DMM current measurement doesn't work when there is a DAQ analog input in the system definition.

[jaime_c]

I have a very simple custom device to measure current using an NI-4070 DMM.  The custom device is based off the LabVIEW example Measure DC Current.  By itself the custom device works to measure current, but if an analog input is added to the system definition using the native DAQ the current measurement channel remains 0 through the entire execution.

Does anyone know how to make the DMM measurement work alongside an analog input?

[Eric-E]

Hi Jaime,

A bit more clarification regarding what your custom device is would help. It is a custom program or a physical hardware device? What is the configuration when the device works by 'itself'?

Thank you,

Eric E.

[jaime_c]

"Custom Device" is the term used in VeriStand for a LabVIEW application that runs within the VeriStand engine, so it's a program.  This particular program is basically the example I mentioned put into the template real time driver vi ... the template real time driver vi being another VeriStand / Custom Device tool.

"By itself"means when the Custom Device is the only thing in the VeriStand System Definition - either before the analog input is added or after it's deleted.  The Custom Device also works well with other Custom Devices we have for power supply, DAQ, and data processing - it just doesn't work with the native DAQ Analog Input.  For all I know it might not work with other native DAQ functions either.

[Kilometers]

Hi Jaime,

It's hard to tell what's going on since this is custom code of yours. One possible cause may be that when you add DAQ to your system definition it is changing the timing source for your controller. Have you tried checking your timing source before and after adding the DAQ device? Also do you have any other indications of errors besides a 0 coming in on the DMM custom device? Are there any errors on deployment?

[jaime_c]

I didn't notice any changes in the Conroller page of the System Definition but several options are added to the Chassis page when the DAQ is added.  The screen shots are attached.

Can you tell me why those would prevent the measurement from the DMM?

There are errors reported on the monitor for the chassis.  The real time driver calls a vi to print errors with every loop iteration.

[Kilometers]

Hi Jaime,

Could you post your block diagram code for your custom device, either as the VI itself or as a screenshot? It is also important to know what type of custom device you are using. You can find information about the different types here if you need it.  Also could you let us know what errors you're seeing. An error message and number may shed some light on what's going on. Finally, what resolution and speed are you trying to sample at?  

[jaime_c]

I'm sorry I meant to write there are no errors reported.

I will post the custom device code soon.  It's an Asyncronous custom device.

[jaime_c]

The driver vi and a zip file containing the source directory for the custom device are attached.

[Kilometers]

Hi Jaime,

I have a few quick questions for you.

1) What current levels are you expecting to be coming into the device?

2) Have you tried slowing down the DMM measurements? Do you see any differing results if you do so?

3) Is it specifically AI channels that cause this problem, or do other DAQmx channels cause the problem as well?

4) What PXI Controller are you working with?