Measurement of contact resistance with microampere currents

The design of an instrument for measuring contact resistance is presented. The design incorporates photo-isolated synchronous rectification. The noise in this instrument is suppressed to 0.1 nV, and contact resistance can be measured with low currents of 0.1 to 100 μA. Several types of contacts are measured with this low-current instrument. When the contacts are contaminated, they are likely to indicate higher resistance than that measured at milliampere currents with widely used commercial instruments. The instrument is clearly effective and the measurement with microampere currents is important for estimating contact resistance under conditions close to actual use