Patent ID: 7148694

Claim:
A contact impedance test circuit for testing contact impedance caused by contaminate between a first electrical contact element and a second electrical contact element, comprising: (a) an AC signal source for applying an A.C. signal voltage to the first electrical contact element, an AC contact voltage being emitted from the second electrical contact element, the first electrical contact element being in physical contact with the second electrical contact element; (b) an AC operational amplifier for amplifying the AC contact voltage from the second electrical contact element, an amplified AC contact voltage being produced by the AC operational amplifier, a LOW input of the AC operational amplifier connected to a LOW output of the AC signal source; and (c) a phase angle voltmeter for detecting phase difference between a phase of the amplified AC contact voltage and a phase of the AC signal voltage at an instance of time, the phase angle voltmeter for detecting an amount of phase lag of the phase of the amplified AC contact voltage with respect to the phase of the AC signal voltage, phase lag caused by a capacitance portion of contact impedance, the AC signal voltage being applied to a reference input of the phase angle voltmeter, the amplified AC contact voltage being applied to a signal input of the phase angle voltmeter.