~ 5 6 y 9
fl Rs ~ R~ ~ I
' ~ Bcal,! calibrate~ i
' i~'~ ~ B7 ~ R7 i 8 i
quivalent ~ - - - - - - - _ ~
mna ta~ rc;
C~ ~ R? i
T--
Fig. 3.9. Block diagram of "Voltmeter" set: 1--preampli-
fier; 2, 7, 8--buffer stages; 3--attenuator; 4, 5--ampli-
fiers; 9--squaring circuit; 10--calibrator
The instrument (Fig. 3.9) has three measurement scales: "X0.1", "X1" and
"X10". Measurements on the "x0.1" scale use a preamplifier with gain of 10.
15
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l~or operation on the "x10" ~acale, a v~itage divider based on reeistora R1
and R2 is connected in the signal circL:~t.
Provision is made in the ampliiier cirr.uit for connecting bandpass filters
ehat are unified into a separate "Filt-er block". The main amplifier of the
"Voltmeter" set has a gain of 1500, which can be regulated over a wide range
by the "calibrate" control. An oscilloscope can be connected to the output
plug when making pulsed measurements. An rms voltmeter (units K6 and R7)
~ is used in the set.
The amplif ier is calibrated by a pulse signal from a calibration oscillator
(unit R3) that generates square-wave voltage with stable amplitude of 100 mV.
The sigr.al is sent to the amplifier input by pr:~ssing the "cal." button.
frequency band setting, kIIz
.r-----~ r--~-=--~ .
- " Iower~ ~ upper ~ b
0 t~(fJ
11fP! ~ - r- -
0,3 ~ ~a~ ~ ~ ~er . ~ 0,415
f f
~ upper fre- '~6 ~ ~ ~B~ower fre- '
quency filte ? ~N' ;quency filter ~
' 1,2 ~e,~ - .
?,4 ~ ~ev ' ~ ~x~ ~ ~4
inpu ,r-----7 output
4,6 ~es ~NS 5,6
~ ,
9,6 $ee ~Nr 13,5
r-----~
19,? ~ ~e~ ~ ~ ~PN~ ~ ?7 .
~ ~
Jd4 ~u ~~e ~4
Fig. 3.10. Block diagram of "Filter block"
The "Filter block" is used in combined operation with rhe "Voltmeter" or
"Generator" (see �3.2). This device (Fig. 3.10) is a set of series-connected
lower-frequency and upper-frequency filters with cutoff frequencies in each
group differing by 1 octave, and the cutoff frequenc3es of the groups stag-
gered by '~-octaves. By switching filters in the necessary combination, the
passband of zhe amplifier can be restricted to a'~-octave.
�3.4. Display and recording devices
Display and recording devices are used for observing, measuring and recording ~
processes at the output of hydroacoustic stations.
In the operation of hydroacoustic facilities, electronic voltmeters and oscil-
_ loscopes are extensively used as displays, and signal-level chart recorders
~ and tape recorders are widely used for purposes of registration.
16
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Ele c t r o n i c v o 1 tme t e r s are usesl to measure voltages resulting from conver-
sion of acoustic processes to electrical, and also for monitor~Cng the working
state of hydroacoustic stations by taking voltage measurements at control
points. Electronic voltmeters are used in combination with with hydrophones
fur measuring sound pressure (see �3.3).
A specif ic requirement to be met by voltmeters used in hydroacoustic work
is the capacity for measuring voltages of complicated waveshapes. This re-
quirement is satisfied by rms voltmeters. In addition, in order to be capable
of ineasuring voltages at different points of hydroacoustic stations, the volt-
meters used must be universal, i. e. suitable for measuring both DC and AC
voltages.
In �3.3 we considered the specialized "Voltmeter" set that is an electronic
AC voltmeter. Monitoring and measurement instrumentation uses a general-
purpose type "IU" voltmeter (signal level indicator).
' 13 1131 ,i8 . � fi
input- 1 2 3 ~
~ 15 � 4n � 79
meas. zeronois y
range set a
6B 76 �
input = ~ 5 ~mode
~,q . 69 ~
' ?aeas . 64 xero
range 6 set~
Fig. 3.11. Block diagram of "IU" instrument: 1, 7--output
circuits; 2--amplifier; 3, 4, 5--vc~ltmeter circuitry; 6--
limiter
The signal level indicator (Fig. 3.11) measures the rms value of sine-
wave and noise voltages and DC voltages in the circuits of hydroacoustic sta-
tions. It has measurement ranges for AC voltages from 0.03 to 100 V, and
for DC voltages from 1 to 1000 V. A potential of 10 mV is taken as the zero
level of the logarithmic scale.
! The functional circuit of the "IU" instrument contains separate DC and AC
voltmeters and a common display. The AC voltmeter circuit contains a cathode
follower loaded by a voltage divider, a wide-band amplif ier and a square-law
detector. The use of a cathode follower with low internal impedance ensures
linearity of the stage up to 100 V, obviating the need for a high-impedance
input divider with lar~e capacitance. The low input capacitance keeps the
high input impedance of the voltmeter constant at 0.5 MS'a up to a frequency
of 100 kHz. In turn, the frequency response of the low-resistance (30 kSZ)
voltage divider that is used is nearly independent of the capacitance of the
following stage.
17
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_ a + . . b
o-?
.4~ d: input
- ~z C V
- "zero .
- V se~b~ �
R.
R~ R R= .
. e .
- ~ese~ " ~
Fig. 3.12. Diagram of voltmeter in "N" set: a--f?C; b--DC
In measuring AC voltage, a square-law half wave detector ie used (Fig. 3.12)
that is based on one half of duodiode A1. The second half A2 is used for
compensating the initial current of A1 under na-signal conditiions. M~eter
V is connected to the output of the instrument through the voltmeter "meas.
mode" selector in positions or "noise" (see Fig. 3.11). In the "noise"
position, capacitance C(Fig. 3.12) is multiplied by six, giving a display
time constant of 4-6 s.
A bridge measurement circuit is used in the DC voltmeter (Fig. 3.12b). To
limit the current through the display meter, a dfode limiter is included that
shunts the input of the bridge circuit when the voltage across it exceeds '
3.8 V. For convenience in using the instrument, a selector is provided for
switching polarity.of the display meter in accordance with the polarity of
the input signal. ,
~ Ele c t r o n i c o s c i 11 o s c o p e s arE widely used f or measur ing amplitude and dura-
tion of pulse signals, for determining the frequency o� signals by Lissa~ou
f igures, and also for on-the-spot monitoring of signal waveshape to detect
nonlinear distortions, clipping distortions and the like.
~Hydroacoustic measurement practice uses general-purpose osciiloscopes that
~must meet special requirements, and in particular the frequency responses
of amplifiers must permit operation at comparatively low frequencies (from
'DC to hundreds of kHz), the CRT is selected to have long persistence, and
a horizontal ecanning range that is matched to the ti~me parameters~ of pulses
to be measured (durations from a fraction of a millisecond to 10 seconds).
'These requirements are met most completely by the S1-4 and S-19 instrwnents,
`and by other low-frequency oscilloscopes. Monitoring and measurement instru-
mentation includes the "OI" (oscilloscope meter).
The "OI" instrument (Fig. 3.13) enables observation of waveshape and mea-
~surements of amplitude and duration of AC pulses; observation of waveshape
and measurements of amplitude of periodic signals; frequency measurement by
'the Lissa~ou figure method in con~unctiAn with the "GV-1M" instrument or some
~ ~other audio-frequency oacillator. . ,
. 18 � .
