Techniques Used in a Fast Computer-Controlled DC Bridge

A computer-controlled dc bridge that uses several techniques to obtain a resistance measurement to 0.01 percent in under 2 ms is described. These include the use of FET range switching, the fast current output of a digital-to-analog converter, a voltage-clamped detector, an unusual current ratio circuit, a fast range-test method, and a PROM memory to reduce computer time. These techniques are discussed generally and some speed versus accuracy data are given for a specific bridge.