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THERMOCOUPLE CALIBRATION PROCEDURE
B
GENERAL
This procedure describes how to calibrate a thermocouple for use with the Model 1140A during
its alignment and calibration. It involves immersing the cold junction in an ice bath and the hot
junction in a stable bath set to approximately 26°C. This temperature is chosen because it is the
operating temperature of the thermocouple connector and the binding posts of the Model 1140A.
Once the error of the thermocouple, if any, has been determined, the junction made is clipped
open so that the thermocouple can be connected to the Model 1140A for alignment or calibration.
EQUIPMENT REQUIRED
1.
Digital multimeter (DMM), Hewlett Packard Model 3458A or equivalent.
2.
Ice-point bath for thermocouple cold junctions with an expanded uncertainty (k=2) of
0°C ± 0.006°C or better.
Stirred bath, Hart 7025 or equivalent. An equivalent must be settable to +26°C.
3.
4.
Platinum Resistance Thermometer (PRT) with expanded uncertainty (k=2) of
±0.006°C or better at 26°C and with its resistance table for temperatures of 20°C to
30°C.
PROCEDURE
1.
Using Special Limits of Error (SLE) thermocouple wire,
such that the hot junction is made by welding (or twisting and soldering) the pair of
thermoelements together. If soldering, the overall length of the portion twisted and
soldered should be no more than 0.25 inches. The cold junction is made with
terminations to copper wire inserted in the ice-point bath. The thermocouple is
calibrated with the hot junction at +26°C. See Figure
DMM can be alternately connected to the PRT and the thermocouple copper
connections.
2.
Set the stirred bath to 26°C and allow it to stabilize.
5 This assumes a laboratory temperature of 23ºC during the alignment and calibration of the Model 1140A. If the
laboratory temperature is different, the wire should be calibrated at 3ºC above the typical laboratory temperature.
6 Special Limits of Error thermocouple wire is available from several sources including the following:
B. J. Wolfe Enterprises, Inc.
P. O. Box 1303
Agoura Hills, CA 91301-3380
800-554-1224 or 818-889-8412
Fax: 818-889-8417
Web site:
www.bjwe.com
APPENDIX B
Omega Engineering Inc.
P. O. Box 4047
Stamford, CT 06907-0047 USA
800-848-4286 or 203-359-1660
Fax: 203-359-7700
Web site:
www.omega.com
B-1
6
fashion the thermocouple
B-1
for the correct setup. The
5
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