~ fAL USE ONLY
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; ~
;
~
~
i
' vertica~ calibxa S4 79n 79d 105,ff7 ~ ~
, inpu 1 ~ 2 d 4 S .
a
; ~y � ~ 4~ � ea �shift=
attenuatio� up, down ~
97
~ /'=50~z
; 59 28 ~ ~1-_put -~n
~ 10 11 Us 1YS � OCll ~
~ s~ �.cali a o oriz. ~,~O�brig tne, s
~ con~ro~ ~D ?5dd e~ input
~ 5B � g 8 7 6
~ 5 V settin
~ - sy.' ~e �scan amplitude -
j ~Yl?~ scan, Hz ~.shift Ieft, right
! '~2
i ~ scan � ~ ~
! 60 � . .
freq. fine .
tuning . .
Fig. 3.13. Bloc~C diagram of "OI" inatr~ent: 1--attenuator;
' 2, 3, 5, 6, 9--amplifiers; 4, 7--cathode follawers; 8--scan
oscillator; 10--AC calibrator; 11--DC calibrator
The process to be studied is sent to the "vertical input" terminals. The
' input attenuator ["attenuation"] permits signal reduction by factors of 10,
' 100 or 200: First-stage amplification in the vertical deflection amplifier
! can be controlled by ad~usting a fine-tuning gain potentiometer.
The a~plitude of the signal arriving at the "vertical input" terminals can
be measured by an amplitude meter. When the "calibrate" button is pressed,
~ the investigated signal going to the amplifier input is replaced by a voltage
~ of controllable magnitude on the line frequency, the amplitude being indicated
~ on a built-in meter. By using the "calibrator control" potentiometer to ad~ust
~ the calibration voltage, the image on the screen is made to coincide with
! the investigated signal, after which a meter reading is taken. The voltage
; fed to the instrument input iR determined by multiplying this reading by the
~ input attenuator index. .
~ The amplitude of DC pulses is measured by using a special input on a side
~ panel of the instrument from which a signal is sent to the cathode follower
of the vertical deflecltion amplifier. The me~asurement is taken by comparing
, the magnitude of beam dflection under the action of the investigated signal
i with the calibration voltage of +2 V that is sent in place of the signal when
a button is pressed under the input ~ack. �
The horizontal scanning generator provides five modes depending on type of
scannin~g: contin~ious, driven-sweep with variable duration, and driven-sweep
- with three fixed durations. The frequency of continuous canning and the dura-
I tion of the driven sweep can be reg~xlated in stages by using the "scan, Hz"
selector.
_i
~ Horizontal scanning is synchronized by a sigrial sent from the first stage
of the vertical deflection amplifier through a syachronization amplifier with
~ ~
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gain tha~ can be controlled by the "sync" potentiometer. The gain of the ~
horizontal deflection channel is ad~usted by the "scan amplitude" potentiom-
eter. When a scanning voltage is sent from an external source, the scanning
generator is automatically disconnected by a microswitch installed in the
"ttoriz. input" ~ack.
~t.should be borne in~mind that the "shift left, r3ght" potentiometer acta
only in the continuous and variable driven-aweep scanning modes. In the fixed
driven sweep mode the spot goes off-screen, and the leading edge of the ob-
served pulse is brought into registration with the zero point of the scale
by the "scan amplitude" potentiometer. .
Signal level chart recorders are used in case of necessity for prolonged
recording of the envelope of an inveatigated process (i. e. the signal level).
The advantage of chart recorders is the capability �or keeping a graphic record
directly during measurement, enabling on-the-spot monitoring of research re-
sults. In operating hydroacoustic stations, the use of signal level chart
recorders in con~unction with other instruments enables automating a number
of labor-intensive 3obs such as measuring directivity patterns, r~ception
interference level, frequency and spectral characteristics and the like.
The most widely used chart recorders in hydrflacoustic measurements are the
Soviet N-110, and the Danish ~ruel and Kjor instrumenta types 2304, 2305 and
2307. The design of these instruments is essentially the same, reducing to
an sutomatic control circuit that enables continuous tracking of changes in
. the level of voltage sent to the input of the instrument.
. ~ ~
amp.
~ inp t ~ ~
recorder 1 re~''~- div. ero 6
inpu " uc.. out d a
~ ~awer ~ . ~t' ~
_ _ ~ . , t s d8
�mode co~st.
~Jr.tV , O ~ ,
tage, mV9 B 7 �
iV;
. ~O �
- recordin
rate, mm~e
. Fig. 3.14. Block diagram of ~T-110 chart recorder: 1--
input attenuator; 2--functional dividpr; 3--amplifier; 4--
detector; 5--adder; 6--reference voltage source; 7--limiter; �
8--DC amplif ier; 9--stator winding of mo t or 10--rotpr
winding of m ocor; ll--vibrotransducer; 12--400 Hz oscil-
lator; 13--10 mV calibrator
The N-110 chart recorder (Fig. 3.14) has three operating modes determined
by the position of the "mode" switch:
20
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- --recording voltage level on audio and ultrasonic frequencies (fram 20 Hz
to 200 kHz) (selectc~r in position);
--recording instantaneous voltages that vary slowly in the range from 0 to
5 Hz (switch in position);
--mode of automatic stabilization of the le~ael of physical quan~tities such
as sound pressure that have been converted to voltage (selector iu midd~.e
position).
As a rule, only the first modE is uaed to measure parameters of hydroacoustic
stations.
In all modes the signal goes to the attenuator input that attenuates the signal
to 50 dB in 5-dB steps. In all attenuator positions the input impedance of
the chart recorder remains constant at 40 kft. The voltage from the attenuator
output is sent to functional voltage divider 2, which is a wire-wound tapped
potentiometer that acts as the sensing link in the automatic control system.
The voltage taken by the sliding contact from part of the functional divider
is amplified by AC. amplifier 3, rectif ied by detector and sent to adder
5 in negative polarity; the adder also receives DC reference voltage in posi-
tive polarity from reference voltage source 6.
The difference signal taken from the adder output is a:nplified by DC amplifier
8 and sent to motor winding 9. Fastened to one si~e o� the motor armature
is the recording pen, and on the other side is the sliding contact of the
functional divider. The armature shifts the sliding contact in the direction
that reduces the voltage difference at the addnr output. Motion stops when
the rectified signal voltage becomes equal in absolute magnitude to the con-
stant reference voltage. Any chnnge in the input voltage causes a motor con-
tr~l signal to appear at the adder output, shifting the sliding contact to
the point of the functional divider where the signal voltage corresponds to
the compensation voltage. In this way, the voltage across the sliding contact
is held constant during operation. This property of the chart recorder is
usPd in the mode of stabilization of physical quantities; the "div. output" '
and "amp. input" plugs are provided in the circuit for realization of this
mode. Obviously in the abs~nce of an input signal the sliding contact will
~ be moved by the reference voltage to the end position (the upper position
in the diagram), i. e. it will lock out, while application of the compensation
voltage to the functional divider will shift the pen to the zero point of
the scale. For the N-110 recorder, this voltage is 10 mV, and readings of
the voltage level are taken from this point in decibels on a logarithmic scale.
In the mode, the contacts of vibrotransducer 10 driven by oscillator 12
' that gznerates voltage on a frequency of 400 Hz are switched into the signal
circuit. Thus in this mode a DC signsl is converted to AC voltage. The ini-
tial recording level is selected by feeding DC vol:age from a special source
through the "con~t. voltage" control.
The nature of the scale is determined by the law of resistance distribution
lengthwise of the f unctional divider. The chart recorder is equipped with
a set of interchangeable dividers: three logarithmic having a dynamic range
21
FOR OFF[CIAL USE ~ONLY
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of 25, 50 and 75 dB, and one linear with dynami~,: range equal to that of [vibro-
transducer] 11. The dynamic range Du for the logarithmic scales is defined
by the expresaion Du = 20 lg (um~/umi~) , where u~x and um~ are the voltages
corresponding to the f inal and initial readings of the scale (u~in = 10 mV) .
