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Speedometer dead, now what to do? 200 1989

uid 27's pic
posted by  Art Benstein on  Mon Aug 15 10:07 CST 2016
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last visit: Fri Oct 17 20:10 CST 2014
[RELATED]

No Phil, the speed meter and the stepper motor are two different animals.

The speed meter is a D'Arsonval movement -- a moving coil in a fixed permanent magnetic field. It should have moved the needle, but if the mechanics of the needle (moving coil, spring, bearings) does not permit it to move under the very low force imparted, it will not. The fact the coils measure ~95 ohms proves this is not an electrical problem. It is mechanical.

The usual reason for it being mechanically stuck is the meter got exposed to a workbench environment with iron filings. The powerful permanent magnet sucks up the little fragments and they jam the moving coil in place. Pretty much, that sort of mistreatment is fatal to a D'Arsonval movement.
--
Art Benstein near Baltimore

What engineers say and what they mean by it:
"Test results were extremely gratifying"
It works, and are we surprised!






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