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US 4,050,019 AGranted
Range switching circuit for solid state electrometer
AssigneeThe United States of America as represented by the Secretary of the Army
InventorJoseph C. Nirschl
Life of this patent
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Abstract
A range switching circuit for a solid state electrometer, e.g., for use in radiacmeter, includes a substantially symmetrical circuit having an n-channel MOSFET and an NPN transistor in one branch and a p-channel MOSFET and a PNP transistor in the other branch. The electrometer includes an operational amplifier with two high value resistors in the feedback path. A latching reed relay selectively shorts out one of the feedback resistors when one of the transistors is gated on by the corresponding MOSFET.
Claims5
An electrometer which comprises:
- an operational amplifier having an input connected to the source of the current to be measured, and an output;
- means for applying a feedback signal from the output of said operational amplifier to the input to control the gain thereof, said feedback applying means including at least first and second feedback resistors serially connected in a feedback loop between said output and input;
- means connected to the output of said operational amplifier for indicating the amplitude of the output signal therefrom;
- means for supplying first and second potentials of opposite polarities;
- means for altering the sensitivity of said indicating means thereby to provide a plurality of measurement ranges for said electrometer;
- and
- polarity sensitive switching means activated by the operation of said sensitivity altering means to selectively short out at least one of said first and second resistors to change the gain of said operational amplifier, said sensitivity altering means including means for selectively applying said opposite potential polarities to said switching means.
4 more elements
Dependencies are inferred from the claim text.