Fdr the linear divider, the dynamic range T is def ined as T= um~/u~n. The '
level of t~he voltage fed to the chart recvrder input relative to umin = 10 mV
is defined as the sum of the reading taken from the chart recorder strip and
- the reading corresponding .~o the selected position of the input attenuator.
~ To convert the result to a zero level equal to 1 V, 40 dB must be subtracted.
It should be emphasized that normal operation of the chart recorder depends

_1 primarily on the state of the commutator field and the sliding contact of
functional divider 2. Corrosion, contamination and mechanical damage of these �
- - components cause an abrupt increase in measurement error, and disrupt stable
operation of the follow-up system.
Amplifier 3 of the chart recorder has a"zero level" control that can be used
for gain calibration of the amp~ifier. For calibra."ion, a voltage of 10 mV
is fed to the chart recorder input from an internal source. Calibration is
done by setting the pen to zero on the scale with the input attenuator com-
- pletely removed.
Capacitor C is connected in parallel with the detector load, and realizes
time averaging of the rectified signal. A change in value ~f this capacitor
shifts the lower limit of the chart recorder passband. .An increase in capaci-
tance expands rhe frequency response in the low-frequency region and reduces
the static error ~f ineasurement. On the oth~r hand, increasing the capacitance
increases the time lag of the follow-up system, resuiting in an increased
dynamic track:ing error, smoothing of level fluctuations, limiting pen di~place-
ment.velo^it; (recording rate) and impairing stab�~lity of the system. Thus
the position of the "lower freq. limit" control must be chosen to conform
to the nature of the process. ~
Potentiometer R is the detector load, and at the same time performs the func-
tion of adding the signal and reference voltages. The "div. limit" control
- has been introduced to compensate for the change in transfer factor of the ~
chart recorder when functional dividers are changed. The transfer factor
of the chart recorder increases with expansion of the dynamic range of the
divider. An extreme increase in the transfer factor may lead to intensifi-
~ cation of self-oscillations of the system, while reduction smooths aut the
processes being recorded. Therefore the position of the "div. limit" control
must be matched to the rating of the working fi.unctional divider.
~The last link of the follow-up system--the actuating motor with DC amplif ier 8
--is covered by negative velocity feedback. The feedback circuit includes
the tachogenerator motor winding 10, and the "recording rate" feedback depth
control. The velocity of armature movement increases as feedback weakens.
An increase in recording rate is advisable only if it has not been previously
restricted by capacitance C. An extreme increase in recording rate may put
the system out of the stable state, and therefore the positions of the "lower
- freq. limit" and "recarding rate" controls must be matched. The maximum possi-
ble recording rate is determined by cantrol signal limiter 7.
22
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The N-110 chart recorder leaves a record on paper tape by scratching a mag-
nesium coating with a needle. The paper is 50 mm wide. Paper of two types
is used: A--with black backing ax~d white coating to get a contrasty image,
and B--with transparent backing and red coating to produce photocopies by
contact printing. The paper is moved at constant velocity by a tape-transport
- mechanism driven either by its own electric motor, or by an external device
through a special shaft. The tape transport speed can be varied from 0.003
to 100 mm/s. The tape transport mechanism can be used to activate a variety
of inechanisms used in conjunction with the chart recorder such as a frequency
spectrum analyzer, audio-frequency oscillator and the like. To do this, two
- rollers with right-hand and left-hand rotation are provided with speeds that
- can be.varied from 0.108 to 3600 rev/hr. The set has a cam switch driven
by one of the rollers and enabling two processes to be sent alternately to
the chart recorder input.
- Tap e r e c o r d e r s, or instrument s f or magnetic recording and playback of
acoustic waveforms are extensively used for recording signals of complex shape.
Their advantage is the capability for repeated playback of a stored process
without repeating a complicated experiment. This is particularly convenient
in cases where the environment in which the recording is done does not perm3.t
the use of cumbersome analyzing and recording equipment. In hydroacoustic
- measurpment practice, tape recorders are used to record the noises of ships,
hydroacoustic interference, and signals with the aim of subsequent processing
and analysis of the recording in the laboratory.
The principle of magnetic recording (Fig.
p 3.15) is based on altering the magnetic
Q~ state of a sound-recording medium by using
~ an alternating magnetic field. The medium
RH pg magnetic tape is moved at constant
D velocity past three heads: EH--erasure;
~2 ~ RH--recording; PH--playback. The tape
_ M is moved by a drive roller D against which
~1 ~ ~A out ut the tape is pressed by pressure roller R.
Alternating current from the output of
~input recording amplif ier RA flows through the
winding of the recording head. The vol-
Fig. 3.15. Block diagram of tape tage of the signal to be recorded goes
recorder to the input of the recording amplifier.
The magnetic field of the recording head
magnetizes the tape. Thus a time change in current is recorded on the tape
as a a change in residual magnetization with respect to length. To ensure
linear dependence between the signal current and the residual magnetization,
~ current of higher frequency is simultaneously sent to the recording head from
magnetizing osci~lator O1.
Residual ~ragnetization forms a magnetic field around the tape, and as this
tape passes the p~aybaclc head, the field induces a flux in the core of the
head that is proportional to the residual magnetization. The emf induced
in the winding of the head in proportion to the rate of change of the flux
is amplified by playback amplif ier PA and transmitted to reproducers as a
copy of the signal recorded on the tape.
23
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I
Before recording, the tape must be demagnetized, i. e. the previ~.ous recording

~ must be removed. The function o� tape demagnetization is performed by the i
erasure head. Current is sent to the winding of this head from erasure oscil-
lator 02 that generates a waveform with frequency much higher than the upper ;
frequency of the signal to be recorded ~nd with amplitude sufficient to satu- ;
rate the tape. '
Thus the following principal components can be dietinguished in any tape re- ~
corder: sound-recording medium, tape-transport mechanism, magnetic heads,
recording and playback amplifiers, magnetizing and erasure oscillators and
reproducers. As a rule, the recording and playback functions in commexcial
. tape recorders are performed by general-purpose heads and mnplif iers, and
the erasure and magnetizing currents are generated by the same oscillator.
The sound-recording medium for most present-day tape recorders is powder-
oxide magnetic tape. Most extensively used are two-layer tapes consisting
- of a base and a working layer. The base material is acetylcellulose or Mylar
film. Ferric gamma-oxide and iron-cobalt ferrite (CoFe203) are used for making
= the working layer. Particle size is no larger than 0.4 ~tm. The powder is
_ applied to the surface of the backing by a special lacquer. The working side
of the tape is polished to reduce head wear due to abrasive action of the
film, and also to enhance sensitivity and improve lengthwise uniformity of
sensitivity. The nonworking side of the tape is dull to improve winding qual-
ity .
Existing standards provide for production of magnetic tapes with total thick-
ness of from 12 to 55 Wn. Thickness of the working layer ranges from 4 to
16 um. The trend toward decreasing tape thickneas results from the attempt
to maximize the duration of continuous reco~rding,. The limiting factor in
this trend is the tensile strength of the tape, and also extensibility under
load. The standard width of magnetic tape is 6.25 mm. The use of old tapes
6.5 to 6.35 mm wide may be detrimental to the directional properties of tape
recorders. Cassette tape recorders use tapes 3.E1 mm wide.
