My USB 6229 showing wrong datas

[kirupacae@gmail.com]

Dear friends,

I am using USB 6229 for my analog voltage aquistion and generating pulses. In the aquistion, the voltage values shows incorrect, since i measure the voltage value is 3mv but it shows 2V sometime 9V sometime. How i check my USB work properly. This problem for kind of inputs like differential, RSE.

Thanks,

Kirupasankar S,

India

[Neal M]

Hello Kirupasankar,

The test panel you are using is the most direct way to test what the hardware is seeing.  From your picture, I have a couple reccomendations of things to try to help troubleshoot your signal.  First, the min/max input limits should be closer to the size of signal you are trying to read (e.g. 0 to 10mV).  Since the analog digital converter has a finite number of "steps", changing these limits will change the gain into the ADC which increases the resolution and may make your reading more accurate.



Another thing to check is to make sure that your signal is hooked up correctly.  The attached diagram, which I found here, is a good summary. The same article also covers some noise issues that may be affecting your signal. 

The noise pattern looks like a resolution issue, but the large magnitude is a little odd.  In order to get a better idea of what the noise looks like, it might be a good idea to use Finite aquisition instead of On Demand and maybe use a higher sampling rate.

Message Edited by Neal M on 10-29-2007 03:12 PM

[zsolt.trenyik]

Neal M,

I read your  answer, thanks for it, but I have still the same promlem... I have a FUG power supply with voltage monitor output, which is a 0-10V signal. I would  like to measure this 0-10V with an USB-6229 AI. from the guide, I connected just the sign to the AI0 and the gnd to the gnd. In the software, I configured the RSE mode with 0-10V limits.

The problem is, that if I had to get for example 5,5V, in average the max test panel (or my application) shows the right valu, but it is moving around this value, from e.g. 5,3 to 5,6. if I measure this return voltage with a fluke multimeter, it doesn't chage at all (1/1000 precision). I made a test with a 9V-battery (its voltage is surely fix), it shows the same result (moving in the mentioned range).

What could be the problem here? In the max test panel I tried the other modes, too, but without any really good result.

thank you for the answer!