National Instruments NI USB-TC01 Bedienungsanleitung Seite 9

During an open thermocouple condition, some invalid values may be returned before
Note
the open thermocouple is reported.
Cold-Junction Temperature Measurement Accuracy
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If an open thermocouple is detected, the NI USB-TC01 software displays a
message and lists the internal CJC temperature, as shown in Figure 8.
Figure 8. NI USB-TC01 Software Open Thermocouple Message
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 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.
9 NI USB-TC01 User Guide and Specifications