Are the 'thermocouples' traveling on the belt through the furnace, or are they measuring 3 points in an oven (i.e.: three places along the oven, as I assume this is a long belt oven)?
A thermocouple is two pieces of special wire which are welded together. There are different types each of which is for a specific temperature range. The ends of these wires are attached to a measurement device which measures electrical potential. Some people call the wire and the measurement device a 'thermocouple', but I'm from the old days where a thermocouple was the welded wire junction.
Thermocouple
There are devices which are a compact, single 'box' which can be run through an oven with a lot which internally records, or transmits to an external analyzer, the temperature as the device proceeds through an oven with a lot.
I need more specific information on what you're referring to - Spot measurements at places in an oven, or a device which actually goes through the oven with the lot.
** I assume this is a belt oven (long oven). Or, is this one big stationary oven?