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MIL-S-20708E
30 June 1987
SUPERSEDING
MIL-S-20708D
1 August 1978
MILITARY SPECIFICATION
SYNCHROS, GENERAL SPECIFICATIONFOR
.
This specificationis approved for use by all
Departmentsand Agencies of the Department of Defense.
1. SCOPE
1.1 *.
This specificationrelates to Synchros, 60 and 400 Hz. It is
not complete in itself,but shall be used in conjunctionwith MIL-S-81963 in
which the latter shall be recognizedas forming an inherentpart of this
specification.
1.2 Classification.
●
1.2.1 Nomenclature. The nomenclatureshall consist of the item name,
followed by a type designationincludinga modificaticmletter and a military
part number. All .9ynchroihaving the same design nomenclatureshall be
physically,mechanically,and electricallyinterchangeablefor all military
appllcatlOnS. The type designationshall be indicatedby a combination of
digits and letters. The type designationof 26-volt synchroe shall be pr”eceded
by 1f26vn.The complete nomenclatureof a size 15, 115-volt, 400-Hz Synchro
Transmitter is illustratedin Table I. Nomenclature for new synchro types will
be assigned by the Naval Air System9 Command, Departmentof the Navy.
1.2.1.1 Item name - (see 6.5.1). The item name shall be one of the
following, as applicable:
SynchroTransmitter
Synchro Receiver
Synchqo DifferentialTransmitter
Synchro DifferentialReceiver
Synchro Control Transformer
Synchro ReceiverTransmitter
However, on small synchros where space is insufficientfor the full item name,
the words “Differentialnand ‘*
Controltfmay be omitted.
.Beneficialcomments (recommendation, additions,deletions)and any pertinent
data which may be of use in improvingthis document should be addressed to
Commanding Officer,Naval Air EngineeringCenter,EngineeringSpecifications
and Standards Department,Code 53, Lakehurst,NJ 08733-5100,by using the
self-addressedStandardizationDocument Improvement Proposal (DD Form 1426)
appearingat the end of thinsdocument or by letter.
FSC 599o
AMSC - N/A
‘D1.9trlbutlon
Statement A. Approved for public release; distributionis
unliinited.
tt
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MIL-S-20708E
1.2.1.2Size. The firsttwo digitsshalldesignatethe maximum diameter
in tenthsof an inch. If the diameteris not exactlya wholenumberof
tenthz, the next higher tenth shall be used.
1.2.1.3 Function. The succeedinggroup of letters shall indicate the
function in accordancewith the following:
.
First Letter
Function
c
Centrol
T
Torque
Succeeding
Letters
Function
D
R
T
Differential
Receiver
Transformer
B
Transmitter
RotatableStator
x
When two synchrosare enclosed within the same housing, the nomenclatureshall
indicate both units; e.g.,37TR-TR6A.
1.2.1
.Q Supply frequency. The succeeding digit shall indicate the
frequencyof the power in accordancewith the following:
Supply Frequency (Hz)
Code
60
6
4
400
1.2.1.5 Design ❑edification. An upper case letter ‘fAnfollowing the
frequency digit shall indicate the original or basic design of a standard
synchro type. The first modificationthat affects the external mechanical
dimensions or the electricalcharacteristic of the baaic type shall be
indicatedby the upper case letter ‘Bm. Succeeding design modificationsshall
be indicated by ‘TCW,‘Dtt,etc., except ‘IV*,‘Lut,**Otv,
and wQn shall not be
used.
1.2.1.6Military part number. The military part number shall consist of
the letter “M”, the basic number of the specificationgheet (not includingthe
revision letter),an assigned dash number”and a suffix letter deaignating-the
latest modificationletter in the type designation,as shown in the following
example:
M
Military
Designator
20708114
—-01
Specification
Sheet Number
Dash
Number
D
Latest
Modification
Letter
o
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L-S-20708E
1.3 Illustration. A synchro classifiedas 15CX4D - M20708/1U-OID (see
Table I) indicates the third modificationto the original design of a
115-volt, 40C-HZ synchro control transmitterwhose body diameter is greater
than 1.40 inches but not greater than 1.5o inches, and the military part
number specifiesthat this gynchro has a splined shaft and terminal
connections. A 26-volt synchro classlfied as 26V-11TX4C - M20708/6-01C
indicatesthe second ❑edificationto the original design of a 26-volt,400-Hz
synchro torque transmitterwhose body diameter 19 greater than 1.00inch but
not greater than 1.10inches, and the military part number specifies that this
synctirohas a gplined shaft and terminal connections.
2. APPLICABLEDOCUMENTS
2.1 Government documents.
2.1.1 Specificationsand standards. The following specificationsand
standards form a part of this specificationto the extent specified herein.
Unless otherwise specified,the issues of these documents shall be those
listed in the issue of the Department of Defense Index of Specificationsand
Standarda (DODISS)and supplement thereto, cited in the solicitation.
SPECIFICATIONS
MILITARY
MIL-S-81963
Servocomponents,PrecisionInstrument,Rotating,Common
Requirementsand Tests: General Specificationfor
(See Supplement 1 of MIL-S-20708Efor list of applicablespecificationsheets.
)
STANDARDS
MILITARY
MIL-STD-105
Sampling Proceduresand Tables for Inspection
by
Attributes
MIL-STD-202
TestMethodsforElectronic
and Electrical
Component
Parts
MS17183
ClampAssembly(Synchro)
MS17186
Washer, Drive (Synchro)
MS17187
Nut, Plain, Hexagon
MS35275
Screw, Machine-DrilledFillisterHead, Slotted,
Corrosion-ResistingSteel, Pas!sivated,
UNC-2A
MS35276
Screw, Machine-DrilledFillisterHead, Slotted,
Corrosion-ResistingSteel, Passivated,UNF-2A
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MIL-S-20708E
STANDARDS
MILITARY
MS35338
Washer, Lock-Spring,Helical, Regular (Medium)Series
MS90406
Gage, Ring, Spline (Go-No Go)
2.1.2 Other Government drawin&. The following other Government
drawing forms a part of this specificationto the extent specified herein.
Unless otherwise specified,the issue shall be the one in effect on the date
of the solicitation.
Bureau of Ordnance
929471
(Spline)Go Composite Ring Gage
and drawings required by contractors
of specifications,
standarda,
in connectionwith specific acquisitionfunctionsshould be obtained from
the contractingactivity or as directed by the contractingofficer.)
(COPieS
2.2 Order of precedence. In the event of a conflict between the text
of this specificationand the referencescited herein (except for associated
detail specifications,specificationsheets or MS standards),the text of
this specificationshall take precedence. Nothing in this specification,
however, shall supersedeapplicablelaws and regulationsunleaa a specific
exemPtiOn haa been obtained.
3. REQUIREMENTS
3.1 Specificationsheets. The individualitem requirementsshall be as
specifiedherein,MIL-S-81963, and in accordance with the applicable
specificationsheets. In the event of any conflict between requirementsof
MIL-S-81963,this specification,and the specificationsheet, the latter shall
govern.
3.2 Qualification. Synchros furnishedunder this specificationshall be
products which are authorizedby the qualifyingactivity for listing on the
applicablequalifiedproductg list at the time set for opening of bids (see
4.5 and 6.4).
3.3 Firgt article. When specified in the contractor purchase order, a
sample shall be subjected to first article inspection(see 4.6and 6.3).
3.4 Des lgn conventions.
3.4.1 Directionof rotation. The standard (positive)direction of
rotationof the shaft is counterclockwisewhen the synchro is viewed from the
shaft extension end.
3.4.2 Electrical angle.
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MIL-S-20708E
3.4.2.1 Transmittersand receivers. The electrical angle ‘la!!
is the
angle, displaced in a vositive directionfrom svnchro zero. which satisfies
the relativemagnitude”and polaritiesof the se~ondary voliage.sof an ideal
synchro transmitteror rsceiver in accordancewith the following equations:
E(S1S3) . N E(R2R1) ain a
E(S3S2) = N E(R2R1) sin a (a + 12@)
E(S2S1) = N E(R2R1) sin a (a + 240° )
Where:
The terminalsequenceas indicatedin the parentheses
designates
the
senseof the voltagevector.
N is the transformation
ratio.
E(R2R1
) is the voltagebetweenterminalaR2 and R1.
E(S1S3) is the voltage between terminalsS1 and S3.
The in-time-phasesecondary voltages are obtained as described in 6.6.8;
other voltages are similarly defined.
3.4.2.2 Differential transmittersand differentialreceivers. The
electricalangle ‘an is the angle, digplacedin a positive direction from
synchro zero, which satisfies the relative ❑agnitude and polaritiesof an
ideal synchro differentialtransmitteror differentialreceiver in accordance
with the followingequations:
E(R1R3) =
E(R3R2) =
E(R2R1) =
E(S1S3) +
N (E(S1S3)sin (a + 120° ) - E(S3S2) sin a)
N (E(S1S3)ain a - E(S3S2) sin (a + 24d))
N (E(S1S3) sin (a + 240° ) - E(S3S2) sin (a + 1200))
E(s3s2) + .E(S2S.1)
= o
Where:
The terminal sequence as indicatedin the parenthesesdesignateathe
sense of the voltage vector.
N is the transformationratio.
E(R1R2) is the voltage between terminala R1 and R2.
E(S1S3) is the voltage between terminalg S1 and S3.
The in-time-phaaesecondary voltages are obtained as described in 6.6.8;
other voltages are similarly defined.
