A dozen different things occur when the hairsprings are bad,
but they all have one common thread. The meter reading is
way off because the spring is part of the calibration. It
also has never, to my recall, caused a "bouncy meter".
He said the meter read nornmally.
When I supervised the precision meter manfacturing of a
plant in Cleveland, Ohio for a few years, we would
occasionally get orders that required a dampened movement.
This was especially a problem with high torque movements.
Air and other friction didn't slow the movement down much
when the losses were a small part of the actual mechanical
energy.
When we could not use a low-torque movement, we would add a
small amount of silicon (we had several types) to the
bearings to increase dampening. There also was a shorted
(shunt) winding we would sometimes use. The shorted turn
would generate a countering force that would slow response.
There are a dozen different ways to build meters and I'm not
sure what Collins had done, but I'm not aware of any methods
to limit response other than:
1.) A dampening oil in the bearings
2.) A closed loop in the moving coil
3.) Controlling motor torque
Of the three, the only two things that could change in a way
making the movement bounce and still allow a meter to read
correctly are:
1.) The bearings drying out or somehow getting a dampening
agent like silicone washed out. Too much heat, too much
pointer movement, or too much time would do that.
2.) A closed loop on the winding opening up.
Of those two only one is repairable.
73 Tom
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