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.
Ice Bath
Reference Thermocouple
Measurement
Thermocouple
Internal DMM
Measurement
Thermocouple
Ice Bath
Internal DMM
(External Reference Junction)
8
Chapter 8 Tutorial
Measurement Fundamentals
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