#11  
Old 04-18-2008, 08:53 PM
carioca's Avatar
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Default Re: Thermocouple design for oven

Hi,

for my 2.2c worth (includes 10 pc tax): I find the thermocouple discussion fascinating and have often cursed myself for not including any in my forno! I even have a Fluke-clone multimeter that will accept K-type inputs...

But in the end I just bought a $40 temperature gauge as a replacement part for a commercial backyard WFO and plan to stick it into a hole in my insulated oven door - heat loss should be minimal, and at least I'll roughly know what the centre front temp will be behind the door...

Cheers,

LMH
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Last edited by carioca; 04-18-2008 at 08:54 PM. Reason: sp.
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  #12  
Old 04-18-2008, 11:57 PM
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Default Re: Thermocouple design for oven

I measure temps just like carioca does. Hole in the door, poke the probe through and it gives you a sort of average heat reading for the air some 20 cm in from the door.

It works really well for me - but then I prefer low-tech stuff anyway...
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  #13  
Old 04-19-2008, 06:55 AM
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Default Re: Thermocouple design for oven

Quote:
Originally Posted by beaglestorm View Post
For my BOM:
KMQSS-125U-6, 3 each, 1/8 Stainless sheath 6" K-type with miniature connectors.

That link shows a probe that is good up to 425F I would think it needs to go higher... say up to 1000F. Maybe like their TJ36-CASUP-316U-12. Just an observation... I know absolutely nothing about TC's.
The Nylon connector body (yellow connector) is rated at 425 deg F, not the TC itself.
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  #14  
Old 04-19-2008, 07:48 AM
Ed_ Ed_ is offline
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Default Re: Thermocouple design for oven

I haven't built yet, so I don't think I can give any real practical advice. But I'm another one of those techie types (I studied physics and electrical engineering) so I thought I'd chime in.

I have a really nerdy compulsion to clear up something about how a thermocouple works. Where the two different metals are in contact, there is a voltage (not a current, although a current will flow if the circuit is closed) developed which is dependent on temperature. The voltage and the useful temperature range depend on which metals are involved. The voltage is quite small, and the effect isn't exactly linear, so some care is required in developing the electronics to read it.

I'll get myself into trouble (and bore you even more) if I try to explain it in more detail, but if you're really interested, look some info up the Seebeck effect.

A question for those of you who have done this: If you use the probes with the 6" steel sheath on the end, do you just embed that right in the mortar? I don't know much about cement, so I don't know which metals are susceptible to corrosion in contact with it. Also, is the TC junction at the very end of the steel bit?

Thanks,
Ed
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  #15  
Old 04-19-2008, 01:51 PM
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Default Re: Thermocouple design for oven

I mortared in a stainless steel tube slightly larger than the porcelain sheath, into the inner dome wall about 1/2 way up the dome. It is a sliding fit into this tube. Seems ok
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  #16  
Old 04-19-2008, 04:45 PM
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Default Re: Thermocouple design for oven

Quote:
Originally Posted by Ed_ View Post

A question for those of you who have done this: If you use the probes with the 6" steel sheath on the end, do you just embed that right in the mortar? I don't know much about cement, so I don't know which metals are susceptible to corrosion in contact with it. Also, is the TC junction at the very end of the steel bit?

Thanks,
Ed
I cannot speak first hand about the mortar corrosion question. I would suspect there may be some but as a comparison, at my "paying job", we get 4 years or so out of our stainless tc's that are sitting in slightly HCl acidic (between a PH of 1 -2) water, which would seem a harsher environment.

I wanted brick temperature so I drilled holes in the brick and inserted mine there.

The junction is in the tip and most TC's of this type are also filled with an insulating ceramic paste.
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  #17  
Old 04-20-2008, 11:13 AM
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Default Re: Thermocouple design for oven

Your BOM is:
KMQSS-125U-6, 3 each, 1/8 Stainless sheath 6" K-type with miniature connectors
TECK10-9, 3 each, 10ft extensions.*
HH308 Mini thermometer - reads 2 K-type TC's at a time.
OSXL653 IR gun thermometer +

+ Could look at the OS562 , is IR gun that also reads a K-type TC input so 2 meters for price of one.

Question, I could not find your part number OS562? is that a mistype? and if I find this unit, would I still need the HH308?
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Old 04-20-2008, 01:41 PM
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Default Re: Thermocouple design for oven

Quote:
Originally Posted by maburton View Post
Question, I could not find your part number OS562? is that a mistype? and if I find this unit, would I still need the HH308?

Well, I am the "king of mistypes" but was lucky and it is correct. Here it is, Low Cost Infrared Thermometer with Adjustable Emissivity

This IR gun reads K-type TC's, so no you will not "need" the HH308 meter. I am assuming you are not going to install more than 3-4 TC's, because to read them you will have to plug in each, one at a time or buy a rotary input selector. Not a big deal, as temps do not change that rapidly. Just depends on how you want to design your system.

Unfortunately for me, they came out with that gun after I had already bought my meter. That is why I bought the two I did.

Should add that I installed my 3 with tips in center of mass in each brick. One in the top center of dome, one at about the midpoint and one drilled sideways into the floor, same side as 2nd one. I figured the IR gun would do fine at giving face temps. You need to decide if you want brick face temp, air temp, mass temp, ect and install accordingly.
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Last edited by wlively; 04-20-2008 at 01:56 PM.
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  #19  
Old 05-15-2008, 12:25 PM
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Default Re: Thermocouple design for oven

Hello,

My name is Gary Heid and my company manufactures thermocouples. We also sell temperature controllers. The name of my company is East Coast Sensors.com We are very cost competitive. We manufacture to your exact specifications. Give me a call at 800-722-4592 with any questions of requests, I would be happy to assist you!


Thanks,
Gary
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  #20  
Old 05-16-2008, 06:54 PM
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Default Re: Thermocouple design for oven

Admirer here since I do not yet have a WFO lol. I figured I would use my IR Temp probe that I already own for other reasons and will use a simple dial type even thermometer when temps goes down to normal ranges for breads and such. I will of course have the dial gauge on a rack of some sort to get air temp and not floor or walls. I also feel that the electronic cooking probes would be a wise investment since you are down to normal temps when they would be needed. If the food item reaches correct temp you pull it. This works in a roast, caserole even bread, Off the top of my head the internal temp of bread when done should be between 185F and 210F depending on the type of bread you are making and the correct temperature for baking a "standard" type bread is 230 Degrees centigrade which is 446 F.
Breads with milk,egg or fruit will usually require a lower temperature.
You can search and find temps for any food you want to cook. As for bread the color and thump method always worked for me. Beef I like rare so I never probe it as long as the outside is a good color. Now pork and poultry are a different story and you need to adhere closely to cooking temps. Just remember to never leave anything in untill temp is reached. I always pull it a bit early and let it finish during resting period. I usually go about 10 degrees below when I pull from cooking area. Now with this being said dont let me talk you out of built in sensors because I may end up with them in mine as well.
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