Browse Prior Art Database

Error Control in Photosensing Devices

IP.com Disclosure Number: IPCOM000088792D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Schaaf, RL: AUTHOR

Abstract

Some photosensing systems having a light-emitting diode (LED) and a photosensing phototransistor PT are multiplexed, making error detection and component failure detection difficult. In general, a photoamplifier signal from a phototransistor (PT) requires a sensing window, called a gate signal, having a predetermined duration. When the gate signal becomes too narrow, errors may be introduced into the sensed data as it is inserted into the register (REG). Also, a problem arises in the LEDs which either stay on or stay off as the performance of such units degrades. A control microcomputer (CMC) senses the signals from REG for detecting errors. The photosensing system has a predetermined sequence of operation including parity which allows the CMC to detect errors.

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Error Control in Photosensing Devices

Some photosensing systems having a light-emitting diode (LED) and a photosensing phototransistor PT are multiplexed, making error detection and component failure detection difficult. In general, a photoamplifier signal from a phototransistor (PT) requires a sensing window, called a gate signal, having a predetermined duration. When the gate signal becomes too narrow, errors may be introduced into the sensed data as it is inserted into the register (REG). Also, a problem arises in the LEDs which either stay on or stay off as the performance of such units degrades. A control microcomputer (CMC) senses the signals from REG for detecting errors. The photosensing system has a predetermined sequence of operation including parity which allows the CMC to detect errors.

Upon error detection, an error control signal (EC) is supplied to the multiplexor control for elongating the gate signal to the EC gate signal. The elongated gate signal effects a retry of the photosensing system in the event that the photosensing system is on a position measurement system. The CMC actuates the positioning system for rereading the tachometer or other positioning indicators (not shown). Additionally, the CMC sounds an alarm that the photosensing system has a marginal operating condition, and hence is subject to failure soon.

The above technique, while implemented in real time for a position controlling apparatus, can be used in diagnostic procedures. Th...