what i see in the voltmeter is not what the computer displays

[camb-rafael]

i am using a very simple VI that reads in continously a voltage. I am using AI acquire Waveform.vi function. However, the value displayed on the computer through this vi is not the same as that read by a voltmeter. When I test the DAQ card via the Measurement and Acquisition software using the Test Panel, and with the data mode "continuous" with a sample rate of 1000Hz, the voltage shown in the Test Panel agrees with the voltmeter. Therefore, I am assuming the problem is in the VI that I built,a nd probably in setting up the Acquire Waveform.vi function. Any suggestions?

[ycw7]

Hi

Is there the same method of wire between test panel and Acquire Waveform.vi ??

I mean Differential, RSN, NRSN

[camb-rafael]

the channel is set as referenced single ended, and this is displayed both in the channel in the vi as well as in the Measurement & Acquire Test Panel

[ycw7]

Hi,

would you paste your vi on the websit~

[camb-rafael]

i attach the vi as well as a picture

[Dennis_Knutson]

The first thing you should do is get rid of those AI Sample Channel functions. Each time you're calling them, it does an AI Config. What you should do at the beginning of the program is explicitly call AI Config and explicitly set the configuration for all channels to RSE. Then, inside the program, do an AI Single Scan for all channels - not a separate one for each channel. You should also do something similar to the AO Update Channel.

[camb-rafael]

I see what you are saying, but since I am a beginner, I cannt really get the wires to not be broken. I create an AI Config outside the loop and connect to it an I/O DAQ Name but the wire is broken. Also, when I replace the Sample Channel by the AI Single Scan, all my wires break. Suggestion? Thanks

[ycw7]

If you are beginning to use LabVIEW at the first time

maybe you could use DAQmx which is easy to use to measure analog signal

[tbob]

My guess is that you are getting broken wires because the lower level functions like AI Config require an array input for Channels.  Look at the attached vi.  I got rid of the high level functions and replace with low level functions.  This way, the DAQ gets initialized once, before the loop.  Inside the loop, all that is called are the actual read and write to/from the DAQ.  No need to re-config on every loop iteration.

If you move your mouse over the broken wire, a pop-up box displays a message about why the wire is broken.  Use this info to fix the problem.

[camb-rafael]

thanks for the vi. However, I couldn't open it since I only have version 6.1 and you saved it in v7.1. Can you save it in v6.1 and re attach it?

Thanks