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Author Topic: Where to get stainless steel NTC thermistor probe?  (Read 3688 times)
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Hi,

I've been googling without much luck trying to find an NTC thermistor probe. I want to use this in a coffee roaster project, so I'd really like a stainless steel probe (preferably threaded) with an NTC thermistor potted in it. I originally ordered some high temperature thermistors and have that part of the circuit prototyped and software written using the PID library available for arduino; however, I figured since I'm going to be consuming the output of this machine, I'd probably better get stuff that should be safe for use in food appliances rather than try to make my own probe. I'd rather not do the thermocouple thing since they require some specific interface hardware. I'd rather just get some high temperature wire to bring out of the machine a little ways and switch over to much cheaper wire. Anyway, I'm not having much luck finding a stainless probe with NTC thermistor - most of what I can find is stuff that is only bulk ordered (request quotes/etc.).  Thanks.
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These folks can supply small quantities.  In addition to these, http://www.omega.com/ppt/pptsc.asp?ref=TH-10-44000&Nav=temd03 look through their web site.  They have lots of variety in such products.
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Thanks for the link. I'm not sure I saw that one earlier or not, but it's only rated to go up to 302F which is about 200F less than I need. smiley I should have stated in my original post that it needs to go up to 450 - 500F.

I originally bought a couple of these: http://www.digikey.com/product-detail/en/103JG1JRA/615-1016-ND/1014544?cur=USD. I'm thinking I might just attach that the the high temp wire (purchased from Omega) with as little bare metal exposed as possible and find some high temp silicone to hold it in place where it won't short on anything.
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At those temperatures I would suggest a thermocouple rather than a thermister.
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Hello!My company can provide the products you need, if you need please send an email to me.
email: liangtaoch@yahoo.com.cn
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At those temperatures I would suggest a thermocouple rather than a thermister.

I'd agree. It's also pretty easy to find stainless/threaded probes on eBay (example1, example2) or elsewhere.

JeeLabs and Adafruit both sell the thermocouple amps you'd need to interface with the Arduino.
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I agree with the recommendation re: adafruit thermocouples and MAX6675 thermocouple boards. Great stuff at reasonable prices and more importantly, well documented libraries that make getting good results relatively easy. I use a K-style thermocouple in my reflow oven project (rocket scream shield).
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Sorry to revive an old topic but I was wondering what you did afterwards?  Are those stainless steel k-type thermocouples food safe?

I'm going to take a stab at making a coffee roaster myself.  Were you happy with the quality of yours?  Is there a significant improvement in the taste over buying roasted beans?

Thanks!
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I have been very happy with my thermocouple (TC), though it is not sheathed inside a probe - the weld is exposed. For your application, a sheathed TC might make more sense (i.e. a stainless steel tube with TC inside) because it's easily cleanable. Besides a higher cost, the other downside of a sheathed TC is the longer time constant re: temperature. However, for your application, you should be fine.

Omega sells lots of stainless-clad TC's and I'd be surprised if E-bay doesn't feature them also. I have no need for food grade safety, as my TC is being used strictly to make printed circuit board assemblies (i.e. mounting surface-mount chips on them). That TC is affixed inside the oven on a PCB so it's time constant is also longer, but hopefully analogous to the time constant of the solder pads on a PCB inside the oven. So far, I have had great success.
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I recently made a yogurt maker with similar requirements--food-grade thermistor probe for temperatures up to boiling point.  This probe worked very well for it; I'd recommend it for similar projects.

http://maverickhousewares.com/et73.htm
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