NI 9211 Accuracy Reading

[arbelaezc]

Hi,

Here's my setup:

-developing code using LabVIEW 2012

-cDAQ-7142 with NI-9211 (calibrated) TC module using J-type TC

-measuring temperature range from 0-100 deg C

I am developing an ATE for a controller my company is developing. The product has a heater output and a TC input (J-type) to read the temperature of a material (in my case, a block of aluminum) that the heater is affecting. The ATE is my reference sensor to prove the temp. accuracy of the electronics in our product. For some reason, my NI-9211 is reporting a temperature reading that is > +/- 2 deg C that the IC is reporting back. The 9211 is calibrated & the ambient temp range is within the bounds that I don't need autozero enabled. I've searched the forums about CJC references and any other settings I might apply to both the module and my VI but still have a big gap in temperature readings.

I've used a FLUKE 87V with a K-Type TC connected and is reporting temp. readings within a +/-1 deg C. accuracy from the IC on the controller.

Any suggestions?

[johnsold]

Type K thermocouple table, printed by Omega from data published by NIST:

"LIMITS OF ERROR

(whichever is greater)

Standard: 2.2°C or 0.75% Above 0°C

2.2°C or 2.0% Below 0°C

Special: 1.1°C or 0.4%"

I do not have the Type J table handy but I think the limits of error are similar.

Getting temperature measurements with less than +/-1 degree error with thermocouples requires considerable care and definitely requires system level calibration.  Not easy.

Lynn

[Prickly_Pear]

It might be good to consider using an RTD for your measurements rather than a thermocouple. This document explains the difference between the two:

http://www.ni.com/white-paper/3778/en/

Jeremy P.

[arbelaezc]

Unfortunately, I need to use a thermocouple for my application since I am verifying my controller's TC read back accuracy (which the IC has a tolerance of +/- 2 deg C) with my ATE. I'm still researching my solution and will (hopefully) post it here when I get one. Thanks all again.

Cristhian

[johnsold]

While the controller needs a thermocouple, you could use an RTD for the tester.

Lynn