Besides Omega, what is a good outlet for purchasing thermocouples?

January 11, 2006 8:48 AM

Besides Omega, what is a good outlet for purchasing thermocouples?

I am looking for really fast thermocouples (low time constants) with tiny weld beads. I've looked through Omega's web site and have a couple in mind. Something like .0001" diameter is what I am looking for. K type calibrated is perfered, as all of our DAQS are K type calibrated.

Bonus question: is there another way to make temperature measurements in a really small and tight place? I've heard of using fiber-optics to read temperature, but the ones I've found online so far have horrible time constants and you need to protect your fiber optic from high temperatures which makes the final instrument bulky.

Thanks for your input.

posted by nickerbocker to Technology (10 answers total)

Cole-Parmer has a very wide selection too, but I'm not sure that they're much better than Omega.

I just had a poke around: Their smallest K-Type is 0.005" dia with a 0.1 s time constant. Probably not what you're looking for.
posted by bonehead at 9:13 AM on January 11, 2006

I've gotten thermocouples from McMaster before, but I don't think they have anything as small as you specified.

As far as fiber optics, I've used pressure sensors from FISO before, but they are expensive - the pressure sensors were about $1200 each and I'd imagine the temperature sensors are similarly priced. Plus you need a signal conditioning unit which will run about $50k for 8 channels. The response time varies from 1 ms to 1.5 s depending on the model, and they're tiny.
posted by mbd1mbd1 at 9:18 AM on January 11, 2006

Can you use a bolometer in your application? Trying to get a wire that fine may not be possible. The more expensive ones have time constants in the 100s of milliseconds.
posted by bonehead at 9:20 AM on January 11, 2006

A little more poking around (you've got me curious and it is my lunch):

Omega does sell a fibre-based system that outputs a "K-type" signal. Special order spot sizes down to 0.004" with a time constant of 10 msec. And it's non-contact.

Have you talked to the Omega technical guys? I've always found them extremely helpful, much more so than other vendors.
posted by bonehead at 9:31 AM on January 11, 2006

Response by poster: bonehead: that is an interesting fibre-based system. Very pricy, though. The CHAL-001 from Omega has a 0.001" diameter and it has a time constant of about 4ms in moving air (which is what I will be measuring). There is a .0005" part (CHAL-0005) available as well, but it doesn't have the response time or maximum temperature listed. I guess that is left to the buyer because it veries so much or something.

I have no experience with bolometers. I'll look them up.

Thanks for input. Open for some more.
posted by nickerbocker at 10:18 AM on January 11, 2006

I think .0001" is thinner than you mean (or think it is)? A sheet of paper is .003". I can't find any wire listed smaller than .003" (40 ga).
posted by 445supermag at 12:53 PM on January 11, 2006

have you ever thought about using a resistive temperature detector? just a thin platinum wire for instance, going into and out of the small area. just plug it into an ohmmeter and look up the coefficient in the CRC handbook.

only really makes sense if the thing you're measuring gets hot enough to dominate the resistance of the wire, and if you can isolate the temperature of the *rest* of the wire and keep it (relatively) constant.

keep in mind though that thermal conduction is a fundamentally slow bulk material process, and that any kind of temperature measurement that relies on conduction is going to be kind of limited. in fact, temperature is only really defined for systems in thermal equilibrium.

are you willing to provide more information about what it is that you're measuring, what sort of temperature range you expect, etc? we could maybe help come up with something else.
posted by sergeant sandwich at 2:46 PM on January 11, 2006

also, here's another pyrometer from omega spec'd at a 3 microsecond time constant.
posted by sergeant sandwich at 2:55 PM on January 11, 2006

oh, some more information about RTDs. i guess you can use a 3-wire system to cancel out thermal variations in the lead wires with a bridge circuit.

los alamos? i'm going to take a shot in the dark and guess that you are working on a vertex tracker?
posted by sergeant sandwich at 3:04 PM on January 11, 2006

or.. maybe not los alamos but someplace entirely and completely different. gah.
i'm an idiot.
posted by sergeant sandwich at 3:19 PM on January 11, 2006