Extending ammeter range

Thread Starter

ronph

Joined Feb 4, 2013
25
I have an old Triplet milliampere meter that reads between 0 & 1 milliamp @55 ohms based on the online specs. Is it possible to extend the range to 1 amp reading using a resistor at one end of the lead coming out of the meter or parallel to the legs of the meter? Its not critical as to the exact output - close enough would do. Working voltage would be between 9 & 30 volts (if this helps).

Thanks
 
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ScottWang

Joined Aug 23, 2012
7,397
1mA Meter for V = 1mA * 55Ω = 55mV.
Total R = 55mV / 1A = 0.055Ω.
Parallel R of I = 1A - 1mA = 999mA
Parallel R = 55mV / 999mA = 0.055055Ω.
Power dissipation of Parallel R = V * I = 55mV * 999mA = 0.055W

Assuming above formular is correct.
So if you can get a 0.055055Ω resistor in parallel with 1mA Meter then you can expanding the measuring range.

If you can't get the 0.055055Ω resistor, then you better buy a new one.
 
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John P

Joined Oct 14, 2008
2,025
If an approximate reading is OK, then you can easily make a resistor by using a measured length of wire of some known diameter. For instance, 24Ga wire has resistance of .026 ohms/foot, so if you want .055 ohms, just over 2 feet ought to do it.
 

ScottWang

Joined Aug 23, 2012
7,397
If an approximate reading is OK, then you can easily make a resistor by using a measured length of wire of some known diameter. For instance, 24Ga wire has resistance of .026 ohms/foot, so if you want .055 ohms, just over 2 feet ought to do it.
I never heard 24Ga wire, but that is a new knowledge to me.
I just heard someone talking about the Manganin shunt, and below is a 2mΩ Manganin shunt, that is used for big current sensor.



The picture was copy from here.

Manganin Shunts.
 

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Last edited:

crutschow

Joined Mar 14, 2008
34,280
A .05Ω resistor or two 0.1Ω resistors in parallel will be within 91% of the correct value, if that's close enough for you.
 

bountyhunter

Joined Sep 7, 2009
2,512
I never heard 24Ga wire, but that is a new knowledge to me.
I just heard someone talking about the Manganin shunt, and below is a 2mΩ Manganin shunt, that is used for big current sensor.



The picture was copy from here.

Manganin Shunts.
We used to buy manganin wire of various diameters on spools to make current shunts. It's resistivity is well known and has zero TC.
 

Thread Starter

ronph

Joined Feb 4, 2013
25
Thanks for all your input. I want to use it to measure current (not voltage). I will try as suggested with a lenght of wire and see if that will do the trick.

Will update if I make any progress on this.
 
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