LDM #258: Magnetic Anomaly Detector AN/ASQ-81(V) - Part 2: Static Pressure Sensor circuits

00:00 - Intro
01:12 - Schematic diagram after reverse engineering
04:15 - Tests
05:35 - Informations transmitted to the aircraft

On this episode you will see in details the circuits of the static pressure sensor. The complete schematic of the board is presented, followed by the test of the sensor.
The sensor itself if a piezoresistive pressure sensor in a Wheatstone-bridge configuration. The bridge is excited with a square signal using a positive feedback which permits the oscillation of the system. The output is a sine signal with a frequency which depends on the static pressure input. Frequency is about 5kHz.
This signal is a part of the general output signal which comprises 3 different signals:
* Sweep frequency of 430 Hz
* Pressure frequency 5 to 5.8 kHz
* Larmor frequency 800 kHz to 2.2 MHz depending on the magnetic field (generated externally by the power supply/amplifier). The larmor frequency varies a little bit because of the sweep required for the detection of the maximum absorption of the He cells. The availability of the 430 Hz modulation frequency permits to reduce the noise by synchronizing the frequency measurement to this signal.
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