[Amps] *** SPAM *** Re: Follow-up on Bouncy Meter

[Tom W8JI]

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