= I~Yagnetic tape quality is characterized by the follawing principal electro-
acoustic parameters: sensitivity and nonuniforffiity of sensitivity, frequency
response, level of nonlinear distortions and noise level,
Sensitivity (effic~ency) characterizes the ratio of the residual magnetic
flux to the intens~ty of the low-frequency field of the recording head. In
_ practice, relative sensitivity is taken as the ratio of sensitivity of the
tape that is used to the sensitivity of a standard tape, expressed in decibels.
- Variation in uniformity of sensitivity by �1 dB is heard as a change in loud-
ness, and is unacceptable for using tapes in measurements. Tape sensitivity
increases with increasing thickne~ss of the working layer.
- ~Frequency response of tape depends on many factors. Chief among these are
� the "penetration effect " and "self-demagnetization", which show up as a drop
in fz~equency response in the high-frequency region. In the self-demagnetiza-
- tion effect, elementary sections of the magnetic tape are demagnetized by
an external f ield with lines of force directed contrary to the internal flux.
24
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I
The intenaity of this effect increases with decreasing ratio of the length
of an elementary magnet to its thickness, i. e. the shorter the wavelength
of the signals being recorded. The penetration effect shows up as a reduction
in depth of penetration of the magnetic f ield into the working layer of the
- tape with increasing signal frequency. This effect is compensated by reducing
the thickness of the w~orking layer.
~ In practice, the frequency response of the tape is defined relative to some
standard tape as the difference between the ratios of efficiency on the upper
cutoff frequency to efficiency on the reference frequencq, which is taken
: on a linear section of the frequency response curve for both tapes.
Nonlinear distortions of the magnetic tape make the greatest contribution
' to the overall nonlinear distortions that arise during magaetic recording.
These distortions are due to nonlinear dependence of remanent induction on
magnetic field strength. Linearity of this dependence is considerably improved
' by sending a high-frequency magnetizing current with amplitude considerably
greater than that of the signal being recorded to the recording head simul-
taneously with the sidnal. Tape sensitivity during magnetization is consid-
erably improved together with the increase in linearity of the remanent magneti-
zation curve [Ref. 31]. The magnetization at which tape sensitivity i~i maximwn
is called optimum magnetization.
The magnitude of distortions is usually evaluated with respect to the level
~ of the third harnconic expressed in percent relative to the level of the funda-
i mental frequency.
~ Tape noises show up as an emf that appears at the output of the plaqback head
' when a tape passes that contains no recording. They are caused principally
; by nonuniformity of the structure of the working layer.
Tape noise can be reduced by shielding the tape and heads from the action
' of external magnetic f ields, balancing the magnetizing current and setting
~ current at the optimum value.
= One special kind of tape noise is print-through. The essence of this effect
is in mutual magnetization of tape layers in contact on the reel. During
playback, the signal will be accompanied by weaker copies of itself that may
lead and trail. The relative level of print-through on present-day tapes
is from -50 to -56 dB.
In measurement practice, consideration must be taken of such a tape property
as reduction of the recording level after the first few playbacks. For exam-
ple after the first playback the recording level decreases by about 30X; the
falloff in recording level staps after about ten playbacks. Therefore, in
especially important cases a control signal of known level should be recorded
on the tape.
' The tape-transport mechanism ensures high constancy in the rate of movement
of the magnetic tape past the heads in the recorder. Standards provide for
the following nominal tape speeds: 38.1, 19.05, 9.53, 4.76 and 2.38 cm/s.
25
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The instability of tape motion due to different mechanical components of the
tape recorder is characterized by wow and flutter defined as
lDr = ~~v~X x 100X,
v
where ~vma~ is maximum drift of tape speed from nominal, and v is nominal ~
tape speed.
Waw refers to fluctuations of.tape speed of less than 10 Iiz frequency, and
flutter refers to fluctuations at a frequency greater than 10 Sz. Wow causes
periodic shifting of the frequency spectrum and is heard as "wavering" of
the sound; flutter causes frequency "chopping" and is perceived as "warbling"
of the sound. Th~ wow and flutter of laboratory tape decks should not exceed
�O.1X.
In addition to handling its main 3ob, the tape transport mechanism also pro-
vides fast-forward and fast-rewind modes, high-quality reeling and fast stop.
The recording head is a ring-type electromagnet made up of two half-rings.
The forward or working gap contacted by the moving magaetic tape is filled
with a thin layer of no~agnetic material. The width of the gap is made ap-
proximately equal to the thickness of the working layer. A relative reduction
in gap width leads to frequency distortions due to the "penetration" effect,
and an increase in gap width increases nonlinear distortions. The possibility
of overloading the recording head is reduced by a rear gap in the core that
increases reluctance. In addition, the rear gap reduces the level of noises
that arise as a consequence of remanence of the core.
The playback head is analogous in design to the recording head. The difference
is absence of a rear gap since the low currents in playback cannot cause satu-
ration of the core. ~
The playback head is the component that a g b ~
Br s re
makes the greatest contribution to non-
iinearity of frequency response of the .
record-playback channel. a/2 t
. a
One of the major causes of frequency ~ Z s'
distortions in playback is the f inite
size of the head gap. It can be seen
from Fig. 3.16 that as the wavelength
a of the recorded signals decreases,
the emf induced in the head decreases, Fig. 3.16. Effect of gap dis- ~
and vanishes when a whole wave fits tortions: a--wavelength greater
into a section of the tape equal to than gap width; b- wavelength
the width x of the gap. This can be equal to gap width
attributed to cancelling of the oppo-
sftely directed magnetic fluxes of elementary sections of the tape of length
a/2. These are called gap distortions. The position of the first minimum
that occurs on the frequency response curve as a result of gap distortions
is detex~nined by the ratio of the width of the working gap of the head to the
26
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i ~
I wavelength of the signals recorded on the tape x/~. Wavelength is defined
as 7~= v/f, and consequently the upper frequency limit of magnetic recording
can be raised by reducing the width of the working gap and increasing tape
speed. In the general case, the width of the gap should not be greater than
half the wavelength of the upper frequencies of the signal. Frequency dis-
tortions similar to gap distortions arise when the working gaps of the heade
~ are skewed; they should be perpendicular to tape motion and parallel to each
. other.
i Uout A second cause of frequency distortions
~ ~ ~ is direct dependence of head efficiency
~ .
j i on frequency ~ s ~r~m sin wt, where w is
~ angular frequencq,and ~m is the ampli-
i ~ tude value of magnetic flux.
~
i ~ ~ ~
' f~ ?f, ~f f The resultant frequency response of
~.section ~ the record-playback channel is shown
' Fig. 3.17. frequency response of th~ in Fig. 3.17. The falloff of the curve
record-playback channel at low frequencies makes it difficult
to play back infrasonic signals.
The erase head differs in a much wider working gap (100-250 ~tm) and higher
current (tens of mA). During travel past the head, each section of the mag-
, netic medium is sub3ected ~o the alternating magnetizing action of a magaetic
field that rises smoothly to saturation and then falls to zero. The frequencq
of the erasure current is selected so that the magnetizing force changes by
~ no more than 1X during a period. .
Uout~ dB
In addition to their usual function of signal *30
amplification, the record and playback ampli- +~0 ~
fiers also handle the no less important job 2
0
of correcting the frequency response of the
channel comprising the recording head, sound- _Z~ ~
recording mediwn and playback head (Fig. 3.18).
' The amplifiers in tape recorders used for mea- ~
surement purposes must be equipped with cali- 100 900
f~ Hzo000
bration devices, step attenuators for ampli-
' fication control, and meters for measuring Fig. 3.18. Amplifier fre-
record and playback levels. quency responses: 1--record;
2--playback; 3--resultant
It should be borne in mind that the same tape
recorder must be used for recording signals and for playing them back during
analysis since each recorder has its own frequency response peculiarities.
