Integrating a Rogowski Coil's Output

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Discussion Overview

The discussion revolves around the integration of a Rogowski Coil's output for current measurement, focusing on whether to use absolute values of the output voltage during numerical integration. The context includes considerations for AC and DC components, power calculations, and the implications of using absolute values on the waveform shape.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants note that the Rogowski Coil does not respond to the DC component of the current, resulting in an AC voltage output that requires integration of this voltage to determine the current.
  • One participant suggests that using absolute values during integration may distort the true wave shape, implying that rectification could alter the waveform.
  • Another participant states that for power calculations, it is necessary to use the absolute value of the current, especially when integrating the product of instantaneous voltage and current.
  • There is a mention of the need to scale the integrated output by a factor related to the mutual inductance between the coil and the wire being measured.
  • Some participants express uncertainty about when it would be appropriate not to use absolute values, particularly in different measurement contexts such as resistors versus diodes.
  • A participant highlights that the Rogowski Coil acts as a high-pass filter, with sensitivity increasing with frequency, suggesting that design considerations are complex.

Areas of Agreement / Disagreement

Participants express differing views on the use of absolute values in integration, particularly regarding its impact on waveform shape and power calculations. There is no consensus on a definitive approach, and multiple competing perspectives remain regarding the integration method.

Contextual Notes

Participants mention limitations in measuring DC current using alternative methods and the need for careful consideration of the Rogowski Coil's characteristics in design. The discussion reflects various assumptions about the integration process and the implications of using absolute values.

Abimbola1987
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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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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.
 
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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.
 
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DaveE said:
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.

DaveE said:
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.
 
CWatters said:
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)?
 
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.
 
Also be aware that a Rogowski coil is an inductor and as such is a high-pass filter, that is it's sensitivity (output voltage) rises with frequency.
Designing with them is not all that simple. See https://www.physicsforums.com/threads/adder-lp-filter.943146/
The last post in that thread lists some sources for commercially available instruments.

Cheers,
Tom
 

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