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Digital display ohmmeter

  • US 4,636,715 A
  • Filed: 07/08/1985
  • Issued: 01/13/1987
  • Est. Priority Date: 08/13/1984
  • Status: Expired due to Fees
First Claim
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1. In an apparatus for measuring the continuity and resistance of an electric wire blasting network of the type where a constant current is passed through the network and a reference resistor;

  • and the voltages across the reference resistor and the network are measured and compared to derive the resistance of the blasting circuits;

    the apparatus including a converter for sensing the measured voltages and converting their values to display resistance of the blasting network directly, the improvement of means for compensating for the effect of voltages due to galvanic currents associated with the blasting network comprisng;

    a reference resistor;

    a storage capacitor for voltage due to galvanic currents associated with the blasting network;

    an input terminal for supplying a test voltage;

    terminals for connection to the electric wire blasting network;

    switch means operable between two positions, the first position being one wherein said storage capacitor is connectible only to said blasting network to assume a charge proportional to the voltage across the blasting network due to galvanic currents in the location of the blasting network and the second one being one in which said input terminal is connectible to said blasting network through said reference resistor, and in which said reference resistor, blasting network, and voltage storage capacitor are connectible to said converter;

    synchronizing means for cyclically moving said switch means between said first and said second positions at a frequency at which the voltage applied to the storage condenser is substantially constant; and

    the time constant of said storage capacitor being adapted to fully charge when said switch means is in said first position.

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