�3.5. Equipment for analyzing phase and spectral characteristics~
The basis of directed action of hydroacoustic stations consists in accounting
for and making use of the phase structure of the acoustic signal field. Cal-
culation and design of receiving and sending acoustic antennas and devices
for directional action boils down to calculating phas~ relations in the elec-
tric circuits of equipment and antenna structures. Therefore rather severe
, 27
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requirements are imposed on the phase characteristics of hydroacoustic equip-
ment, and particular attention must be given to checking them. Phase meters
are used for analyzing the phase characteristics of hydroacoustic equipment.
Pha s e me t e r s measure the phase shif t between two voltages, and in hydro- .
acoustic measurement practice they are used to verify phase identity of multi-
channel receivers and amplifiers. Besides, phase meters may be incorporated
into sound speed meters based on using the phase method of ineasurement. And
finally, nearly all hydroacoustic d~.rection finders are devices that in one
way or another measure the phase difference of acoustic waveforms received
by separate components or reception groups of an acoustic antenna.
lfao techniques are used for m~asuring phase difference in hydroacoustic tech-
nolbgy: the compensation method, and the method of converting a phase shift
to a proportional time interval.
The compensation method involves using a graduated phase shifter to cancel
the phase shift between two voltages. Phase equality is determined by a null
indicator, and the sought phase shift is read out from the scale of the phase
shifter. The method is realized in hydroacoustic stations for determining
the direction to a signal source, where the phase shifter is a compensator
coupled to the course angle scale.
The method of converting a phase shift to a proportional time interval is
used in low-frequency phase meters for direct measurements in the circuits
of hydroacoustic stations. One of these, named the "Phase shifter", is in-
cluded in a special set. ~
. R% 1-10
.8410- ~ . . .
2 c annel ~ftJ
K~ I' u~ ' ~ t
' ' phase ~ ~
sh3fter ~ . R9 1-10 , ' ~ ~ ~ ~ ~ t
inpu~ase R3 � es ~o-~ ` !il ~ ' ~
� ~haanel
~ f req~en~~c~y � e2 3 ' ' ; , ; , , L
~z YI' u~1 /V
t
I ~ ' ~a v t
K5
- � K2
meter 61� / y /1! ~3111a ' , Bdlll3
input . ~ jK v , _ ~ o~
al~brat B ~ }
~ BJb � R2 ~K ~ zero aet - ~
� internal ry RS �
external I1 5 set �
mode
x~ B3}lla
IIII -
Fig. 3.19. Block diagram of "Phase shifter" set: 1--phase shifter; 2, 3--
output attenuators; 4, 5--limiter amplifiers; 6--coincidence gate; 8--volt-
meter circuit
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The "Phase shifter" set (Fig. 3.19) measures the phase shift between two
sinusoidal waveforms from external sources, and splits the sinusoidal signal
' from an external oscillator into two voltages phase-shifted through a continu-
ously variable angle. The phase shift is monitored by the scale of the phase
meter in the phase shifter.
The phase shifter (K1) is made in an RC circuit. To get the required frequency
band, the values of the circuit components are selected by the "frequency kHz"
switch that has three positions. Output voltages phase-shifted by 10-90�
are sent to the "channel I" and "channel II" plugs through calibrated attenu-
ators that are analogous in construction to those used in the "Generator"
and "GV-1M" devices. The voltage sent to the attenuators 1 V-- is moni-
tored by built-in voltmeter KS in selector position B3-"IV". The phase shift
is checked by the phase meter with selector B1 in the "internal" position.
The phase meter of the instrument contains two identical limiter amplifier
channels K2 and K3 that convert the phase-shifted sine-wave voltages sent
to their inputs into square pulse sequences that are time-shifted relative
to one another. The time of coincidence of negative polarity of both series
of pulses is f ixed by coincidence gate K4. Obviously, pulse duration at the
output of the coincidence gate is proportional to the phase shift. A meter
connected to the output of the coincidence gate in the "180�" position of
the B3 selector measures the average current of the pulse series, enabling
calibration of the instrument scale in degrees of phase shift from 0 to 180�.
Zero phase s:if t of the input voltages corresponds to complete time coincidence
of negative-polarity pulses, and the average current of the coincidence gate
is maximtnn; therefore the zero of the meter is on the right.
The phase meter has provisions for three auxiliary modes switched by selector
~ B3. In the."zero set" position, both inputs of the coincidence gate are open
and the millivoltmeter needle is zeroed by the "zero.set" potentiometer. In
calibration modes "IK" and "IIK', voltage from an external source can be sent
- to the input of the device. Calibration involves setting phase identity of
both channels by simulating zero phase shift alternately for each channel.
~ An exceptionally important place in hydroacoustic measurements belongs to
spectral analysis of complex signals, ship noises and interference to recep-
tion of hydroacoustic information. Theoretically, a complex function can
be represented by a Fourier series consisting of sep~rate harmonic components.
The procedure of resolving a complex waveform into components of definite
frequency and amplitude is called spectral analysis. Spectral analysis can
be used to solve such problems as ob~ectiv? classification of signals, locat-
ing sources of elevated noise and interference and the like.
Modern methods of s;~ectral analysis can be ~ivided into two groups: filtra-
tion methods and Fourier transform methods. Filtration methods, w~ich have
been more widely used in practice, have three varieties: direct f iltration
methods, methods with preheterodyning and methods with time compression of
the signals be ing studied. Instruments for spectral analysis are divided
into harmonic analyzers for sequential analysis of the apectrum, and spectrom-
eters for simultaneous or parallel analysis.
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Instrinnents for sequential analysis may be based on using the method of direct
filtration and the method with preheterodyning.
The former method is used in selective amplifier circuits with working princi-
p1e that consists in sequential tuniag of a frequency-selective negative feed-
back circuit of a wide-band amplif ier to separate frequency components of
the process. As a result af action of the feedback circuit, all frequency
components of the signal will be suppressed except those that correspond to
- a dip in the frequency response curve of the feedback circuit at the given
instant. The width of the passband of selective RC amplif iers is constant
relative to the tuning frequency, i. e. Of/fo= const throughout the frequency
band. Readout is usually by a meter with scale graduated in decibels or per-
cent of the measured frequency component with respect to the fundamental har-
monic of the signal.
In connection with expansion of the absolute band of analysis in the high-
frequency region, the use of selective amplifiers is limited to the infra-
sonic and audio ranges. The frequency band of analyzers can be expanded into
the high-frequency region by using heterodyning to convert the frequency spec-
trum. ~
The working principle of the heterodyne analyzer consists in continuous shift-
ing of the investigated process relative to the narrow passband of a filter
with fixed tuning. The spectrum is shifted.by a heterodyne with frequency
- fh mixed with the signal frequency fs. The narrow-band filter isolates one
of the side frequencies fh+fs or fh- fs at the mixer output. The level of
the isola�ted frequency component is measured by a display. Since the width
of the f ilter passband does not change, the absolute width of the passband'
of heterodyne analyzers does not vary throughout the frequency band. This ~
limits the use of heterodyne analyzers in the 1ow-frequency region. .
Instruments for parallel analysis are designed on the basis of using a direct
filtration method. The working principle of�devices of this type is based
on using a system of narrow-banc~ f ilters with inputs connected in parallel, ,
and outputs alternately switched to the display by an automatic commutator.
The overall frequency response of the spectrometer is a"comb" made up of
the frequency responses of individual filters int~rsecting on the level of
70X dec'line of the curve from the maximiun value of the .transfer factor of
the f ilter. When the investigated process is sent to the f ilter inputs, all
frequency components of the spectrum of this process that are isolated by
the filters will be observed simultaneously at the outputs. The spectrometer.
filters have a constant relative passband width measured in fractions of an
octave.
