Method and apparatus for measuring hysteresis of a position sensor

Abstract

A method and apparatus is provided for measuring the hysteresis error of a position sensor for a reciprocating element, such as the sensor for determining piston TDC in a reciprocating engine. The sensor is of the proximity type and has a sensing region past which a vane relatively moves. Event timing signals are provided by voltage transitions occasioned by the leading and trailing edges respectively of the vane passing the sensor. The method includes moving a pair of test vanes in opposite directions past the sensor to simulate two passes thereby of a reciprocating vane to generate the event timing signals from the sensor. This may be done by mounting the test vanes on a pair of rotating discs. Independently of the sensor, reference timing signals are generated which are accurately indicative of the positioning of the leading and trailing edges of the one or more test vanes. These reference timing signals may be determined optically. An event timing signal is then compared with a respective corresponding reference timing signal for each of two of the reference timing signals symmetrically disposed with respect to the position to be determined, i.e. TDC, and a difference value is determined for each of those two comparisons. Finally, the two difference values are compared to determine a further difference value, that further difference value being a measure of the hysteresis error.