Integrating a Rogowski Coil's Output

In summary, when using a Rogowski coil to measure current and performing numerical integration on the output, it is important to consider whether to use absolute values or not. If the result is being used to calculate power, then absolute values should be used. However, if trying to measure the power dissipated in a diode or using the output to calculate power in a specific scenario, then only the positive part of the cycle should be used. Additionally, it is important to keep in mind that a Rogowski coil is a high-pass filter and requires careful consideration in design.
  • #1
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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  • #2
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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  • #3
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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  • #4
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.
 
  • #5
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)?
 
  • #6
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.
 
  • #7
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
 

1. What is a Rogowski coil and how does it work?

A Rogowski coil is an electromagnetic device used to measure electrical current in a conductor. It consists of a flexible wire wound in a helix shape and connected to an output circuit. When the current being measured passes through the center of the coil, it generates a voltage that is proportional to the rate of change of the current over time.

2. How is the output of a Rogowski coil integrated?

The output of a Rogowski coil is integrated by using an electronic integrator circuit, typically a resistor-capacitor (RC) circuit. The voltage output from the coil is passed through the integrator, which converts the voltage to a current and then integrates it over time to give the total current passing through the coil.

3. What are the benefits of using a Rogowski coil for current measurement?

Compared to traditional current transformers, Rogowski coils have a number of benefits. They are more flexible and can be easily wrapped around irregularly shaped conductors, and they are also lightweight and non-intrusive. Additionally, Rogowski coils do not require an external power supply and have a wider bandwidth for accurate measurement of high frequency currents.

4. What are some potential sources of error when integrating a Rogowski coil's output?

One potential source of error is the non-linearity of the coil's output, which can be caused by factors such as temperature changes or variations in the conductor's shape. Additionally, any noise or interference in the signal can affect the accuracy of the integration. It is important to carefully calibrate and shield the coil and integrator circuit to minimize these sources of error.

5. Can a Rogowski coil be used for both AC and DC current measurement?

Yes, a Rogowski coil can be used for both AC and DC current measurement. However, for DC measurement, an additional electronic component, such as a DC-blocking capacitor, is required to remove the DC offset from the signal. It is also important to note that the integration process for DC current measurement is different from that of AC current measurement.

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