Turning IEPE OFF (DC Coupling Mode)

[AT12]

Hi,

Sorry in advance if I have put this posting in the wrong place.

I have a USB-4431 and use it in Voltage Setting (the only setting that makes sense for what I am doing). How do I turn the IEPE off in DC Coupling?

The IEPE is currently providing an unwanted 2.2 V on the AI0 channel and I can't find an option to turn Iex to None.

Many thanks,

AT12.

[ShalimarA]

Hi,

It seems as though you can alter the IEPE settings programatically or by configuration settings in MAX. The following KnowledgeBase article goes through how to enable or disable IEPE settings using both methods.

'How Do I Enable IEPE Excitation Programatically?'

http://digital.ni.com/public.nsf/allkb/D2D5A38279AA1431862576F20061DEEF?OpenDocument

[AT12]

Hi,

Thanks for the reply.

I've tried doing this both ways and failed. I'm uNsure how to incorporate the DAQmax into my existing vi. I've put a lot of work into my working vi and don't want to have to start from scratch with it (as well as not having the time). Could you look at my vi (attached) and wire this DAQmx in place of the current DAQ Assistant? It would be a tremendous help.

Any ideas why there isn't an option in the Voltage DAQ Assistant for Iex = None? It would be very handy to just switch this off, perhaps it should be included in future versions?

Many thanks,

AT12

[ShalimarA]

Hi,

You can convert the DAQ Assistant into low level DAQ code by using the following instructions. Here, you'll be able to follow the provided article in order to disable/enable IEPE. 

'Generating code using the DAQ assistant'

http://digital.ni.com/public.nsf/allkb/921A6DC1393E3CEC862577FF0074A68B?OpenDocument

In terms of there not being the port that you require on the DAQ Assistant, perhaps you can suggest it on the LabVIEW Idea Exchange?

http://forums.ni.com/t5/LabVIEW-Idea-Exchange/idb-p/labviewideas

[AT12]

Hi,

Thanks again for replying, and I will do my best to follow the instructions in the article. I'll let you know how I get on!

Good idea, I'll post something about it when I get time.

AT12

[AT12]

Dear Shalimar,

I've tried to do what you suggested and thought I'd succeeded. However, when I checked with a multimeter, there is still 2.281 VDC coming out of AI0. I've attached the vi (my) and the subvi (untitled 4), could you look at what I've done and tell em where I've gone wrong please?

Many thanks,

AT12 

[AT12]

Any chance you could take a look at the vi?

Thanks,

AT12.

[ShalimarA]

Hi AT12! 

I haven't forgotten you! I'm still looking into the best way to do this and have a few ideas that I will update you with.

[ShalimarA]

Hi, 

I have a few questions. I've looked at the first VI you attached and am having trouble understanding where the issue lies. What was the need for the section of code within your loop that had a DAQmx Create Task connected to the sample clock and start task? This isn't connected to anything so when I simulated the device and ran the code, an error occured.

Also, in your DAQ Assistant, you were reading a current. I thought that you meant that you were reading a voltage on AI0?

When I changed the DAQ Assistant to read voltage, I received a reading without any DC Offsets, as per the attached image. 

Can you clarify where you see the offset? 

[AT12]

Hi!

Thanks for getting back to me.

I have a few questions. I've looked at the first VI you attached and am having trouble understanding where the issue lies. What was the need for the section of code within your loop that had a DAQmx Create Task connected to the sample clock and start task? This isn't connected to anything so when I simulated the device and ran the code, an error occured.

Ignore this - doesn't run as an error for me so I've never cleaned it up.

Also, in your DAQ Assistant, you were reading a current. I thought that you meant that you were reading a voltage on AI0?

I'm using a transimpedance amplifier, so the DAQ sees a voltage signal. Therefore I'm ultimately measuring current, which is why I factor a gain correction in my vi.

When I changed the DAQ Assistant to read voltage, I received a reading without any DC Offsets, as per the attached image.

Can you clarify where you see the offset?

I have a BNC connected to AI0, with the end of this cable terminated by two crocodile clips. A multimeter is connected between these clips and it reads ~ 2.2 V DC. I need to get rid of this.

Hope this helps,

AT12.