Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1998-11-12
2001-02-06
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S723000
Reexamination Certificate
active
06184695
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a diagnostic circuit for potentiometric sensors.
BACKGROUND OF THE INVENTION
A potentiometric sensor is used to detect and/or measure translational or rotational position (angles, fluid levels, distances, etc.). A potentiometric sensor is essentially a voltage divider comprising a sliding contact which engages a carbon film strip or other electrically resistive means, the resistive means being electrically connected to a supply voltage. The output voltage from the sensor is the voltage on the sliding contact or a proportion thereof. The position which is being detected or measured affects the position of the sliding contact relative to the resistive means, and so the value of the output voltage from the sensor can be used to provide an indication of the detected or measured position. A potential problem with such sensors is that a contact resistance may build up between the sliding contact and the resistive means, which, if undetected, can give rise to erroneous readings from the sensor.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a diagnostic circuit which can detect such a build up in the contact resistance between the sliding contact and the resistive means.
A diagnostic circuit in accordance with the present invention for a potentiometric sensor having an electrically resistive means and a sliding contact in connection with the resistive means and providing an output from the sensor at a sensor output terminal, comprises a low pass filter connectable between the sliding contact and the sensor output terminal; alternating voltage supply means having a high impedance connectable to the sliding contact; and amplitude modulation demodulating means connectable between the sliding contact and a diagnostic output terminal, the voltage at the diagnostic output terminal providing an indication of the contact resistance between the sliding contact and the resistive means of the sensor.
The present invention provides a diagnostic system for a potentiometric sensor which can detect any increase in contact resistance between the sliding contact and the resistive means without interfering with the output signal from the sensor, whilst the sensor is still operating. This allows appropriate steps to be taken before the sensor starts to provide inaccurate output signals.
REFERENCES:
patent: 5049827 (1991-09-01), Tasma
patent: 5165272 (1992-11-01), Kleinhans et al.
patent: 3643945 (1988-06-01), None
patent: 4116603 (1992-11-01), None
Bergmann Jürgen
Glaser Michael
Delphi Technologies Inc.
Jones Richard A.
Kerveros James C
Metjahic Safet
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