Some probably dumb questions, but worth mentioning: You are using "T" thermocouples. Are you absolutely positive that you have "T" extension wire? If I recall correctly, "T" thermocouples use a black jacket or some other form of black marker. You should be using ordinary wire nuts to connect the TC wire to the extension wire: twist the conductors tightly so that they are contacting each other. The wire nut serves only to hold the conductors tightly in contact with each other and does not introduce any error (that I've ever been able to measure). Allow the rooms to reach ambient temperature. Now take a hair dryer or heat gun and go along the entire run from thermocouple to measuring device. Applying heat anywhere along the run should NOT cause the temperature reading to change. Only the actual thermocouple junction should cause a temperature reading change. If your splices are separated, heat each connection separately. A good connection will not change the reading even if its temperature changes by a significant amount. Like you, I'm suspecting the extension wire. dwayne At 09:29 AM 2/21/2008, Chaoua, Rashid wrote: >Yes, the TCs are in the same room as the heaters. We use the heaters to >control the temperature in each room. They are radiant heaters. I should >add that when I take my measurements I also take the temperature in the >room using a "control" TC that was provided with the meter. The TC's and >the control always read within +/- 0.5 of each other. Even if it was >reading the heat from the heater I should still see correct readings at >the end of the extension wire. I am almost 100% that the thermocouples >themselves work correctly but I can't figure out where else the problem >lies (the extension wire is my guest). > >Rachid Chaoua -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist