Temperature Measurements; Thermocouples - Keithley 2750 User Manual

Model 2750 Multimeter/Switch System User's Manual

Temperature measurements

The Model 2750 can measure temperature using thermocouples, thermistors, and 4-wire
RTDs. When deciding which temperature sensor to use, keep in mind that the thermocou-
ple is the most versatile, the thermistor is the most sensitive, and the 4-wire RTD is the
most stable.

Thermocouples

For thermocouples, temperature measurement range depends on which type of thermocou-
ple is being used. Thermocouples that are supported include types J, K, N, T, E, R, S, and
B.
Type
K
N
T
E
R
S
B
When two wires made up of dissimilar metals are joined together, a voltage is generated.
The generated voltage is a function of temperature. As temperature changes, the voltage
changes. The thermocouple voltage equates to a temperature reading. This is the basic
operation principle of the thermocouple.
NOTE
When you connect a thermocouple directly to the input of the Model 2750, at least one of
those connections will be a junction made up of two dissimilar metals. Hence, another
voltage is introduced and is algebraically added to the thermocouple voltage. The result
will be an erroneous temperature measurement.
To cancel the affects of the unwanted thermal voltage, the thermocouple circuit requires a
reference junction that is at a known temperature.
Range
J -200°C to 760°C
-200°C to 1372°C 0.001°C
-200°C to 1300°C 0.001°C
-200°C to 400°C
-200°C to 1000°C 0.001°C
0°C to 1768°C
0°C to 1786°C
+350°C to 1820°C 0.1°C
The equation to calculate thermocouple temperature is provided in
Resolution
0.001°C
0.001°C
0.1°C
0.1°C
Basic DMM Operation
Appendix
3-25
F.