MIL-DTL-81963C
4.9.7 Insulation resistance. The insulation resistance shall be measured in accordance with method
302 of MIL-STD-202 to determine conformance with 3.6.7.
4.9.8 Current. The servocomponent shall be brought to the stabilized operating condition of 4.2.2.2 in
the standard test conditions of 4.2.1. The current drawn by each winding shall be measured and shall be
in accordance with 3.6.8.
4.9.9 Power. The servocomponent shall be brought to the stabilized operating condition of 4.2.2.2 in
the standard test conditions of 4.2.1. The power consumed by each winding shall be measured and shall
be in accordance with 3.6.9.
4.9.10 Impedance. The servocomponent shall be brought to the stabilized operating condition of
4.2.2.2 in the standard test conditions of 4.2.1 and, while energized at the applicable standard test
voltage and frequency specified in the applicable general specification, the impedance of each winding
shall be determined and shall be in accordance with 3.6.10.
4.9.10.1 General. Impedance methods of measurements described hereunder are applicable within
specified limitations to all types of servocomponents. However, because of the high accuracy attainable
with methods described hereunder, measurements lend themselves more to synchros, resolvers,
transolvers, and linear resolvers rather than servomotors, where in general, less sophisticated methods
are acceptable.
4.9.10.1.1 The Wien-modified Maxwell bridge. Figure 8 shows the circuit diagram of the bridge,
together with the appropriate equations necessary for calculating the servocomponent impedances. The
following practical points should be noted:
a. The screen connections on the bridge elements should be arranged as shown on figure 8, so that
the capacitance currents to ground are drawn directly from the supply and are not permitted to shunt the
elements.
b. The use of a double screen transformer is essential, in order to eliminate the effect of stray
capacitance and the ground leakage path from the power supply generator or transformer to the ground
terminal of the null detector.
c. The resistance of arm R3 should be kept as small as possible in order to minimize frequency
variation errors.
d. Magnetic coupling between the power supply transformer and the null detector transformer(s) may
cause additional errors. The power supply transformer should be so positioned that, with the bridge in its
balanced condition, rotation about its axis causes no significant alteration of null indication.
e. Careful attention should be paid to accuracy in setting up the voltage and frequency of the supply.
f. If a synchro, resolver, or transolver is under test, it should preferably be set to zero within ± 3
minutes of arc.
g. The accuracy of the bridge components should be within 0.1 percent of the nominal values.
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