I can't get the voltage measured by voltmeter.

[Jshen6]

Hello,

When I use the VI "Cont Acq&Graph Voltage - Write Data to File (TDMS).vi" to show the voltage from NI PCI6251, the voltage is around -5V. However, the voltage I measured by voltmeter from the chanels on PCI 6251 is around 0.3. Also, when I use other VI to show the voltage, it is around -5V too. I don't know what is the problem. Thanks a lot.

[LV_Pro]

There can be a number of things at play here, including scaling, how the DAQ device is connected, what the "signal" looks like. Do you have the Measurement and Automation Explorer (MAX) installed. If you are using National Instruments DAQ hardware that is almost a certainty. If so, click on it and look for your device. There will be screens that allow you to run the device to make measurements without a LabVIEW program. Running this can reveal a lot of interesting "stuff" like whether the connection method is allowing a large amount of "noise", which the meter, with a slow response wouldn't display. Is the signal supposed to be a DC level? Give MAX a try and report back the results. A screen capture of the MAX, saved as a ".png" file might be helpful too.

[Dennis_Knutson]

Have you done any of the basic trouble shooting mentioned in similar posts? Did you look at similar posts?

You could have a wiring error. You don't mention the channel or the physical pins you are using. You also don't mention the input configuration (RSE/DIFF) and whether you tried changing that.

[Jshen6]

I ran PCI6251 in MAX. When input configration is RSE, the voltage showed is around 0.3 v similar with the voltmeter. But when input configration is Differential, it is -10v, this is neither labview value nor voltmeter value.

When I use labview VI, the voltage is around -5v.

What can I do now? Can I change the input configration in Labview?

Thanks a lot.

[Dennis_Knutson]

Of course you can change the configuration. Don't you have Context Help turned on? Have you even looked at the inputs for the DAQmx Create Channel function.

[GerdW]

Hi Jshen,

both MAX pics show "differential" measurements, regardless how you named the pics...

[Jshen6]

Sorry. This is the RSE. I not good at programing. Could you tell where should I change in program? Or if there is an example? Thanks.

[GerdW]

Hi Jshen,

configure a DAQ assistent with the same settings as those in MAX. It should give the same outputs.

When the DAQ assistent runs fine you can open it's front panel to convert it in a "standard" VI. Then you can look at the block diagram to see the internals...

[Jshen6]

I changed the input channel configration into RSE. But it said two terminals are not match. Where else can I change?

[GerdW]

Hi Jshen,

I would clean up those broken wires... Doh! Do you read what the error message says?

Btw. where did you change to RSE?