PROXIMITY SENSOR MONITOR

摘要

A proximity sensor, such as an aircraft landing gear detector, comprises a proximity sensing impedance 20 and a series reference resistor 21. A digitally-generated excitation sine waveform is applied to the circuit 20,21 by amplifier 22 and the voltages on either end of the reference resistor are measured, from which the processor 23 determines the value of the sensing impedance 20 and thus the proximity of an object. A monitor circuit 100, which is independent of the proximity sensor, performs similar measurements and computations, disagreement of the outputs of the proximity sensor and the sensor monitor indicating a fault. Although the clock in the proximity sensor monitor is independent of the clock in the proximity sensor the measurement process effected by the monitor 100 is adapted to compensate for this frequency difference.