Some considerations of eddy current proximity sensor applied for motor speed measurement

The eddy current proximity sensor or probe is composed of exciting winding, detection winding and post processing circuit. Models of the key structural and electromagnetic parameters of the sensor are analyzed. The mutual influence characteristics induced by the structural and electromagnetic parameters are provided accordingly. The pull up resistor used to improve the reliability of the sensor will influence the output waveform. The determination methods both of the structural parameters of the encoder and the pull up resistance for the sensor are introduced. And the sensor is adopted as a speedometer for testing the line speed of the gear wheel. Research indicates the duty ratio of the waveform outputted from the sensor is directly influenced by the structural and electromagnetic parameters. Some typical relation curves as the tooth width versus the speed of the gear wheel, detection distance versus the speed of the gear wheel, and duty ratio versus the speed of the gear wheel are generated.