Measuring AC voltage in Labview 8.5

[Azhure]

I have all my channels set up fine in MAX and the hardware is working correctly.  I'm trying to measure the power as a function of voltage and resistance but my voltage is ac and I'm not sure how to get a single value through the vis.  When I try using a DAQ Express VI  or virtual channels it gives me 24 regardless of the input voltage.  In MAX it does change and gives me a waveform. I am fairly new to the labview environment.

[BenjaminR]

Hello,

Can you attach you VIs? It will be easier to help you.

Thanks

[johnsold]

In addition to what BenjaminR asked you will generally need to process the waveform to get the power. The RMS measurement is the standard way to measure AC power. In analog instruments the averaging (or mean) part is done continuously in circuitry or by mechanical filtering. In digitized systems you may need to be more careful to average over integer numbers of cycles of your AC waveform to avoid errors.

Lynn

[Azhure]

I figured it out!

[Nathan_R]

Some great examples of how to process the acquired waveform to get the RMS voltage are Basic Amplitude Measurements.vi, Basic DC-RMS Measurement.vi, and Advanced DC-RMS Measurement.vi. These examples can be found by going to the Help menu and selecting Find Examples.... Once the NI Example Finder is open select Analyzing and Processing Signals» Level Measurements. Let me know if you need any more help.

Thanks,

[Shogunmanga]

Hi there,

I am a beginner in LabVIEW. I use LabVIEW 8.6 and I am facing the same issue. I am trying to read AC current signal from a lock-in amplifier through a BNC board connected to PCI 6221 interface. However, by using DAQmx and virtual channels, I get a constant read out. The test bench in NI MAX 2012 can read the AC signal as shown in the amplifier. It would be a lot of help if you could help me out here.

Thanks in advance,

Karthik. 

[crossrulz]

Are you just reading 1 sample?  What is the frequency of your signal?  What is your sampling frequency?