3.4.2.3 Control transformers. The electrical angle ‘an is the angle
displaced in a positivedirection from synchro zero, which gatisfiesthe
relative magnitude and polaritiesof the secondaryvoltages of an ideal
synchro control transformerin accordancewith the following equations:
E(R1R2) = N (E(s1S3) sin (a + 120° ) - E (E(S3S2)Sin a))
E(S1S3) + E(S3S2) + E(S2S1) = O
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MIL-S-20708E
Where:
The terminal sequence as indicatedin the parenthesesdesignatesthe
sense of the voltage vector.
N is the transformationratio.
E(R1R2) is the voltage between terminals R1 and R2.
E(S1S3) is the voltage between terminals S1 and S3.
The in-time-phasesecondary voltages are obtained as described in 6.6.8;
other voltages are similarly defined.
3.4.3 Synchro zero. Synchro zero is that position of the rotor with
respect to the stator at which minimum voltage is induced in the secondary
circuit specified,and at which the secondaryvoltage(s)Spe Ci fied
is
in-time-phase(see 6.6.8)with the primary voltage specified (see 4.3.4). The
order in time of maximum voltages in the stator terminals is in the Opder S1,
S2, S3, when the rotor is turned in a positive direction (see 3.4.1).The
minimum voltage position with the secondaryunloaded is defined as the angular
positionwhere the secondaryvoltage of fundamental frequency that is
in-time-phaae
with the secondaryvoltage at maximum coupling is zero. The
phase-gensitivevoltmeters in Figures 1, 2, and 3 shallbe the typeas
describedin 4.8.12.
3.4.3.1 Transmitter and receiverg. Synchro zero of transmitters and
receiversshall be determined w ith the gynchro connected in accordance with
Figure 1. When the synchro shaft i9 rotated in the positive direction (not to
exceed 180° ) from synchro zero, the voltage E(S1S3) ghall be in approximate
time phase with E(R2RI).
o
3.4.3.2 Differential transmitter and differentialreceivers. Synchro
zero of differentialtransmittersand differentialreceiversshall be
determined with the gynchro’connected in accordancewith Figure 2. When the
gynchro shaft is rotated in the positive direction (not to exceed 180° ) from
synchro zero, the voltage E(R3R1) ghall be in approximate time phaae with
E(S3S2).
3.4.3.3 Control transformers. Synchro zero of control transformer shall
be determined with the synchro connectedin accordancewith Figure 3. When
the synchro shaft is rotated in the positive direction (not to exceed 1800)
from synchro zero, the voltage E(R2R1) shall be in approximate time phase with
E(s3S2).
3.4.4 Spline shafts. The end function of the spline on Synchrog with
aplined shafts is as a rotationalpositive fastening. These splines are not
to be USed as gears. The tooth form shall be full depth involuteon all
splines. Splines for 9ize 11, 15, or 18 synchros shall be inspected by
(Spline)Go Composite Ring Gage MS90406-1. Splines for size 23, 31, or 37
synchros shall be inspectedby (Spline)Go Composite Ring Gage Buord 929471.
3.5 Designand construction.
3.5.1 Termination identification. Winding terminationsshall be a9
solder pin or
in MIL-s-8196s.
Identification
of
terminal
9crew,
wire lead types shall be as specified in Table II herein.
specified
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MIL-s-20708E
3.5.2 Synchro zero markings. The synchro zero markings shall be checked
in accordance with 4.8.24and shall ❑eet the requirementsspecified in
MIL-S-81963.
3.5.3.Dimensions.Outlinedrawingsfor the diPferentsizesOP synchros
are includedas FiguregQ, 5, 6, 7, 8, and 9. Lettereddimensionsshown on
the outli~e drawings are provided in Table III.
3.6 Performance.
3.6.1 Visual and mechanical inspection. Visual and mechanical inspection
shall be performed in accordancewith 4.8.1and shall meet the requirementsof
MIL-S-81963.
3.6.2 Variationof brush contact resistance. Brush contact resistance
test shall be conducted in accordance with 4.8.2. This test shall be the
flrSt test performed and shall also be the first test performed after
environmentaltegts as indicated in Table IV. The variationin resistance
shall be as specified in MIL-S-81963.
3.6.3 Shaft radial and end play (see 6.6.1
1). Shaft radial and end play
shall be tegted”in accordancewith L8.3 and shall meet the requirements
specified in MIL-S-81963.
3.6.4 Shaft runout.
When tested in accordance with 4.8.4;shaft runout
shall not exceed the value 9pecified in the specificationsheet.
3.6.5 Mechanicalbreakaway torque (see 6.6.1
2). When tested in
accordance with 4.8.5,mechanical breakaway torque shall meet the requirements
specified in MIL-S-81963.
3.6.6 Torque gradient (see 6.6.1
3). When tested in accordance with
4.8.6,the torque gradient of torque synchros shall conform to the
requirements in the applicablespecificationgheet.
3.6.7 Dielectricwithstandingvoltage. When tested in accordance with
4.8.7,the synchro shall meet the requirementsof MIL-S-81963.
3.6.8 Insulationresistance. lnaulationresistancemeasurements shall be
performed in accordancewith 4.8.8and shall meet the requirementsof
MIL-S-81963.
3.6.9 Primary current. When tested in accordance,with 4.8.9,the value
Of the current of each primary winding shall be as specifiedin MIL+-81 g63.
3.6.10 Primary power. When teated in accordance with 4.8.10,the value
of the power of each primary winding shall be as specified in MIL-S-81963.
3.6.11 Transformationratio (see 6.6.9). When tegted in accordance with
4.8.11,the value of transformationratio shall be as specified in the
specificationsheet.
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3.6.12 Phase shift (see 6.6.10). When tested in accordance with 4.8.12,
the value of the phase ehift ehall be as specified in the specificationsheet.
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3.6.13 Electricalerror (see 6.6.2). Uhen tested in accordance with
4.8.13,the electricalerror shall not exceed the value gpecified in the
specificationsheet.
.
3.6.14 Residual (null) voltage (see 6.6.14).When teated in accordance
with 4.8.14,the null voltage shall not exceed the value specified in the
specification sheet.
3.6.15 Receiver error (see 6.6.3). When tested in accordance with
4.8.
I5, the maximum error shall not exceed the value specified in the
specification sheet.
3.6.16 Spinnin& When tegted in accordance with 4.8.16,the rotor of a
receiveror differentialreceivershall synchronizeor cone to reet from any
initial angular position without spinning.
3.6.17 Synchronizingtime (ace 6.6.4). When tegted in accordance with
4.8.
I~, the synchronizingtime shall not exceed the Value epecified in the
specificationsheet.
3.6.18 security of terminals or wire leads. The gecurity of each screw
type or solder pin type of terminal or of each wire lead, as applicable to the
particulartype of aynchro, shall be tested in accordancewith 4.8.18and
shall meet the requirementsof MIL-S-81963.
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3.6.19 Impedance (see 6.6.5). When meaaured in accordance with 4.8.19,
the impedance valuea shall be as specifiedin the specificationeheet.
3.6.20Temperature
rise (see6.6.1
6). When ❑easuredin accordancewith
4.8.20,
temperature
riseshallbe as epecif
ied in MIL-S-81
963.
3.6.21 Variationof voltage and frequency. Synchros shall be capable
of operatingsatisfactorilyfrom power eourcee subject to a ~1O percent
voltage regulationin combination with frequencyvariationof ~5 percent.
When teated in accordancewith 4.8.21,the power drawn from the source shall
not exceed that epecified by the specificationeheet.
3.6.22 Audible noise,‘structureborne.When required by the applicable
specificationsheet, structurebornenoise ehall be tested in accordance with
4.8.22and ehall meet the requirementsof MIL-S-81963.
3.6.23 Electromagneticinterference. When required by the applicable
specificationsheet,electromagneticinterferenceshall be tested in
accordance with 4.8.23and shall meet the requirement of MIL-S-81963.
3.7 Environmental.
3.7.1 Vibration. Vibration shall be conducted in accordance with 4.9.1.
After vibrationthe aynchrosshall meet the requirements of MIL-S-81963 and
Table IV herein.
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MIL-S-20708E
3.7.2 Shock.
3.7.2.1Shock, specified pulse. Shock shall be conducted in accordance
with-4.9.2.1.After shock. svnchros shall ❑eet the requirementsof
MIL-S-81963 and Table IV “her_ein.
3.7.2.2 Shock, high impact. Shock shall be conducted in accordance with
4.9.2.2.After shock, synchros shall meet the requirementsof MIL-S-81963
and Table IV herein.
3.7.3 Altitude.Duringaltitudetesting,synchrosshallbe capableof
operationfrom the low temperaturegpecifiedin MIL-S-81963to 125° C.
Synchros gize 23 and smaller shall meet the requirementsof Table IV.
3.7.3.1 Altitude,low temperature. Altitude, low temperature, shall
be conducted in accordancewith 4.9.3.1and shall meet the requirementsof
Table IV.
shall
3.7.3.2Altitude,
high temperature.Altitude,high temperature,
be conductedin accordance
with 4.9.3.2
and shallmeet the requirements
of
TableIV.
●
3.7.4 Endurance. Endurance shall be conducted in accordance with ”4.9.4.
After testing, the gynchros shall meet the requirementsof Table IV.
3.7.5 Ambient temperature.
3.7.5.1Ambient low temperature. The synchro shall be tested in
accordance with 4.9.5.1and shall ❑eet the requirementsof Table IV.
