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Making current measurements with VFDs in circuit

Question asked by DDSchrader on Apr 30, 2015
Latest reply on Jun 8, 2015 by hmani



We are using the ADE7878 with three Pulse Rogowski coils to monitor the current used by a three-phase 480 VAC blower motor that has its speed controlled by a VFD. When the blower is operating at its low speed, we seem to be measuring the current correctly and these measurements correspond pretty well with other metering equipment. However, at the high speed, there are all sorts of spikes and odd readings sometimes as high as 50 Amps and these currents are way too high for this motor to have ever used. We are measuring the current at the input of the VFD, so it is not an issue of trying to measure the output side currents. What is it about our circuit's (identical to the AD demo board schematics, filters, etc are all in place) design or possibly register settings that may be causing this? I would like to start a dialog between us to work through this as I am now designing this same part into another product with substantially higher sales potential and really don't want to see this failing in the field like this first product is now doing. I am attaching a PNG of the graphed data from this device for your reference. I can provide whatever details you need so that we can sort this out.