Agilent Technologies Switch/Measure manual Thermocouple Measurements, Type thermocouple

Features and Functions 2

Thermocouple Measurements

•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 (34921A only), an external thermistor or RTD measurement, or a known fixed junction temperature.

•The internal reference junction source is valid only on channels 1 through 40 on the 34921A with the 34921T terminal block installed.

•If you select an external reference, the instrument makes thermocouple measurements relative to a previously- stored RTD or thermistor measurement stored in a reference register. To store a reference temperature, first configure a multiplexer channel for an RTD or thermistor measurement. Then assign the measurement from that channel as the external reference. When you initiate a measurement on an external reference channel, the acquired temperature is stored in volatile memory in the reference register. Subsequent thermocouple measurements use the stored temperature as their reference. The temperature remains in memory until you measure a subsequent external reference value in the reference register or remove the mainframe power.

•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 (you must maintain the known junction temperature). The internal isothermal block reference (34921A only) requires no external wiring but provides lower accuracy measurements than a fixed reference.

•The thermocouple check feature allows you to verify that your thermocouples are properly connected 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).

34980A User’s Guide 31