power factor in signal express

[RJJE]

I have my voltage and current waveforms into SE and am having trouble trying to measure the phase angle between them so that I may calculate PF for logging purposes. Is this possible with SE or do I need a higher powered platform (LabView)?

Thanks

Randy

[DFGray]

Provided your current and voltage are repetitive waveforms, this is fairly easy.  Use Analysis->Frequency Domain Measurements->Tone Extraction to get the phase of the waveforms (you can turn off exporting the time signal and power spectrum, since you don't need it, to save a bit of time and memory).  Use Processing->Analog Signals->Formula to find the difference and calculate the power factor in one step.

[RJJE]

Well that was easy, I didn't think to look at that function.

Now my other problem is after I run Amplitude & Levels on the voltage and current waveforms to get the RMS value I can't find a way to mutiply them to get VA. If my understanding of AC power calcs is correct and I have unity PF then I could just multiply the volt & current waveforms, which works fine because with unity PF VA is Watts.

Thanks for your help.

[DFGray]

You can use the Formula step to do this multiplication (select the two RMS values as the inputs).  You may want to multiply the voltage and current waveforms together before taking RMS (use the Arithmetic step to multiply two waveforms).  This may give you better values, but will also be slower and take more memory.  The difference should not be significant if you have clean, repetitive waveforms.

[Brett_B.]

There is an Electrical Measurements Palette available for download that was just released.  There is also a DevZone document on "How to measure current and make power measurements" that may be helpful.

How to Measure Current and Make Power Measurements: http://zone.ni.com/devzone/cda/tut/p/id/8198

Download link for EPM palette: https://lumen.ni.com/nicif/us/codelvelectpwr/content.xhtml

hope this helps,

Brett

[RJJE]

Thanks Brett

I have all my signal condtioning done and my V & A waveforms into SE 2.5, just having a little trouble crunching the numbers in SE for real data, still fairly green on using SE.

The other tips have proven helpful.

Does that power pallette work in SE? I haven't explored on how to use LabView VI's in SE.

[CharlesD]

Good morning Randy,

The EM Palette is only available for LabVIEW and cannot be used in SignalExpress.  These are VIs that are imported into LabVIEW and become part of the user library palette.  Therefore unless you start using LabVIEW the above palette will not be useful to you.  However the developer's zone is still applicable for your application.  

Are you still having trouble crunching the numbers in SignalExpress?  Do you have any specific questions regarding this or have the previous posts answered your questions? 

Regards, 

CharlesD

Applications Engineer

National Instruments

Message Edited by CharlesD on 01-26-2009 11:20 AM

[RJJE]

Hello CharlesD

So far I have taken into SE 2.5 my voltage & current waveforms, scaled them to actual values and used tone extraction to get my phase difference or power factor. From there I can calculate the necessary values for monitoring power consumption. So far so good.

Now I need to calculate kW over time for kWhrs. So far I have been unsuccessful.

After I figure that out I would like to set an output of my USB-6008 high which will signal another USB DAQ unit that a kW (sec or min) has occurred. From there I would like to drive the 2 analog outputs with the volts and amps RMS values again to another USB DAQ unit. This is because I use DAQFactory as my scada/logging software which cannot talk to your USB-6008 but will to Labjack's USB DAQ modules.

I know it is complicated but I have to work with what I have and I don't think my wife would be to happy if I purchased Labview ($$$) so that I could properly measure and log home power use.

Thanks for your help.

[DFGray]

To calculate kW-Hours, you really need an integrate, which SignalExpress does not currently support.  However, you can get pretty close using the Statistics step with the sum function checked (boxcar integration).  Turn off restart measurement to keep from zeroing at each iteration.  You will need to scale the result by the step size to get the actual result.

[CharlesD]

Hello all,

I would like to clarify that LabVIEW VIs can be used in signal express, however they need to follow specific guidelines defined in the following knowledgebase articles:

VI Guidelines for User Defined Steps In SignalExpress

Using a LabVIEW VI with LabVIEW SignalExpress

The EPM VI's , linked in previous post, could be modified to conform to these guidelines, however to do so LabVIEW is required.  

To use LabVIEW VI's in Signal express follow these steps:

1. Add Step --> RUN LabVIEW VI (choose proper version for VI). 

2. Select VI or source distribution (.llb) Path and configure the proper settings for  your application.

More detailed information on how to run a Labview VI in Signal Express can be found at the following link: Signal Express Help: Run a LabVIEW 8.6 VI