Re: Avometer Movements
The early type horseshoe movements have a magnetic shunt with quite limited effect- once you turn it past 45 to 55 degrees the influence actually starts to decrease, so you are unlikely to see one where the shunt has been moved beyond 45 degrees.
The Model D movement pictured was found lacking by around 6 to 7% (judged by needle deflection on the 3 Volt DC range), well beyond the trimming capacity of the swivel shunt. It was experimentally boosted with a Neodymium (10mm diam) magnet. From memory this method of placing the booster magnet on the concentrator rather than on the magnet proper may have been casually called the Japanese method, due to being popularised on the web by a Japanese chap on his website.
I have seen a case where success was achieved by strategically placing less powerful grey magnets around the horseshoe in order to get linearity, but having had success with the Japanese method i would try it again as it took very little time to get the Neodym shuffled to a good position, then araldite it in place. I don't know quite what tool I would use if I ever needed to shift it...something bronze probably. Note that in my case the Neodym now prevents the swivel shunt from rotating. If i had been able to source a slightly smaller booster magnet this might not have occurred. (But not a problem anyway)
My latest source of (very)miniature Neodyms was a pair of old specs. that had a tinted overclip with lozenge shaped magnets at either end. A very useful size that might even allow an Avominor to be given the booster treatment in future.
Dave
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