#1  
Old 10-23-2006, 07:59 PM
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Question Using thermocouples

I have read the posts regarding thermocouples and I still don't feel comfortable that I will buy the equipment/materials to make the thermocouples work properly. I understand the how they work but there are many different kinds of K type thermocouples(max temp/ length/ etc.) Setting the thermo's in the dome cap is only done once (we hope) and I would prefer to buy a kit that gives me 4-6 themocouples with a digital reader that I could install with the comfort that I am doing it with the right equipment. I wonder if James could float the idea of some kind of themocouple kit to sell on Forno Bravo? If there was high enough interest it may be something to look into.

Cheers, Versachi
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  #2  
Old 10-24-2006, 05:04 AM
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Ciao Versachi,

I will research this and get back to you. I have to agree that it makes sense for Forno Bravo to do this, and put together an instruction sheet. I will get back with move information on this.

If anyone has any leads for us to pursue, products you have used and like, read about, etc., let me know.

Also, I want to poll everyone. We would only want to offer one kit - to keep things simple. Should it have two sensors and a dual readout, or four and a quad readout?

Let me know what y'all think.
James
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Old 10-24-2006, 06:46 AM
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Versachi,

This could be an extensive answer since I am going to use answers from past threads. However I think that the following paragraphs would give you the peace of mind that could be necessary to obtain the thermocouples best adapted to your oven.

“It is acceptable splicing the thermocouple wires, twisting (joining by twist) them (same thermocouple type wire and color, please).

Of course, could be better if using a pair of thermocouple connectors.

If soldering, the solder to be used will be silver one.



I would like to explain what this mean.

I know that I had answering this question in another thread of this forum and I am sorry by repeating myself. However, may be the next sentences could clarify other oven builders about the thermocouple installation and use (becoming more common each day).

I´ll try to be simples (sorry, I am an engineer).

A thermocouple is a temperature measurement sensor, that consist of two dissimilar metals joined together at one end (a junction) that produces a small voltage when heated. This voltage is interpreted by temperature measure equipments as a change in temperature.

There are several thermocouple types, being the K and E types the most common ones, each one with a different temperature range. Being that K type could reach until 1800°F and E type 1000°F.

Normally, the oven builder would like to use the K one. It is identified by the yellow color on the match connector and the wire material is Nickel (positive – yellow color) and Chromel (negative – red color – yes, red is negative here!)

The thermocouple could be purchased by ft (open wires), by ready made thermocouples (certain junction type, a quantity of wire and the match connector) and several other combinations and types that we do not discuss here.

Even either you have several ft of wire or a short ready made thermocouple you will need either to make the junction or to extend the ready made thermocouple wire.

To extend the short one, another same thermocouple wire type need to be spliced. There are the possibilities above descripted.

If soldering (this is not longer necessary, but the professional choice), silver solder need to be used.

When using a matched pair of thermocouple connectors, they will be corresponding to the thermocouple type, in our example, the yellow (type K one) connector.

Do not forget that the red wire is the Negative One! These connectors are made from some plastic material, do not accepting high temperatures!

Splicing the thermocouple wires by twisting is the easy option to non professionals. The isolation of the wires will be retired approximately 1 inch from the end. The two naked extremities of the wires to be spliced will be crossed and firmly twisted three or four times (only the first junction will produce the small voltage when heated, but the remainder ones are there to maintain the wires in place and to assure the wires connection). These naked twisted wires could be isolated from any conductor material and environment, if necessary.”



Another point

“The position of the thermocouples could be good or bad, highly depending on your experience.

There are two temperatures that, I believe, are the most important ones.

The first one is that gives you the reading of the hearth temperature. Hearth temperature is the temperature in which the dough is going to be baked. The only heat that really ‘reach’ the dough is the one in the surface edge. Where the thermocouple need to be installed depends on your reference.

For example, comparing temperatures with someone in this site, the ones in my over were consistently higher that the others in the second oven. This was because these were installed an half of inch deeper in the bricks. However, both of us consistently baked the dough at ‘our’ temperature target.

I have two temperatures in the hearth at same deep, being one in the middle of the oven in front of the door and the other is a palm before the dome wall. The first one is in the normal pizza ‘position’ and is the one that I care/watch more.

