Thermocouple sensors are meant to provide a single measurement to a system an not meant to be connected to one measurement channel. When more than one measurement is needed, dual thermocouples provide that extra measurement signal.
When splicing thermocouples into an existing application, keep in mind that:
Omega does not recommend that thermocouple wires be soldered. With the exception of the Type T copper leg, thermocouple alloys do not solder easily. It is possible to solder these materials, but very aggressive flux is typically needed to remove oxides from the surfaces during soldering. If soldering is done, then it is important that the flux is completely cleaned from the wires, and a close inspection for cold solder joints is made.
The conductors in Type C thermocouples will readily oxidize when exposed to soldering temperatures in the presence of oxygen.
When thermocouple cables must be extended, Omega suggests the use of thermocouple connectors or other mechanical means. This helps to insure that the polarity is maintained (since the connectors have the polarity marked on them), thermocouple connectors are keyed to insure that they only go together in the correct manner.