Temp Probes and Ebay Thermometers

[headchange4u]

I've been using my multimeter and the included thermocouple to monitor roast temps. Not long ago my thermocouple wire got wrapped around the rotisserie arm of my RK Drum and destroyed the wire. I need to pick up a new thermocouple wire but I'm having trouble finding what I need. The wire plugs into my multimeter via a banana plug type connection. I've found a couple of options but most seem overpriced or the use a flat spade or "V" shaped connection which won't work on my multimeter. Any suggestions on  good place to find a replacement wire using the banana plugs would be greatly appreciated.

While surfing Ebay to see what they offer I found quite a few thermometers, some with dual temp probes. Most ship out of China so that makes me a little wary. I would like to know if anyone has any experience with these units.

Examples:
LCD Display Precision Thermometer Thermocouple K Type

Digital Thermometer Thermocouple 2 K-Type Probe Sensor

K or J Type Thermometer Thermocouple with 4 Probes Temp(I like this one)

[peter]

If you have enough of the wire left, I think you can re-join the two ends and it should work.

[milowebailey]

If you have enough of the wire left, I think you can re-join the two ends and it should work.

It has to be welded

[Goose]

The folks at Thermoworks should be able to help you out, contact them and let them know what you need.

http://www.thermoworks.com/

FWIW I would be very cautious with the links you provided, the last one especially is making some outrageous claims about the range of temps, more than likely its the range of the meter they are showing. Many thermocouples will fry at 500 degrees or even less.

[headchange4u]

If you have enough of the wire left, I think you can re-join the two ends and it should work.

It has to be welded

True.

Cool story: I went to Jim Galt's house to get his help in fixing some problems with my PID system on my Gaggia. I noticed a mean looking device that had several HUGE capacitors sitting on his work desk. Upon my inquiry he told me he makes his own thermocouple wires and what I was seeing was his DIY welder for the ends of the TC wire. VERY cool.

[Tex]

If you have enough of the wire left, I think you can re-join the two ends and it should work.

It has to be welded

Not really - twist the wires together and crimp the ends. Works fine.

[milowebailey]

If you have enough of the wire left, I think you can re-join the two ends and it should work.

It has to be welded

Not really - twist the wires together and crimp the ends. Works fine.

I question the long term reliability of doing it this way.  It's the junction of the two dissimilar metals is what creates the voltage.

[Tex]

If you have enough of the wire left, I think you can re-join the two ends and it should work.

It has to be welded

Not really - twist the wires together and crimp the ends. Works fine.

I question the long term reliability of doing it this way.  It's the junction of the two dissimilar metals is what creates the voltage.

True - but I've got a roll of type K wire that I use to make up thermocouples all the time. So it is feasible. Personally, I recommend buying ready-made t/c's from Omega. They're cheap, reliable and they ship fast: http://www.omega.com/ppt/pptsc.asp?ref=5SC&ttID=5SC&Nav=

[ButtWhiskers]

If you have enough of the wire left, I think you can re-join the two ends and it should work.

It has to be welded

Not really - twist the wires together and crimp the ends. Works fine.

I question the long term reliability of doing it this way.  It's the junction of the two dissimilar metals is what creates the voltage.

...and that potential will shift over time due to oxidation and other chemical changes.  This rate of this shift will increase if the junction is not stable. 

To have reliable temperature measurement with any electronic thermometer / thermocouple combination, the device (specific thermocouple and electronic thermometer combination) needs to be calibrated at two or more temperature points that encompass the range of use.  For a K-type thermocouple, you really can go up to 1350°C, but for our purposes (roasting) we usually calibrate at 25°C (room temperature) and 300°C (about 570°F).  You cannot just plug any thermocouple into any electronic thermometer and get a valid measurement.

[milowebailey]

BW

Without calibration... how accurate or inaccurate is an off-the shelf k type thermocouple?

[ButtWhiskers]

BW

Without calibration... how accurate or inaccurate is an off-the shelf k type thermocouple?

That varies greatly...  Most of them are pretty accurate AFAIK.  I had one (from eBay) that was within 1°C on both ends when I received it, and another (from Harbor Freight) that was 13°C off at ~500°C when checked vs. a recently-calibrated thermocouple in a tube furnace.  While 13°C may not sound like a lot, it is over 23°F at that extreme, which translates to around 10°F in the caramelization range (assuming the error is linear).  Unfortunately I couldn't figure out how to input new factors on that device, so I was stuck with raw voltage measurements...

[J.Jirehs Roaster]

if you get a thermocouple of the same type (usually K) as your broken one you can get the banana plugs at most electronics parts store/site... even ~gasp~ Radio Shack ~ducking~
just get your leads in the right input... I picked up some built into a metal tube... that style may hold up better in your drum...

[headchange4u]

if you get a thermocouple of the same type (usually K) as your broken one you can get the banana plugs at most electronics parts store/site... even ~gasp~ Radio Shack ~ducking~
just get your leads in the right input... I picked up some built into a metal tube... that style may hold up better in your drum...

Already checked Radio Shack and other local electronics retailers. No dice. I've still got the plugs off my old unit. I found a couple of places that carry a probe, but they are made for HVAC applications and nowhere near the temp range I need.

[Tex]

if you get a thermocouple of the same type (usually K) as your broken one you can get the banana plugs at most electronics parts store/site... even ~gasp~ Radio Shack ~ducking~
just get your leads in the right input... I picked up some built into a metal tube... that style may hold up better in your drum...

Already checked Radio Shack and other local electronics retailers. No dice. I've still got the plugs off my old unit. I found a couple of places that carry a probe, but they are made for HVAC applications and nowhere near the temp range I need.

Check eBay - lots to choose from: http://shop.ebay.com/?_from=R40&_trksid=m38&_nkw=k+thermocouple 

A type K t/c is what you should look for. A type J t/c is also in the correct temp range for roasting, but I'd avoid using ferrous leads.

[headchange4u]

A type K t/c is what you should look for. A type J t/c is also in the correct temp range for roasting, but I'd avoid using ferrous leads.

I performed that same search before posting this thread. I didn't see any in the listing that use the banana plug connection. They are all an "L" or "-" type connection. The have adapters but the spacing is not correct for my multimeter.