Contact judging circuit and contact judging method for impedance

Abstract

The contact between a device under test (DUT) and a measuring terminal is accurately judged with a simple circuit for impedance measurement. The conduction detecting means injects a judging current into the voltage terminal (L.sub.P) for low voltage. When the device under test (DUT) and both the current terminal (L.sub.C) for low voltage and the voltage terminal (L.sub.P) for low voltage are normally contacted with each other, since the inverting input terminal of the inverting amplifier is virtually grounded, and the L.sub.C and L.sub.P are substantially kept at the ground potential, the contact judgment for L.sub.C and L.sub.P is made by detecting the potentials of L.sub.P. In addition, when the impedance measurement value is larger than the predetermined lowest limit value and the current measurement value is lower than the predetermined lowest limit value, the DUT and the current terminal (H.sub.C) for high voltage are considered to have improper contact with each other. When the current measurement value is larger than the predetermined lowest limit value, and the impedance measurement value is lower than the predetermined lowest limit value, the DUT and the voltage terminal (H.sub.P) for high voltage are considered to have improper contact with each other.