I'm running a cDAQ-9174 with modules 9225 and 9239 to measure voltage (120, 208-240, 277 VAC) and current (via Fluke i400 amp clamp - 10mA/A output) respectively.
I have the scale set at Differential/No Scale (so 1:1 I'm assuming) for voltage, and 100:1 for current. With the acquisition mode set at "N Samples", 10 samples to read, at a Rate of 500m. This is feeding into "EPM_Power.vi" (polymorphic VI from the EPM palette... can be downloaded here, http://sine.ni.com/nips/cds/view/p/lang/en/nid/209826)
I'm attempting to verify my numbers with a Fluke 435 Power Quality Analyzer and backing that up is a Fluke 179 True RMS DMM with i200 amp clamp (for reading current)
Now, what I'm running into is my numbers as I'm taking data look like they're following a sin curve... the averages are about right, but where my voltage should be relatively stable, it's all over the map... same story with my current readings. I've tried several different filters with no luck. I'd like to have relatively stable values for both voltage and current so my other values are correct. Is there a filter or signal conditioner that will help with this?
As always, a point in the right direction would be greatly appreciated!
I'm curious about the magnitude of your sine wave oscillations, and the frequency of the wave. How high and low does the sine wave go, and what value are you expecting? If the frequency is around 60Hz, it's possible you have some grounding issues to attend to.
To find out, would you mind posing screenshots of the behavior you're seeing?
Will Hilzinger | Switch Product Support Engineer | National Instruments
Your request for a screen shot actuall lead me to the solution. Not enough samples! I was taking to little data too slowly and only seeing part of the AC sin wave each iteration. ..which became glaringly obvious when I attempted to graph it. So, I increased my sampling to 100 samples at 5Hz and things seem to have settled things quite a bit. Thank you for asking the right question!