conversion from the voltage generated to the temperature of the junction can be made. For example, a
voltage measurement of a T-type thermocouple (made of copper and constantan wire) might look like this
Notice, however, that the connections made between the thermocouple wire and the internal DMM make
a second, unwanted thermocouple where the constantan (C) lead connects to the internal DMM’s copper
(Cu) input terminal. The voltage generated by this second thermocouple affects the voltage measurement
of the T-type thermocouple.
If the temperature of the thermocouple created at J2 (the LO input terminal) is known, the temperature of
the T-type thermocouple can be calculated. One way to do this is to connect two T-type thermocouples
together to create only copper-to-copper connections at the internal DMM’s input terminals, and to hold
the second thermocouple at a known temperature.
An ice bath is used to create a known reference temperature (0 °C). Once the reference temperature and
thermocouple type are known, the temperature of the measurement thermocouple can be calculated.
The T-type thermocouple is a unique case since one of the conductors (copper) is the same metal as the
internal DMM’s input terminals. If another type of thermocouple is used, two additional thermocouples are
created. For example, take a look at the connections with a J-type thermocouple (iron and constantan):
4Measurement Tutorials
186 Keysight DAQ970A User's Guide
To Next Page
Loading...
Need help?
General