3.7.5.2 Ambient high temperature. The synchro shall be tested in
accordance with 4.9.5.2and shall meet the requirementsof Table IV.
3.7.6 Moisture resistance. Synchros shall be teated in accordancewith
4.9.6. After testing in accordance with 4.9.6,synchroa shall meet the
requirements of Table IV.
3.7.7 Explosion resistance. When required by the applicable
specificationsheet, synchros shall be tested in accordancewith 4.9.7and
shall Meet the requirementsof MIL-S-81g6j.
3.7.8 Salt atmosphere. When required by the applicablespecification
sheet, synchros shall be tested in accordancewith 4.9.8and shall meet the
requirementsof MIL-S-81963.
3.7.9 Identificationmarkin~. Identification❑arkings shall
specified in MIL-S-81963.
be
as
3.7.10 Workmanship. Workmanship of the synchro shall conform to the
requirementsof MIL-S-81963.
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MIL-S-20708E
4. QUALITY ASSURANCE PROVISIONS
4.1
Responsibility
for
inspection. Responsibilityfor inspectionshall
be as specified in MIL-s-81963.
4.2 General
specifics-ieet,
MIL-S-81963.
Unle99 otherwise specifiedherein or in the applicable
all testing shall be conducted in accordancewith
4.2.1 Test equipment and inspectionPacilitieg. The accuracy of test
equipment and inspectionfacilitiesshall conform to MIL-S-81963.
4.2.2.Alternatetest methods. Alternate test methods shall conform to
MIL-S-81963.
4.3 Tegt conditions.
%3.1
Standard
test conditions. Unless otherwise specified, the standard
test conditionsshall be ag specifiedin MIL-S-81963,and each test ghall be
carried out with the gynchro in the applicablemounting fixture in accordance
with MIL-S-81963. Mounting hardware shall conform to the requirementsof
Table V.
4.3.2’Temperature,stabilizedOperatin~. The stabilized operating
temperatureof the synchru shall be as specified in MIL-s-81963,using the
applicablesecondary windings stipulated in Table VI herein for the periodic
dc resistancemeasurement.
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4.3.3 Temperature,stabilizednon-operatinf+ The stabilized nonoperatingtemperatureof the synchro shall be as specifiedin MIL-S-81963
using the applicablesecondarywindings stipulated in Table VI herein for the
periodic dc resistancemeasurement.
4.3.4 Standard test voltage and frequency. Unless otherwise .9pecified,
the test voltage and frequency of a true sins wave shall be as apecirled in
Ta ble
VI. The voltage and frequencyshall be maintained within a toleranceof
21 percent. The total harmonic content shall be leas than 1 percent.
6.4 Cla99iPicationof tests. The ❑ethods of sampling, inspection,and
tegtg conducted on gynchros shall be classifiedas follows:
a. Qualification (4.5)
b. First Article (4.6)
c.
Quality Conformance (4.7)
4.5 Qualificationinspection. Qualificationinspectionshall be
performed at a laboratoryapproved by the Naval Air Systems Command and shall
be performed in accordancewith MIL-S-81963and Table IV herein.
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4.5.1
specified
Qualificationsample. The qualificationsample shall be as
in MIL-S-81963.
4.5.2
Qualificationinspectionroutine. The qualificationinspection
routine shall be performed in accordancewith MIL-s-81963and Table IV herein.
4.5.3 Assessment of qualificationapproval test results.
4.5.3.1
Qualification
sample
failure.
be as specified in MIL-S-81963.
Qualificationsample failure shall
4.5.3.2
Degradation
of performance.
The following relaxation may be
permitted at the discretionof the qualifyingactivity in accordancewith
MIL-S-81963.
4.5.3 .2.1
Acceptanceteata. All the specified performance
characteristic must be attained.
4.5.3.2.2Environmentaltests. As appropriate during or following each
of the environmentaltests, the followingminor relaxationsin specified
requirementsmay be permitted. It should be noted that the relaxationsare
not cumulative; e.g.,electricalerror, if accepted at up to 1 minute of arc
in addition to the specifiedmaximum value following vibration,shall still
not be more than 1 minute of arc in addition to the specifiedmaximum value
following low impact shock.
4.5.3.2.2.1 Variation of brush contact reaiatance. A maximum variation
ohms or 0.75percent of rotor dc resistancespecified in the
specificationsheet ❑ay be permitted. Following high impact shock, a ❑aximum
variation of 2.25ohms or 1.125percent of rotor dc resistancegpecitied in
the specificationgheet is permissible.
of
1.5
4.5.3
.2.2.2 Receiver error. An increase of 6 minutes for sizeg 11 and
15, 5 minutes for sizes 18 and 23, and 4 minutes for sizes 31 and 37, in
addition to the maximum receivererror value specified”inthe specification
sheet, is permissible. Following high impact shock, en increaaeto 1 1/2
times the maximum receivererror value specified in the specificationsheet
i9 permissible.
4.5.3
.2.2.3 Electricalerror. An increase of 1 minuta in addition to the
maximum electricalerror value specifiedin the specificationsheet ❑ay be
permitted. Following high impact shock, an increaseto 1 1/2 times the
❑ aximum electricalerror value specifiedin the specificationgheet la
permiasibie.
4.5.3
.2.2.4 Mechanical breakaway torque. An increage to 2 times the
maximum breakaway torque value specifiedin the specificationsheet at
9tandard test temperaturemay be permitted. Followinghigh impact shock, an
increa9eto 3 times the maximum breakaway
torque
value
specifiedin the
specificationsheet at standard test temperature ia permissible.
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4.5.3.2.2.5Shaft radial play. The maximum permissible radial play is
1 1/2 times the maximum value specifiedin the specificationsheet. Following
high impact shock, radial play not exceeding2 1/4 times the maximum value
specified in the specificationsheet is permissible.
4.5.3
.2.2.6 Shaft end play. Irrespectiveof the limits specified in the
specificationsheet, a minimum end play value of 0.0001inch is required. The
maximum permissibleend play is 1 2/3 times the maximum value specified in the
specificationsheet. Following high impact shock, end play not exceeding 2
1/2 times the ❑aximum value specifiedin the specificationsheet ia
permissible.
4.5.3
.2.2.7 Residual voltage. Following high impact shock, an increase
of 50 percent in the maximum fundamentaland total residual voltage values
specified in the specificationsheet is permissible.
4.5.3
.2.2.8Dielectricwithstandingvoltage. Following high impact
shock, a winding leakage current increaseto 1.5milliamperes peak maximum is
permissible.
4.5.3
.2.2.9 Insulationresistance. Following high impact shock and
having been immediately preceded by dielectricwithstandingvoltage, a
reduction to 25 megohms insulationresistance i9 permissible.
4.5.3.2.2.10
Major
failures
during
or following environuiental tests.
Allowances having been made for the relaxationsquoted in 4.5.3.2.2,
failures
experiencedduring or following environmentaltests shall be dealt with as
provided for in MIL-S-81963.
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4.5.3.3 Qualificationsample isolatedfailure. In case of catastrophic
failure, the proceduresof MIL-s-81963
shall
apply.
4.5.3.4 Qualification approval by analogy. Qualificationapproval by
analogy shall be ag specified in Figure 10 herein and MIL-S-81963.
4.5.3.4.1
Rules for selection. Test samples shall be selected in
accordance with 4.5.3.4.1.1through 4.5.3.4.1.3as depicted in Figure 10,
4.5.3 .4.1.1
From
a group of units submitted for qualificationapproval by
analogy tegting,the test samvles shall be selected by successivelydividing
the gt+up
in tie following 9equence:
a. Frame Size
b. Voltage: 26v or 115v
c. Frequency: 60 Hz or 400 Hz
d. Synchro Function: Control or Torque
*
Having made the sub division
as
above, the units shall then be grouped together
with no more than three types comprisingany one group.
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MIL-S-20708E
4.5.3 .4.1.2
From each urouD.
. . four units shall b e selected for the entire
qualificationapproval test program. When there are only two types in a
group, two of each shall be selected;but in the case of three types in a
group, two shall be selected from the differentialtype and one each from
the other two.
4.5.3.4.1.3
The sample group of units having been selected shall then be
subjected to the qualificationtests.
4.5.4 Dispositionof qualificationsample. Dispositionof the
qualificationsample shall be as specifiedin MIL-S-81963.
4.5.5 Requalification. The frequencyof qualificationinspection in
order to retain qualificationapproval shall be as specified in MIL-S-81963.
4.5.6 Changeg. After samplea have been submitted for qualification,no
change shall be ❑ade.in the materials,design, or manufacturingprocesses
without prior approval of the qualifyingactivity.
4.6 First article sample inspection. When required by the contracting
activity, first article shall be as specified in MIL-S-81963.
4.6.1
First article sample failure. Action following first article
sample failure shall be as”specifiedin MIL-S-81963.
“
4.7 Quality conformance inspection. Quality conformance inspectionshall
be as specified in MIL-S-81963and Table IV herein.
4.7.1 Quality conformance inspectionsamplin& Statisticalsampling and
inspectionshall be as specified in MIL-S-81963. When MIL-STD-105specifies
an action by the Government, it shall, at the option of the Government, be
performed either by the Government or by the contractorunder the supervision
of the Government.
4.7.2 Quality conformance inspectionroutine. The minimum of inspection
to be verifiedby the Government Inspectorshall be the requirementsof
MIL-S-81963and Table IV herein. The GovernmentInspectormay substitute
100 percent inspectionfor all or part of the sampling procedure.
