Downloaded from https://www.everyspec.com MIL-STD-1311D METHOD 1031A VIBRATION 1. Purpose. Vibration test is performed for the purpose of determining the effect on component parts of vibration in the specified frequency range. 2. Procedure. 2.1 Fixturing and control points. For each axis of vibration, the TUT shall be rigidly mounted on a suitable fixture that is free from mechanical resonance over the test frequency. The test fixture shall not cause attenuation of the energy level exhibited at the platform using accepted standards of measurements for calibration of the shock level and time duration. The TUT may also be mounted directly on the vibration table.
If a fixture is used, it shall be so designed as to transmit the acceleration along the required axis. The vibration input shall be monitored and controlled at a point on the fixture close to the attachment points of the TUT. 3. Low-frequency (25 Hz) vibration. The tube shall be rigidly mounted on a table vibrating with simple harmonic motion at a frequency of 25 ± 2 Hz with a fixed amplitude of .040 ± .0025 inch (total excursion of .080 ± .005 inch).
Each tube shall be vibrated in positions X and Y, except that if the cumulative result of tests on 50 or more tubes of a construction shows that more than 75 percent of the tubes have higher output voltages in one position, subsequent measurements shall be taken only in the position giving the higher readings. The voltages specified on the TSS shall be applied to the tube during vibration. The value Eb under test conditions shall be regarded as Ebb and shall be applied to the tube through the specified resistor (Rp). The impedances of anode and screen voltage supplies shall not exceed that of a 40- µ F capacitor at 10 Hz.
(Preheating of the tube at these voltages is permissible.) The value of the alternating voltage (Ep) produced across the resistor (Rp) as a result of vibration shall be measured with a suitable device. This device shall have an appropriate voltage range and shall have the ability to measure with an error of less than 10 percent, the rms value of a sine wave of voltage of all frequencies from 20 to 5,000 Hz. Thermal or VU meters may be used provided the shunting effect on the anode load does not result in error greater than the 10 percent allowed above.
Unless otherwise specified, each tube shall be vibrated for a time necessary to obtain a stable reading of output voltage or for a maximum period of 30 seconds in any one position. The stable reading shall not exceed that specified on the TSS. However, if at the end of 30 seconds, the average value of the meter reading exceeds 50 percent of the maximum specified voltage and is increasing, the tube shall be vibrated for a total time of 3 minutes, and the tube rejected if the average value of the meter reading at the end of this period exceeds the maximum specified voltage.
When this test is conducted and no measurement is made of output voltage, each tube shall be vibrated for 60 seconds each in positions X and Y. This test shall not result in tap or permanent shorts or defects which will cause the tube to be inoperable. 4. High-frequency (50 Hz) vibration. The test shall be conducted as specified in 3 above, except that the frequency of the vibrating table shall be 50 ± 2 Hz. Upon completion of the test, the tube shall comply with the criteria specified in 3 above. 5. Operation vibration. The tube shall be vibrated in accordance with 3 above, with the specified operating conditions applied.
A test load shall be arranged to pick up some power output from the tube. If the load is not vibrated with the tube, it shall be arranged so that the frequency pulling of the tube is negligible compared to the variation in frequency due to the vibration of the tube. The total radio frequency spectrum, including any permanent change in frequency, shall not exceed the limit specified on the TSS. For klystrons, the test load, as seen by the tube, shall be as specified on the TSS. Spectrum bandwidth determination shall be made during the test, with the operating conditions held unchanged. 6. Nonoperation vibration.
The tube shall be vibrated at the specified frequency and acceleration in accordance with 5 above. The conditions of operation before and after vibration, including the adjustment of the tuner mechanism and reflector voltage, shall remain unchanged. The difference between the oscillation frequencies before and after vibration shall not exceed the limit specified. 7. Sweep-frequency vibration. The tubes shall be fastened rigidly to the vibration platform and vibrated with simple harmonic motion over a frequency range of 50 to 2,000 Hz at the peak acceleration value specified on the TSS. If not specified, the peak acceleration shall be 10 G.
The acceleration over the frequency range shall be within ± 10 percent of the referenced acceleration at 100 Hz. At all frequencies from 50 to 2,000 Hz, the total harmonic distortion of the acceleration waveform shall be less than 10 percent. The frequency shall increase from 50 to 2,000 Hz with approximately logarithmic progression versus time and shall require 4 minutes minimum, 5 minutes maximum, to traverse the range.
Each tube shall be vibrated in axes X and Y, except that if the cumulative results of tests on 50 or more tubes of a given construction show that more than 75 percent of the tubes have a higher output voltage on one axis, subsequent measurements need only be taken in the axis giving the higher readings. For special construction tubes, vibration axes shall be indicated on the TSS. METHOD 1031A 1031-1 25 March 1970