User`s guide

271

Chapter 7 Tutorial

Measurement Fundamentals

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

Measurement

Thermocouple

Ice Bath

(External Reference Junction)

34970A Refresh UG.book Page 271 Wednesday, February 17, 2010 12:34 PM