Measurement Computing 6222 - Manual (Page 16)

3-4 Thermocouple Input 897690 6222 User ’s Manual
Cold-Junction Temperature Accuracy
Heat dissipated by the 6222’s internal circuitry and other nearby heat sources can heat up the unit’s terminals,
placing them at a different temperature than that of the cold-junction compensation sensor. The thermal
gradient generated across the terminals can cause terminals of different channels to be at different
temperatures; the resulting measurement creates errors not only in absolute accuracy but also in the relative
accuracy between channels.
The accuracy specifications (presented in Chapter 8) include the errors caused by the gradient across the
module terminals, and assume the use of properly installed connector backshells.
Minimizing Thermal Gradients
Thermocouple wire can be a significant source of thermal gradients if it conducts heat or cold directly to the
terminal junctions. To minimize these errors follow these guidelines:
Use small-gauge thermocouple wire. Smaller wire transfers less heat to or from the measuring
junction.
Run thermocouple wiring together near the screw-terminal connector to keep the wires at the same
temperature.
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.
Install connector backshells.