PSN-L Email List Message

Subject: Re: Not so simple photoelectrics, or are they?
From: Mark Robinson other@...............
Date: Fri, 01 Jun 2001 20:16:45 +1200

>> This brings to mind the Centronics QD7-5 quadrant photodetector that
>> sell as part number 652-027.
>> This is a windowed hermetic TO5 package with foursensor elements
>> arranged as quadrants. It seems rather well suited to measuring very
>> small angular defelections in one or two dimensions when illuminated by
>> a cheap diode laser. Sadly the detector itself is not cheap.
>> have fun folks
>> Mark
>This can be replaced by two solar cells plus either a small incandescent or
>laser diode
>projected through a hole which covers half of each cell at a cost of about

The particular advantage of this part is that the two differential
elements are separated by a submillimetric distance allowing much higher

Also, making a small spot at the end of a long throw beam is really easy
if you put a short focal length lens at approximately it's focal lens
over the detector.


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Larry Cochrane <cochrane@..............>