| 摘要 |
A method and system is disclosed for accurate remote reading of an electricity meter. An optical detection arrangement, including a light emitter and sensor, have positioned in the light path therebetween a cutout portion of the meter shaft. Rotation of the shaft affects the amount of light passed to the sensor. Registration errors which may occur in a linear transition operating range are avoided by provision of detector threshold hysteresis. A microprocessor sets timing pulses for emitter energization, establishes a detection period of uniform length of time for each energizing pulse and produces, during each detection period, a digital signal having a logic level indicative of the presence or absence of light transmitted to said sensor, whereby a correlation between light transitions and power usage can be made. Accuracy of detection is improved under microprocessor control by introducing hysteresis in the delay between emitter energization and detection, in the voltage threshold in a comparator connected to the detection circuit, or in emitter energization driving current. The hysteresis is determined in accordance with the memorized state of the last previous detected signal.
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