Ammeter?

What can stop a moving-iron ammeter working?
Current is flowing through it, the coil is sound and not leaking, bearings
and hair spring fine, needle moves by hand, and resistance of coil is
identical to a working one.
Anybody have any suggestions please?
regards
Roland
Reply to
Roland and Celia Craven
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Daft question Roland, If you can easily move the needle with your finger you had it out of the case. Is it dragging on the glass after a jolt or something.
Martin P
Reply to
Campingstoveman
Nope. Its completely free to move. Puzzler isn't it :-) ttfn Roland
Reply to
Roland and Celia Craven
Thanks Roland, your question has caused me to read up on the Web as to how it works and maybe you iron is no longer magnetic enough to be affected by the coil. The Lorenz affect is an interesting read.
Martin P
Reply to
Campingstoveman
That's where I'd got to Martin.
Is the moving iron piece magnetised Roland? If not, have a look at another one that does work to see if it is a magnet or not.
Regards,
Kim
Reply to
J K Siddorn
It is magnetised as is a working one. ttfn Roland
Reply to
Roland and Celia Craven
Is it a linear graduated scale or mildly logarithmic?
Peter
Peter -- Peter A Forbes Prepair Ltd, Luton, UK snipped-for-privacy@easynet.co.uk
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Reply to
Prepair Ltd
Linear - Crompton c 1930. As in the working meters there is a curled strip with one end sticking out inside the (what I guess amounts to a) stator. Is this purely a limit stop or is its position critical? ttfn Roland
Reply to
Roland and Celia Craven

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