An automatically balancing isolation amplifier for the decoupling of measuring systems with high impedances

It is theoretically shown that different conditions of coupling and grounding cause error voltages with the simultaneous use of two high-impedance measuring systems (e.g. pH electrodes). By the use of special amplifiers using optical transmission systems these error voltages are prevented. The transmission characteristics of the couplers are sensitive to changes in temperature due to the incorporation of infrared emitters in the system. An amplifying equipment with high d. c. stability was developed. The temperature drift was suppressed by the use of a special chopper stabilisation.