Abstract: A potentiostat for an amperometric sensor uses a voltage-controlled current source (VCCS), which may be either unidirectional or, preferably, bidirectional. An error amplifier compares the potential of the sensor's reference or counter electrode, relative to ground potential, to a set-point potential. The error voltage serves as an input to the VCCS. The output of the VCCS--a current proportional to the error voltage--is supplied to the sensor's auxiliary electrode. In a steady state, the error voltage is just large enough to supply current that is equal to the current through the sensor's working and auxiliary (or counter) electrodes. The error voltage can either serve directly as an output voltage or it can be amplified without introducing a feed-back loop disturbance. The VCCS permits direct grounding of the sensor's working electrode and operation of the error amplifier at a low or moderate gain, so as to increase the circuit's frequency response and reduce the probability of oscillation.

Abstract: Logic elements are provided for a reactor period meter trip circuit. For one element, first and second inputs are applied to first and second chopper comparators, respectively. The output of each comparator is O if the input applied to it is greater than or equal to a trip level associated with each input and each output is a square wave of frequency f if the input applied to it is less than the associated trip level. The outputs of the comparators are algebraically summed and applied to a bandpass filter tuned to f. For another element, the output of each comparator is applied to a bandpass filter which is tuned to f to give a sine wave of frequency f. The outputs of the filters are multiplied by an analog multiplier whose output is 0 if either input is 0 and a sine wave of frequency 2f if both inputs are a frequency f.