MIL-PRF-25435D
4.4.4 Tapping. Unless otherwise specified, the transmitter shall be lightly tapped or vibrated
after initial indicator readings are taken and the difference recorded. The difference between
readings before and after transmitter vibration is friction error.
4.5 Tests.
4.5.1 Examination. The transmitter shall be examined for compliance with requirements for
dimensions, materials, weight, electrical connector, pressure connections, markings, and
maintainability.
4.5.2 Dielectric strength. A potential of 200 Vrms and 60 Hz shall be applied between any pin
of the electrical connector and any metal part of the transmitter case for 5 seconds. There shall be
no insulation breakdown.
4.5.3 Scale and friction error. The transmitter shall be connected to pressure and electrical
power sources and to the standard indicating unit. The transmitter at ambient temperature shall
be tested for scale error, both up-scale and down-scale, at the test points specified in the contract.
Two readings shall be taken: the first before, and the second after, the transmitter is tapped or
vibrated. Scale and friction errors shall not exceed the tolerances in the contract (see 6.2).
4.5.4 Position error. The transmitter shall be energized to obtain a reading of one-half scale on
the standard indicating unit. The transmitter then shall be rotated from the normal operating
position to a position 90° clockwise and then 90° counterclockwise (longitudinal axis vertical).
The indicating unit reading change shall not exceed the position error tolerance in the contract
(see 6.2).
4.5.5 Leakage.
4.5.5.1 Nonhermetically sealed case. The pressure and vent connections shall be sealed and the
transmitter immersed in water inside an enclosure to a depth of 18 inches maximum. The
absolute pressure of the air above the liquid shall be reduced to 2.5 in Hg. Any bubbles coming
from within the case indicates a leakage and shall be cause for rejection.
4.5.5.2 Hermetically sealed case. The leakage rate measured with a helium mass spectrometer
with a differential pressure of 24 in Hg minimum shall be 0.1 micron cubic foot per hour
maximum.
4.5.6 Vibration. See MIL-STD-810 Method 514.2 for further guidance. The transmitter shall be
mounted directly to a vibration exciter without vibration isolators. Tests shall be conducted under
both resonance and cycling conditions as specified in paragraphs 4.5.6.1 and 4.5.6.2. Time
consumed performing resonance tests plus time consumed cycling in cycling tests shall equal 3
hours for each axis. Vibration displacement, velocity, and acceleration shall be measured at the
specific instantaneous test frequency applied. Loose transmitter components that impact each
other resulting in a high noise content of the applied vibration shall be considered as vibration
input. If such noise is encountered, a low pass frequency filter that cuts off at approximately
twice the test frequency shall be employed to reject the noise.
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