Problem with power factor measurements (ADE7816)

Question

Hi, 
 we have a problem with ADE7816, we started the design of a new device with multi-input CT, we bought the evaluation board and connected a inductive load at channel A, and we used in parallel a analyzed power to calibrate it....these are the results: 
 1) we got differents power factors: 
 ADE7816 (channel A) : 0.985 
 Analyzed power(calibrated): 0.850 
 2) we got this angle by two ways, and get the same result: 
 ADE7816 method (1) --> cos(arctg(AVARHR / AWATTHR))= 0.985 
 method (2) --> directly reading ANGLE0 --> cos(ANGLE0*(50-360)/25600)= 0.995 
 We don't know what happend but we get different power factor when use reactive load ( 0.985 =/ 0.85 ), 
 it's a big different between these values. 
 I think this driver (ADE7816) should work well, but we don't know what happend. 
 Thank you at all.

EZAdministrator · Accepted Answer

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ADIApproved · Answer

Hi agarciaoteros 
 I understand that you have connected a reference meter and ADE7816 Evaluation board to a same load, in order to check the accuracy of PF. I would like to make sure if you have done phase calibration prior to this, because CTs can add a considerable phase shift and hence the PF measurement can be erroneous. 
 Also, the two methods that you have used to measure PF are a little different: 
 1. cos(arctg(AVARHR / AWATTHR))= 0.985 
 This method uses energy register readings and hence includes harmonic content as well (upto 2KHz). 
 2. directly reading ANGLE0 --> cos(ANGLE0*(50-360)/25600)= 0.995 
 This method measures the angle using ZX circuitry which is filtered to 70 Hz and so, is a fundamental only measurement. 
 So if the phase calibration is done correctly, the difference between these two readings will correspond to the harmonics. 
 And can you let me know what is the bandwidth of the reference meter that you are using? 
 Regards 
 hmani

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Problem with power factor measurements (ADE7816)