The TC-120 is expecting a cold junction temperature reference so that it can properly
calculate the delta T reported by the TC sensor. There is a cold junction sensor built
into the CB-3 connector block. I expect you could duplicate the function of the CB-3 if
you can find out what sensor is built into the CB-3 and use one of those in your setup.
Probably easier to just get a CB-3, however.
Without a cold junction reference you won't get an accurate temperature measurement.
Matt