4.7.3 Quality conformancegample failure. Action following quality
conformancesample failure shall be as specified in MIL-S-81963.
4.8 Test methods and examinations.
4.8.1
Visual
and mechanical examination. The synchro shall be examined
in accordancewith MIL-s-81963and shall meet the requirementsof 3.6.1.
4.8.2 Variationof brush contact resistance. Brush contact resistance
teat shall be conductedin accordancewith MIL-s-81963and shall be performed
between terminals R1-R2 of transmitters,receivers,and control transmitters;
between terminalsR1-R2 and R1-R3 of differentialtransmittersand
differentialreceivers;and between S1-S2 and S1-S3 of rotatablestator
synchros, and shall meet the requirement of 3.6.z.
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4.8.3 Shaft radial and end play. Shaft radial and end play shall be
tested in accordancewith MIL-s-81963and shall meet the cequirementaof
3.6.3.
4.8.4 Shaft runout. The 9ynchro housing shall be rigidly mounted. A
dial gauge shall be applied to the shaft within 1/8 inch of the bearing
Pace
and the shaft rotated. The differencebetween the extreme indicatorreadings
shall be the shaft runout and shall meet the requirementsof 3.6.4.
4.8.5 Mechanical breakaway torque. Mechanical breakaway torque test
shall be conductedin accordancewith MIL-S-81963and shall meet the
requirements of 3.6.5.
4.8.6 Torque gradient teat.
4.8.6.1 General. The aynchro shall be energized in accordance with 4.3.4
until it reaches stabilizedoperating temperature (see 4.3.2). Torque shall
be applied by weights suspended from a thread attached to the rim of a torque
pulley rigidly mounted on the synchro shaft. The thread diameter shall be
less than 0.01 times that of the pulley. A measuring device which will enable
changes in angular positionof the synchro shaft to be read within 15 minutes
of arc shall be attached to the fixture. Predeterminedweights of equal
increments shall be applied to cause deflectionsof approximately2, 4, 6, 8,
and 10 degrees in both clockwise and counterclockwisedirections. The
correspondingdeflectionsshall be recordedand a torque-deflectioncurve
plotted as the straight line best fitted to the observed points, and shall
meet the requirementsof 3.6.6.
0
4.8.6.1.2 Torque transmittersand receivers.
4.8.6
.1.2.1 Method 1. Torque transmitters and receivers shall be
energized by applying voltage and frequency as specified in 4.3.4to the R1-R2
terminals of the synchro. The stators of rotatablestator synchros ghall be
locked at synchro zero. Terminals S1 and S3 shall be connected together and
the synchro tested in accordance with 4.8.6.1.The torque gradient shall be
one-half the slope of the line expressedin ounce-inchesper degree.
4.8.6
.1.2.2 Method 2. Torque transmitters and receivers shall be
electricallycoupled to another transmitterof the same frame size and nominal
impedanceand energized by applyinga voltage and frequencyas specified in
4.3.4to the RI and R2 terminals of-the gynchros and tested in accordance with
4.8.6.1.The atatora of rotatablesynchros ghall be locked at synchro zero.
The torque gradient is the slope of the line expressed in ounce-inchesper
degree.
4.8.6.1.3 Torque differentialtransmittersand receivers.
4.8.6
.1.3.1 Method 1. Torque differential transmitters and reoeivers
shall be energized by applying the voltage and frequencyaa specified in 4.3.4
between terminal S1, which is connectedto S3, and terminal S2. Terminals R1
and R3 shall be connectedtogetherand the synchro shall be tested in
accordance with 4.8.6.1.The torque gradient shall be one-half the slope of
the line expressed in ounce-inchesper degree.
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MIL-S-20708E
4.8.6
.1.3.2 Method 2. Torque differential trangmittet’sand receiverg
shall be energized by applying the voltage and frequencyas specified in 4.3.4
betweenterminalS1, which is connectedto S3,and terminalS2. The rotor
terminalsshallbe connectedto a torquetransmltter!s
stator. The
transmitter
shallbe the same framesizeand frequencyratingas the synchro
undertestand shallbe locked on synchro zero and tested in accordancewith
4.8.6.1.The torque gradient is the slope of the line expressed in ounceinches per degree.
4.8.7 Dielectricwithstandingvoltage. The dielectric withstanding
voltage test shall be conductedas specified in MIL-s-81963and Table VII
herein and shall meet the requirementsof 3.6.7’.
4.8.8 Ins~lationresistance. The insulationresistancebetween the
application
Pointsstipulated
in TableVII shall be measuredas specifiedin
MIL-S-81963
and ghallmeet the requirements
of 3.6.8herein..Forsynchros
with maximumoperating
voltagesgreaterthan50 voltsrms,500voltsdc shall
be appliedbetweenall points.For synchroawith ❑aximumoperatingvoltages
leSS than 50 volts rms,100 volts dc shall be applied between all application
points.
4.8.9 Primary current. Current drawn by the primary winding shall be
with the secondarywinding open-circuited,the synciiroenergized in
accordance with 4.3.4,and as specified in MIL-s-81963.
The current drawn
shall meet the requirements of 3.6.g.
m e asure d
4.8.1o Primary power. Power drawn by the primary winding shall be
meamred with the gecondarywinding open-circuited,the synchro energized in
accordancewith 4.3.4,and as specified in MIL-S-81963. The power consumed
shall meet the requirements of 3.6.10.
4.8.11
Transformation
ratio
test.
The synchro shall be energized and
stabilized in accordance with 4.3.4and 4.3.2,then the rotor turned in the
positive directionfrom synchro zero until the first positionof ❑aximum
coupling is reached. The secondaryshall be comected to a measuring device
which indicatesor compares the rms voltage of the fundamentalfrequencyand
does not alter the open circuit secondaryvoltage by more than 0.1 percent.
The transformationratio shall meet the requirementsof 3.6.11.
4.8.12 Phage shift test. Phase shift shall be measured with the synchro
energized, stabilized, in accordance with 4.3.4and 4.3.2and rotorpositioned
as in 4.8.11
above. The secondary ghall be connected to a measuring device
which indicatesor compares the phase shift to an accuracyof 215 ❑ inutesand
does not alter the open circuit voltagegby more than 0.1 percent. The pnage
shift ghall meet the requirementsof 3.6.
I2.
4.8.13
Electrical
error
test.
The synchro shall be energized as
specified in 4.3.4and stabilized as specified in 4.3.2. The electricalerror
shall be measured and recorded at every 5-degree positionof the rotor and
shall meet the requirementsof 3.6.13. The total combined error of the teSt
equipment during testing shall not exceed 30 seconds of arc. The stators of
rotatablestator synchros shall be locked at synchro zero. The electrical
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MIL-s-20708E
error of both the rotor and stator shall
be determined for differential
transmittersand differentialreceivers. Examples of electricalerror test
setups for differenttypes of units ara shown in Figures 11 and 12.
4.8.14
Residual
(null)
voltage
test.
The synchro shall be energized as
specifiedin Table VIII and the null readings made with the synchro at the
electrical angles
shown in Table VIII. The voltage-meaauringdevices used in
4.8.14.1and 4.8.14.2gnall indicate the average value of the voltage wave in
terms
of
the rms value of an equivalentsine wave and shall have an input
impedance of at least 500,000ohms reaigtanceshunted by a capacitanceof
30PF. The residual (null)voltage shall meet the requirementsof 3.6.14.
4.8:1.4.1Frequency sensitivevoltmeter ❑ethod. A frequency sensitive
shall be used which has a fundamentalfrequencyfilter with
characteristicsfor a change of ~1 percent in energizingfrequency. The
output voltage shall change no more than ~0:5 percent and be at least -30 db
at halP and twice rated frequency. The meter shall be properly compensated
for the insertionloss of the filter. The aynchro rotor shall be turned until
a minimum voltage is obtained on the frequencysensitive voltmeter. The
voltage is the fundamentalcomponent of the null voltage. Without disturbing
the I’Ot,Or position, the total null voltage shall be meaaurad.
Voltmeter
4.8.14.2 Phase-sensitivevoltmeter method. The synchro rotor shall be
turned until the in-phase component of the null voltage is zero as indicated
on a phase-senSitivevoltmeter. The quadraturevoltage shall be read. This
voltage is the fundamentalcomponent of the null voltage. Without disturbing
this rotor position, the total null voltage shall be measured.
o
4.8.15 Receiver error test.
4.8.15.1 General. The synchro under test ghall be connected to a
calibratedtransmitter of the game frame size and the same nominal
impedance. The calibratedtransmitter(s)and synchro under test shall then be
rotated at 1 rpm. This calibratedtransmitter(s)shall have met the
acceptance requirementsof this specification. The transmitter(s)and the
synchro under test shall be energized in accordance with 4.3.4and stabilized
in accordancewith 4.3.2.Statorsof rotatablestatorsynchrosshallbe
locked at synchro zero. If a low-paas filter is incorporatedinto the test
equipment, it shall pass 10 Hz and below. The calibratedtransmitter(s)and
synchro under test shall be set at aynchro zero with respect to the same
referenCe. Receiver error shall be determinedand recordedeither
contiIIUOuslY
or at no greater than 5 degree intarvalsfor both clockwise and
counterclockwisecompatible with the direction of rotationof both synchros.
