Circuit breaker with digital solid-state trip unit fitted with a calibration circuit

Claim 1

A digital solid-state trip unit for an electrical circuit breaker, comprising: current sensor means for generating analog current signals proportional to respective currents flowing through conductors protected by said breaker; peak-detector means for rectifying said current signals and for producing a direct analog signal representative of a maximum value of said current signals; calibration circuit means connected to said peak-detector means for multiplying said direct analog signal by at least four gains to produce at least four calibrated outputs to be connected to at least four inputs of an addressable multiplexer means, said gains related by predetermined ratios, said calibration circuit means comprising at least two amplifiers having a predetermined gain ratio, each amplifier having an input connected to said direct analog signal and an output connected to a respective one of said at least four inputs of said addressable multiplexer means and a respective divider bridge, each divider bridge having a mid-point connected to a respective one of said at least four inputs of said addressable multiplexer means; said addressable multiplexer means having at least four inputs, connected to said calibrated outputs, for selecting one of said calibrated outputs to provide a multiplexer output signal, said multiplexer output signal being a continuous analog signal representative of said selected calibrated output; digital-to-analog converter means, connected to said multiplexer means, for converting said multiplexer output signal to a sampled digitized signal; digital processing means, connected to said analog-to-digital converter means, for providing a circuit breaker tripping order instantaneously or after a short time delay or long time delay when said digitized signal exceeds respective predetermined levels, said multiplexer means being controlled by said processing means to select one of said calibrated outputs compatible with an input range of said analog-to-digital converter means; and circuit breaker trip means activated by said tripping order.