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Model M Manual : Appendix
Microphone Test
A microphone test can be performed after the Amplifiers and Filters Test has shown that the battery and electronics are performing properly, and the Microphone Cable Test indicates that the cable is operating properly. The microphone test is used to measure the output of the microphone when a pre-determined pressure pulse is applied to the microphone. A rubber squeeze bulb attached to a plastic threaded cap is supplied with the gas gun so that the gas gun microphone can be tested whenever desired. The rubber squeeze bulb applies a compression pressure pulse to the microphone when the bulb is squeezed. Continue to squeeze the bulb for approximately 5 seconds, then release the bulb. When the bulb is released, a rarefaction pressure pulse is generated which is opposite in polarity. When testing the Compact Gas Gun, the internal gas valve and the casing bleed valve must be closed. Lifting the cocking arm closes the internal gas valve. When testing the Remote Fire Gun, close the gas valve by charging the volume chamber. Be sure that the casing bleed valve is closed. When testing the 5000-psi gun, close the valve between the microphone and the volume chamber. When testing the 15000-psi gun, rotate the gas valve control knob until the internal gas valve is shut. Then, close the casing bleed valve.
Attach the rubber test bulb to the end of the gas gun securely. Attach the microphone cable to the microphone outlet BNC connector and to the instrument INPUT. Set the sensitivity controls as shown below depending on which gas gun is to be tested. Turn the Power Switch ON. Set the filter switch to LOWER COLLARS. After the chart drive stops, turn the Chart Drive Switch ON. Squeeze the test bulb. Hold for approximately 1 second, and then release the test bulb. The response should be similar to the examples below.
Collar Gain Setting Liquid Level Gain Setting Compact Gas Gun 4 2 Remote Fire Gas Gun 3 ½ 1 ½ 5000-psi Gas Gun 3 1 ½ 15000-psi Gas Gun 3 1 ½
Squeeze Bulb Release Bulb 