Go Down

Topic: Oven thermometer probe requirements check (Read 2 times) previous topic - next topic

zeedo

Feb 11, 2011, 10:13 pm Last Edit: Feb 11, 2011, 10:46 pm by Barrie Dempster Reason: 1
First post here :-)

I'm planning to build something similar to this:
http://www.amazon.co.uk/Mastrad-Meat-Jam-Thermo-Sensor/dp/B000W02F0G/ref=tag_tdp_sv_edpp_i

However mine will be much more awesome as it will have wifi and a hundred other unnecessary features, the output/interfacing etc.. I'm fine with but the temperature probing end I want to make sure I've covered all the bases with, so just looking for confirmation that I'm not overlooking anything with specs of this component.

My questions relates more specifically to the temperature probe end of the project. I'm basically looking at something similar to this
http://www.picotech.com/pt100_sensors.html#insertion (expensive)
or this:
http://www.sparkfun.com/products/251 (the right price :-)  )

I'm thinking:-
The range will need to be 0-300°C. (most home ovens don't go much above 260ish, mine doesn't anyway)
Accuracy ±1°C or less won't kill my kids when the roast is on the plate.
The cable will likely need to be PTFE(Teflon) or similar to stand up to those temperatures (No cables melting to the oven!).
Stainless steel for the probe should be perfectly food-safe.
A metre long cable will be fine.

Is there anything else I'm not considering here for the temperature probe itself? Also if someone has a probe they could recommend that they have used with Arduino before in similar circumstances I'd be keen to hear about it.

Cheers!
With Regards..
Barrie Dempster (zeedo) - Fortiter et Strenue

              - http://www.reboot-robot.net -

"He who hingeth aboot, geteth h

liudr

I recollect from experience that Teflon is not rated at 300degC. You may need to insulate your wires with ceramic tubes (don't know their names) for the section that is very close to 300degC. I don't see other problems from your plan.

gardner

I would be tempted to buy a cheap conventional digital meat thermometer and steal the probe from that.
http://www.taylorcanada.ca/classic-digital-oven-thermometer.html

retrolefty

Typically the lead wire doesn't have to be rated for the same high temperature that the probe will be measuring. In a RTD probe the platinum wire sensor is only at the very tip inside it's stainless steel sheath, so only the end of the probe needs to be in the environment to be measured. This is can be done either by having a thermoweld type piping component, kind of a tube, closed at one end and the probe fits into the inside of the tube. For simple oven applications you just need some kind of piping fitting that allows the probe to slid into a drilled hole in the oven, a few inches and then lock the probe to the fitting with a tubing fitting. So much of the probes length and wire end will be outside the oven proper and thus normal higher temp insulated cabling can be used.

draythomp

This is such a cool idea !!  I second the idea of buying an existing cheap oven meter and 're-purposing' the probe.  This way you beat the problem of melting cord and have something that can be removed for cleaning easily.  The idea of putting this on the web is just awesome; you can watch your food cook on your cell phone from the patio.

Talk about bragging rights over the neighbors...
Trying to keep my house under control http://www.desert-home.com/

zeedo

#5
Feb 12, 2011, 11:29 am Last Edit: Feb 12, 2011, 11:31 am by Barrie Dempster Reason: 1
Thank you for the input folks :-)

Yeah I am considering stealing one from a cheap package, but I want something reliable and when scavenging from other devices it's hard to be sure of the spec of the individual component. I don't mind paying a couple of pennies more if I know what I'm getting.

Also, I've been looking at buying one of these thermometers for a while but the reviews of them are pretty bad, they all seem to suffer from quality issues unless you go in to the high end catering devices. So I'm thinking if I splash a bit of cash on the main sensor, similar to the catering models, but make the brains from arudino parts. I'll have a catering quality device with multi-function coolness, good parts doing the measuring and a at reasonable cost.



Typically the lead wire doesn't have to be rated for the same high temperature that the probe will be measuring.


Indeed mate, but in this case the probe is actually in a cooler environment than the wire is. Since this is feeding in to an oven and reading the temperature of a roast in there live. So the wire will be going in to the oven partially, subject to the highest heat. If it was being used as a candy thermometer it'd be different, but the feed through in to the oven is where the issue of wire coating becomes important.


I recollect from experience that Teflon is not rated at 300degC. You may need to insulate your wires with ceramic tubes (don't know their names) for the section that is very close to 300degC. I don't see other problems from your plan.


You're right, yeah Teflon is right on the edge of my requirements, I've seen some of the glass coated options, thinking I might be safer going for a higher rated coating. Thanks!
With Regards..
Barrie Dempster (zeedo) - Fortiter et Strenue

              - http://www.reboot-robot.net -

"He who hingeth aboot, geteth h

Go Up