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data aqusition of Vac with usb-6259

1.I am having problems with meaqsuring AC signal 400 hz. THe reading is juping all the time. When I conect a normal voltmeter every thing is ok.
2. I am having problem with reading of data flow from rvdt again the same problem. How can I buld a software signal conditioner or I need hardware one
 
our device is usb-6259.
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Comparing DAQ readings with a meter can be tricky for a lot of reasons. To begin with, what is your sample rate and period? Because the signal you're reading is an AC source it's level is constantly varying (at a 400 Hz rate Smiley Wink ).  Hence, you need to sample enough of a waveform that you can calculate the appropriate AC parameter (peak-to-peak, RMS, or what have you).

Also remember that meters always have a certain amount of built-in hysteresis or dampening to make the output easier to read.

Mike...


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Hi,

Also make sure that your sampling frequency is at least twice the sampling bandwidth(Nyquist Theorem). For a very accurate signal you may try a sampling frequency of around ten times the sampling bandwidth.
Signal Conditioning can be done in both hardware and software. It is traditionally done in hardware using NI products but you do have the option of setting up a lowpass filter in LabVIEW to act as signal conditioning. I hope this helps!
Regards,

Ima
Applications Engineer
National Instruments
LabVIEW Introduction Course - Six Hours
Getting Started with NI-DAQmx
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