Ground shift compensated parameter measurement system
First Claim
1. Apparatus comprising:
- a signal source;
a variable impedance sensor having one end connected to an electrically conductive member and its other end connected to said signal source;
switch means for selectively turning said signal source on and off;
measuring means having a first terminal connected to said other end of said sensor and a second terminal connected to a point on said electrically conductive member different than the point to which said sensor is connected, said measuring means including first means for providing a first signal indicative of the voltage developed across said sensor when said signal source is on, second means for providing a second signal indicative of the voltage developed across said sensor when said signal source is off, said measuring means providing an output signal indicative of the difference between said first signal and second signal.
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Accused Products
Abstract
A parameter sensor system includes a sensor, one terminal of which is grounded on a metal chassis or the like. The ground potential of the metal chassis at the point of connection may shift above or below true ground potential due to the operation of other, high current devices also attached to the chassis. A switchable current source is connected to the second terminal of the sensor, and is turned on and off. A measuring circuit is also connected to the second terminal, and provides an output signal representative of the difference between the voltage on the second terminal when the current source is on and when it is off. The output signal varies as a direct function of sensor resistance, and is unaffected by shifts in ground voltage at the sensor.
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Citations
10 Claims
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1. Apparatus comprising:
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a signal source; a variable impedance sensor having one end connected to an electrically conductive member and its other end connected to said signal source; switch means for selectively turning said signal source on and off; measuring means having a first terminal connected to said other end of said sensor and a second terminal connected to a point on said electrically conductive member different than the point to which said sensor is connected, said measuring means including first means for providing a first signal indicative of the voltage developed across said sensor when said signal source is on, second means for providing a second signal indicative of the voltage developed across said sensor when said signal source is off, said measuring means providing an output signal indicative of the difference between said first signal and second signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of measuring a parameter with a variable impedence, parameter-sensitive element having first and second terminals, comprising the steps of:
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connecting said first terminal of said variable impedance, parameter-sensitive element to a structural grounding element, connecting said second terminal of said variable impedance element to signal-applying and voltage-measuring elements, applying a known signal to said second terminal of said element, measuring the resulting signal at said second terminal of said element, turning off said applied signal, measuring the resulting signal at said second terminal of said element, and using the second measured signal to correct the first measured signal for stray signals on said grounding element so as to thereby provide an output signal correctly representative of the impedance of said element. - View Dependent Claims (9)
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10. Apparatus comprising:
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a current source; a variable impedance sensor having one end connected to an electrically conductive member and its other end connected to said current source; switch means for selectively turning said current source on and off; measuring means having a first terminal connected to said other end of said sensor and a second terminal connected to a point on said electrically conductive member different than the point to which said sensor is connected, said measuring means including first means for providing a first signal indicative of the voltage developed across said sensor when said current source is on, second means for providing a second signal indicative of the voltage developed across said sensor when said current source is off, said measuring means providing an output signal indicative of the difference between said first signal and second signal.
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Specification