If the calibratedelectricalerror of the transmitter(a)exceeds 3 minutes,
the receiver error shall be corrected. The receiver error shall meet the
requirements of 3.6.15.
4.8.15.2 Receivers.
4.8.15.2.1Method 1. The shaft of the torque transmitter Shall be
mechanicallycoupled to the shaft of a control transformer. The statora of
the receiver under teet, the torque transmitter,and the control transformer
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MIL-S-20708E
shall be electricallyconnectedand compatible to directionof rotation. A
calibratedphase-sensitivenullmeter shall be placed acroas the output of the
control transformer. The shaft of the control transformershall be rotated
and the receivererror interpretedfrom the calibratedphase-sensitive
nullmeter when tested in accordance with 4.8.15.1.
4.8.15.2.2
Method
2.
Stator
terminals of the receiver and transmitter
shall be connected. Both housings shall be locked rigidly together with
respect to the same referenceand the transmitterrotor secured at synchro
zero. The aynchros atiallbe tested in accordance with 4.8.15.1.
4.8.15.2.3
Method
3.
Electrically
connect
a transmitter
to an Angle
Position Indicator (API)and record the digital output from the API with a
data logger. While driving the transmitterat 1 rpm, record the readings at
the rate of six per second for en intervalof 70 seconds starting when the API
reads 0.000degrees. Repeat the process with the transmitterrotating in the
opposite direction. A programmablesynchro standard with the game nominal
impedance aa the aynchro under teat may be aubatitutedfor the transmitter,
eliminating the need for the previous readings. Electricallyconnect the
synchro under test to the transmitterand the API. Mechanicallydisplace the
shaft of the synchrounder teat 1 degree from the transmitterto determine the
scale factor. The scale factor is a number, that when multiplied by the
change in the API reading, equals 1 degree. Obtain enother set of data by
repeatingthe previous readings while the synchro under test ia connected to
the transmitter. The receiver error is the scale factor timeg the difference
in the two setg of data.
4.8.15.3
Differentials.
4.8.15.3.1Method 1. The shaft of the torque transmitter shall be
mechanicallycoupled to the shaft of a transformer. The stators of the torque
transmitterand control transformershall be electricallyconnectedto the
rotor of the differentialreceiver under teat in such a manner aa to maintain
compatible directionof rotation. The stator of the differentialreceiver
shall be connectedto the stator of a second torque transmitter,the anaft of
which is locked at aynchro zero. A calibratedphase-aenaitivenullmeter shall
be placed across the output of the control transformer. The shaft of the
control tranafornershall be rotated and the recelvkrerror interpretedwith
the calibratedphase-sensitivenullmeter when tested in accordancewith
4.8.15.1.
4.8.15.3.2
Method
2.
Terminala
of
the
differential
receiver
rotor
shall
be connected to the stator of a transmitter,and the differentialreceiver
stator terminals shall be connected to the atator of a second transmitter.
Stator housings of the differentialreceiverand one transmittershall be
❑echanicallylocked with respect to the same reference. Both transmitter
shafts shall be locked at synchro zero to prevent rotaticmand the test shall
be conducted In accordance with 4.8.15.1.
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4.8.15.3.3 Method 3. This method is the same as 4.8.15.
z.3 except the
stator of the differentialsynchro is electricallycomected to a second
transmitters stetor with it; shaft locked on synihro zero. The rotor is
electricallycomected to the driven tcanamittervastator
after the first aet
of readingsare recordedand prior to testing the differentialsynchro.
Q.8.16 Spinning test. The applicable test dial used for mechanical
breakaway torque as specified in MIL-s-81963shall be mounted rigidly on the
shaft of the receiveror differentialreceiver. The synchro receiver shall be
connectedto the appropriateterminals of a ‘torquetransmitter,or in the case
of a differentialreceiver,to two transmittersof a size 37 for 115-volt
synchros or a size 11 for 26-volt synchres. The rotor(s)of the
transmitter(s)shall be locked in the gynchro zero position. The rotor of the
aynchrounder test shall be displaced 177° ~20 from synchro zero and the
synchrosenergizedwith 120 percent of gtandard teat voltage at rated
frequency. This procedureshall be performed five times for a clockwise
displacementand fiVe times for a counterclockwisedisplacementand shall meet
the requirements of 3.6.16.
4.8.17 Synchronizingtime test. Terminals of the synchro under teat
shall be comected to the appropriateterminala of a torque transmitter of
the same size and the same nominal impedance aa the synchro under teat. The
rotor(s)of the transmitter(s)shall be locked at synchro zero. The
applicabletest dial used for mechanical breakaway torque aa specified in
MIL-S-81963 shall be rigidly mounted on the ahaft of the synchro under test.
The synchro under test shall be displaced30° ~Z0 clockwise,energized in
accordancewith 4.3.4,
and the time requiredto returnto synchrozero and
remain within 1 degree of zero shall be ❑ eaaured. The synchronizingtime
shall be the average of thre e
succeaaivetests. This test shall be repeated
at a displacementof 30°~Z0 counterclockwise.
The above teat ghall be
repeated at displacementsof l’77° +Z0.
clockwise and counterclockwise. The
synchronizingtime for any test p~aitien shall meet the requirements of 3.6.17.
o
4.8.18 Securityof terminals and wire leada. The security of each screw
type or solder pin type of terminal or of each wire lead shall be tasted in
accordance with MIL-s-81963 and shall ❑ eet the requirementsof 3.6.18.
4.8.19 Impedance. The impedance of the synchro windings shall be
neaaured in accordancewith MIL-S-81963when energized in accordancewith
4.3.4and Table IX herein. Impedance shall be determined at synchro zero and
shall meet the requirementsof 3.6.19.
4.8.20 Temperature rise. Temperature rise shall’be conducted in
accordancewith MIL-s-81963and shall meet the requirementsof 3.6.20,USlng
secondary windings for dc resistance❑easurements. Windings shall be
energized as specified in 4.3.4.
4.8.21
Variation
of voltage
and frequency.
The synchro shall be
energized and stabilized in accordance with 4.3.2and 4 . 3 . 4 . The voltage
shall then be adjuated to 110 percent
of voltage specified in Table VI an~ the
frequencyadjusted to 9 5 percent of the value specified in Table VI. The
power drawn from the energizinggource shall meet the requirementsof 3.6.21.
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4.8.22 Audible noise, structureborne. Structurebornenoise test shall be
conducted in accordancewith MIL-S-81963,energized in accordancewith 4.3.4,
and shall meet the requirementsof 3.6.22,when required by the applicable
specificationsheet.
4.8.23 Electromagneticinterference. Electromagneticinterferenceteat
shall be conducted in accordancewith MIL-S-81963. The rotor of the synchro
shall be rotated at 1150 ~50 rpm and shall be energized as indicatedin
Table X. The aynchro shall meet the requirementsof 3.6.23,when required
by the applicablespecificationsheet.
4.8.24 Synchro zero markinq. The applicable synchro windings shall be
connected as shown in Figure9 1, 2, and 3, phased in accordance with 3.4.3,
and the rotorturneduntilthenullmeterminimumreadingis obtained.The
relativepositionof the synchrozero index ❑arked on the housing and the
index marked on the shaft shall be in accordancewith 3.5.2.
4.9 Environmental.
4.9.1
Vibration.
MIL-S-81
963.
During
All
aynchroa
shall
be
tagted
in
accordance
with
the test, the synchroa shall be energizedin accordance
with Table X with their rotor shaftg free to rotate while mechanicallyloaded.
Immediately after the teat, each gynchroshall be examined for loose or
damaged partg tid ghall meet the requirementsof 3.7.1.
4.9.2
-Shock.
4.9.2.1 Shock, specified pulse.
accordance
with MIL-s-8196B,
All aynchros shall be teated in
energized in accordance with Figure9 13, 14,
or
with their rotor ahafta free to rotate while mechanicallyloaded and shall
meet the requirements of 3.7.2.1.
15
4.9.2.2 Shock, high impact. All synchros shall be tested in accordance
with MIL-S-81963,energized in accordancewith Figures 13, 14, or 15 with
their rotor shafts free to rotate while mechanicallyloaded and shall meet
the requirements of 3.7.2.2.
4.9.3 Altitude.
4.9.3.1 Altitude low temperature. Synchros shall be tested in accordance
with MIL-S-81963,energized in accordancewith 4.3.4and shall meet the
requirements of 3.7.3.1.
4.9.3.2 Altitude high temperature. Synchros shall be tested in
accordance with MIL-S-81963,energized in accordancewith 4.3.4and shall ❑eet
the requirements of 3.7.3.2.
0
ti.9.
U Endurance. Synchros, except rotatablestator unite, shall be
tasted in accordancewith MIL-S-81963,energized in accordancewith 4.3.4,and
the rotor turned at 1150 ~50 rpm. Synchros of the rotatablestator type shall
be continuouslyoperated for 2000 hours, energized in accordance with 4.3.4,
the housing held stationary,and the rotatablestator rotated at 200 ~10 rpm.
Synchroa shall maet the requirements of 3.7.4.
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4.9.5 Ambient temperature test. The temperature extremes required under
4.9.5.1and 4.9.5.2are tests for storage extremes and are required to be
accomplishedonce per synchro.
Synchroa may be conditionedat the operational
temperaturesas often as neceseary to perform the required tests. Upon
completionof the temperaturetest, the synchro shall be removed from the test
chamber and allowed to remain at the gtandard teat ~onditiO~ of 4.3.1for at
leaet 4 hours before undergoing further tests.
