I can't get a zero voltage from my SCXI-1100

[superspy]

Morning all,

I'm using an SCXI-1100 with a 1303 terminal block for data aquisition.  For some reason I can't seem to get a zero voltage, instead I seem to have a fairly consistent 80 uV offset.  I've tried different channels and they're all the same.  I also tried a different 1100 module, which for some reason gave me the same offset but negative!? Does anyone have any ideas as to what I can do about this? I'm not happy with this amount of offset as it relates to 2 degrees in temperature for my thermocouples.

Also another quick question......the 1303 terminal block has a thermistor integrated for cold junction reference for thermocouples.  How do I use this? I tried using the SCXI temperature scan VI but couldn't get it to work, I only have thermocouples (K-type) on 10 of the channels.

Any help with these issues would be very much appreciated!

Thanks, 

Anna 

[AEI_JR]

Anna,

What programming platform are you using?  Also, do you have the latest driver set for DAQmx?

In MAX, you should be able to create a task (Data Neighborhood > NI-DAQmx Tasks, right-click, Create New NI-DAQmx Task) .  Select Acquire Signals > Analog Input > Temperature > Thermocouple.

Select the channels on the SCXI-1100 you are using for data acquisition.  Name the task, then for each channel, select the input range, units and TC type.  Setting the CJC source to Built-in will reference the TC signals to the 1303's thermistor.  Run the task to test your measurement.  If you're using LabVIEW, you can drop this task in, and even have LabVIEW generate the code.

JR

[superspy]

Hi JR

Thanks for getting back to me.  I'm running running on LabVIEW 8.2 and as for the drivers, I'm not really sure but it was all installed on my computer in the last 6 months or so.  I have tried self calibrating the PCI card and I have tried changing the pull up and bias resistors but nothing seems to make a difference.

The help with the thermocouples is much appreciated, I should have been able to work that one out for myself really, I was obviously in another world! 

Thanks

Anna 

[Andrew McL]

Hi JR,

Judging from the information that you have given, I would suggest that you need to calibrate this device. I don't know if you have this document but it details a lot of the technical information. I have attached the manual to this post. If you refer to Page A-2, you'll see that the input voltage uncalibrated is 70uV. If you then look at pages 3-12 onwards, this details the calibration procedure. 

All of this information can be found  in the attached 1100.pdf file. 

If you are concerned about upgrading your DAQmx drivers, you can find the latest DAQmx driver here

Hope this helps,