Thermocouple question

[Sananguero]

Hi all I am midway through constructing a 42" tuscan style dome oven with reclaimed firebrick in Hawaii. My family has a warehouse and had some thermocouples laying around that I thought I might be able to use. However they are not a thin wire, but more like 1/2" dia of stainless steel, and about 8in long connected to a thermometer at the end that goes up to 1000 deg F. Would this work if I planted them in the mortar in the dome or would cracking be an issue due to expansion of the metal? Thanks in advance for the help! This is a great website and I hope to be posting some pics soon!
aloha,

Karl

[ThisOldGarageNJ]

Re: Thermocouple question

I know there are members who have thermocouples installed similar to that,, I was looking into it and was convinced by most here that the infared thermometer is the way to go, On the other hand, Since you do have them, I dont see what it would hurt to put them in.. As far as expansion and cracking,,, ??? I cant help you other than to say they use stainless needles in refractory cement for added strength..

Do a forum search for thermocouples,,, you will find a ton to read,,

Out of curiousity and off topic,, What kind of wood will you be burning ?

Mark

[dougrappe]

Re: Thermocouple question

Hey Karl, maybe you could post a picture of the thermocouple/thermometer you are considering using. I know there is a lot of experience with various devices here on the forum. If it's one piece, it seems like you'd have to really plan the exact location so you can get a good reading of temperature while still having access to the thermometer dial to read it. I have a single k-type thermocouple in the oven floor, it's a flexible 3/16" dia. rod that I embedded in the center hearth brick half way, I already owned a meter it would connect to so it was a cheap way to go.

I remember reading somewhere on the forum that if you can only have one thermocouple put it in the floor, so that's what I did. It is nice to know what the floor temperature is for pizza and bread. If I didn't have the meter already, I probably would have purchased a hand held IR thermometer.

Doug

[Sananguero]

Re: Thermocouple question

Thanks guys I found a link to what essentially looks like the same thermometer, mine are also Tel-Tru. By the way after looking more closely I found there was another fitting on there, maybe a thermowell, that made the dia appear much larger on the probe. One is 1/2" and the other is 5/8". Should I use this as well or skip it? I should mention that the warehouse sells industrial parts like tube fittings, couplings, valves, etc so the attachment may have a completely different use for their customers. Anyhow the rod inside connected to the thermometer is only about 1/4" dia and looks like the ones in the link.
Industrial Thermometers
Do you have any pictures of how/where you drilled the hole in the center hearth brick? I was thinking of using one for the oven dome, and the other for a smoker I would like to incorporate. I laid my first 38 hearth bricks yesterday and ran out of fireclay/sand mortar. Can you use too much of the stuff? I used about 1/2" maybe more than I needed, but it is level now and hate to have to redo them, plus I am working in a remote area.
By the way I will be using strawberry guava, vie vei here which is considered invasive, and mesquite/kiawe, and perhaps O'hia.

Karl

[dougrappe]

Re: Thermocouple question

Hey Karl, I wish I could find a couple of those lying around. The thermocouple in the hearth was routed through a pipe that I cast into the reinforced concrete hearth slab, then through a hole drilled in the insulation board, and then into a hole drilled halfway through a hearth brick. So you probably don't want to start messing with that, and I'm not sure how you'd read that dial without climbing under the oven.

I was trying to find the thread that showed placement of a similar device, about halfway up the dome. I think the idea is to get the temperature of the brick, so you'd still want to drill half way through a brick from the outside. The larger diameter sleeve you describe is probably for installing the thermometer into some kind of tank, so it would be removable. My guess is you don't need the outer casing and could just use the 1/4" dia. section.

hope that is some help. it is nice to have an idea of what kind of temperature you have in the oven, but I have also found that you kind of get a feel for it pretty quickly too.

Doug

[Sananguero]

Re: Thermocouple question

Thanks Doug, that is interesting. So I guess you just had wire up there to the firebrick? I looked up thermocouple and got the definition basically any two materials that differ in conductivity create a voltage that is read and converted to temp. simple enough haha It seems that are a few different types and so it is a bit confusing for me since this is my first oven and never done this. Before I was thinking of putting the tip of the 304ss 1/4" rod directly in the fireclay mortar mix near the surface joint in the dome, but yeah good point I dont want to get under the oven to read the temp!! inserting it in the side and just let the tip rest on part of the hearth and one in the smoker even if just a novelty. Also I planned on finishing the exterior with lava rock, but It may just be long enough, they are both 14 1/2" long with the thermowells attached. What is temp anyways? A reference point and reference temp is all I need and interesting for the spectators. Can save the test for the infrared and do some comparsions hehe...

Oh before I forget back to my original concern.. but wont that thick of a probe in stainless expand and crack the joints bad? Or I was thinking somehow make the hole bigger to leave room for an expanded joint...

Karl