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From the Q&A

With TJ Byers


Meter Metrology

Question:

Some of my panel meters (milliameter and voltmeter) change the zero position depending upon being held in a vertical or horizontal position. Can this be remedied, or is this the job for a meter professional?

Richard H. Abeles
via Internet


Answer:

I assume you’re talking about analog meters with a needle. Generally, the needle rests on a pivot that has to be balanced so that its weight remains the same around the pivot point (see diagram). Notice that the needle is actually in the form of a cross, with the pointer longer than the legs. Weight is added to the shorter legs via coiled springs that slide back and forth to change the center of gravity.

However, this is a lot easier said than done. That’s because everything about the movement is delicate and very fragile. One false move and you can dislodge the jewel, damage the return spring (or taut ribbon), or the needle itself. This adjustment requires a steady hand, a loop magnifier, and jeweler tools. That said...

Start by rotating the meter in a gimbaled circle to find which axis has the off-balanced weight. This is the hardest part because if you guess wrong and move the wrong counterweight, you could be in for a long day.

Sometimes (not often) it’s necessary to bend the weighted tabs up or down, but this has to be done ever so carefully. It’s usually better to keep the cross on the same plane so that all the legs are flat. Also be warned that some cheap panel meters, especially iron vane meters, need to be mounted in one orientation only and have to be re-zeroed as their position changes. Good luck!


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