The principal characteristic of the spectrum analyzer is its resolution de-
fined as the capacity of the analyzer to distinguish ad~acent components with
near f requencies. Quantitatively, resolution is evaluated by the smallest
frequency interval within which two ad~acent components are observed with
a dip equal to 50y of the maximum value. Resolution is primarily determined
by the parameters of the analyzing filters, and corresponds approximately
to the interval between average frequencies of spectrometer filters or to
the analysis bandwidth of the harmonic analyzer.
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An advantage of harmonic analyzers over spectrometers is high resolution of
the instruments with fairly simple design. The cumbersome selective system
of spectrometers on low audio frequencies precludes the use of filters with
bandwidth of less than 1/3 of an octave. A considerable disadvantage of se-
quential-action devices is the limitation on rate of analysis that depends
on the duration of transient responses that arise in the selective part of
the instrwnent during retuning.
It can be shown [Ref. 53] that the time necessary for rise of a signal to
95X of the steady-state value for a tank circuit with passband width ~f is
defined by the relation
tl = 1/Af, (3.6)
i. e. tl is the time necessary for analyzing an individual frequency component.
The time required for analyzing an entire spectrum by the sequential-action
instrument with absolutely constant analysis band Of in the case of continuous
and uniform tuning of the analyais frequency can be found as
Ta)4~fupper 2flower~~ (3.7)
~
where fuPper and flower are the limiting frequencies of the band being studied.
Thus for values of ~f = 6 Hz, f lower = 20 Hz and fupper = 20 kHz the minimum per-
missible analysis time is 38 minutes.
In instruments of simultaneous analysis used for studying standard processes,
the rate of analysis is nearly unrelated to parameters of the filters used
in the selective system of the spectrometer since the investigated process
, is continuously sent to all filters during the entire time of observation,
and the wavefor~s in the filters can be taken as steady-state for steady-
~ state processes. In this case, the maximum permissible rate of parallel anal-
, ysis will be determined by the time constant of the display that is used.
Spectrum analysis may be practically instantaneous when electronic displays
are used in combination with high-speEd commutators.
Use of the method of time compression o:F the signal in sequential-analysis
~ devices increases the rate of analysis a.lmost to the level of parallel-action
devices while retaining high resolutiun. It can be shown [Ref. 55] that time
compression of the process leads to multiplic~*_ive transfer of its spectrimm
as a result of multiplication of the frequencies ~hat make up the spectrum
.by the time-scale transformation factor, or compres$ion coefficient kt (Fig.
3.20):
Ti.r fc.r _ kt~ (3.8)
Tc.r f i.r
where Ti.r, Tc.r are the durations of the investigated and converted realiza-
tion, f i.r, fc.r are the frequency components of the investigated and converted
spectrum.
Using (3.8) to transform (3.7) we get
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4(ktfupper - ~tflower~ 4~fupper' f lower~
~ Ta~ kt~~f) kt(~f)~. (3.9)
Expression (3.9) implies that the time of analysis of a compressed signal
deCreases in proportion to the increase in the time-scale transformation faa~
tor. Physically, acceleration of the process of analysis can be attributed
to the fact that a kt wider analysis band can be used for the expanded signal
spectrum while retaining the former resolution by reducing the duration of
transient processes in the filter kt times. For example, in accordance with
(3.6) the time of analysis of an individual frequency component in a band
of 0.025 Hz should be 40 s; after signal compression with kt = 4~J0 000, the
band of analysis can be increased to 10 000 flz, and the time of analysis re-
duced to 0.1 ms.
a U ~ ' U ~
~ t t
. to ~'2 ,
U U 4 u '
.
t t
' ~2 t p 2~'~ 2fz
Fig. 3.20. Deformation of spectrum in time compression:
a--realization and spectrum of process before conversion;
� b--after conversion
Any time-scale converter includes a re- ~ delaq
cording device, storage unit and readou~. dt~~-k,~ I~r_e
Signal compression is realized by increas- _J
ing signa_l readout rate by kt times over input~ gy~ _ output
the recording rate. Miniature equipment i~ 2
most frequently uses a delay line as +
the storage unit (Fig. 3.21). d;/Xr ~
_ The input of the device receives a signal Fig. 3.21. Block diagram of time
- that is converted by switch Sw to a se- comvressor
quence of individual samples (Fig. 3.22). According to Kotel'nikov's theorem,
the sampling period ~t is deteimined by the condition
- . ~t~ 1 , (3.10)
. 2f~PPer
where fuPper is the highest frequency contained in the spectrum.
If duration Ti.r is given, the number of samples is defined as
~ Ti.r 9
N ~t 2fuPPerTi.r� ~3.11)
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j
I
I
i
; a Uin Z 6 ,
i
~ ~ 4 5
+ dt
~ i.r t
' ~ ~ ~ ~ i ' ~ ~ ~ .
i Uout~ Td ~ i j j i: i i
b I I I~ t
I t~ ~
I I ~ I i ~
il ~I
/ ~ ~ I ~ ~
I ~ . i ~
~I
~ ~ II
i Fig. 3.22. Illustrating ~
~ time compression princi- ~ ~
~ ple: a--input signal; i j
b--output signal
' I ~ i
. I
Each sample reading goes simultaneously to the output of the device and to
~ the input of the delay line where it is shifted at a f inite rate. During the
~ time between two ad~ ~ , (4. 3)
where d is the greatest dimension of the active part of the antenna.
Relation (4.3) is also valid for the case of location of the hydrophone in
the fi~ld of a cylindrical measurement emitter that has vertical dimension
d when measuring the sound pressure developed by this emitter.
' A necessary condition of relative placement of transducers during measurements
is coincidence of their acoustic axes since the major parameters of hydro-
acoustic stations overall sensitivity and sound pressure must be de-
termined in the direction of their maximum valuea. Inaccurate orientation
of the acoustic axis of a narrow-band antenna relative to the position of
measurement transducers may lead to appreci-
able errors in measurement. In some cases, p~ p~ p~~~pir=
deviation of the hydrophone from the acoustic a~coustic axis~
axis of the emitter may cause an apparent ef- ~
~ fect of pressuse increase with increasing dis-
tance due to a reduction of the angle between r'
the direction to the hydrophone and the acoustic r:
~ axis of the antenna (Fig. 4.3).
Fig. 4.3. Choosing depth of
Bringing the acoustic axes into line, or estab- immersion of hydrophaze
lishing coaxiality is done first in tt~e vertical,
and then in the horizontal plane. Coaxiality in the vertical plane is estab-
lished by selecting the depth of immersion of ineasurement transducers. In
a
dp
b
Fig. 4.4. Establishing coaxiality of the reception antenna
and emitter direction: a--correct; b--incorrect
doing this, the acoustic axis of the antenna must first be established hori-
zontally (Fig. 4.4). The instant of coincidence of the acoustic axes is
' 39
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determined from the maximum signal level at the output of the hydroacoustic
statioa r~nd the hydrophone operating in the mode of reception of the sound
f~eld of the radiator, or from the maximwn voltage level at the output of
the hqdrophone th~t receives signals fram a hydroacoustic st~tion operating
irt the active mode.
Establishment of coaxiality in the horizontal plane is done by rotating the ~
directivity pattern of the antenna until the maximum signal is attained at
the output of a station operating in the passive mode, or at th~ output of
a hydrophone that~ receives signals of an actively operating station. if the
- station has a stationa..ry directivity pattern, coaxialitq in the horizontal
pl~ne is established by shifting the measurement transducer relative to the
acoustic center of the antenna at the same distance away.
