Proximity sensor with health monitoring

摘要

A proximity sensor includes a relatively simple health monitoring circuit. The proximity sensor includes a variable gain oscillator, a feedback circuit, and a proximity determination circuit. The variable gain oscillator has a gain that varies with the proximity of a target to a sensor coil, generates an oscillating electrical signal having a substantially constant amplitude magnitude, and generates an energy signal representative of the electrical energy needed to sustain oscillations. The feedback circuit supplies feedback to the oscillator, and the proximity determination circuit, based on the energy signal, supplies a proximity signal representative of target proximity to the sensor coil. The health monitor circuit also receives the oscillating electrical signal and supplies a health status signal representative of proximity sensor health.

主权项

1. A proximity sensor, comprising:
a variable gain oscillator adapted to receive electrical energy, the variable gain oscillator including a sensor coil and having a gain that varies with proximity of a target to the sensor coil, the variable gain oscillator coupled to receive a feedback signal and configured, in response to the feedback signal, to (i) generate an oscillating electrical signal having a substantially constant amplitude magnitude and (ii) generate an energy signal representative of the electrical energy received by the variable gain oscillator; a feedback circuit coupled to receive the oscillating electrical signal and configured, in response thereto, to supply the feedback signal; and a proximity determination circuit coupled to receive the energy signal and configured, in response thereto, to supply a proximity signal representative of target proximity to the sensor coil, the proximity determination circuit comprising:
a low-pass filter circuit coupled to receive the energy signal and supply a filtered energy signal,a near/far comparator circuit coupled to receive the filtered energy signal and configured, in response thereto, to supply the proximity signal (i) at a logic-LOW state when the target is within a first predetermined distance of the sensor coil and (ii) at a logic-HIGH state at least when the target is not within a second predetermined distance of the sensor coil, andtwo resistors coupled between the low-pass filter and the near/far comparator, at least one of the two resistors providing temperature compensation for the proximity determination circuit.