Thermocouples -- what to do?

[ihughes]

I've been researching thermocouples and I'm still unsure about them. Probably because I've no technical background at all.
The Omega site left me even more dazed - so much information.
For something that seems so simple it's just so confusing so bear with me as I ask some really basic questions. (if someone has an instuction guide link it might give me some better understanding)

• Will I burn everything if i just go with a infrared thermometer. I thought one of the joys of an oven like this was like an old car - you got to know it's personality by breaking down in the middle of the night on a country road and you still loved it ....?
• Exactly how are they installed? If I leave a hole in the hearth to feed the wires do the wires thread between the bricks or do I drill a hole to feed them through?
• In the floor do they sit at the bottom of the brick, halfway up or poke out the top? Similar for those in the top of the oven
• IF you've no idea like me, what kind of thermocouple wire do I get? And what type of reader is best if you use 4 wires?
• If I don't install thermocouples while I'm building, can I put them in later when my feeble mind has understood the process?

[wlively]

Re: Thermocouples -- what to do?

I will try and help.

Thermocouples are not neccessary, hey how many pizzaria's use nothing but a hand. I put them in because I work with them every day and wanted to learn/explore the characteristics of my oven. OK I am a geek.

Putting them in later is quite possible but depends on where you want to put them and what type of enclosure you have.

Where to locate depend on what you want to measure; heat saturation of the brick, then in the center of the brick. Face temp saturation, then say 1/4 inch from face. Air temp, then the tip needs to protrude just barely past the face of the brick. The same goes for what area of the oven you want to measure, top wall, floor, ect. Mine are in the center of the brick because I wanted stauration readings and am going to use an IR to get surface temp. You could go under floor, but that wiring is more complicated or you have to drill a very long hole for the probe to come in from underneath. For simplicity, I drilled sideways into the floor, but as a trade off I don't get center floor reading, but about 8 inches from dome. This way it is also easier to change out if it fails. I used mortar to seal them in and make good thermal contact with the brick.

For our oven temp range and cost you want K type thermocouples. The type rating for thermocouples is based on the material they are made from. A thermocouple is made of two different types of metal wire that meet at a beaded junction. These disimilar metals produce a millivolt output that is directly related to the temperature they are exposed to. It is best to go with sealed probes in stainless or glass sheath. I went stainless. Ceramic are cheaper, but being exposed to atmosphere the tip will corrode over time and the bead junction will fail (somewhere around 1-2 years most likely). Any meter that will read K-type is good, I went with a cheaper hand held (see my oven pictures) that reads two inputs simutaneously, $85. Omega also makes a hand held IR gun that accepts a K-type TC input for $120, so you could use it for both if you wanted. You could by a switch to cycle thru the TC's, but again I went simple. I have 3 TC's and can read 2 at the same time. When I want to read the third, I just swap plugs, only one more hand action than turning a rotary switch. Also, the temp is not changing fast enough to need instant readings. Same goes for wire, you want K-type. I almost bough a spool, but found they make 10 ft, premade extension wires and 3 of those was cheaper than a spool, plus I didn't have any left over wire.

[ihughes]

Re: Thermocouples -- what to do?

Hey Wade, thks for the info. The positioning had me a bit stumped but your explanations have hit the spot. The IR gun sounds a good idea. I think I'll go that route and get the thermocouples
Ian

[nissanneill]

Re: Thermocouples -- what to do?

