Applying Thermocouple Calibration Corrections - CAS DataLoggers

Applying Thermocouple Calibration Corrections
Utilizing the dataTaker DT80 Intelligent Universal Data Logger
CHESTERLAND OH—November 10, 2011
To improve the accuracy of thermocouples, it’s common to have them calibrated by a calibration lab. In
this particular scenario, a calibration lab has already provided you with certificate which identifies
calibration data at certain temperatures, and you want to apply these calibration connections. All you
need are a dataTaker DT80 range data logger, the thermocouples with their calibration certificates, and
a PC running Microsoft Excel.
To apply these calibration corrections in the dataTaker data logger, you’ll utilize polynomials, but first
you must generate the polynomial. The technique is to calculate a polynomial equation to calculate the
adjustments. To calculate the polynomial factors, the results from the calibration lab are expressed as
corrections at the measured temperatures. An example of this calibration data is given below:
Thermocouple Test Temp Measured Temp Correction
1 -50.40°C -47.30°C -3.10°C
2 0.04°C -0.70°C 0.74°C
3 200.85°C 202.40°C -1.55°C
4 301.10°C 298.40°C 2.70°C
Open Excel and enter the ‘Test’ and ‘Measured’ values into two columns. Now use the Chart Wizard in
Excel to create an XY scatter graph using the data that you just entered. Add a trend line to the graph by
right-clicking on one of the graph points and choosing ‘Add Trendline’, or using the Trendline Wizard in
the ‘Layout’ tab in Excel 2007 and 2010. For trendline type, choose polynomial and set the order to 5. In
Excel 2007 and 2010, make sure you check the ‘Show equation in chart’. In Excel 2003, click on the
‘Options’ tab in the Trendline window and check the ‘Show Equation’ box.
To add the polynomial to your DEX program, go to the thermocouple input in the DEX web interface and
click on the ‘Scaling’ tab. Click on ‘Add’ and choose ‘Polynomial’. Enter the coefficients for each of the
‘x’ variables in the K boxes. (Note: The factors are listed in reverse order in the DEX software). Now
simply save the program to the datalogger and check your values to make sure that everything is in the
correct range.
For further information on the dataTaker DT80 Intelligent Universal Data Logger, other dataloggers in
the highly successful dataTaker line, or to find the ideal solution for your application-specific needs,
contact a CAS Data Logger Applications Specialist at (800) 956-4437 or visit the website at
www.DataLoggerInc.com.

Contact Information:
CAS DataLoggers, Inc.
12628 Chillicothe Road
Chesterland, Ohio 44026
(440) 729-2570
(800) 956-4437
sales@dataloggerinc.com
http://www.dataloggerinc.com