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Old 06-26-2007, 05:50 AM
ihughes's Avatar
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Default Thermocouples -- what to do?

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?
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Old 06-26-2007, 06:15 AM
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Default 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.
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Last edited by wlively; 06-27-2007 at 11:31 AM. Reason: Addition and typos
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Old 06-27-2007, 05:23 AM
ihughes's Avatar
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Default 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
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Old 06-27-2007, 06:37 AM
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Default 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
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Old 06-27-2007, 07:47 PM
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Default Re: Thermocouples -- what to do?

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





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Old 06-27-2007, 09:46 PM
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Default 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 (Thermocouple Queries) 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 (Hendo's Oven) 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.
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Old 06-28-2007, 04:51 AM
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Default 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
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Old 06-28-2007, 07:12 AM
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Default 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 voilà!

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.
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Old 06-11-2008, 06:44 AM
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Default 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.....
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Old 06-12-2008, 02:54 AM
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Thumbs up 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
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