Keithley 2182 User Manual page 44

2-4 Voltage and Temperature Measurements
NOTE
In order to make accurate temperature measurements, the thermocouple connections
(reference junction) have to be maintained at a known temperature. You have the option to use
the internal reference junction, or an external simulated reference junction. These reference
junctions are discussed as follows:
Internal Reference Junction — The internal reference junction of the Model 2182 is the
input connector. A temperature sensor is located inside the unit, adjacent to the input connector.
The sensor is measured continuously to maintain accuracy.
Thermocouple connections (reference junction) have to be made at the input connector of the
Model 2182. To utilize the internal reference junction, the thermocouple wires must be soldered
directly to a LEMO connector that mates to the input connector.
A disadvantage of using the internal reference junction is the connection requirements. You
cannot use the supplied input cable as is. You will have to modify the cable or use a separate
LEMO connector (Model 2182-KIT).
Simulated Reference Junction — An external apparatus, such as an ice bath, can instead be
used for the reference junction. The thermocouple wires are connected to the copper lugs of the
supplied input cable. The connection points are then immersed in the ice bath. The temperature
of the ice bath must be entered into the Model 2182 as the simulated reference temperature.
The Model 2182 can also measure its internal temperature. Whenever the internal
temperature changes more than 1 degree, an ACAL must be performed to maintain
specified accuracy. See "Performance
section) for details.
considerations, ACAL procedure" (in this