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# How to scale a micro ammeter? Answered

I need to measure the current of a Tesla coils secondary output and have found that it is under 1mA and above 50uA so how can I scale a 50uA DC micro ammeter or a DC milliammeter (can't remember its range) to the appropriate range?

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## 4 Replies

rickharris (author)2011-07-20

This should answer your question - you will need to shunt some of the current round the ammeter mechanism.

Dr.Bill (author)2011-10-16

Ya know, "This" , is very good to have around as a refrence so I copied it.

iceng (author)2011-07-20

You can always use a resistor and Steve's favorite tool a scope
even a mili-voltmetre.... and math.

Alos, a pick axe and rope can help you scale the difficult domains :-)

A

steveastrouk (author)2011-07-20

The meter SHOULD specify its resistance. With that, you can work out the shunting resistance you need.

I = Imeter x Gmeter + Ishunt x Gshunt

I is the total current flowing.
Imeter is the current in the meter.
Gmeter = 1/Rmeter
Ishunt= current to flow in shunt = I-Imeter
Gshunt= 1/Rshunt.
Rearrange for Gshunt.

Steve