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4 Documentation Number TCDA0997 Manual
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
The error caused by the thermocouple non-linearity over the
-50
°C to 200°C range is relatively small, so it is ignored in the
factory calibration of the TCDA. If more accurate readings must be
taken, the following techniques can be used:
1. If all temperatures are taken near a certain temperature,
calibrate the TCDA at that particular temperature.
2. Implement a look-up table in your software program to
correct for error.
3. Use a piece-wise linear model for your thermocouple output
to correct for error.
The terminal blocks on the TCDA and the leads of the
thermocouple bead are made from dissimilar metals. This creates a
second, unwanted thermocouple at the terminal blocks. This
unwanted thermocouple is called the cold junction. The temperature
of this cold junction will affect the results of the actual thermocouple.
The TCDA has cold junction compensation that automatically
corrects for small changes in the cold junction temperature. It is
important that nothing comes in contact with the terminal blocks or
the two external diodes near the terminal blocks as this may cause
large, rapid changes in the cold junction. The cold junction should
be kept at a constant temperature, if possible.
Different types of thermocouples are made by joining a wide
variety of metals. The TCDA is designed to amplify K-type
thermocouple only. Thermocouples have a positive(+) and a
negative(-) lead. These two leads must be connected to the correct
terminals on the TCDA module. Connections will be covered in the
next chapter.