Features and Functions 4
Keysight 34970A/34972A User’s Guide 137
Thermocouple measurements
To connect a thermocouple to the module’s screw terminals, see page 39.
– The instrument supports the following thermocouple types:
B, E, J, K, N, R, S, and T using ITS-90 software conversions.
The default is a J-Type thermocouple.
– Thermocouple measurements require a reference junction temperature. For
the reference junction temperature, you can use an internal measurement on
the module, an external thermistor or RTD measurement, or a known fixed
junction temperature.
– If you select an external reference, the instrument automatically reserves
channel 01 on the multiplexer in the lowest slot as the reference channel
(thermistor or RTD measurement). If you have more than one multiplexer
installed, channel 01 on the module in the lowest slot is used as the reference
for the entire instrument.
– Before configuring a thermocouple channel with an external reference, you
must configure the reference channel (channel 01) for a thermistor or RTD
measurement. An error is generated if you attempt to select the external
reference source before configuring the reference channel. An error is also
generated if you change the function on the reference channel after selecting
the external reference for a thermocouple channel.
– If you select a fixed reference temperature, specify a value between
-20 °C and +80 °C (always specify the temperature in °C regardless of the
temperature units currently selected).
– The accuracy of the measurement is highly dependent upon the thermocouple
connections and the type of reference junction used. Use a fixed temperature
reference for the highest accuracy measurements. The internal isothermal
block reference provides the lowest accuracy measurements. For more
information on reference junction temperature measurements and associated
errors, see the sections on pages 278 and 286.
–The thermocouple check feature allows you to verify that your thermocouples
are properly connected to the screw terminals for measurements. If you enable
this feature, the instrument measures the channel resistance after each
thermocouple measurement to ensure a proper connection. If an open
connection is detected (greater than 5 kΩ on the 10 kΩ range), the instrument
reports an overload condition for that channel (or displays “OPEN T/C” on the
front panel).
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