Consideration should be taken of the fact tha~. spherical and cylindrical trans-
ducers in the horizontal plane as a rule have a real directivity pattern that
does not correspond to circular. Therefore in such transducers the d"irection
of the acoustic axis must be chosen beforehand in the sector that corresponds
to the smoothest change in sensitivity. This direction is indicated by a
reference line that ia made on the transduceY housing and is used to estab-
lish coaxiality of the transducers. Immersion of the measurement transducer ~
in water and orientation of its acoustic axis should be done by using a rigid
bar.
The stability of ch,aracteristics of ineasurement transducers to a consid-
erable extent determines the error of the entire measurement. For example,
the frequency response of the sound pressure meter is used to correct the
readings of an instrument in the measurement process. Practice has shown
that hydrophone characteristics change with time, which must be taken into
consideration in doing calculations, and in this connection, measurement hydro-
phones should be calibrated at least once a year.
- The stability of ineasurement results also depends on preparation of the mea-
surement transducers. Before immersing in the water, the surface of the trans-
ducers must be carefully cleaned and degreased to ensure better wetting of
the trnasducer. Before doing measurements, the transducer is held in water
for the time required to equalize the transducer and water temperatures.
Particular attention must be given to secure fastening of the transduaers
to prevent them from shifting relative to the acoustic antenna of the statton
, during measurement. Even slight shifting of the transducer (as a result of
rocking of the ship) in the field of an antenna with sharp directivity charac-
teristic relative to the platform to which the transducers are secured causes ~
considerable fluctuation of the signals being measured. If it is not possible
to avoid signal fluctuation, the number o~ readings must ensure the capability
of statistical processing of ineasurement results.
Linearity of reception and amplificat.'Lon channels of a hydroacoustic etation
is one of the necessary conditions for accuracy of ineasurements of parameters
that have the physical sense of the trransfer ratio: overall aensitivity,
frequency response and directivity pattern. Measurement of these parameters
40
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involves determining the ratio between the output and input quantities, i. e.
between the voltage uout at the output of the channel and the sound pressure
p accing on the antenna. In the given case, the requirement of linearity
of the reception and amplification channel is formulated as the condition
uOllt ~p a COIISt ~ ~~1. ~4~
i. e. the output quantity is proportional to the input, and the ratio of these
quantities does not depend on the absolute value of either of them. Graphi-
cally, the concept of linearity of a channel is illustrated by a linear segment
of its amplitude characteristic. Linearity of a channel is lost if the in-
put signal quantity goes beyond the limits of the linear section of the ampli-
tude response curve (Fig. 4.Sa). This leads to nonlinear distortions of the
' a' ~out~ _ i
~ b Uout c Uout
i~ i? -
~ - - I -
~ k2`k+ rl
~D t IP t . I P t.
I - - ~ .
--r-- , i ~ i i
r- ~ ~ ! ~ I
I Pm~ Pm~ Pm2 ~ v~ i
i 3 ~c ~
a ~ I oo N
I
W O,
i ~ O ~ q,~.1 ~
~
~ N ~ ~ A~. O ~
y,~,~ ri ~-a C~1 y~ x c~d ' c~d
a ~ d
b o ~ e~o ~ ~N D4
- ~ - * , .
62
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~ GOST specifications [Ref. 36], repairability is the term given to the property
of a system that consists in gdaptability to prevention and detection of the
~auses of failures, damages and elimination of their consequences by carrying
~ out technical servicing and repairs. The or ganizational aspect of the problem
! ie.more in evidence on the operational stage, i. e. admini~trative and material
support and training of service personnel. Figo 6.1 shows the classificatfon
of factors that determine restor,ability of equipment.
I
' The influence of various factors on operability of equipment enables us to
~ use operational experience to determine the necessity of carrying out so-
called planaed repairs, i. e. repairs provided for in normative documents
' [Ref. 48]. Elimination of sudden failures that arise usually when th~ equip-
' ment is being used for its purpose is handled immediately after detection
' by unplanned repair.
, Depending on the psrticulars of operation, degree of wear and the technical
- state of equipment, as we11 as the labor inputs for regulatory work, a dis-
~ tinc~ion is made between navigational repair, routine maintenance and Qverhaul.
~ Navigational repair, which is sometimes called pseventive maintenance, is
' done during preparation for the voyage, and consists in upgrading the level
of equipment operability by replacement or restitution of individual campo-
; nents utilizing the efforts of service personnel over periods that usually
~ do not exceed a few days. ~
; Routine maintenance involves restoring the output functional characteristics
~ of a system by carrying out repairs or replacing malfunctioning components
w:Lth elimination of detected problems. Routine maintenance is handled by
repair facilities electronics shops or the electronics departments of ship
repair plants.
Overhaul has the purpose of restoring operation of equipment and total or
nearly total restitution of the work life of the system with replacement or
' restitution of any components, which may amount to more than 50~ of the entire
= equipment. This kind of repair is done by land-based repair enterPrises.
After i~utine maintenance and overhaul, a complete check is run, and the equip-
ment is aligned with measurement of electroacoustic parameters immediately
after repair, and measurement of output p3rameCers on a shakedown cruise..
Guaranteed time of troub le-free operation of equipment after repairs is usu-
ally indicated in the repair-release documentation; oth~rwise the warranty
extends to three months after routine maintenance, and to six months after
' overhaul. Times between repair for equipment that has undergone routine main-
tenance or overhaul are shortened by 20-30X [Ref. 2].
~ Unplanned repair is also provided for by normative documentation, only without
stating times. Depending on the extent of damage~to the equipment, a distinc-
~ tion is made between running and emergency unplanned repairs. Running re-
pairs can be handled by service personnel using spare components, units and
modules. ~As a rule, emergency repairs require the facilities of repair orga-
nizations and more components than are avaialble in the ship's inventory.
~
i
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- If equipment has failed during the warranty period, it is the right of the
users to make a cla3m againet the manufacturing enterprise. In doing this,
a claim sheet is filled out stating the complaint against the manufacturer
regarding deviation of working qua3.ity of a hqdroacoustic station from tech- '
n~.cal specifications during the warranty period.
Flaws that are cause for a claim are: premature wear or breakage of parts,
components and modules of the equipment, and also malfunctions of the device
as a whole that cause it to fail; considerable deviation of pa~ameters from
the norm that cannot be eliminated by following operating instructions for
ad~ustments and alignments.
- The claim sheet is t~ be compil.~d by the manufacturer's representative; if
this is not done within 10 days of notification of the defect by telegram,
the claim is compiled by the chief of the electronics service on the vessel,
signed by the captain and presented to the SERP [expansion not givenl which
transc.iits the cla~m to the manufacturer. The plant must eliminate the defect
at no charge by repairing or replacing the failed component.
- The level of repairability of marine hydroacoustic stations fs assumed to
- be characterized by quantitative indices that can be grouped into two cate-
gories [Ref. 2]: operational (temporal) and economic. Operational indices
include: average recovery time TB, probability of restoring operability within
a'predetermined time P(tB), and operability restitution parameter u(t$). The
time of restoring~operability of equipment is comprised first of all by the
�active repair time, and secondly by the time for ensuring repair. Calculation
of the active repair time for any facility is l~ased on knowledge of the failure
rate of its components and the time neceasary for repairing these components.
- On this basis, the average repair time Ta is found fram the relation
n ' n n
T~ =I}~ 9Jta ! = v~ ~/t~! l~~
wtiere q3 is the conditional probability of failure of alements of the 3-th
group; t8i is the acti~e repair time upon failure of elements from the ~-th
group; n is the number of groups of elements.
