In numerous control requirements, including those related to nuclear reactors, a variety of comparator/bistable circuits are used to monitor critical parameters and initiate alarm and other control functions for safe equipment operation. In most of the conventional comparator/bistable circuits, the bistable reset level is a constant magnitude signal developed by the fixed voltage output of the bistable circuit during the bistable circuit tripped state (on-state). Inasmuch as the voltage output of the bistable circuit in its trip state is of a constant value and is not a function of the bistable input trip voltage level determined by the input signals to the comparator circuit, the selection of a trip voltage level having a magnitude less than the magnitude of the reset level will prevent resetting of the bistable thus rendering the comparator/bistable circuit inoperative. In this situation it is required to then remove excitation power to the bistable circuit in order to reset it. This situation can be more clearly understood if it is assumed that a reset level having a magnitude of 5 volts is established by the output of the bistable circuit which means the bistable circuit will be reset when the magnitude of the trip level developed by the comparator circuit diminishes by 5 volts. If, however, a trip level of 3 volts is selected to trip the bistable circuit, then it is apparent that the trip level will never diminish the required 5 volts necessary to reset the bistable circuit.
USPTO Backgrounds
USPTO Backgrounds