MIL-DTL-38394E
3.3.1.7.1 Synchro bearings. The precision ball bearings used in the synchro shall be
corrosion resistant alloy steel (stainless steel) conforming to SAE-AMS-QQ-S-763, class 440C,
and shall be made to ABEC tolerance 5P per ABMA 12.1 or 12.2 as applicable.
3.3.1.7.2 Electrical zero. A means shall be provided for readily setting the synchro at
electrical zero. The synchro transmitter shall be designed so that the synchro electrical zero
position can be set and locked securely so that it will remain in that position for the service life
of the transmitter or until reset.
3.3.1.8 Overpressure stop. An overpressure stop shall be provided to restrain the prime
mover. The stop shall permit the transmitter rotor to rotate 12 degrees to ±3 degrees beyond the
500 pounds per square inch (psi) position. The stop shall not be damaged by the application of
750 psi.
3.3.1.9 Gears, pivots, joints, and bearings. The gears, pivots, joints, and bearings shall
resist wear, corrosion, and friction when interfacing with one another. The interfacing materials
shall not be dissimilar as described in MIL-STD-889.
3.3.1.9.1 Large area interface surface. The gears, pivots, joints, and bearings shall have
substantially large interface surfaces for the purpose of minimizing the effects of wear upon the
calibration and accuracy of the transmitter. Single point type surfaces, such as attained by pivots
made of two perpendicular cylinders, will not be acceptable. Interface surfaces made up of two
parallel cylinders or curved surfaces will be acceptable if sufficient interface area is provided to
minimize the effects of wear.
3.3.1.10 Attitude. The transmitter shall be so designed that it will operate as specified
herein in any position.
3.3.1.11 Connections. The transmitter shall have a pressure port connection and separate
vent port connection as shown in figure 1.
3.3.1.12 Containment. There shall be no flow path between the two port connections or
either port connection and the outside of the transmitter. Except for the pressure and vent ports,
no single transmitter failure shall result in such a path.
3.3.2 Construction. The transmitter shall be constructed so that no parts will work loose
in service. It shall be built to withstand strains, jars, vibrations, and other conditions incident to
shipment, storage, installation, and service. Pivots, bearings, and gears shall not bind or shake
and shall be as nearly frictionless as possible.
3.3.2.1 Mounting provisions. The mounting flange of the transmitter shall be
constructed in accordance with figure 1. The four mounting holes shall be provided with screw
locking helical coils in accordance with NASM21209 inserted from the electrical connector side
of the transmitter. The helical coils shall accept and lock #6-32 threaded screws.
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