To make a more accurate measurement, the copper test leads of the
meter should be extended closer to the measurement and the connections
to the thermocouple be held 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 the 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
Meter
Ice Bath
Meter
Ice Bath
REFERENCE THERMOCOUPLE
7
Chapter 7 Measurement Tutorial
Measurement Techniques and Sources of Error
267
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