Accuracy current probe
Accuracy current probe
(OP)
Hi
How do I calculate the overall accuracy of an AC current probe (In= 1000 A) when measuring the motor current for a frequency drive having 2 kHz switching frequency. The measured current is approx. 400 A.
The accuracy of the current probe is 0,5 % of 1000 A (sinusoidal current), the bandwith is 10 kHz.
B.R.
hhhansen
How do I calculate the overall accuracy of an AC current probe (In= 1000 A) when measuring the motor current for a frequency drive having 2 kHz switching frequency. The measured current is approx. 400 A.
The accuracy of the current probe is 0,5 % of 1000 A (sinusoidal current), the bandwith is 10 kHz.
B.R.
hhhansen





RE: Accuracy current probe
To add to your question: Does anyone have any experimental data on probe accuracy on the output of drives?
RE: Accuracy current probe
RE: Accuracy current probe
Irms,total=sqrt[(Irms1±0.5%)^2 + (Irms2±0.5%)^2 + (Irms3±0.5%)^2 + ... + (Irmsn±0.5%)^2]
Now, if +0.5 upper error is considered, then it can be extracted, leading to:
Irms,total,+0.5%=1.005 x sqrt[(Irms1)^2 + (Irms2)^2 + (Irms3)^2 + ... + (Irmsn)^2]
Irms,total,-0.5%=0.995 x sqrt[(Irms1)^2 + (Irms2)^2 + (Irms3)^2 + ... + (Irmsn)^2]
The expression may be normalized per 1000A.
RE: Accuracy current probe
RE: Accuracy current probe
Specifically, whether or not 0.5% accuracy is constant from 0A to 1000A.
RE: Accuracy current probe
I searched a lot but could not find a way to accurately measure the PWM current. I wonder how drive measures/ controls, is it on incoming AC side ? may someone enlighten us.
Best regards,
RE: Accuracy current probe
I did compare a drive reading with a shunt with an accurate rms meter and found the drive readings were a little low. This told me that the circuitry in this 5HP drive was using some generic hardware/software to come up with this number. I do not know for sure how drive mfg's do this but have learned not to trust their readings (at least the inexpensive single phase drives).
Clamp-ons are not that accurate to begin with depending on the conductor size. As an experiment, place your clamp-on on some current carrying conductor and move it slowly around the conductor and watch the reading change more than it should based on the accuracy they give you at that current level. I have found that most exceed their accuracy spec by simply moving the meter window in relation to the conductor.
RE: Accuracy current probe