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From: dave@sdeggo.UUCP
Newsgroups: sci.electronics
Subject: Re: Library Book detectors
Message-ID: <45@sdeggo.UUCP>
Date: Wed, 29-Apr-87 23:26:37 EDT
Article-I.D.: sdeggo.45
Posted: Wed Apr 29 23:26:37 1987
Date-Received: Fri, 1-May-87 06:47:51 EDT
References: <146@illusion.UUCP> <868@oliveb.UUCP> <1726@kitty.UUCP> <1732@kitty.UUCP>
Organization: Lazy Programmer's Society of San Diego
Lines: 20

In article <1732@kitty.UUCP>, larry@kitty.UUCP (Larry Lippman) writes:
> 	This system is decently immune to fraud.  The magnetizer uses a
> capacitive discharge into an electromagnet, resulting in a pretty high
> momentary magnetic field; a permanent magnet will not work to deactivate the
> sensor.  

San Francisco Public Library (and a few others I've seen, but can't remember
which) appears to use a permanent magnet.  It's an awfully big sucker, though.
(About the size of a brick).

Would the field generated by this be enough to do it or are we back to square
one on theories about their system?  Originally they used a powered gadget,
but not anymore.  I think the sensitizer is powered.


-- 
David L. Smith
sdcsvax!sdamos!sdeggo!dave, ihnp4!jack!man!sdeggo!dave, hp-sdd!crash!sdeggo!dave
sdeggo!dave@sdamos.ucsd.edu
"Morals are one thing.  Ratings are EVERYTHING!"