[time-nuts] Need some wisdom from the cesium beam tube gurus out there

[paul swed]

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.stobbe at 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 <kb8tq at n1k.org> wrote:
>
> > Hi
> >
> > > On Nov 11, 2016, at 8:02 AM, jimlux <jimlux at 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.. )
> > >
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