Hi Ian,
depending on what stage you are at with your build will depend on what you can do (if anything worthwhile).
You may find it difficult to obtain any worthwhile readings from your hearth if the oven id built but you can very easily drill your dome bricks to inset a couple od shallow and/or deep wires.
I positioned two 3/16" copper tubes into the foundation before it was poured, one in the centre which will penetrate a hearth brick to around 1/2" from the surface and one on the right (with the red tape on it) which will be cut off around 1/4" into the bottom of the brick which is intended to read the botton hearth brick temperture. This one will give me the 'soak' or degree of heat penetration into the hearth which will with a little experience will indicate how long I can pizza cook. I tend to light my fires across the width of the hearth and then push the coals to the back and to the sides when cooking pizza.
The two tubes terminate near to where I plan on mounting the read-out meter. I need to buy 4 longer K type thermocouple wires and feed them down the tubes to contact the brick inner surfaces (drilled hole end) to give me the temperatures. I have also included the same type of readings for the dome. The one in the centre is drilled 4" into the brick to give me close to surface temperatures and another around 6" up from the floor at approx the 3 o'clock position which will read the outer dome brick temperature, (also the dome soak amount). I used the tubes because I can replace or problem solve if needs be further down the road.
I had delivered yesterday my infra red digital thermometer which will also be used for checking surface temperatures within the oven and when I install the thermocouples, will put up a posting of the results.

Neill

[Archena]

Re: Thermocouples -- what to do?

Who knew ya needed a degree in geek to build a pizza oven?

[Hendo]

Re: Thermocouples -- what to do?

Ian,

I pondered this same question, and had some good input at the time from CanuckJim - see http://www.fornobravo.com/forum/f6/t....html#post7484 and later posts.

There is an excellent industrial instrument supply company here in Adelaide (OneTemp - also in Sydney), from which I have obtained and installed four thermowells in the hearth slab to fix thermocouple probes, three of which will measure temperatures around the floor approx 15mm below the surface, and one in the centre between the hearth insulation and floor which will give an idea of the degree of soak. See http://www.fornobravo.com/forum/f21/....html#post9320 and subsequent posts for more info and photo's.

The thermowells for me were an easy way to go construction-wise, and provide some insurance if ever I need to replace a thermocouple probe. They weren't exactly cheap though, but neither are the display and switch unit. You may want to consider the overall cost of the exercise before you commit to it - it has certainly worked out to be far more expensive than I initially thought.

Many members have opted for a portable infrared thermometer. OneTemp also sell these and even have one with a stab probe for checking your freshly baked bread temperature! Check out Hand Held Infrared. These measure only surface temperature however, so if you want an idea of the degree of soak (handy I'm told for baking), you really need thermocouples in my opinion.

But Wade is correct - none of this is really necessary!

Good luck,
Paul.

[ihughes]

Re: Thermocouples -- what to do?

This why I love this forum, great answers and I even get a link to a local supplier. I've been looking for weeks on the internet for a local supplier - thks Paul.

Neil, that pic helped me enormously because I was having trouble picturing it.



Cheers
ian

[Hendo]

Re: Thermocouples -- what to do?

Ian,

Always a pleasure! I took a while to find this firm as it had changed name from IPA (Industrial Pyrometers (Aust) Pty Ltd) and several (clay) brick companies I contacted didn't know its new name. But I eventually found one that did and voil?!

I never cease to be amazed by the World Wide Web. We type 'www' so often, but it's easy to become complacent about the sheer volume of info out there in cyberspace. It really is 'world wide', and the world sure is getting smaller - info-wise at least! And I keep wondering - is the information trapped by the web, or are we???

Feel free to contact me via a PM anytime re contacts in Oz. I surely don't know them all (even in Adelaide) but I've kept a reasonable record of suppliers over the past several months.

Cheers, Paul.

[SpringJim]

Re: Thermocouples -- what to do?

Searching Google anymore you usually run into FB Forum posts....resurfaced this one when looking for thermocouple info....by now Neill must have them installed.....

[nissanneill]

Re: Thermocouples -- what to do?

