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Today, practically every control and monitoring circuit uses shunt-based current measurements as an alternative to sensors. To make these measurements accurately, it is useful to understand how shunts work. Because the method is categorized as a precision measuring technology, it should not be regarded as trivial.

A shunt is a low-value resistor used to measure current – it is therefore also referred to as a current-sense resistor. The shunt typically connects in series so it carries the current of interest. A voltage measurement device then connects in parallel with the shunt. The current through the shunt generates a voltage drop that is measured. The current value is derived from Ohm’s law and the known resistance (I=V/R). To keep power loss – and thus heat development – to a minimum, shunts must have resistive values no higher than the milliohm range. Some are even below that.


V=IR

I=V/R


Shunt Resistor:

  • needs to be small such that it does not disrupt existing circuit.
  • large enough to get a measurable voltage


Be careful about power rating.

P=I2

p=102 x 10Ω

= 1000w


Example Shunt for 12V :

Max Amp50A
R10 Ω
I = V(measured)/R8v/10 = 0.8A
P=I2

=502 x 10Ω

=250 kw

References

ReferenceURL
Measuring current with shunt resistorshttps://www.powerelectronictips.com/measuring-current-shunt-resistors/
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