Downloaded from https://www.everyspec.com MIL-STD-1311D NOISE AND MICROPHONICS, PEAK OR INTEGRATED A TSS may specify noise and microphonics, peak, or noise and microphonics, integrated, or both tests. However, the integrated test alone gives good agreement with swept frequency vibration noise output and with the applications studied. The peak test should be an unusual requirement. 1. Mounting. The TUT shall be mounted in the test socket and tapped at least 2 times in each of two planes 90 ° ± 10 ° apart. During tapping, the tube shall be supported only by the socket and light finger or soft cushioned mechanical pressure on the dome of the bulb.
The finger or mechanical pressure on the dome of the bulb shall be used only when necessary to prevent the tube from coming out of the socket and shall be so applied that it offers negligible restraint to lateral motion at the top of the bulb. The tap blows shall be delivered to the tube approximately two-thirds up on the holddown height. 1.1 Tapper impulse.
The tapping device shall be so designed and adjusted that it will deliver an impulse of approximately one- half sine wave of 300 ± 50 microseconds duration, as measured 10 percent from the base of the impulse and having an amplitude equivalent to 45 ± 5 G peak acceleration as measured on a Gulton Manufacturing Company Type A-305 accelerometer, or equivalent. The tapper impulse shall be measured with the accelerometer mounted in a standard production type (replaceable cap and clips) T5-1/2 socket and having no other support. The tap blow shall be delivered to the accelerometer in the plane of its maximum sensitivity.
The output of the accelerometer shall be coupled through a cathode follower and low-pass filter to an oscilloscope having amplitude and time base calibration. The frequency response of the filter shall not be down more than 3 dB at 5,000 Hz. The tapper calibration using a T5-1/2 accelerometer applies regardless of the size of the tube to be tested. On tapping devices, where the hammers are accelerating just before impact, the hammer travel distance must be the same during testing as it was during calibration. On devices where the hammers approach the tube at essentially constant linear or angular velocity, the travel distance need not be controlled. 1.2 Test limits.
The test limit(s) shall apply to the response of the output indicators to the voltage developed by the TUT across a load resistor Rp in response to the mechanical excitation (see figure 1239-1). Peak and integrated audio frequency noise and microphonics tests may be performed simultaneously. 1.3 Anode voltage. The value of Eb under "test conditions" shall be regarded as Ebb for this test. Cathode and screen bypass capacitors, when specified, shall be regarded as minimum nominal values. 1.4 Anode circuit decoupling/screen voltage-dividing network.
The anode-circuit decoupling network is permitted if its resistance is less than 10 percent of Rp and its series impedance is greater than the reactance of its bypass capacitor at 10 Hz. A screen voltage-dividing network is permitted if the bleeder current is at least 10 times the operating screen current and if the screen is bypassed by a capacitor whose reactance at 10 Hz is less than 10 percent of the effective resistance of the two sections of the divider in parallel. 2. Noise and microphonics, peak. Test equipment and procedures specified in 1 above, shall apply.
The indicating system shall respond to the absolute peak value (peak positive or negative value, whichever is larger) of noise output voltage of the TUT resulting from each tap blow. The system shall indicate, within ± 20 percent, the peak value of sinusoidal voltage of all frequencies between 100 and 15,000 Hz. It shall indicate, within ± 20 percent, the peak voltage of a single 20 µ s square pulse. 3. Noise and microphonics, integrated. Test equipment and procedures specified in 1 above, shall apply. The indicating system shall measure the integral of the absolute value of noise output voltage of the TUT during a period, t, following each tap blow.
The integrating period, t, shall be a minimum value and shall be specified. 3.1 Calibrating signal. A sine wave calibrating signal, E rms volts, applied to the anode pin of the test socket for a period, t milliseconds, should read 0.9 tE millivolt seconds (mVs). The indicating system shall be capable of measuring this quantity, to an accuracy of ± 10 percent at 5,000 Hz, at each of two signal voltage amplitudes, one of which is 100 times the voltage of the other, with a single gain setting of the system. The larger voltage shall be measured for a period of 1-millisecond minimum. The smaller voltage shall be measured for a period of 100 ms minimum.
An oscilloscope may be connected to the indicator to show that integration is correct for the required periods. 3.2 Frequency response. The frequency response of the amplifier and rectifier portions of the system shall be within ± 3 dB of the response at 1,000 Hz over the frequency range from 100 to 15,000 Hz. METHOD 1239 METHOD 1239 1239-1 19 April 1968