4.%5.1
Ambient
low
temperature.Synchros shall be subjected to the
ambient low temperaturetests in accordancewith MIL-s-81963 and 4.9.5herein.
The synchroe shall be energized in accordancewith 4.3.4and ghall meet the
requirements of 3.7.5.1.
4.9.5.2 Ambient high temperature. Synchros shall be subjected to
ambient high temperaturetesta of 125° &20C, unless otherwise specified in
the applicablespecificationsheet, in accordancewith MIL-S-81963 and 4.9.5
herein. The synchros shall be energized in accordance with 4.3.4and shall
meet the requirementof 3.7.5.2.
4.9.6 Moigture resistance. Synchros shall be subjected to the moisture
resistancetest in accordancewith MIL-s-81963,energized in accordance with
4.3.4,and shall meet the requirements of 3.7.6herein.
4.9.7 Explosion resistance. The synohro shall be tegted in accordance
with MIL-STD-202,Method 109, while being vibrated according to 4.9.1and
energizedas specified in Table X. The synchro shall meet the requirementsof
3.7.7,when required by the applicablespecificationsheet. For additional
informationpertainingto explosionresistance,gee MIL-S-81963.
4.9.8 Salt atmosphere. Synchros shall be subjected to the salt
atmosphere tegt in accordaneawith MIL-s-81963and shall meet the
requirements of 3.7.8,when required by the applicablespecificationsheet.
4.9.9 Inspectionof packaging. The sampling and Inspectionof the
preservation-packaging,
packing,and containermarking shall be in accordance
with the requirementsof MIL-S-81963.
5. PACKAGING
5.1
Packaging
requirements.
The requirements for packagingshall be in
accordancewith MIL-S-81963.
6. NOTES
6.1 Intended use. The intended use for synchros covered by this
specificationshall be in accordancewith MIL-s-81963.
6.2 Ordering data. Ordering data shall be as specified in MIL-S-81963.
6.3 First article inspection. Information pertainingto first article
inspectionof synchros shall be obtained aa specified in MIL-s-81963.
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6.4 Qualification. With respect to products requiring qualification,
awards will be made in accordancewith MIL-S-81963. The activity responsible
for the QualifiedProducts List is Naval Air Systems Command (AIR-5143),
Department of the Navy, Washington,DC 20361-1000;however, information
pertainingto qualificationof productsmay be obtained from Commanding
Officer, Naval Weapons Support Center (Code 7022), Crane, Indiana 47522-5070.
6.5 Definitionof synchro and synchro system types.
6.5.1
Synchro.
which,
A synchro
13 an electromechanical
analog
converter
through electromagneticmeans, gives an electricaloutput that is a function
of its rotor positionor positions its rotor to an angle that is a function of
the electrical input.
input
6.5.1.1
(rotor
input
6.5.1.2
into
6.5.1.3
transmitter
electrical
Synchro
position)
Synchro
a rotor
A synchro
transmitter.
into
receiver.
an
tranamltter
a ❑echanical
converts
output.
ele ctric al
A synchro
receiver
converts
an
electrical
position as a ❑echanical output.
Synchro
differential
transmitter.
A synchro
gives
an electrical
output
which
is a function
input
and Its
mechanical
input
(rotor
position).
differential
of two
inputs--its
A synchro differential receiver
6.5.1.4
Synchro
differential
receiver.
gives a mechanicaloutput (rotorposition)which is a functionof two
electrical inputs--itsprimary input and its secondary input.
6.5.1.5 Control transformer. .4control transformer, in conjunctionwith
an amplifier and servomotor,converts an electrical input into a rotor
position in high torque applications. The electricaloutput of the control
transformer is amplified and applied to a servonotor which driveg the load and
the transformer to the null position.
6.5.2 Synchro system. A synchro system i3 a circuit containingone or
ore synchroe that operate on angular informationand convey this information
over a distance.
❑
6.5.3 Torque synchro system. A torque synchro system is a system in
which the transmittedsignal does usable work.
synchro system is a system in
6.5.4 Control synchro sygtem. A c ontrol
which the transmittedsignal controlsa source of power which does work.
6.6 Definitions and conventions.
6.6.1 Rotor angular displacement.
The rotor position of any synchco is an angular
Rotor
position.
6.6.1.1
mechanical rotor displacementfrom”the“synchrozero position,measured in the
positive direction.
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MIL-S-20708E
6.6.1.2 Rotor angle. The rotor angle of a practical synchro is the
angular mechanicalrotor displacementfrom the synchro zero position, measured
in the positive direction, at which the synchro’soutput voltages exactly
correspondto the output voltages of an ideal synchro aet at any speciffc
rotor position.
6.6.2 Electricalerror. The electrical error at a given rotor position
is the electricalangle minus the rotor position or the rotor position minus
the rotor angle (ace Figure 16).
6.6.3 Receiver error. Receiver error 13 the difference in the shaft
displacementof the receiver under test to the correspondingshaft position of
a torque transmitterof equal size.
6.6.4 Synchronizingtime. Synchronizingtime ia the time required for
the rotor of a synchro receiver or differentialreceiver to approach and stay
within 1.0 degree of rest when energized.
6.6.5 Impedance.
6.6.5.1 Rotor open-circuitimpedance. The rotor open-circuit impedance
of a synchro is:
Zro = The impedanceof the rotor with the stator terminal.?
open.
6.6.5.2 Stator open-circuitimpedance. The
of a synchro la:
atator
open-circuit impedance
●
Zso = The stator impedance with the rotor terminalsopen.
6.6.5.3 Rotor ghort-circuitimpedance. The rotor short-circuitimpedance
of a synchro is:
Zrs . The impedance of the rotor with the stator terminalg ehorted.
6.6.5.4 Stator short-circuitimpedance. The stator short-circuit
Impedance of a synchro is:
Zsa . The impedance of the stator with the rotor terminals shorted.
6.6.6 Primary and secondary windings. For transmitter and receiver
synchros,the rotor is the primary and the stator is the secondary. For
controltransformers
and differential
synchros, the stator ia the primary and
the rotor is the secondary.
6.6.7 Rated voltage. The rated voltage OP synchros is the line voltage
of the synchro system power supply; i.e.,115 volts or 26 volts.
6.6.8 In-time-phasesecondaryvoltages. The in-time-phasesecondary
voltage 19 the time phase ~uhdamental
component
of
the
secondary
voltage
at
the first positionof ❑aximum couplingwhen the synchro rotor 19 turned
in
positive
direction
from
9ynchro
zero.
the
o
22
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o
MIL-S-20708E
6.6.9 Transformationratio. The transformationratio is the ratio of the
fundamentalfrequencycomponent of the no-load secondaryvoltage at maximum
coupling to the voltage applied to the primary.
6.6.10
Phase
shift.
Phase
shift is the differencebetween the time phase
of the fundamentalcomponent of the primary voltage and the tine phase of the
secondary voltage of the synchro at the first positionof maximum coupling in
the positive directionfrom synchro zero.
6.6.11
Radial
play
and end play. The radial play of a synchro rotor is
the shaft displacementperpendicularto the shaft axis due to the reversal of
a force applied perpendicularto the shaft axis. The end play of a gynchro
rotor
19 the
axial
shaft
displacement
due to the reversal of an axial force.
torque
6.6.12
Mechanical
breakaway
requirec
to turn
the rotor
Mechanical
torque.
of a synchro
from
breakaway
torque
ia
the
rest when unenergized.
6.6.13Torquegradient.Torquegradientis the initialrate of changeof
torquewithangulardisplacement
of therotorfroma position where the torque
is zero, when”the synchro 1S energizedfrom a standard torque transmitterof
the same frame size and rating. The torque gradient is normally given as the
mean value obtained in the range of j10 degrees from the zero torque po9ition.
6.6.14 Residual (null)voltage. Residual voltage in a synchro is the
aCtUal voltage present at the secondaryterminals at that positionat which
the theoreticalsecondaryvoltage 1s zero. Thig volta g e
c onsists
of the
quadraturecomponent of the energizingfrequencyand a component which is made
up of harmonics of the energizingfrequency. Fundamentalresidual voltage is
the quadraturecomponent of the energizingfrequency;total residual voltage
is the fundamentalresidual voltage and harmonics.
6.6.15 Time phase. The time phase at a point in a synchro system is the
phase of the voltage,atthat point with respect to the phase of the enerSiZin13
voltage of the system.
6.6.16 Temperaturerise. Temperature rise is the increaseof the
internaltemperatureof a synchro above the ambient temperaturedue to the
dissipationof the energizingpower.
6.6.17 Units. Unlese otherwise specified, units of measurement are ag
follows:
a.
b.
c.
d.
e.
f.
s.
h.
Angles - degrees,minutes
Potential- volts, rms
Impedance - ohms
Current - ampere9, rma
Temperature- degrees, centigrade
Time Phase - degrees
Torque - ounce-inches
Time - seconds
23
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MIL-S-20708E
6.7 Subjectterm (keyWord)listin~.
Analogconverter,
electromechanical
Design❑edifications
Electrical
tests
Environmental
tests
Firstarticle
Mechanical
tests
Militarypartnumbers
Militaryapecificationa
Qualifiedproductslist (QPL)
Qualification
Qualityconformance
Rotatablestator
Rotatingcomponents
Servomotors
Specification
sheets
Standardization
Synchrocontroltransformers
Synchrodifferential
receivers(torque)
( c ontrol)
Synchrodifferential
transmitters
Synchrodifferential
transmitter(torque)
Synchroreceivers(tOrqUe)
Synchroreceivertransmitters
(torque)
Synchrotransmitters
(control)
Synchrotransmitter(torque)
6.8 Changes Prom prevloua issue. Asterigka are not used in this revision
to identify changes with respect to the previous igsue,due to the
extensivenessof the changes.
