A low-powered resistance and conductivity measuring circuit for use with remote transducers
P Hawkins · Measurement Science and Technology · 1990
A novel and versatile circuit for accurately measuring the resistance or conductance of remote transducers has been developed. The circuit can be used to measure resistances over a wide range but it is especially suitable for measuring high resistances (e.g., in the range 1-100 M Omega ). The same circuit can be used to measure accurately small changes in ionic conductivities in solutions, using conductivity cells which have conductances typically in the range 0.01-1 mu S. The design is based on a self-oscillating circuit which produces a sine wave voltage across the transducer with a frequency (usually in the range 100 Hz-1 kHz) which is proportional to the square root of the conductance (or reciprocal of the resistance) of the transducer. The circuit has good temperature stability and is particularly suitable for applications where low cost, high accuracy and low power consumption are essential. A square wave voltage produced by the circuit with a frequency the same as that of the sine wave can be used to determine the resistance or conductance of the transducer.