Ie. Rat AND WILDLIFE SS
a && ON

COMBINED-ENVIRONMENT TESTING OF SHIPBOARD
ELECTRONIC EQUIPMENT
Second of a series
Additional test data are presented, and a regression equation is derived

Which verifies the contribution of synergistic (interacting) effects to
deterioration in performance by relating output power to environmental factors

F. Robinson Research and Development Report 18 March 1968

This document is subject to special export
controls and each transmittal to foreign
governments or foreign nations may be made
only with prior approval of the Naval Elec-

tronics Laboratory Center, San Diego,
California 92152.

MBL/WHOI

I

MEN

tll

O O03 Mi 40

AN

PROBLEM

Verify the occurrence of synergistic (interacting) effects in combined-
environment testing and show their contribution to the deterioration in perform-

ance of a shipboard electronic module.

RESULT

The test revealed that synergistic effects occurred and contributed to the
degradation in performance of an intermediate-frequency, amplitude-modulation
(if/am) amplifier module. This specific module is used in the signal converter

which is part of the AN/SRC-16.

RECOMMENDATIONS

1. Conduct a conventional environmental test according to MIL-E-16400E
(NAVY)* and a combined-environment test on a shipboard electronic module and

compare the results.

2. Continue assessment of the effect of combined environments on shipboard
electronic equipment with various types of shipboard electronic modules.

3. Continue work to develop a ‘‘standard’’ combined-environment test

procedure.

ADMINISTRATIVE INFORMATION

This report covers work from October 1907 to January 1968 and was ap-
proved for publication 18 March 1968. The work was performed under the SEEDS
program, SF 013 14 04, Task 5788 (NELC R114), by the Equipments Effective-

ness Division.
Thanks are extended to C. J. Van Vliet, of the Mathematical Division,

for preparing the computer programs in conjunction with the derivation of the
regression equations.

“Department of the Navy Military Specification MIL-E-16400E (NAVY), Elec-
tronic Equipment, Naval Ship and Shore, General Specification, 15 June 1962.

REVERSE SIDE BLANK

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2-7

CONTENTS

INTRODUCTION ... page 5

THE TEST PROGRAM... 5

Test specimen... 5

Operating conditions... 6
Performance measurements... 6
Test conditions ... 6

VERIFICATION OF SYNERGISTIC EFFECTS... 7
CONCLUSION ... 17

RECOMMENDATIONS ... 17

APPENDIX: TEST FACILITIES AND INSTRUMENTATION .. .

ILLUSTRATIONS

Environmental chamber and vibrator, photographs ...page 20
Control console and monitoring instrumentation, photographs .. .

Test instrumentation, block diagram 22

TABLES

Various applied treatments ...page 8

Test data of three if/am amplifier modules ... 9-14
Estimates of output power from regression equation... 16

REVERSE SIDE BLANK

19

21

fiw

\

INTRODUCTION

The reliability of operational shipboard electronic equipment has not im-
proved appreciably over the past few years. Failure rates of electronic equipment
are still high and means to lower them should be ascertained. In many instances,
equipment which has been subjected to environmental testing in the laboratory
fails once it is installed and operating in its actual shipboard environment. Indi-
cations are that the present test methods have inherent deficiencies in that they
do not produce these potential failure modes and effectively simulate field fail-
ures during laboratory testing. Scrutiny of the test method for subjecting elec-
tronic equipment to environments in a sequential manner reveals two obvious
discrepancies: (1) the test method does not simulate the actual environmental
conditions in which the equipment is to operate, and (2) it does not subject the
equipment to the synergistic (interacting) effects of the true environments.

If the reliability of shipboard electronic equipment is to improve in the
future, then, the potential failure modes and problem areas must be detected prior
to mass production of the equipment. This may be accomplished through simulat-
ing the total effects of the actual shipboard environment. In other words, the
equipment should be exposed to the synergistic effects as well as to the main ef-
fects in an environmental test. These combined effects have a detrimental effect
on the performance and failure rate of shipboard electronic equipment, as prior
tests have revealed. *

The purpose of this report is to show the occurrence of the synergistic
effects in combined environments and their contribution to the degradation in per-
formance of shipboard electronic equipment.