6.9 Internationalstandardizationagreements. Certain provisions of this
specificationare the subject of internationalstandardizationagreements
reached by the NATO Study Group on AnalOgue and Digital Servocomponents
of this
(AC/301
(SGI)(STG/1
)). When amendment,revision,or cancellation
.9pecification
ia proposedwhichaffacts or violates the international
agreement concerned,the preparingactivity will take appropriate
reconciliationaction through internationalstandardizationchannela,
includingdepartmentalstandardizationoffices, if required.
o
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M I L - S - 20708E
TABLE I. Nomenclature.
15
Synchro
Cx
4
D
M20708/14-OID
Transmitter
(Type Designation)
Item Name
Size
(1.2.1.1)
Function supply
Design
Frequency Modification
Military
Part Number
:1.2.1.2)1.2.1.3) (1.2. .4) (1.2.1.5) (1.2.1.6)
TABLE II. Terminationidentificationmarking.
Terminal No.
Wire Lead Color
Winding
R]
Red, White tracer
Rotor 1
R2
Black, White tracer
Rotor 2
R3 (if used)
Yellow, White tracer
Rotor 3
sl
Blue
Stator
S2
Black
Stator 2
S3
Yellow
Stator 3
25
I
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—
M I L - S - 20708E
I
1
1
—
1
1
—
1
!
—
1
!
—
,
1
—
1
—
:
2
5
—
,
1
I
—
;
.
5
—
m
26
Downloaded from http://www.everyspec.com
—
—
L&l
0
0
++
—
m
z
~
+!
1
I
I
—
1
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1
I
—
I
1
I
1
—
1
—
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1
1
1
I
I
~
1
~
z
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—
r.
m
Q
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—
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—
—
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a
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0
cd
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0
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27
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t
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—
nm
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—
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—
—
—
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—
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1
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1
1
M I L - S - 20708E
1
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.
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M I L - S - 20708E
30
Downloaded from http://www.everyspec.com
M I L - S - 20708E
31
Downloaded from http://www.everyspec.com
a“
al
ij
8
1
ii
ii
El
MIL-S-20708E
32
0
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33
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M I L - S - 20708E
0
!M.SLEV. MountingHardwaI’e.~/
Number
Required
Machine Screw
5EA~/
Standard
Sy n c h r o
Size
MS-35276-203
11
MS-35275-213
15, 18, 23
Military
MS-35275-227
Lack Washer
5EA~/
MS-35338-134
11
MS-35338-135
15, 18, 23
MS-35338-136
3.37
MS-171864
Drive Washer
Nut
31, 37
11, 15, 18, 23
1E4
ht3-17186-8
31, 37
MS-17187-2
11, 15, 18, 23
MS-17187-3
31.
# 37
1E4
~/ For information
only,see MS17183,ClampAssembly(Synchro)
~/ Differential
tranamit@rs(CDX,TDX and CDXB)require6 each
machinescrewsand lockwashersineteadof the5 eachrequiredon
al1 othertypeeof synchros.
34
●
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o
MIL-S-20708E
TABLEVI. Standardtestenergizing
connections.
Voltage in Approximate
Time Phase 1/ 2/
Secondaryand Primary
Primary
SynchroType
Olts ~1
Transmitter
& Receiver
115 or
26 ~/
‘erminals
4/
R1-R2
E(S1S2)
and
Secondary
rerminals
S1-s3
E(R2R1 )
E(S3S2)and E(R2R1
)
Differential’
Transmitter
& Receiver
78 or
10.2 y
S2-S1S3
E(R3R2)and E(S3S2)
E(R1R2)and E(S1S2)
R1-R3
Control
Transformer
78 or
10.2 y
S2-S1S3
E(R1R2)and E(S2S1
) 6/
E(R1R2)and E(S2S3)~/
RI-R2
E(S1S2) is the voltage between terminalsS1 and S2. Other voltages are
similarlydefined.
The sequence as indicated in parenthesesdesignatesthe sense of
voltage
vector.
Frequencyof 60 or 400 Hz, as applicable.
S1S3 indicateathat terminalgS1 and S3 are connected together.
Applies to 26-volt synchros.
For small counterclockwisedeflectionsfrom gynchrozero.
iABLE VII. Dielectricwithstandingvoltages and applicationpoints.
Maximum Rated
Voltage,rms
Initial Test Voltage9,
rms (50 or 60 Hz)
SubsequentTest Voltagea
rms (5o or 60 Hz)
Each winding to housingand
primary to secondarywindings
Each winding to housing and
primary to secondarywindings
200
2U2 to 250
194
51 to 100
485 to 500
388 to 400
101 to 200
870 to 900
696 to 720
up
to
50
35
to
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o
MIIA-20708E
TAPLE VIII. Connections,energizing voltage end
angular displacements
for residual
nullvoltagetest.
Test Unit
a,
m
Primary supply
Test Voltage
Across
115-volt
26-Volt
Terminals 1/
Synchros
Synchros
TX*
CDX , TDX
TDR
CDx , mx
mR
CDX , TDX
‘IDR
CT
115.0
m-w
78.0
s2-s1s3
I
I
Residual (Null)
Voltage Reading
Across At Electrical
Tex70imls
Angles
26.0
S1-S3
s3-s2
S2-S1
0° and 180°
60° and 240°
120° and 300°
10.2
R1-R3
R2-Rl
R3-R2
0°
60°
120°
and 180°
and 240°
and 300°
s3-sLs2
78.0
10.2
F&m
R3-R2
IU-R3
0°
60°
120°
and 180°
and 240°
and 300°
S1-S2S3
78.0
10.2
R3-R2
R1-R3
R2-Rl
0°
60°
120°
and 240°
and 300°
R3.-R2
m-w
R1-R2
0°
60°
120°
and 180°
and 240°
and 300°
2-s1s3
;-s2s3
s3-sIs2
I
78.0
78.0
78.0
I
10.2
10.2
10.2
I
and 180°
L/ S3.S3
indicatesthatternd.mlsS1 and S3 are comected together.
Gther
connection are similarly defined.
0
36
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MIL4-20708E
TASLE IX. hnpedancedesignation.
Impedance
Typeof Synchro
UnderTest
Terminalsfor
Impedance
lleas~nts ~1
VoltageAcross
Additior?al
Synchro
Terminals
Connect
iotx
2bV
1.15v
synchros Synchrw
Rotor, @en
circuit
Impedance
Zro
Stator,@en
Circuit
Iqxx2ance
Zso
Cx, TX. m, TRx
26
22.5
10.2
-
78
10.2
-
R1-R2
g/
~1
sls2s3
W-RIR3
~1
~1
S1S2S3
s2-sLs3
~1
21
R1.R2
s2-sls3
~1
~1
RIR2R3
FU-R2
CT
~X, TOX,TDR
RI.-R2
R2-RlR3
All types
s2-s1s3
Rotor,Short Cx, TX. Cl’,m, TRx
circuit
~dence
COX,TDX,TDR
Zre
115
57.3
78
0“
Stator,ShortCx, CT, TX, TR, TRx
Circuit
Impedance COX,TDX,TDR
Zss
RIR3 indicatesthatterminals
Rl andR3 are connectedtogether.Other
comectioneare similarlydefined.
The voltagenecessaryto inducea currentwithin~ 3 percentof currentin
Zro measurement.
The voltagenecessaryto inducea currentwithin~ 3 percentof currentin
Zso measurement.
37
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MUA3 - 2 0 7 0 8 E
TABLE X. Conriections
end voltagesfor electrmagna
tic
interference,
vibration,
enduranceend
explosionteeta.
Vo ..tage
Type
1 1 5 volt
TeIminels ~/
Synchros
Tramnittersend receivers
Differentialreceivers and
differentialtranmittera
Control trenafo~rs
~/
I
/
RI.-R2
R2-FUR3
RI-R2
.
1 1 5 ~ 5%
2 6 . 0 f 5%
78 ~ 5$
1 0 . 2 f 5%
I 57~5%1
Z2.2~5%
R I R3 indicatee
thattermimls Rl and R3 are connectedtogether.
38
<.
I
2 6 Volt
Synchros
I
I
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MIL-s-20708E
o
II
.——
—
PSASE
SENSITIVE
VOLTMETER
s e e 4 . 3 . 4+ f Q ) ~
.——
—
J
1
I
+---J
FIGURE 1. Diagram for determiningsynchro zero
position of transmittersand receivers.
~————
1
See 4.3.4
S3
L————4
FIGURS 2. Diagram for determiningsynchro zero
position of differentialtransmitters
and differentlalreceivers.
See
4.3.4
S3
L——
——-l
FIGURE 3. Diagram for determiningsynchro zero
position of control transformers.
39
Downloaded from http://www.everyspec.com
M I L - S - 20708E
NOT E :
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41
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MI L-S-20708E
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42
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MI L-S-20708E
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43
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MIL-S-20708E
NOTE:
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45
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FIGURE
10.
MIL-S~20708E
—
I 61
. B r e a k downo f a n a l og y testi
46
nq.
