Browse Prior Art Database

Microcomputer Control of Zero Crossing Detection Accuracy

IP.com Disclosure Number: IPCOM000048728D
Original Publication Date: 1982-Mar-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Dodge, JH: AUTHOR [+2]

Abstract

Synchronization through zero-crossing detection of AC power line input is enhanced by using a microprocessor to mask out noise spikes on the line voltage so as to minimize false zero-crossing detections. This is effectively done by performing a counting operation in association with the microcomputer clock to generate an inspection window in the general vicinity of the anticipated zero-crossing time. Thus even if a noise spike occurs during the window causing an early apparent zero-crossing, the random nature of such spike occurrences does not impair full synchronization with the actual line zero-crossings at a later time.

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Microcomputer Control of Zero Crossing Detection Accuracy

Synchronization through zero-crossing detection of AC power line input is enhanced by using a microprocessor to mask out noise spikes on the line voltage so as to minimize false zero-crossing detections. This is effectively done by performing a counting operation in association with the microcomputer clock to generate an inspection window in the general vicinity of the anticipated zero- crossing time. Thus even if a noise spike occurs during the window causing an early apparent zero-crossing, the random nature of such spike occurrences does not impair full synchronization with the actual line zero-crossings at a later time.

Fig. 1 presents a generally self explanatory flowchart of a micro-computer control system for maintaining accurate timing intervals with a noisy interrupt signal. Copiers frequently employ microcomputers and operate on a real time clock, such as zero-crossings of an AC power line. A timing signal of 8.3 milliseconds is obtained from a 60 Hz power line. Counting zero-crossings is useful to time intervals in the logical control of the machine. If this clocking signal is noisy, the time interval varies and introduces problems in the logical control of the machine.

The means of ignoring undesired noisy zero-crossings so an accurate timing interval is available is implementable in software of a micro-computer such as an NEC uPD 546. Once the zero-crossing is accepted as an interrupt, another...