As we can see the quantity that determines the average time of restitution
_ of operability is time ta3. This time depends to a censiderable degree on
the type of failed component, the complexity of the equipment and its design
peculiarities. ~
In the case of a large volume of statistical data, such a point evaluation
~~an be used, but in the case of few data it is necessarg to determine int~rval
- eatimates by known methods of probability theory. FoL a rough estimate of
~repairability, particularly on the design stage, use can be made of statistical
data obtained in the operational process or on tests of equipment of similar
types or purpose. Some of these data for individual electronic components
- are summarized in T~ble 2[Ref. 7].
Analysis of operational experience with marine hydroacoustic st~tions has
enabl~ed us to define the reliability of reatitution time among other
- 64
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TABLE 2
Statistical indices of restoration of operability
of electronic equipment by typFS of failed components
Detection Correction. Average repair time, hr
Type of failed component time, hr time, hr
min max
: Vacuum tubes 0.72 0.22 ~ 0.23 0.96
Oscillator tubes 0.4 0.44 - -
Resistors 0.4 0.27 0.3 0.98
~ Capacitiors 4.4 1.8 0.4 1.7
Tuning controls 3.0 5.2 - -
Switches - - 0.25 1.06
- Motors - 1.26 5.13
Tanks circuits - - 0.65 2.8
_ Wiring 1.26 1.37 - -
Fuses - - 0.75 3.2
quantitative indices. For example, for the Paltus-M hydroacoustic station
this index is 2.4 hr, for the most reliable Soviet fish-locating hydroacoustic
station the Kal'mar it is 0.75 hr, and for the sonar unit in the Pribor-
_ 101 fish-locating ~et with little cumulative operating experience, it is
3.4 hr.
The pro~.,bility of timely restoration P(tB) = ProbITB ~ tB~, i. e. the proba-
bility that the running recovery time TB will not exceed a prPdetermined time
_ 'tB, is found reom the expression
re
P (te) _ ~ f (TB) dTa~
where f(TB) is the probability density function of recovery time. For example
in the case of an exponential law
f (~B) = r8 exp (-telTH)
probability P(tB) = 1- exp(-tB/TB). ~
f~ts) ~
n5~ '
, ~
_ a, 4 - ~
O.J -
0.? -
0.1 ~
~0 7,0 5,0 10 ta, hr
- Fig. 6.2. Histogram of time of recovery of operab ility of
the Paltus-M hydroacoustic station
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Statistical data on the times of recovery of operability for the Paltus-M
hydroacoustic station have been used to plot a histogram of the distribution
of these times (Fig. 6.2) in accordance with the relation
- f~te) = n(Bt, c)~~ ~te) OtB c~
where ~tBi is the i-th interval of grouping of v~lue~ tB; n(~tBi) is the number
of values of tH in the i-th interval AtB; N(tB) is the total number of re-
coveries.
The flow of recoveries uB characterizes the recovery rate, or the number of
repairs that have been made in a unit time. This quantity can be determined
from statistical data for n failures as the reciprocal of the average recovery
_ time uH = N(tB)/tB. In the case of an exponential law of distribution of the
probability density of recovery time, u(tB) = 1/TH = const.
Generalization and dissemination of experience with equipment op~ra~ion as
- well as a numbe~ of techn~cal measures are improving u(tB) with a corresportd-
ing reduction in tB, which can be illustrated by the way that t:~is last quan-
tity (yearly average for the Paltus-M hydroacoustic station) depends on oper-
ating time:
Year of operation 1970 1971� 1972 1973 1974
. tH, hr 2.3 1.8 2.1 l.f~ 0.5
Economic quan.titative indices characterize the expen~ii'cures of labor �
and material resources on restoring operability of equipmc:nt. These include
[Ref. 2]: repair cost, average repair cost, and also the coefficient of
recovery cost. The repair cost depends on a large nuanber of factors, among
which are: cost of components, materials, el2ctric energy, depreciated cast
of equipment, payments to repair agenci~s. t)bviously this is a rando~n quan-
tity, but the average cost of repair can be deduced from operational experience
as the mathematical expectation of the co~t. Depea~ding on expenditures for
restoring operability in the case of a specific failure, equipment can ~ie
categorized as either repairable or noi~-repairable. Advisability of repair
can be established from the ratio of expenditures for repair Cr to the cost
of making and installing the given equipment Cpr, i. e. from the coefficient
� of recovery ~:,st kr~ = Cr/Cpr. Depending on remaining service~life and other
factors, the critical or threshold value of this parameter that corresponds
to making a decision about advisability of repair may range from very small
- values to nearly unity. In Che latter case, ~he decision about advisability
of repair is made when there is no possible way to replace the failed compo-
nent, unit or module. ~
Let us note possible ways of improving the repairability of technical sys-
tems: improvement of the method of locating failures; using sutomated moni-
toring systems; optimizing the spare.parts inventory; improving the skill
of service personnel; improving repairability of equipment; improving the .
_ method of predicting failures; improving technical documentation.
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�6.2. Troubleshooting methods
The process of running repair of equipment can be divided into four stages:
determination of failure; establishing the nature of the failure and localizing
the malfunction; correcting the malfunction; post-repair check of operability.
These stages are common to all known methods of repair regardless of the method
of recovery of operability--automated or manual. Analysis of the steps taken,
and also experience in operating hyd., coustic equipment, have enabled de-
termination of the average proportion of time expend~tures with respect to
each of the stages. According to Ref. 4, the average time of preparing moni-
toring and measurement equipment and localizing malfunctions in electronic
equipment takes up about 77%, correcting the malfunction 15X, and post-
repair check 8% of the technical time of recovery, which in turn takes
up only about~~ of the total recovery time. More than 70X of this time goes
for nonproductive expenditures, e. g. various steps to organize repair, in-

~ cluding down time due to lack of spare parts. Analysis of statistical data
over five years of operation shows that proportion of required time expendi-
tures for finding and correcting malfunctions in hydroacoustic stations, for
example in fish-locating gear, is 31X and 69X respectively for the Paltus-M
hydroacoustic statian, and 42 and 58Y for the Priboy-101 set. As we can see,
a considerable part of the active repair time goes to locating the malfunc-
tions. This fact makes it necessary to optimize the algorithm for locating
malfunctions so.as to reduce the pinpointing time.
The location of malfunctions in modern hydroacoustic equipment is increasing-
ly difficult because of g�rowing complexity, which increases the time for check-
ing the working state and determining the causes of a failure. The search
algorithm can be simplified if certain a priori data are available on the
properties of the equipment: probability of failure of given components,
time for checking operability of these components and so on.
Analytical determination of the optimum check sequence in locating a failed
component involves the following assumptions; the equipment consists of n
components with independent failures; q~ is the probability of failure of
the j-th component; Tj is the time spent in checking the component.
_ It can be shown [Ref. 7] that in the case of equipment failure, the conditional
probability q~ of failure of the ~-th component leading to equipment failure
is determined by the relation
n
9i = ~9~1 P~) 9~~P1+
where q~ and p� are the a priori probabilities of failure and trouble-free
operation of t~e ~-th component, and n is the niunber of camponents. When
~ the number of the component coincides with the number of the check over time
T~, the time for locating a malfunction when the i-th component has failed is
t~.,, ~_,~"~~T~, and the average time for pinpointing the failure is defined as
the mathematical expectation in the form
67 ~
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n-1 1 n
te. x=~[~9c~Pi) T) ' 9t~PJ�
The optimum sequence f_~_r checking operability of components, or the optimum
algoritt~m for pinpointing a failure, is found by solving the variational prob-
lem on minimizing tn.H, giving condition T,p,/ql