Electrometer with low voltage indicator
First Claim
1. In an electrometer system for non-contact detection of an electrostatic charge comprising a probe electrode and an electrometer circuit having a power supply voltage and including an electrically floating input circuit for said probe electrode, said electrometer circuit providing an output signal to an output level indicator means indicating a voltage on said probe electrode, and wherein said electrometer circuit has zeroing means and switch means selectively connecting said zeroing means with said input circuit for normally providing zeroing of said indicator means with a zero output signal, the improvement comprising:
- reference voltage means providing a reference voltage,inhibited voltage comparison means comparing said power supply voltage against said reference voltage and providing an indicator signal output only in response to said power supply voltage falling below said reference voltage;
and connecting means for connecting said inhibited voltage comparison means to said input circuit when said switch means is connecting said zeroing means to said input circuit to provide a non-zero output signal only when said indicator signal is produced by said inhibited voltage comparison means, said non-zero output signal corresponding to said indicator signal and being indicated by said indicator means during said normal zeroing of said indicator means, indicating a low power supply voltage.
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Accused Products
Abstract
An electrometer system particularly adapted for non-contact measurement of electrostatic charges in electrostatography, such as the charge level on photoreceptor surface areas in xerographic machines. The electrometer circuit has a very high impedance normally floating input, and a simple D.C. measurement circuit. The measurement circuit output can be read by a conventional test meter. The electrometer is controlled by a simple switching arrangement providing an automatic zeroing position in which the initial level of the input circuit is automatically reset by a feedback amplifier from the output to compensate for any temperature induced or other variations in the measurement circuit. The power supply voltage is automatically monitored and the output meter is driven to a non-zeroing position in response to a low supply voltage by a feedback amplifier circuit operative only in the zeroing position, overriding the automatic zeroing circuit.
8 Citations
7 Claims
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1. In an electrometer system for non-contact detection of an electrostatic charge comprising a probe electrode and an electrometer circuit having a power supply voltage and including an electrically floating input circuit for said probe electrode, said electrometer circuit providing an output signal to an output level indicator means indicating a voltage on said probe electrode, and wherein said electrometer circuit has zeroing means and switch means selectively connecting said zeroing means with said input circuit for normally providing zeroing of said indicator means with a zero output signal, the improvement comprising:
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reference voltage means providing a reference voltage, inhibited voltage comparison means comparing said power supply voltage against said reference voltage and providing an indicator signal output only in response to said power supply voltage falling below said reference voltage; and connecting means for connecting said inhibited voltage comparison means to said input circuit when said switch means is connecting said zeroing means to said input circuit to provide a non-zero output signal only when said indicator signal is produced by said inhibited voltage comparison means, said non-zero output signal corresponding to said indicator signal and being indicated by said indicator means during said normal zeroing of said indicator means, indicating a low power supply voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification