Ice water temperature is measured at 2 degree C instead of Zero with my SCXI1102, SCXI-1303, and PCI6251 system

[HJH]

We recently acquired the NI system with the following configuration: PCI6251, SCXI1000, SCXI1102, and SCXI-1303. The system is up and running but I understand why the ice water temperature reading is 2 degree C instead of zero. I am using K-Type TC. Does the length of the TC degrade the accuracy? Is this just a zero calibration problem (if so how do I do that)?

Thanks of the help!

HJH

[devchander]

hi,

Just check for following

1. Make sure you are using proper Cold Junction Compensation  setings, your temperature measurement's accuracy largely depends on this single factor.SCXI 1102 comews with onboard(built in) CJC which is software selectable
2. ps: refer to this link http://digital.ni.com/public.nsf/allkb/5ca3a774944ddbd8862564eb0060234b
3. If you are using extender cables for thermocouple, make sure you are using proper compensation cables to increase the length of your thermocouple.
4. Thirdly, i suggest yopu cross verify with a higher temperature say 20 degrees too, this is to confirm wheather what you are assuming to be at 0 degree C  might not actually be at 0 degrees C!

regards

Dev

[wilvil2000]

HJH,

You should try to temporarily remove the 10MOhm Pull-up/bias resistor banks. If this solves the problem then read page four from the
Installation Guide.

http://digital.ni.com/manuals.nsf/websearch/9DA3B7D5C7F572F986256694004DEFE6

This talks about the possibility of current leakage from the open thermocouple circuit detection which may cause that type of error. I hope this helps.

Wil

Message Edited by wilvil2000 on 09-30-2005 02:52 PM