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
MEASUREMENT
THERMOCOUPLE
REFERENCE
THERMISTOR
ISOTHERMAL BLOCK
REFERENCE
TEMPERATURE
METER
Chapter 7 Measurement Tutorial
Measurement Techniques and Sources of Error
268
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