If you want sub degree precision, you will need to make your connections to dissimilar metals on an isothermal boundary, a terminal block is better than clips in free air.
On Fri, Nov 11, 2016 at 8:28 AM, Bob Camp <kb...@n1k.org> wrote: > Hi > > > On Nov 11, 2016, at 8:02 AM, jimlux <jim...@earthlink.net> wrote: > > > > On 11/10/16 10:28 PM, Mike Millen wrote: > >> It would work as well if you used a pair of regular copper wires to > >> connect the meter to the thermocouple... > >> > >> The junctions created by all the new connections will cancel out. > >> > > > > as long as the temperatures are "exactly" the same, > > (Seebeck coefficient varies with temperature) > > and the two metals at the junctions are the same, > > (ditto, but the curves are different for different materials) > > and the mechanical configuration is the same > > (current density also affects it) > > The gotcha is that few of us weld copper directly to the thermocouple > leads. The far more > common approach is to grab clip leads. At least around here, the clips on > the leads are > not made of copper. They are some sort of (badly worn) plating over > (oxidized) base > material. > > I grab a “copper wire” clip lead and hook up to the thermocouple. There > isn’t a lot of > delta T in most bench situations. In this case you have a heated gizmo > warming things up …. > Who knows what the delta T may be or how small the contact area actually > is. > > Simple answer: Don’t trust the first number you get. Try it a couple of > times with *different* > leads. Make sure you do indeed get within a degree or three on each of > them. Depending on > how you have your cold junction set up, that may also need the same > treatment. > > Bob > > > > > > > > For run of the mill "measure to 1 degree at room temperature" you can > probably make that assumption. > > > > But if you're looking for precision, you need to take this stuff into > account (that's what "cold junction compensation" is all about.. ) > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.