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Wide-range resistance monitoring apparatus and method

  • US 4,736,157 A
  • Filed: 07/18/1986
  • Issued: 04/05/1988
  • Est. Priority Date: 07/18/1986
  • Status: Expired due to Fees
First Claim
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1. Apparatus for monitoring the resistance between first and second bodies, comprising:

  • comparing means, electrically connected to said first and second bodies, for inducing current to flow between said first and second bodies and for producing an output signal whenever the magnitude of said current flow exceeds a reference level;

    swithching means, operatively connected to said comparing means and connected to receive a periodic control signal, for alternating said reference level between first and second values in response to said control signal; and

    indicator means, connected to receive said output and control signals, for providing a first indication when said current flow is less than said first value and for providing a second indication when said current flow exceeds said second value, wherein;

    said comparing means comprises;

    operational amplifier means having first and second input terminals and an output terminal for producing an output signal at its output terminal whenever the signal level present on its first input terminal exceeds the signal level present on its second input terminal,a resistive element electrically connected between said first body and said operational amplifier first input terminal, andreference voltage level producing means, having a first terminal connected to said second body and a second terminal connected to said operational amplifier second input terminal, for producing a fixed reference voltage across said first and second terminals; and

    said switching means comprises;

    a first resistor connected between said operational amplifier first input and output terminals,a second resistor having a first end connected to one of said operational amplifier output terminal and said operational amplifier first input terminal, said resistor having a further end, anda switching element having a control terminal and first and second switching terminals, said control terminal being connected to receive said control signal, said first switching terminal being connected to said second resistor further end, said second switching terminal being connected to the other one of said operational amplifier output terminal and said operational amplifier first input terminal.

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