Microprocessor controlled circuit breaker trip unit

Abstract From the Canadian patent

A microprocessor based trip unit for a circuit breaker is disclosed. The instantaneous current magnitudes in each phase and in the neutral of the circuit being protected are simultaneously and sequentially sampled by respective sample and hold circuits. The measured values are then applied to a respective analog-to-digital converter and the digitized values are sequentially applied to a microprocessor. The microprocessor calculates true RMS current and sums the signals of all phases and neutral to determine presence and magnitude of a ground fault current. To permit use of an 8-bit microprocessor while maintaining, high resolution of measured current over a large range novel automatic scale …