# Integrating a Rogowski Coil's Output

Dear Sirs,

I measuring current with a Rogowski Coil and I want to perform numerical integration on the output.

Since the output is fluctuating around ground level, the question is: Should I use the absolute values of the output or not?

Thank you.

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DaveE
Gold Member
The coil will not respond to the constant (DC) part of the current being measured. So the coil output will be an AC voltage and the current being measured will be the integral of this voltage with the DC part removed, also AC. You may want to "add in" the DC via analysis of the circuit or a different DC current measurement. In any case if you perform an absolute value you will distort the true wave shape (rectification). I suppose you may want to do that, but I doubt it.

• Abimbola1987
CWatters
Homework Helper
Gold Member
If you are using the result to calculate power then yes use he absolute value.

More specifically for power you want to integrate the product of the instantaneous Voltage and instantaneous Current.

If the voltage is constant you can take that outside the integral. Eg integrate the absolute current then multiply by the voltage.

• Abimbola1987
The coil will not respond to the constant (DC) part of the current being measured. So the coil output will be an AC voltage and the current being measured will be the integral of this voltage with the DC part removed, also AC. You may want to "add in" the DC via analysis of the circuit or a different DC current measurement.
Thank you and duly noted, however I havn't been able to measure any DC current using the shunt resistor method. Also it is my understanding that after integrating the output voltage, it has to be scaled by a factor of 1/M, where M is the mutual inductance between the coil and wire being measured.

In any case if you perform an absolute value you will distort the true wave shape (rectification). I suppose you may want to do that, but I doubt it.
What do you mean by "true wave shape"? the instantaneous current?

And as CWatters noted in the post above, I will be using the value to calculate power.

If you are using the result to calculate power then yes use he absolute value.

More specifically for power you want to integrate the product of the instantaneous Voltage and instantaneous Current.

If the voltage is constant you can take that outside the integral. Eg integrate the absolute current then multiply by the voltage.
Thank you and duly noted. So when would I not use the absolute value? I mean if the instantaneous current is 1/M∫abs(voltage)?

CWatters
Homework Helper
Gold Member
If you are trying to calculate the power dissipated in a resistor then use the absolute value.

If you are trying to measure the power dissipated in a diode that is part of a rectifier then it would only be (for example) the positive part of the cycle you use because the negative half flows through another diode.

Tom.G