Abstract: Numerous signal conditioning circuits on a plurality of printed circuit boards are calibrated remotely by a signal processing unit which sends coded signals to each board, either sequentially or in parallel, to connect either on-board or off-board test signals to one of the conditioning circuits in place of its field generated input. The processing unit utilizes the actual and expected responses of each conditioning circuit to low and high test signals to generate a gain and an offset which are applied to the conditioned field signal to provide a calibrated signal. The time constant for each conditioning circuit is also measured periodically, or upon a selected temperature change, for use in generating a minimum waiting period for obtaining valid data following transfers between the field generated signals and the test signals.

Abstract: In differential input DC gain amplifiers with high input impedance, a capacitive attenuator is built-in in order to reduce the amplifying effect on the AC component due to interference by the industrial power lines. Such attenuation is obtained by feeding back through cross capacitors the AC signal at one output to the input on the opposite side so that the ratio of the differential outputs to the differential inputs for the AC component is substantially unity.