Jim,
my thermocouples have been installed since day one. However, I do not use them and have established that they are a waste of time, effort and money for what I use the oven for. As I am not into extended cooking/baking of breads etc, they serve no useful purpose that justify their expense.
Mine, although only costing me around $50 for the thermocouples, switching, copper tubing etc, I would not incorporate them in another oven.
A hand held infra red digital thermometer is all that any pizza baker needs, with sufficient heat for bread baking/roast meats etc. together with a little experience and how long and fierce your fire was is sufficient indication as to what you can expect to achieve. After all, the stored heat in the dome bricks must come out through the oven, do it's job and then dissipate into the air or come out in your food as it can't escape through all that insulation.
Now, for a serious bread baker, they are invaluable together with experience and record keeping in determing the amount of stored heat within your oven for batch numbers, quantities and baking times.
Initially, we are not going to install them into Hendo's oven as nobody out there understands them and I see them using his oven for the same as mine. We can however, install them at any time if needed.

neill

[Cooter]

Re: Thermocouples -- what to do?

Hi Neill
I am building a Pompei igloo oven up at Norton Summit in the Adelaide hills
i am approaching the hearth slab concrete pour stage
I have experience with pottery kilns and own a digital reader for my kiln Pyrometer
I appreciate and understand your comments on the necessity for using thermocouples,and may not go down that path
I see myself mainly using the oven for pizza entertainment so the infra read thermometer may be all i use....
but while I am in the early building stages what would you suggest in making provision for them to keep my later options open?

If i placed copper sheathes in the pour ,would you suggest they go through the concrete hearth pour or can they be placed laterally in the vermiculite/cement mix under the hearth bricks?
Would a center top and center bottom be sufficient?

cheers Cooter

[nissanneill]

Re: Thermocouples -- what to do?

Hi Cooter and yet another Aussie welcome to the forum.
A further Adelaidian as well to boot!
Look, my oven was built on a concrete reinforcing wall and I needed to place the copper (only because I had the left over tubing from some lpg vehicle installations) in place prior to the pour of the slab and vermiculite layer.
If you follow my guide with such tubes, just ensure that the bends that you make in the tubes are not too sharp to inhibit the feeding of the wire through them. Also measure 'accurately' their length because you can mark that length on your thermocouple wires to ensure that they are fully in position to give you accurate measurements.
Check out Hendos set up (although he died some time ago, I am still doing some work to finish his oven and kitchen for his widow), we are not planning on installing them but they can be put in at any time if needed.
I placed mine in the centre of the hearth and dome, 4 in all to measure close to the brick hot surfaces and the second to measure the amount of 'soak'. If you want any sort of control or indication of your temperatures, then you should have at least 2 in the hearth and 2 in the dome. You could, if needs be, put more in the hearth in different locations BUT they will only provide temps in those locations which will be different to other cooking/baking surfaces on your hearth where you have had your fire/coals or where you have 'used' some of your stored heat.
By the way, you could use 'Bundy tubing' rather than copper tubing for cost saving, eg, used fuel/return/brake lines from a car would do. A couple of bucks from U-Pull-it or a wrecker would be much cheaper than copper!

Neill

[Cooter]

Re: Thermocouples -- what to do?

Neill
many thanks
a really good idea regarding the tube measurement
hopefully i will have some photos posted soon
cheers cooter

[Cooter]

Re: Thermocouples -- what to do?

Neill
Thanks for the info on thermocouples
I met myself half way and made provision for one in the centre of the floor and will do likewise in the dome
As an after thought is it feasable to place 2 thermocouples in the same tube reaching different depths?
I have just cracked the uploading of photos and started a new thread "cooter's pompei" with a few progress pic's
Being a fellow Adelaide dweller thought yuo might like a squiz
cheers cooter

[nissanneill]

Re: Thermocouples -- what to do?

Hi Cooter,
I wouldn't put 2 thermocouple wires (or pairs as they ned to be) in a single tube as I believe the thermocouple welded end needs to be in contact with the surface to read that temperature rather than the air around it.

Cheers,

Neill

PS. What area of Adelaide do you live? It looks like the outer suburban foothills, but only guessing from your terraced retaining walls.