On Tue, 7 Dec 2010 09:27:52 -0500, you wrote: >Is there really one reference junction, though? I am under the >impression that any joint of dis-similar metals in the thermocouple >circuit will cause a voltage difference which is temperature >dependent. This includes even things like bond wire connections inside >the IC used to read the thermocouple. So, I'm not sure that it makes >sense to couple the cold junction sensor so closely with the TC >connector unless you are also coupling it closely with the rest of the >electronics in the circuit which reads the TC. > >I am speaking as a heavy user of TCs who has never designed a circuit >to interface with them so perhaps someone with more experience here >can chime in. > >Sean No - the voltage you get is the difference between the hot and cold juncti= ons. After the cold-junction terminal block, all connections are symmetrical - terminal t= o PCB, pcb to chip package, bond wires etc., so any thermoelectric voltages get cancelled out.= =20 =20 Special connecitons are used where you don't wanr to createa cold junction,= so the contatcts match the TC metal composition. As long as you know the temp at the pont where th= e TC wires transition to normal metals, you know everything needed to derive the hot junction temp.= =20 > >On Tue, Dec 7, 2010 at 8:29 AM, PICdude wrote: >> Same-ish here. =A0I use regular screw-terminal blocks for this, and >> ensure that the reference junction is inside the enclosure, with the >> temp sensor next to the terminal block, on the side the wires connect >> to. >> >> Cheers, >> -Neil. >> >> >> >> Quoting peter green : >> >>> Do you actually need a special thermocouple connector? Last time I >>> needed to hook up a thermocouple I just used an ordinary micro spox. >>> >>> Afaict all you achive by using a special connector is moving the >>> reference junction from the cable-connector interface to the >>> connector-pcb interface. That gets the reference junction slightly >>> closer to whatever temp sensor you are using as a reference but I doubt >>> it will make much difference in practice. >>> >> >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .