Measurement Tutorial 7
Keysight 34420A User’s Guide 293
This circuit is the best solution for accurate thermocouple connections.
In some measurement situations, however, it would be nice to remove the need
for an ice bath (or other fixed external reference). To do this, an isothermal block is
used to make the connections. An isothermal block is an electrical insulator, but a
good heat conductor. The additional thermocouples created at J1 and J2 now
held at the same temperature by the isothermal block.
Once the temperature of the isothermal block is known, accurate temperature
measurements can be made. Typically, a thermistor is mounted to the isothermal
block and used to measure the temperature.
Thermocouples come in a variety of types. The type is specified by a single letter.
The following table shows the most commonly used thermocouple types and
some key characteristics of each.
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