Subsequent sections will describe the test procedures and the verification
of synergistic effects in combined environments.

The test facilities and instrumentation are described in the appendix.

THE TEST PROGRAM
Test Specimen

The intermediate-frequency, amplitude-modulation (if/am) amplifier
module was chosen for this particular test because of availability and suscepti-
bility to the environments as demonstrated in a previous combined-environment
test. The active components in the module are all solid-state devices. The
module receives a 500 (£3)-kHz intermediate-frequency signal, demodulates and
amplifies the audio signal superimposed on it, and provides automatic-gain-
control bias.

The module contains four major circuits: (1) four-stage intermediate-
frequency amplifier, (2) mixer-detector, (3) two-stage audio amplifier, and (4)
automatic-gain-control amplifier.

* Navy Electronics Laboratory Report 1292, Environmental Test for Electronic
Equipment for Southern Cross, by W. R. Beye, 8 June 1965; and

Navy Electronics Laboratory Report 1366, Combined-Environment Testing of
Shipboard Electronic Equipment, by F. Robinson, 7 April 1966

Operating Conditions

The if/am amplifier modules were operated with an input signal level of
1000 microvolts and a carrier frequency of 50043) kHz, modulated 30 percent with
a 1000-Hz tone. The supply voltages to the modules were held at +27 Vde and
-27 Vdc by two regulated power supplies. The modules were adjusted for 1 milli-
watt of output power across a 600-ohm balanced load and the volume control wag
locked to prevent alteration as a result of vibration.

Performance Measurements

Performance measurements were recorded for each of the 27 treatmenis
that were applied to the test specimens. These measurements consisted of the
voltage at three test jacks, output power, and distortion. Prior to each run, a set
of initial readings was taken at room ambient condition for each of the three test
specimens.

Test Conditions

A three-factor, three-level, full-factorial test which consisted of 27 com-
binations of temperature, humidity, and vibration was applied six different times
to each test specimen. Each of the 27 treatments was allowed to stabilize for 1
hour to expedite the complete test. Stabilization was verified by monitoring wet-
and dry-bulb charts and by monitoring the internal temperature of each module with
thermocouples. After the elapse of an hour, performance measurements were re-
corded for each specific treatment. In the interest of repeatability, the tempera-
tures and humidity levels were programmed from two cams. The 27 treatments
along with levels of the three environments are shown in table 1.

VERIFICATION OF SYNERGISTIC EFFECTS

The presence of the various interacting effects of combined environments
and their contribution to the overall degradation in performance of an if/am
amplifier module were verified by subjecting three if/am amplifier modules to a
3x3x3 full-factorial test.

The regression equation which relates the output power of the if/am am-
plifier module to the environmental factors will be derived for the test data.

Tables 2 through 7 show the levels of the environments along with the
output power of each module. The enormous number of data involved necessitated
the use of a computer to facilitate calculations in the derivation of the regression
equation.

In the 3x3x3 full-factorial test, the general regression equation contains
26 terms and takes the form shown below.

P= bgt b,T + boH + b,V + b,T + bgH? + beV? + bLTH + bgHV + BVT

2 2 2 2 2 2m
+ bj TH + b,? H + b HV + b, 4H V+ b,,VT + bv 1
2772 272 2m 2 2
+ b, 40 H* + b, 7H Ve + bigV T* + by gTHV + bj yTHV + bs, TH V

a bo) T “HV + by gTH?V? + Dy lta Dol BEY SD ey

However, to facilitate the derivation of the response equation, only the
first nine of the 26 terms were considered in the regression equation, since these
terms included the main effects as well as the two-factor interacting effects.

