DAQ Assistant does not read signals from SCXI 1000/SCXI1112

[MTU]

I am using two SCXI 1112 modules (Slots 3&4) in an SCXI 1000 chasis.  The digitizer is a SCXI 1600 (Slot 1).  There is a SCXI 1531 (Slot 2) not being used.   I am able to see the thermocouple signals when using the test panels in measurement & Automation explorer for the SCXI 1112s (for example on SC1Mod3/aio).  In test panel, the response is as expected for all channels on the SCXI 1112.   When I read the channels with DAQ Assistant, the data is bad -  all channels show the about the same values (approximately the Constant CJC value - no signal present) and noisy, even disconneted thermocouples give the same result.     Thinking that i had a software issue with DAQ assistant, I manually set up the channels using  DAQmx Create channel-DAQmx Timing-DAQmx Start Task-DAQmx Read chain, only to get the same results.   So, in summary, I can see the signals fine in the Automation Explorer test panels, but can't get the signals with Labview DAQMx or DAQ Assistant.  Below shows how the DAQ assistant is configured.

[visuman]

See i have worked with SCXI-1112 modules and was facing the same problem when i connect thermocouple to one channel others will also read the same value. Its because of grounding issue. connect other channels negative point to system ground.
And also take care input configuration

Regards

Visuman

[AdnanZ]

I would agree with that. Just make sure that you have set your channels right. Have a look at the following link and search for Table 1:

Field Wiring and Noise Considerations for Analog Signals

[MTU]

Thanks for the input.   I don't really understand how to ground the AI as shown in the link you provided. i am using thermocouples with K-Type plugs that plug directly into the SCXI 1112.   I am doubtful that this is the issue because I get a response to temperature change on the first channel (SC1Mod3/aio for example) and channel 2 (SC1Mod3/ai1) responds too, but when the thermocouple of channel 2 is heated, there is no response on either channel.  Plus, in MAX test panels everything works great - no ghosting and all channels repond like they should.    For some reason, Labview just isn't seeing what MAX sees.   I am attaching more snapshots of my block diagram.  As you'll see, i have tried accessing two channels on separate SCXI boards as well, but still with the same results.    The data out of DAQmx or DAQ assistant only has one channel's data, and it is always the first channel in the list.  

[aNIta B]

In response to Adnan's post, there's also this document that discusses the importance for grounding thermocouples.  To do so, you would just want to wire a resistor from the negative terminal to one of your ground lines. As well, thanks for posting a screenshot of your code- but I'm also wondering, have you tried using one of the LabVIEW examples?  In particular, I'd be curious if you get a good reading using an example like the one titled " Cont Acq Thermocouple Samples-Int Clk.vi". 

[VincentP.]

Hello,

I think I have the same problem: I use SCXI 1000 + 1102 + 1303.

my thermocouple are linked to ground  in 1303 box via resistors (factory settings).

With DAQmx: all my measures are a copy of the first one: (cf message 4 of this topic: it's the same of MTU's problem)

- if I heat #1, all measures go up.

- if I heat #2 ou any other else, nothing happen.

- all measures have a little noise.

I think MTU had the same problem, but I don't know how he resolves it.

Anyone has an idea ??

Many thanks

[VincentP.]

OK, I found a solution:

in DAQmx:

left pannel

> SCXI 1000

 > properties

 > "chassis" tab (I don't know the right word in english)

 > make sure that you specifie the right PXI card and the right SXCI card were the communication device is (SCXI 1349 for me).

I hope this can help somebody else.

[MTU]

The issue is still unresolved.  After several days of troubleshooting, I think that it is a hardware incompatability with Labview (SCXI-1000 with SCXI-1600 A/D board just doesn't seem to work with Labview).   In additional to the thermocouple problems mentioned above, I am unable to get any response out of my SCXI-1531 board wtih a 0-5 VDC input.   There's more at issue here than just properly grounding the thermocouples.   I would like to know if anyone else has had success using this hardware combination with Labview 8.5.   A few years ago I used this SCXI-1000 and these SCXI conditioning boards with great success with my PCMCIA E-Series A/D card, but when NI dropped support of this E-Series device with Labview 8.5, we were forced to use the slower SCXI-1600 board in the SCXI-1000 as a work-around, without much success.    As for the above comment of using NI example code, yes I have tried many all with the same results.    Still looking for help if anyone has had experience with these issues.

[VincentP.]

Well,

I think "chassis" (in French) is "Frame" in English and is the metalic box where you put your cards.

Did you check my solution ?

Maybe it's "just" this, cause our problems were very similar.

Vincent

[VincentP.]

And I forget:

I use this configuration:

PXI with a PXI6221

PXI 6221 is connected to SCXI1000 with a 1349 connector.

In my case, the 1349 was specified (in DAQmx) on a wrong slot (I use 2 SCXI acquisition card).