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Browse Prior Art Database

Automatic Gain Control for Photomultiplier Tubes

IP.com Disclosure Number: IPCOM000082515D
Original Publication Date: 1974-Dec-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Brecke, RA: AUTHOR [+2]

Abstract

Circuit 10 provides an automatic gain control (AGC) for a photomultiplier tube (PMT) in a laser scanner for reading bar coded labels. This circuit overcomes problems associated with widely variable laser output power, high-ambient light conditions, irregular and lengthy interruptions in scanning, and sluggish response of the PMT power supply to AGC signals.

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Automatic Gain Control for Photomultiplier Tubes

Circuit 10 provides an automatic gain control (AGC) for a photomultiplier tube (PMT) in a laser scanner for reading bar coded labels. This circuit overcomes problems associated with widely variable laser output power, high- ambient light conditions, irregular and lengthy interruptions in scanning, and sluggish response of the PMT power supply to AGC signals.

In the scanner, not shown, the laser and PMT are located under a countertop having a transparent window, over which coded articles are passed. An opaque safety shutter moves under the window when no article is present. The AGC reference is a set of known-contrast labels located under the countertop just beyond the ends of the window.

A test-window signal on line 11 indicates that the scan pattern is traversing the area in which the reference labels are located. A shutter-open signal on line 12 indicates that the shutter position is such as to allow the reference labels to be scanned. Counter 13 divides the window signal by sixteen. This frequency division slows the response of circuit 10 to match the response of the PMT power supply, which must be frequency limited in order to preserve its filtering and noise-suppression characteristics. The shutter signal input to flip-flop (FF) 14 prevents multiple triggering when the signals on lines 11 and 12 coincide closely in time.

Single-shot 15 transmits the output of counter 13 to the set input of sample FF 16. Negative-peak detector 17 transmits a signal to...