The regression equation which was derived took the following form:

2 2 2 y 7
P= bo + b,T + boH + b4V + b,T te b.H + bv? + b/TH + bgHV + bo\ oT

The coefficients of the above regression equation have the following
values:

ty = lata b, = -0.000045701 bg = -0.00039512
b, = 0.0013594 b. = 0.000015696 by = -0.00047497
b, = -0.0014441 b, = -0.0025789

bz = 0.063866 b, = -0.000020144

TABLE 1. VARIOUS APPLIED TREATMENTS.

Level
Treatment Vibration, g Temperature, °F Humidity, %
1 50 35
2 50 35
3 50 35
4 86 35
5 86 35
6 : 86 35
7 0.50 122 35
9 122 35
10 50 65
11 50 65
12 50 65
13 86 65
14 86 65
15 86 65
16 0.50 122 65
17 1.25 122 65
18 2.00 122 65
20 1.25 50 93
25 0.50 93
26 1.25 122 93
27 2.00 122 93

TABLE 2. TEST DATA OF THREE IF/AM AMPLIFIER MODULES, RUN NO. 1.

Output Power, mW

ean Vibration, Temperature, Humidity,

2 3 g °F %

1.12 1.09 1.14 0.50 50 30
1.38 1.12 1.29 1.25 50 30
1.20 | 1.09 129) 2.00 50 35
0.96 1.00 0.98 2.00 86 39
0.91 0.96 0.93 1.25 86 30
0.85 0.96 0.96 0.50 86 35
0.50 0.17 0.46 0.50 122 93
0.50 0.14 0.40 1.25 122 93
0.35 0.13 0.35 2.00 22 93
0.62 0.16 0.48 2.00 86 93
0.86 0.15 L 0.81 1.25 86 93
0.93 0.88 0.88 0.50 86 93
0.93 1.04 1.04 0.50 50 93
1.09 1.06 1.14 1.25 50 93
0.98 1.06 1.14 2.00 50 ua] 93
0.52 0.60 0.56 2.00 122 35
0.58 0.54 0.60 0.50 122 35
0.50 0.56 | 0.56 1.25 122 35
0.97 1.04 1.04 1.25 50 65
1.06 1.14 1.14 2.00 50 65
1.06 1.14 Ioil?/ 0.50 50 65
0.86 0.93 0.91 0.50 86 65
0.79 0.86 0.86 1.25 86 65
0.81 0.84 0.86 2.00 86 65
2.00 22 65

1.25 122 65

0.50 122 65

10

TABLE 3.

Output Power, mW

Vibration,

Temperature,

TEST DATA OF THREE IF/AM AMPLIFIER MODULES, RUN NO. 2.

Humidity,

Module
oF
0.40 0.48
0.40 0.46
1.01 | 1.06
0.96 1.04
0.88 1.03
0.72 0.79
0.70 0.72
0.68 0.70
0.45 0.54
0.38 0.54
0.36 0.52
0.66 0.72
0.86 0.88
0.96 | 0.96
0.66 0.79
0.74 | 0.79
0.74 0.77
0.45 0.58
0.41 0.48
0.36 0.50
0.96 1.01
1.04 1.04
1.04 1.04
0.70 0.74
0.70 0.74
0.72 0.72

TABLE 4. TEST DATA OF THREE IF/AM AMPLIFIER MODULES, RUN NO. 3.

Output Power, mW

Temperature,

cal)

Humidity,

11

12

TABLE 5. TEST DATA OF THREE IF/AM AMPLIFIER MODULES, RUN NO. 4.

