Acquiring AC voltage signal using NI 9206 9205 and cRIO

Hello.  I am having difficulty accurately acquiring an AC voltage signal using a NI 9206 and cRIO.  I'm attempting to acquire voltage signals from two types of Magnelab Current Transformers: split core and rope.  In Labview, I first populate an array of size 2,500 with the sensor signal (DIFF mode), then compute the RMS of the array.  For the split core CTs, I am able to accurately acquire the correct voltage reading (verified by measuring the corresponding amp on the line using a Fluke 434 Power Analyzer.  For the rope CT, however, using the same array/RMS method, I am unable to accurately acquire the correct voltage reading.  Measuring the amp on the line using the Fluke 434 PA, the correct voltage from the rope CT should be 0.05v.  Using the 9206 (DIFF mode), the RMS from the array gives a voltage reading of 0.071.  Now the interesting part is when I measure the line voltage using two different True RMS DMMs, I get two different readings.  One multi-meter, a Klein CL2000, reads the correct voltage at 0.05v.  Another multi-meter, a Fluke 189, reads incorrectly at 0.071, the same as I get using LabView and the NI 9206.  I suppose the question is how is the Klein interpreting the signal differently than the Fluke 189 and the NI 9206 via LabView.  One difference between the split-core and rope CTs is that the rope CTs require an external power supply 12-30v AC or DC.  I am providing them with 12v DC.  I have tried multiple voltages in both AC and DC and still get the same incorrect reading.  I'm quite certain it is not a power supply issue, although perhaps the integrator in the rope is creating a unique signal.  Any ideas?  I appreciate any input.
Thanks,
J.Grant
Solved!
Go to Solution.

AK2DM:
Update - solution found
While the Butterworth low-pass filter sort of worked, it was NOT the solution.  I spent some time analyzing the rope CT signals by sampling at a very high rate.  The AC signal coming off the rope CTs is triangular NOT sinusoidal.  The RMS function in LabView assumes a sinusoidal waveform and essentially calculates the RMS as the average of voltage peaks (for each cycle) / sq.rt (2).  Since the AC voltage single emanating from a regular split-core CT is basically sinusoidal, the LabView RMS of the signal gives an accurate reading of the voltage signal.  Unable to find a RMS function in LabView for a triangular AC voltage signal, I ended up developing my own custom triangular RMS function in LabView.  My function analyzes the signal by finding the peak of every cycle within the signal, takes the average of these peaks, then divides this average peak by sq.rt (3).  see this link for formulas:
http://www.optics.arizona.edu/nofziger/OPTI%20380B/Lab%201/AVG%20and%20RMS%20Values%20of%20Periodic%...
Using the triangular method, I am able to accurately acquire the signal off the rope CTs. 
Thanks for your help!

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