National Instruments USB-TC01 - Cold-Junction Temperature Measurement Accuracy; Minimizing Thermal Gradients

Figure 8. NI USB-TC01 Software Open Thermocouple Message
Note During an open thermocouple condition, some invalid values may be
returned before the open thermocouple is reported.
Cold-Junction Temperature Measurement
Accuracy
Heat from other nearby heat sources can cause errors in thermocouple measurements by
heating up the terminals so that they are at a different temperature than the cold-junction
compensation (CJC) sensor used to measure the cold junction.
Minimizing Thermal Gradients
Thermocouple wire can be a significant source of thermal gradients if it conducts heat or cold
directly to terminal junctions. To minimize these errors, use the following guidelines:
• Use small-gauge thermocouple wire. Smaller wire transfers less heat to or from the
measuring junction.
• Avoid running thermocouple wires near hot or cold objects.
• If you connect any extension wires to thermocouple wires, use wires made of the same
conductive material.
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