The second temperature, that I believe be important, is the ambient dome one.

This one is mostly used to bake bread, or any food baked with residual heat. This thermocouple will be installed passing thru the bricks (to the inner dome ambient) and the sensor element will be in direct contact with the internal dome environment.

The position of the thermocouple was discussed in another thread as at 10 and 2 hours over the door (horns of devil position LOL – round or Pompeii oven)

Of course, I agree with Jim in reference to the prove 4.

The experience with my oven, with 8 fixed and one floated thermocouple, make me think that the transference of temperature by conduction is almost similar in the cladding mass below the hearth as it is in the cladding over the dome, then, if I could use only four thermocouples, I will install the third thermocouple in between the cladding and bricks and the fourth one between cladding and top vermiculite layer.

Resuming it,

Probe 1 in the bricks near of the hearth surface (oven floor) and in the pizza dough average position for baking.

Probe 2 as ambient dome temperature (devil horns position).

Probe 3 between cladding and bricks (higher in the dome) and

Probe 4 between cladding and top vermiculite layer.

This arrangement could give you the better moment (hearth temp) to bake the pizza, the great moment (ambient temp) to bake bread or food without fire and the temperature gradient, to be sure how is your oven behaviour and how many batches you will be capable to bake with one charge.

However, even I use to use (with a lot of spreadsheets and curves studied) all the 8 thermocouples information, you would not be worried about this.

There is nothing there, that two or three mississipies do not solve LOL.”



James:



IMHO, it will be a good idea that Forno Bravo sells a thermocouple kit with instruction sheet. I brief information in it showing how the thermocouple works will help too.

Answering your poll I believe that a 4 temperatures kit will give more complete information about the oven and I will go with it.

However, even if I am sure that two temperatures is not so great, you would like to think that the vast majority of the bakers prefers to bake by feeling, that to read only two temperatures is easy than four, and the aggregated costs of going to four temperatures could be sufficient to justify that Forno Bravo offers the two possibilities.

Sorry by this long answer. I hope this help.



Luis
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  #4  
Old 10-24-2006, 07:36 PM
Versachi's Avatar
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Default thermocouples

Thanks arevalo for your response. I had read your posts on thermocouples which were helpful. James, I would prefer to have 4 thermocouples and a quad readout. Any more than 4 for me would give me paralysis by analysis. I would probably not bake anything trying to wait for 15 thermocouples to get to the right temps. . Glad to hear that a door is going to be available on Forno Bravo. I won't be able to build my oven until next spring (it's cold here in Thunder Bay, Ontario) but I plan on buying a door this fall to support Forno Bravo. Least I can do imo!

Cheers, Versachi

Last edited by Versachi; 10-24-2006 at 07:43 PM.
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  #5  
Old 10-25-2006, 02:32 AM
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Default Thermos

Versachi,

I use four thermocouples in my AS oven and find that the readings supplied give me all I need: hearth, slab, dome, cladding. The major benefit with this arrangement (I bake bread) is knowing how much the mass has been saturated with heat. When it's up to where I think it should be, then I'm confident in doing multiple bakes. This is particularly helpful in winter, even though I'm significantly south of you in Ontario.

Cheers,
Jim
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  #6  
Old 01-25-2007, 03:51 AM
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Default Re: Using thermocouples

Quote:
Originally Posted by arevalo53anos View Post

The position of the thermocouple was discussed in another thread as at 10 and 2 hours over the door (horns of devil position LOL – round or Pompeii oven)
Luis,

What's LOL? Are the 10 and 2 o'clock positions looking from above (plan view), or from the front (elevation)?

Cheers, Paul.
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  #7  
Old 01-25-2007, 07:55 AM
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Default Re: Using thermocouples

LOL = Laugh Out Loud
ROTFLMAO = Rolling On the Floor Laughing My A$$ Off
IMO = In My Humble Opinion
QED = Quite Easily Done

Mr. Feinman = My hero

10 & 2 o'clok are elevation/front view
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  #8  
Old 11-16-2007, 04:25 PM
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Default Re: Using thermocouples

James, what ever happened to the idea of FB selling the thermocouple kit? I would jump on it if you had the kit.
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