Output Power, mW

SS dae CES Vibration, Temperature, Humidity,
1 2 3 g on %
0.40 0.54 | 0.38 2.00 122 35
0.38 0.50 | 0.36 1.25 122 35
0.68 0.91 | 0.91 2.00 50 35
0.96 0.91 1.01 1.25 50 35
1.04 Tet, 1.06 1.25 50 65
1.06 1.14 1.14 2.00 50 65
0.79 0.79 0.84 2.00 86 65
0.79 0.81 0.81 1.25 86 65
0.45 0.45 0.38 1.25 122 65
0.38 0.48 0.32 2.00 122 65

==
0.96 0.93 1.04 2.00 50 93
0.96 TT 1.04 1.04 E25) 50 93
0.70 0.74 0.74 1.25 86 93
0.66 0.72 0.74 2.00 86 93
0.40 0.43 a 0.32 2.00 122 93
0.35 0.41 0.26 1.25 122 93
1.06 1.06 1.12 0.50 50 35
0.74 0.81 0.81 0.50 86 35
0.74 0.79 0.79 1.25 ise 35
0.48 0.62 0.45 0.50 122 35
0.56 0.86 0.96 0.50 50 65
0.72 i 0.79 0.77 0.50 86 65
0.45 0.54 0.48 0.50 122 65
0.84 | 0.88 0.98 0.50 50 93
0.68 0.72 0.72 0.50 86 93
0.36 0.43 0.28 0.50 122 93
0.79 | 0.86 0.81 2.00 86 35

TABLE 6.

Output Power, mW
Module

TEST DATA OF THREE IF/AM AMPLIFIER MODULES, RUN NO. 5.

Temperature, Humidity,
OTe

Vibration,

%

13

14

TABLE 7. TEST DATA OF THREE IF/AM AMPLIFIER MODULES, RUN NO. 6.

Output Power, mW

Modula Vibration, Temperature, Humidity,
1 2 3 g oR %
den | a 0.96 2.00 35
0.96 1.17 1.12 1.25 50 35
0.96 1.06 1.12 0.50 50 35
0.72 | 0.93 0.80 0.50 86 35
0.68 0.79 0.79 1.25 86 35
0.68 0.84 0.79 2.00 86 35
0.36 | 0.64 0.30 2.00 122 35
0.41 0.41 0.30 1.25 122 35
0.35 0.62 0.20 0.50 129 35
0.66 0.52 0.88 0.50 50 65
0.79 | 101 0.88 1.25 50 65
0.86 1.06 1.04 2.00 50 65
0.68 0.84 0.79 2.00 86 65
0.56 0,70 0.74 1.25 [es 65
0.64 0.79 0.74 0.50 86 65
0.33 | 0.46 | 6.28 0.50 122 65
0.29 0.38 0.21 1.25 129 65
0.28 | 0.36 0.19 2.00 122 65
081 | 093 | 1.04 0.50 50
(ee! jue 1.25 50
0.91 0.91 1.09 2.00 50
0.62 0.79 0.81 2.00 86
0.58 | 0.77 0.77 1.25 86
0.64 0.77 0.79 0.50 86
0.15 0.28 0.22 2.00 122
0.25 im Oa 1.25 122
0.28 0.29 0.18 0.50 12

The regression equation for the three-factor test of temperature, humidity,
and vibration becomes now

P= 1.1117 + 0.0013594T - 0.0014441H + 0.063866V ~ 0.000045701T”
+ 0.000015696H? — 0.0025789V? — 0.0000201447H — 0.00039512HV

— 0.00047497V T

where

P = output power in milliwatts

T = temperature environmental factor

H = humidity environmental factor

V = vibration environmental factor
TH = temperature-humidity-interaction factor
HV = humidity-vibration-interaction factor
VT = vibration-temperature-interaction factor

The coefficient of correlation that was computed for the regression equa-
tion had a value of 0.906. This high value of correlation is indicative of the
closeness of fit between the regression equation and the true-response equation.
This was substantiated by several estimations of the output power using the re-
gression equation. The estimations are shown in table 8.

From the above regression equation, one observes that synergistic effects
do oceur and have a detrimental effect on electronic equipment operating in com-
bined environments. It is these additional interacting effects acting in conjunc-
tion with the main effects that influence the failure rate and performance of ship-
board electronic equipment.

