7Measurement Tutorial
296 Keysight 34420A User’s Guide
Thermocouple Measurement Errors
The meter allows you to use one of three types of temperature reference for
thermocouple measurements:
– Fixed Reference value (entered). The fixed reference is the most accurate, and
is the type of thermocouple measurement described earlier using isothermal
blocks and an external known reference temperature.
– Measured Reference value (external thermistor). A thermistor is connected
to channel 1 input of the meter. The thermistor is then mounted to the
isothermal block. The meter measures the temperature of the isothermal block
and uses the measurement in the temperature calculation.
– Internal Reference value (internal thermistor). The meter contains an internal
thermistor, mounted just behind the input connector. The internal thermistor is
the least accurate way to measure temperature. If you use the internal
thermistor, you should connect the thermocouple wire directly to the input
connector (do not use the copper test leads or an isothermal block). See
page 299.
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