MOVING COIL IN ANALOG MULTIMETER

[pgr2002]

I want to replace moving coil in one of the analog multimeter. How do I find the suitable one to be replaced and work as before. There are many panel meters available in Volts & Amperes. Will these suit in the multimeter. Is there any indication of finding a suitable one to fit in a multimeter? There are no indications as to the coil specifications. But there are some markings on the multimeter scale such as :
1. 20.000 ohms/V DC
2. 10.000 ohms/V AC
Now how do I select from these specifications a correct coil meter. Separate coils are not available. I will have to select from VU meters which are enclosed in plastic cases. Please advise.

 

[barry]

I think you’re going to have to get this from the manufacturer. The odds of finding the identical coil elsewhere so that you maintain accuracy are slim. You may just have to replace the meter.

 

[danadakk]

You could rewind the coil if thats whats broken. Very fragile assembly to work with.
And tedious, you would use same length to get roughly the same number turns.


Regards, Dana.

 

[BradtheRad]

I agree you probably need to look many places to find an exact replacement.

20k DC, 10k AC are common specs in an everyday multimeter.

Do you intend to keep the printed scale? A new movement needs to be rated for the same full-scale current as the original. (This may be marked on the meter or schematic somewhere.)
Typical figures are 50 uA, 60 uA, 100 uA, etc. Tentatively it's the same as the most sensitive Ampere reading on your meter, although it's not a guarantee.

The needle should be the same length as the original for obvious reasons.

 

[FvM]

20 kohm/V refers to 50uA meter, or less if there's an adjustment resistor across the meter.

 

[danadakk]

You can always buy a meter with appropriate scale on it, then use
an OpAmp circuit to handle any mismatch between its sensitivity
versus old meter. Times past DIY'ers even made scales using simple
drafting techniques to get meter scale they wanted.

http://www.rfcafe.com/references/po...aged-parts-popular-electronics-april-1974.htm

http://www.rfcafe.com/references/qst/rejuvenating-old-meters-feb-1943-qst.htm

http://e2e.ti.com/support/amplifier.../fao-paul-grohe-re-building-a-microgram-scale

Meter - the meter scale drawing program from Tonne Software

www.tonnesoftware.com

Regards, Dana.