Hello to the group. I somewhat suspect we have veered way off the track on the thread or the thread changed and I missed it. Typical of me. Useful comments on Tcouples and wires.
But with respect to the start of the subject of unmarked CS tubes easily a 5 or more degree range is fine. You can adjust up or down after you are in range for optimum performance or life as a trade off. Granted you may not actually know what the temperature is to 1 degree. But on an unknown tube its a great place to start. As an example Frankenstein runs 10 C hot approx. It resulted in some fumes of C and I beam. When I started Frankenstein it would have been good to know it was a Tcouple and it should have been an obvious guess. I was just reading and matching voltage outputs after the bridge. Regards Paul WB8TSL On Fri, Nov 11, 2016 at 9:16 AM, Scott Stobbe <scott.j.sto...@gmail.com> wrote: > 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. > _______________________________________________ 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.