#11  
Old 11-04-2008, 01:12 PM
Cooter's Avatar
Peasant
 
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Location: Australia
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Default 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
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  #12  
Old 11-04-2008, 02:31 PM
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Il Pizzaiolo
 
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Location: Adelaide, South Australia
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Thumbs up 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
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  #13  
Old 11-05-2008, 01:20 PM
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Default 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
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  #14  
Old 11-16-2008, 04:54 PM
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Default 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

Last edited by Cooter; 11-16-2008 at 04:58 PM.
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  #15  
Old 11-16-2008, 10:55 PM
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Thumbs up 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.
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  #16  
Old 11-16-2008, 11:36 PM
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Default Re: Thermocouples -- what to do?

I have a thermocouple in my oven, but can't really recommend it. I find the best instrument is the stopwatch function on my cheap digital watch. One hour for bread or roasts, one and a half for pizza. The thermocouple can just complicate the issue. The temp it displays usually lags by about 1/2 hr when firing up. We use one of those thermometer probes you jab into roast meats- it's really good. I'm told you can also use it for bread, but the smell of the food when it's done is all the indication I need.
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Old 11-17-2008, 02:05 PM
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Default Re: Thermocouples -- what to do?

Neill
We are up in the beautiful Norton Summit what about yourself?
I'm off on a scrounging day chasing up vermicullite,bricks etc
Thought I would start at I think its called Thermal Ceramics out near the powerhouse stadium in torrensville somewhere
Cheers Cooter
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  #18  
Old 11-18-2008, 12:58 AM
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Thumbs up Re: Thermocouples -- what to do?

Give them a call. They are exceptionally helpful and have all the insulation materials needed. I'm not sure whether they still carry fireclay as I think the batch they had when I bought mine, was their last and weren't planning on carrying it anymore. I still have 2 x 25kg bags if you want some. They are only a couple of stone throws away from the Powerhouse stadium.
I also have around 60 firebricks, a few tapered and the remainder standard rectangular. What sort of brick are you looking for anyway, firebrick, old common reds or what I would use in my next build, Littlehampton fired clay pavers?
I'm just up behind the Flinders Uni at Flagstaff Hill if you wish to come and check the oven out.
.
Cheers.

Neill
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  #19  
Old 11-18-2008, 06:36 PM
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Default Re: Thermocouples -- what to do?

I agree with Neill when I built my oven I installed TC wires in 2 locations in the floor and 2 in the dome. I never use them a handheld IR thermometer from HF and a food probe with transmitter to a remote unit is all I ever need or want.

Cooking is always variable (dough moisture, thickness, topping variables, etc) we adjust for these variables in the end by adjusting cooking times, location in the oven etc. These differences are what makes our food Art. Wonderbread is consistent but who amoung us prefers it to a wonderfully prepaired loaf of homade bread that looks different from the other 3 loaves cooked at the same time.

The cheapest K type TC meters I have found are on a HF digital electric meter they put it on sale regularly for about 20.00 US. I bought TC wire from Allen Scott (Bread Builders) the standard K type plug fits into the electric meter and you can read F or C. The plugs are a available on the net cheap. The heat sensing end of the TC wire is stripped of about 1/4" of insulation then the tip of the two wires are silver soldered. It is the temprature at the conection that you are reading.

I still have all of the parts to rig TCs and I won't put them on another oven.

One rule I use is that the oven air temprature is about 100 degree F less than the surface temp of the hearth. If I want to bake bread @400 I'm looking for an IR reading of 500.
I always use a remote probe in one loaf of bread and take it out when the internal temp is about 15 degrees lower than the boiling point at my altitude. I use 195 in Houston TX

Doug
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