7Tutorial
282 Keysight 34970A/34972A User’s Guide
To make a more accurate measurement, you should extend the copper test leads
of the internal DMM closer to the measurement and hold the connections to the
thermocouple at the same temperature.
This circuit will give accurate temperature measurements. However, it is not very
convenient to make two thermocouple connections and keep all connections at a
known temperature. The Law of Intermediate Metals eliminates the need for the
extra connection. This empirical law states that a third metal (iron (Fe) in this
example) inserted between two dissimilar metals will have no effect upon the
output voltage, provided the junctions formed are at the same temperature.
Removing the reference thermocouple makes the connections much easier.
This circuit is the best solution for accurate thermocouple connections.
Measurement
Thermocouple
Reference Thermocouple
Ice Bath
Internal DMM
Internal DMM
Measurement
Thermocouple
Ice Bath
(External Reference Junction)
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