Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!lll-winken!elroy.jpl.nasa.gov!sdd.hp.com!hp-pcd!hplsla!tomb
From: tomb@hplsla.HP.COM (Tom Bruhns)
Newsgroups: sci.electronics
Subject: Re: Inductive pickups.
Message-ID: <5170138@hplsla.HP.COM>
Date: 31 May 91 01:00:15 GMT
References: <1970@ole.UUCP>
Organization: HP Lake Stevens, WA
Lines: 22

ssave@ole.UUCP (Shailendra Save) writes:

>  I am trying to get a signal from the drive shaft of my car
>using an inductive pickup. (To calculate and display speed)
>Before I get under and get dirty, I wanted to know if anyone
>has had any experience with a similar transducer? Can you 
>recommend one? The car being a big hunk of metal, and the 
>tolerances between the "magnet" and the pickup being of the
>order of 0.2 in., will it work? 

How about you pick up a replacement coil and magnet for an after-
market automatic speed control?  I once installed one from Sears
that works fine to this day.  The magnet was a tiny rare-earth thing
that held to the shaft just by magnetism; it's never come loose.
Never noticed any problem with imbalance; the magnet is very small 
compared with the mass of the shaft.  The pickup was a coil of
wire maybe an inch od, on a steel core as I recall, kinda like a
relay coil, but not very many turns.  If you need a sears part
number, I might be able to find the 'manual'.

Guess it may not be totally obvious:  magnet goes on the shaft and
coil is mounted to the car, nearly an inch gap as I recall.