The contribution of each environmental factor may be obtained from the
regression equation. If a unit change is assumed for each environmental factor,
then, the magnitudes of the coefficients of the various factors represent the de-
grees of contribution. After the scrutiny of the interacting terms, one notices
that the humidity-vibration and the vibration-temperature interactions contributed
about equally to the degradation in output power of the if/am amplifier module.
However, the temperature-humidity interaction contributed approximately one-
tenth less to the degradation in output power than the other two interactions.

During a particular combined-environment test, the significance or insig-
nificance of the different main and interaction terms will depend to a large degree
on the type of electronic equipment being tested. The susceptibility of electronic
equipment to the different environments and their interactions will definitely vary

15

16

as a result of the variety of components which go to make up different equipments.
For instance, one type of electronic equipment may contain components that are
susceptible to all the environmental factors; however, another type may contain
components which are susceptible only to vibration-temperature and temperature-
humidity interactions and insusceptible to the humidity-vibration interaction.

This should not be construed to imply that the interaction of humidity and vibra-
tion is not essential in combined-environment testing, nor should any environ-
mental factor be discounted because it did not affect a piece of electronic equip-
ment during a specific combined-environment test.

The important point is that these additional detrimental effects are
present in combined environments and they have an opportunity to influence the
failure rate and performance of shipboard electronic equipment.

In summary, synergistic effects have been shown to exist in combined
environments and to have contributed to the degradation in output power of an
if/am amplifier module. Furthermore, it is quite apparent that synergistic effects
are essential to environmental testing of shipboard electronic equipment and
should be seriously considered in it.

TABLE 8. ESTIMATES OF OUTPUT POWER FROM REGRESSION EQUATION.

Relative Observed Estimated
Temperature, Humidity, Vibration, Output, Output, Difference,
OR % mW mW

CONCLUSION

Synergistic (interacting) effects of combined environments were shown to
exist and to have contributed to the degradation in output power response of an
if/am amplifier module.

RECOMMENDATIONS

1. Conduct a conventional environmental test according to MIL-E-16400E
(NAVY) and a combined-environment test on a shipboard electronic module and
compare the results.

2. Continue assessment of the effects of combined environments on ship-
board electronic equipment with various types of shipboard electronic modules.

3. Continue work to develop a ‘‘standard’’ combined-environment
test procedure.

REVERSE SIDE BLANK

Ie

sh"

fim, of DM
ob eh aa 2

APPENDIX: TEST FACILITIES AND INSTRUMENTATION
Environmental Test Facilities

The environmental test facilities used to perform the test are shown in
figures Al through A4.

The vibrator (figs. Al and A2) was designed to vibrate a maximum load
of 1000 pounds at a maximum acceleration level of 10 g.

The table top of the vibrator may be rotated 90°, without the removal and
remounting of the test specimens, to permit horizontal vibration in either the fore-
and-aft or lateral axis. Vibration in the vertical axis is accomplished by posi-
tioning two phase-locking pins at the rear of the vibrator. Acceleration levels of
the vibrator table are maintained within +5 percent of the set g level overa fre-
quency range of 14 to 60 Hz by a closed-loop feedback system.

The vibrator may be withdrawn from beneath the chamber to facilitate the
accessibility and installation of large test specimens. The vibrator can be re-
motely operated in two different modes; namely, constant amplitude with variable
acceleration, and constant acceleration with variable amplitude. Automatic
changeover from constant acceleration to constant amplitude is accomplished at
any desired frequency by presetting the upper and lower transition points on the
vibrator control panel. The vibrator has built-in safety factors that enable it to
be operated unattended for long periods of time.

Temperature and humidity are controlled by the two racks of instrumenta-
tion and controls on the right of the environmental chamber (fig. A2).

The control console (fig. A3) consists of the vibrator control panel, six
channels of acceleration readout, and a multichannel oscilloscope for simulta-
neous display of acceleration, velocity, and displacement.

