A method for reducing the effects of cable capacitance on admittance measurements

A technique to reduce the effect of large variations in cable capacitance on admittance measurements is investigated. The cable capacitance variations are produced by environmental changes and are larger than the capacitance measured. The technique utilized is referred to as "bootstrapping" and takes advantage of the negative feedback in a feedback amplifier using operational amplifiers.

Several possible bootstrapping configurations are examined of which two are selected for further investigation. . In one of the selected configurations, a noninverting negative feedback amplifier provides the bootstrapping, while an inverting negative feedback amplifier provides bootstrapping in the second configuration. Each configuration is examined experimentally and is found to successfully reduce cable effects. The percent change in an admittance measurement for an added cable capacitance is found to increase with decreasing probe admittance for the noninverting bootstrapping amplifier configuration examined. On the other hand, the percentage change in the measurement due to an added cable capacitance is constant with probe admittance changes in the inverting bootstrapping amplifier configuration.