PROGRAM CLOCK FOR AN ELECTRONIC DEMAND REGISTER WITH AUTOMATIC CALIBRATION BASED ON SENSED LINE FREQUENCY

摘要

An electronic demand register includes a microprocessor including a program clock for performing timekeeping functions for the register. A power supply connected across the AC voltage source provides power to the microprocessor through a voltage regulator. The program clock is maintained by the line frequency of the AC source. Means are provided for calibrating the program clock to be compatible with either a 50 Hz or a 60 Hz line frequency. A detection signal corresponding to the line frequency is generated by a line frequency detector circuit in the power supply. A reference signal is generated by a quartz crystal clock. Frequency comparator means includes a microprocessor program that measures the time period between detection signal pulses. This time period is compared to the known period of a 50 Hz or a 60 Hz signal and respective counters are incremented accordingly. The microprocessor and program clock operating parameters are established for either 50 Hz of 60 Hz operation when one of the counters has reached a value of five, indicating that five zero crossings have been detected at the particular frequency. The electronic demand register also comprises a display including an array of LCD segments for continuous simultaneous display of the time and date. The display also includes an array of LCD segments, arranged in a pattern, that are sequentially illuminated corresponding to the rate of rotation of the shutter disk of the pulse initiator.