Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!ucsd!rutgers!iuvax!bsu-cs!dhesi
From: dhesi@bsu-cs.UUCP (Rahul Dhesi)
Newsgroups: sci.electronics
Subject: Re: Library book detectors.
Message-ID: <2509@bsu-cs.UUCP>
Date: 30 Mar 88 21:39:36 GMT
References: <5398@swan.ulowell.edu| <1261@uop.edu| <2521@ihuxv.ATT.COM| <2530@ihuxv.ATT.COM> <2258@c3pe.UUCP> <341@bacchus.DEC.COM>
Reply-To: dhesi@bsu-cs.UUCP (Rahul Dhesi)
Distribution: na
Organization: CS Dept, Ball St U, Muncie, Indiana
Lines: 18

In article <341@bacchus.DEC.COM> reid@decwrl.UUCP (Brian Reid) writes:
>When a book is checked out, the librarian runs it over a "deactivator".
>In fact, that deactivator is another sweep pinger, and it records the
>frequency signature in a short-term database.

However, all the libraries I've used deactivate books that are checked
out so that they will not trigger the detector even days or weeks
later.  This lets the user bring checked-out books into the library for
reference during subsequent visits.

Speculation:  A deactivator simply changes the magnetization in the
little "target" strip that's in the book.  This changes the
characteristics of the L-C circuit in the strip because the inductance
of a coil changes as its magnetic core gets saturated.

Alternatively, it could just be casting a magic spell which, after all,
is indistinguishable from any sufficiently advanced technology.
-- 
Rahul Dhesi         UUCP:  <backbones>!{iuvax,pur-ee,uunet}!bsu-cs!dhesi