Downloaded from http://www.everyspec.com
o
MIL-S-20708E
I
i
1
1
I
PONER
SUPPLY
INDEX
I STAND
FIGURE 11.
Example of electricalerror test setup for
transmitters,receivers,and rotors of differentials.
OUT
INDEx
STAND
8.
FIGURE 12. Example of electricalerror test setup for
control transformersand stators of differentials.
47
Downloaded from http://www.everyspec.com
MIL-s-20708E
See 4.3.4
FIGURE 13. Energizationof transmittersand
receivers for shock test,
‘ee4”EE
o
FIGIJRE14. Energizationof differential
transmittersand receivers
for shock test.
“’4”3”4-%
13,000
ohms
Resistance
1
FIGURE
15. Energizationof control
transformersfor shock test.
48
d
Downloaded from http://www.everyspec.com
MIL-S-20708E
Signal output of Test Synchro
referred to a perfect Synchro
or ElectricalAngle of a perfect
Synchro. Error equals
ElectricalAngle minus Rotor
Position.
7
0° Synchro Zero
Q,
SpecifiedRotor
Position of Test Synchro
Q=
Qp
Rotor Angle of Test
Synchro required to produce
an ElectricalOutput equal to
the SpecifiedRotor Position.
ElectricalError equals Rotor
Positionminus Rotor Angle.
Qr = Rotor Angle
Q= = ElectricalAngle
Qp = Rotor Position
FIGURE 16. Rotor angular geometry.””
49
Downloaded from http://www.everyspec.com
MIL-s-20708E
0
INDEX
Nomenclature
Paragraph
Acceptancetests
Alternatetestmethods
Altitude
Altitudehigh temperature
Altitudelow temperature
Ambienthightemperature
Ambientlow temperature
Ambienttemperature
Applicable
documents
Assessment
of qualification
approval
testresults
Audiblenoise,atructureborne
4.5.3.2.1
4.2.2
3.7.3,
3.7.3.2,
3.7.3.1,
3.7.5.2,
3.7.5.1,
3.7.5,
2
4.5.3
11
4.9.3
4.9.3.2
4.9.3.1
4.9.5.2
4.9.5.1
4.9.5
3.6.22, 4.8.22
9:019
9, 19
9, 19
9, 20
9, 20
9, 20
3
11
8,
19
~
4.5.6,
4.4
6.5.1.5
3.6.9,
Change9
Classificationof tests
Control transformer
Current, primary
6.8
4.8.9
13,
24
10
7:’15
g
Definitionsand conventions
Definitionsof aynchro and synchro types
Degradationof performance
Design and construction.
Design ‘convent
ions
Design modification
Dielectricwithstandingvoltage
Differentials
Dimensions
Direction of rotation
Dispositionof qualificationsa mples
6.6
6.5
4.5.3.2
:::
1 .2.1.5
3.6.7,
4.8.7
6.5.1.3,
3.5.3
3.4.1
4.5.4
4.5.3.2.2.8,
.6.5.1.4
21
21
11
6
4
2
7, 12,
15
21
7
4
13
&
Electricalangle
Electricalerror
3.4.2
3.6.13,
4.5.3.2.2.3,
4.8.13,
6.6.2
3.6.23,
4.8.23
3.7.4,
4.9.4
3.7,
4.5.3.2.2,
4.9
3.7.7,
4.9.7
Electromagneticinterference
Endurance
Environmentaltesta
Explosionreaistame
50
4
8, 11,
15, 22
8, 19
9, 19
8, 11, 19
9, 20
0
Downloaded from http://www.everyspec.com
MIL-S-20708E
●
INDEX
Nomenclature
Paragraph
~
g
First article
First article inspection
First article sample inspection
First article sample ~ailure
Frequencysensitive voltmeter ❑ethod
Function
4
20
13
13
16
2
3.3
6.3
4.6
4.6.1
4.8.14.1
1 .2.1.3
~
Governmentdocuments
3
2.1
.
3.7.9
Identificationmarking
Illustration
Impedance
In-time-phasesecondary volta g e
Irispection
of packaging
Insulationresistance
i .3
3 . 6 . 19 , 4 . 8 . 19 , 6 . 6 . 5
6.6.8
4.9.9
3.6.8,
4.8.8
Intended use
Internationalstandardization
agreements
Item name
4.5.3.2.2.9,
9
3
8, 18, 22
22
20
7, 12,
15
20
24
1 .2.1.1
1
M
4.5.3.2.2.10
Major failures during or following
envlronmentaltests
Mechanicalbreakawaytorque
3.6.5,
4.5.3.2.2.4,
4.8.5,
6.6.12
1 .2.1.5
3.7.6,
4.9.6
4.3.1
Modification,design
Moisture resistance
Mounting hardware
12
‘7, 11,
14, 23
9,220
10
~
Nomenclature
1 .2.1
~rder of precedence
Ordering data
Other governmentdrawing
Outline drawings
2.2
6.2
2.1.2
3.5.3
‘1
51
4
20
4
7
Downloaded from http://www.everyspec.com
MIL-S-20708E
INDEX
Paragraph
Nomenclature
P
Packaging
Packaging requirements
Part number, military
Performance
Phase-sensitivevoltm eter
Phase shift
Phase shift test
Power, primary
method
5
5.1
1.2.1.6
3.6
4.8.14.2
3.6.12, 6.6.10
4.8.12
3.6.10, 4.8.10
20
20
2
7
16
8, 23
15
7, 15
3.2, 6.4
4.5.3.4
4.5
4.5.2
4.5.1
4.5.3.1
4.5.3.3
4
4.7
4.7.2
4.7.1
4.7..3
4, 21
12
g
Qualification
Qualification
approvalby analogy
inspection
Qualification
inspectionroutine
Qualification
sample
Qualification
3ample failure
Qualification
sample - isolatedfailure
Qualification
Qualitya9surance provisions
Qualityconformanceinspection
Qualityconformanceinspection routine
Qualityconformanceinspectlon sampling
Qualityconformancesample failure
10
11
11
11
12
10
13
13
13
13
0
~
Rated voltage
Receiver error
6.6.7
3.6.15,
4.8.15,
6.5.1.2
Receivers
Requalification
Requirements
Residual (null) voltage
4.5.5
3
3.6.14,
4.8.14,
4.1
6.6.1.2
6.6.1
6.6.1.1
Responsibility
for inspection
Rotor angle
Rotor angular displacement
Rotor position
4.5.3.2.2.2,
6.6.3
4.5.3.2.2.7,
6.6.14
22
8, 11,
16, 22
21
13
4
8, 12,
16, 23
10
22
21
21
g
Salt atmosphere
Scope
Security of terminalsor wire leads
Shaft end play
Shaft radial and end play
Shaft radial play
Shaft ‘runout
3.7.8, 4.9.8
7
3.6.18, 4.8.18
4.5.3.2.2.6
3.6.3, 4.8.3, 6.6.11
4.5.3.2.2.5
3.6.4, 4.8.4
52
9,
20
8,’18
12
7, 14, 23
12
7’,14
0
Downloaded from http://www.everyspec.com
MIL-S-20708E
Nomenclature
INDEX
Paragraph
~
~ - (continued)
Shock
Shook, high impact
Shock, specifiedpulse
Size
Specifications
Specificationsheets
Spinning test
Spline shafta
Standard test conditions
Standard test voltage and frequency
Standards
Subject term (key word) listing
Supply frequency
Synchro
Synchro zero
Synchro zero marking
Synchronizingtime test
3.7.2,
3.’7.2.2,
3.7.2.1,
1 .2.1.2
2.1.1
;:~.16,
3.4.4
4.3.1
4.3.4
4.9.2
4.9.2.2
4.9.2.1
4.8.16
2.i.l
6.7
1 .2.1.4
6.5.1
3.4.3
3.5.2,
3.6.17,
temperature rise
Temperature,stabilizedoperating
Temperature,stabilizednonoperating
Termination identification
Test conditions
Test equipmentand inspectionfacllitiea
Test ❑ethods and examinations
Time phase
Torque gradient test
Transformationratio
Transmitters
4.8.24
4.8.17,
6.6.4
3.6.20, 4.8.2o, 6.6.16
4.3.2
4.3.3
3.5.1
4.3
4.; .1
4.8
6.6.15
3.6.6,
3.6.11,
6.5.1.1
4.8.6,
4.8.11,
6.6.13
6.6.9
9, 19
9, 19
9, 19
2
3
4
8, 18
6
10
10
3
24
2
21
6
7, 19
8, 18, 22
8, 18, 23
10
10
6
10
10
13
7:314, 23
7, 15, 23
21
g
6.6.17
Units
23
~
Variationof brush contact resistance
Variaticnof voltage and frequency
Vibration
Visual and mechanicalexamination
3.6.2, 4.5.3.2.2.1,
4.8.2
3.6.21, 4.8.21
3.7.1, 4.9.1
3.6.1, 4.8.1
7, 11,
8;318
8, 19
7, 13
~
Windings
Workmanship
6.6.6
3.7.10
22
9
53
I
Downloaded from http://www.everyspec.com
●
MIL-s-20708E
Custodians:
Army-AR
Navy-AS
Air Force-85
Preparing Activity:
Navy-AS
(ProJect5990-0333)
Review Activities:
Army-AV,MI
Navy-EC,SH,OS
Air Force-99,17
DLA-ES
User Activities:
Army-AT,ER
Navy-CG,MC
Air Force-19
54
Downloaded from http://www.everyspec.com
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