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-   -   Thermocouples (http://www.fornobravo.com/forum/f6/thermocouples-795.html)

james 07-15-2006 12:09 AM

Thermocouples
 
I wanted to run an informal poll and see what everyone thought about thermocouples. Did you install one? Would you recommend one? How do you use yours? Where did you set it/them (floor or dome, how far from the interior)?

Comments greatly appreciated. Please, jump in.
Thanks.
James

arevalo53anos 07-15-2006 05:12 AM

4 Attachment(s)
James:



Being myself an electronic engineer working in aircraft prototypes instrumentation, it is logic to think that I could be a kind of fanatic by obtain and register any data.

Actually, I am J.

Even being a suspect supporting the thermocouple idea, I believe that these are a great tool to help anyone to understand the baking characteristics of his oven.

Of course, the thermocouples are not essential to bake, as you could learn using another tool or friend experience or even to acquire knowledge with trial and error. However, if you are looking by constant and strong results, obtaining data (IMHO) is the way to go.



Following, some excerpt (not edited) from previous mails in this forum.

There are some installation tips, too.







My 42 inches Pompeii type brick oven have eight thermocouples installed, being four of these distributed in the hearth and four in the ceiling.

There are another one, free to measure at any place that necessary.





Visualizing the layers by cutting the oven vertically by the middle we could see, from down to upward, a first layer of three inches of vermiculite mixture as isolation, a second layer of two/three inches of concrete slab, a third one of sided fire bricks arranged to be the hearth, following by the empty semi sphere space corresponding to the oven dome, surrounded by a four and half inches dome wall of half firebricks, then the one inch of cladding and three inches of vermiculite isolation.

The thermocouples are installed, from down to up: one just below the isolation in the horizontal center of the oven, another between the slab and the hearth bricks (in the center too), two ones embedded in the sided bricks, 1/3 inch from the hearth floor, one of these in the hearth center and the other in a half way between the center and the back of the hearth.

The remainder four are in the dome ceiling, one measuring directly the ambient chamber air, the second embedded in the ceiling brick (1/3 inch from chamber surface), another between the brick and cladding and the last one just facing the outer limit of the vermiculite isolation.

Eventually I use to measure the entry of chimney, too.



I use to register the oven temperatures when firing, baking and ‘resting’, having recorded history files of the oven temperatures behavior.





It is acceptable splicing the thermocouple wires, twisting (joining by twist) them (same thermocouple type wire and colour, 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 colour) and Chromel (negative – red colour – 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 made 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.

If 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! This 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). This naked twisted wires could be isolated from any conductor material and environment, if necessary.



I hope this helps.Luis

christo 07-15-2006 05:37 AM

I like data
 
I will put a few thermocuples in my oven.

I think it will speed up the process of getting to know the characteristics of the oven.

Truely necessary - absolutely not. Fun - for me yes.

Christo

arevalo53anos 07-15-2006 06:30 AM

James and Christo:


And, of course, is absolutally no necessary to have a lot of thermocouples in the oven.
You would like to install at least one thermocouple a half inch deeper in the center of the hearth floor and another in the ceiling, measuring ambient temperature.
Both of them excellent indicators of the oven behavior. Great help.

Luis


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