Abstract: A circuit breaker includes a digital electronic trip unit having a microprocessor. The front panel of the trip unit includes a potentiometer connected across a reference voltage, and a numeric display device. The potentiometer is adjusted by an operator to enter a value of a parameter defining the time-current characteristic of the circuit breaker. An analog-to-digital converter receives the voltage supplied by the potentiometer and converts it to a digital quantity for use by the microcomputer in performing limit checks with the current flow through the contacts of the breaker. The microcomputer formats the converted digital value of the potentiometer voltage and supplies it to a front panel-visible numeric display so that the value of the potentiometer setting as interpreted by the microcomputer in defining the time-current trip characteristic is presented on the numeric display to provide real-time feedback to the operator as he adjusts the parameter value.

Abstract: A circuit breaker includes a microprocessor-based trip unit and a power supply for supplying operating power to the trip unit and the trip coil of the circuit breaker from either the internal current transformers of the circuit breaker or a plurality of external sources. The trip unit includes a numeric display for displaying a sequential series of parameter values under normal conditions. Under low-power conditions, the power supply provides pulses of operating power sufficient to enable the trip unit to execute all of its limit check functions and present a flashing display of a single parameter value.

Abstract: A lighting apparatus which provides for high voltage pulses for starting a high pressure sodium lamp. This apparatus uses a zener diode circuit which provides appropriately timed starting pulses even at relatively low line voltage. The apparatus can be designed to supply either one pulse or two pulses per cycle.

Abstract: To prevent high-intensity-discharge (HID) lamps from extinguishing for prolonged periods due to a power interruption or an appreciable drop in line voltage, a rectifier-battery combination provides standby power for operating a high-frequency inverter. The output of the inverter connects to the HID lamps through impedance means which passes a greatly reduced high-frequency current as compared to the normal lamp operating current, in order to sustain the operation of the lamps at a very reduced power level. Upon restoration of the normal line voltage, the lamps again operate with normal power consumption. The same wiring can be used for both the normal lamp operating current and the high-frequency sustaining current or separate wiring systems can be used if desired. The high-frequency current can be supplied simultaneously with the normal operating current or the high-frequency current can be supplied only during periods of power interruption.