Test Instrumentation

The test instrumentation shown in figure A4 was used to operate and
monitor the performance of the test specimens. The instrumentation consisted of
a potentiometer pyrometer which was used to monitor the internal temperatures of
the test specimens, one rack of excitation and control equipment, one rack of
readout and monitoring equipment, and an electric counter.

A block diagram of the instrumentation is shown in figure A5.

19

Figure A1. Internal view of environmental chamber and vibrator, with test
specimens mounted.

Figure A2. Environmental chamber and vibrator with temperature and humidity
control instrumentation.

qo Nee . a os

Figure A3. Control console with vibrator control pane! and monitoring instrumentation.

Figure A4. Instrumentation used in operating and monitoring the test specimens.

21

HP-524C
ELECTRONIC

COUNTER

HP-606A
HIGH-FREQUENCY
OSCILLATOR

HP-400H RMS
VOLTMETER

CRAMER TIMEMETER
(TEST TIMER)

POWER SWITCHES
AND SUPPLIES

PARAGON 4001-0
TIME SWITCH

115 VAC

COLLINS
IF-AM MODULES
PN 528-0317-005

LOAD SWITCHES

MODULATOR-
SELECTOR
SWITCH

VOLTAGE
SELECTOR
MEASUREMENT

SELECTOR

NONLINEAR SYSTEMS
V35A DIGITAL
VOLTMETER

HP-400H RMS
VOLTMETER

HP-331A
DISTORTION
ANALYZER

LOAD RESISTORS

HP-400H RMS
VOLTMETER

OSCILLOSCOPE

Figure AS. Block diagram of if/am module test instrumentation.

UNCLASSIFIED

Security Classification

DOCUMENT CONTROL DATA-R&D

(Security classification of title, body of abstract and indexing annotation must be entered when the overall report is classified)
1. ORIGINATING ACTIVITY (Corporate author) 2a. REPORT SECURITY CLASSIFICATION
NAVAL ELECTRONICS LABORATORY CENTER UNCLASSIFIED
for Command Control and Communications :
San Diego, California 92152

3. REPORT TITLE

COMBINED-ENVIRONMENT TESTING OF SHIPBOARD ELECTRONIC EQUIPMENT

4. DESCRIPTIVE NOTES (Type of report and inclusive dates)

Research and Development Report October 1967 to January 1968

5. AUTHOR(S) (First name, middle initial, last name)

F. Robinson

Sie NO. OF REFS

8a. CONTRACT OR GRANT NO. 9a. ORIGINATOR’S REPORT NUMBER(S)

b. PRosect no. SEF 013 14 04, 1546
Task 5788

(NELC R 1 14) 9b. eee en NO(S) (Any other numbers that may be assigned

10. DISTRIBUTION STATEMENT

This document is subject to special export controls and each transmittal to
foreign governments or foreign nations may be made only with prior approval
of the Naval Electronics Laboratory Center, San Diego, California 92152.

11. SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY

Naval Ship Systems Command
Department of the Navy

13. ABSTRACT

Lack of improvement in reliability of operational shipboard electronic equipment
over some years has led to an investigation of present test methods. This report
shows that the method presently used for subjecting electronic equipment to environ-
ments in sequence fails to simulate actual environmental conditions and to subject
the equipment to the synergistic (interacting) effects of the environment.

A combined-environment test consisting of 27 combinations of temperature,
humidity, and vibration is applied to several specimens of an if/am amplifier
module to verify the presence of synergistic effects, and these effects are shown to
contribute to deterioration in performance.

The development of a standard combined-environment test procedure is
recommended.

DD (2r"..1473 (Pace 1) UNCLASSIFIED

S/N 0101- 807-6801 Security Classification

UNCLASSIFIED

Security Classification

KEY WORDS

Environmental tests

Electronic equipment - Reliability

DD 01473 (eack) UNCLASSIFIED
(PAGE 2) Security Classification

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