CONFIGURING PCI 6221 DAQ CARD IN LabVIEW

[unni_vat]

Dear All,

I have this program with my PCI 6221 DAQ and LabVIEW 7.1, which reads in three line current and three line voltages in a 50Hz three phase power supply. I used a PCI 6221 DAQ. When I give a sampling rate of 11KHz, the recored signals shows discontinuity as evident from the time stamping. What could be the reason? Please advice.

I am attaching the program and also the recorded output, alternate columns in it starting from column A are time stamps and the remaining are current and voltage data.

Thanks in advance

[hoffiz]

Hi

How are you reading the current? Do you have a connector block with a resistor pack so you can relate the voltage drop to a current? I = V/R. If you can plot the voltage vs. time or current vs. time and show me the discontinuity it will help me a lot, I tried doing it myself and I did not see any.

Also there is a good point to explain here in your code you have a DAQ assistant reading from the 6221, every time it finishes it has to compete the processing and then it goes and read again. Relay, Spectral measurement and write to LabVIEW measurement file are things that take time and in your while loop you have to finish all this before you go and read again. At 11 KHz you have aprox 1/11 KHz seconds to finish all these operations.   You can isolate the problem by reducing the amount of calculations and watching how the discontinuity goes away. If this is the problem your solution would be changing your design scheme. My favorite one is this one: Application Design Patterns: Producer/Consumer.

Let me know if it helps