An in-circuit ohmmeter is provided, including a pair of input terminals connectable to a resistance of an unknown value. A pair of current generators are connected electrically in series for generating an electrical current to be passed through the unknown resistance to develop a differential voltage across the input terminals, and a circuit is provided for determining the amount of the electrical current passed through the unknown resistance. A semiconductor switch switches the pair of current generators on and off. A current generator protection circuit comprising a plurality of diodes is connected across the input terminals. A differential amplifier circuit receives and amplifies the differential voltage so that a value of the unknown resistance may be calculated based on the differential voltage and the determined amount of electrical current passed through the resistance. An inverter circuit is disposed intermediate the input terminals and the differential amplifier circuit. The inverter circuit includes an inverter buffer circuit for electrically isolating the inverter circuit from the from input terminals. A pair of resistors and a pair of diodes electrically isolates each of the input terminals from the inverter circuit and the pair of current generators, respectively.
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