Proximity sensing system and inductance measuring technique
First Claim
1. A method for determining the inductance L of a network, wherein the network includes an equivalent resistance in series with the inductance L and an equivalent capacitance in shunt with the inductance L, comprising the steps of:
- establishing a current i through the network, said network current having a time-variable waveform;
thereafter, constraining the voltage across said network to be constant when said network voltage reaches a reference voltage VL, whereby the effect of the equivalent capacitance is cancelled;
while so constraining said network voltage to be constant, determining the rate of change of said network current with respect to time when said network current is zero, whereby the effect of the equivalent resistance is cancelled; and
determining the inductance L in accordance with the relationship ##EQU7##
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Abstract
A proximity sensing system including an improved variable inductance measuring technique to provide an indication of the proximity of a target object to a remote sensor unit 10 which includes a sensor inductor. A variable inductance measuring apparatus measures the inductance of the sensor inductor, which inductance corresponds to the proximity of a target object. The variable inductance measuring network includes a sensor current pulse generator 20 which, in each of successive system periods, establishes a time-varying current through the sensor unit 10. A sensor control loop stage 30 senses when the resulting sensor voltage reaches a predetermined level and then captures the sensor current so as to clamp the sensor voltage at this level. A retrieval stage 40 then determines the rate of change of the sensor current at the time the sensor current is zero, establishing a calibrated analog voltage of the inductance of the sensor inductor which is substantially temperature independent. The inductance analog voltage is applied to a proximity detection and switching stage 50 which provides a quantized target-near detection pulse if the inductance analog voltage corresponds to a threshold proximity of the target object. Integration over successive system periods then provides a time-average proximity voltage which is applied to a Schmitt trigger and proximity switching network 58, the output of which indicates the proximity of the target object to the sensor inductor with respect to a threshold actuation gap.
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Citations
46 Claims
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1. A method for determining the inductance L of a network, wherein the network includes an equivalent resistance in series with the inductance L and an equivalent capacitance in shunt with the inductance L, comprising the steps of:
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establishing a current i through the network, said network current having a time-variable waveform; thereafter, constraining the voltage across said network to be constant when said network voltage reaches a reference voltage VL, whereby the effect of the equivalent capacitance is cancelled; while so constraining said network voltage to be constant, determining the rate of change of said network current with respect to time when said network current is zero, whereby the effect of the equivalent resistance is cancelled; and determining the inductance L in accordance with the relationship ##EQU7## - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for monitoring the proximity of a target object to a sensor unit wherein the sensor unit includes a sensor inductor whose inductance LS varies in a known relationship with the proximity of the target object, the sensor unit also having a temperature-dependent or otherwise variable equivalent resistance in series with said inductance LS and a temperature-dependent or otherwise variable equivalent capacitance in shunt with said inductance LS, comprising the steps of:
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periodically establishing, during each of successive system periods TS, a current iS through the sensor unit, and thereby through the sensor inductor, said sensor current having a time-variable waveform; and
, for each such system period TS,thereafter constraining the voltage vS across the sensor unit to be constant when said sensor voltage reaches a reference voltage VL, whereby the effect of the equivalent capacitance is cancelled; while so constraining said sensor voltage to be constant, determining the rate of change of said sensor current with respect to time when said sensor current is zero, whereby the effect of the equivalent resistance is cancelled; establishing an indication of the inductance LS when said sensor current is zero in accordance with the relationship ##EQU9## and, providing a target proximity indication representative of the proximity of the target object to the sensor unit in accordance with a known relationship between the proximity of the target object and the inductance LS. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16)
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17. An inductance measuring apparatus for determining the inductance L of a network, wherein the network includes an equivalent resistance in series with the inductance L and an equivalent capacitance in shunt with the inductance L, said apparatus comprising:
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current means for establishing a current i through the network, said network current having a time-variable waveform; control loop means for thereafter constraining the voltage across said network to be constant when said network voltage reaches a reference voltage VL whereby the effect of the equivalent capacitance is cancelled; retrieval means for determining, while said network voltage is so constrained to be constant, the rate of change of said network current with respect to time when said network current is zero, whereby the effect of the equivalent resistance is cancelled; and
,measuring means for determining the inductance L in accordance with the relationship ##EQU11## - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25)
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26. A proximity sensing system for monitoring the proximity of a target object to a sensor unit wherein the sensor unit includes a sensor inductor whose inductance LS varies in a known relationship with the proximity of the target object, the sensor unit also having a temperature-dependent or otherwise variable equivalent resistance in series with said inductance LS and a temperature-dependent or otherwise variable and equivalent capacitance in shunt with said inductance LS, the proximity sensing system comprising:
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current means for periodically establishing, during each of successive system periods TS, a current iS through the sensor unit and, thereby, through the sensor inductor, said sensor current having a time-variable waveform; control loop means for thereafter constraining the voltage vS across said sensor unit to be constant when said sensor voltage reaches a reference voltage VL, whereby the effect of the equivalent capacitance is cancelled; retrieval means for determining while said sensor voltage is so constrained to be constant, the rate of change of said sensor current with respect to time when said sensor current is zero (whereby the effect of the equivalent resistance is cancelled) so as to establish an indication of the inductance LS in accordance with the relationship ##EQU13## and, proximity determination means responsive to said inductance indication to provide a target proximity signal representative of the proximity of the target object to the sensor unit in accordance with the known relationship between the proximity of the target object and the inductance LS. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46)
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Specification