Calculate Shunt Resistance

[inlineskater]

Question:

To extend the range of a 0-8.4 mA, 46.3 ohm DC ammeter, what size of shunt resistor should be used to obtain a 92 mA range?

Using the following formula:

Ish/Im = Rm/Rsh

Rsh = shunt resistance
Rm = meter resistance
Ish = shunt current
Im = meter current
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Rsh = (46.3 ohms) (8.4 x 10^-3) / 83.6 x 10^-3

= 3.8892 x 10^-1 / 83.6 x 10^-3

= 4.65 ohms

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Could of I calculated this differently. Looking this it seems correct.
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[john monks]

Yes. You can calculate the voltage needed for full scale meter deflection based on the current and resistance of the meter. With the current of the meter you can calculate the value of the current in the shunt resistance. Now you have the voltage and the current of the shunt resistor and now you can calculate the resistance of the shunt resistor.