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  #11  
Old 06-04-2013, 12:37 AM
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Default Re: how many thermocouples?

Thanks for the info Faith. RichC Glad to see you’re still considering.

I have not done a whole lot of research to see what’s available and the associated cost. I notice on Utah beehiver’s build, he has placed tubing during the dome build process, I think that’s an excellent idea. I’m not sure if he has finished and what his final plans are.

I work in power generation industry and thermocouples are common place. There are many types of thermocouple. Type K thermocouple is one that should work fine. Usually thermocouple probes are housed in some type of thermo well. This keeps the probe safe from the process measured and allows the thermocouple to be removed easily. A common type thermocouple probe found on gas turbine generators consist of 1/16” stainless tube like probe in various lengths. The probe can be easily removed and reinserted. This probe is inserted in into stainless tubing with it terminating at the point inside the machine where the measurement is needed. The probe lead wires are connected to the extension wire and they continue to the readout instrumentation and controls. My plan is to use an inexpensive thermocouple probe of some sort. I have not found an inexpensive probe that will work in the tubing. With that being said push comes to shove I figure I can take inexpensive thermocouple extension wire and fabricate my own for pennies. I figure I should be able to get a digital read out for less than $75 not sure on a multiple selector switch.

I’ll let you all know what I figure out. I’m all open for any suggestions and or comments.
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Last edited by kbartman; 06-04-2013 at 01:26 AM.
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  #12  
Old 06-04-2013, 02:51 AM
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Default Re: how many thermocouples?

Most people find that fancy temp measuring equipment is pretty redundant after a while as you tune in to how the oven behaves with the fire. It is rather incongruous to use electronic devices on an ancient oven. I find my stopwatch, observation and a little semolina flour on the floor surface is all I need for pizza and for bread or a roast a cheap air temp thermometer placed inside the oven is perfectly adequate. Thermocouples and IR thermometers are helpful when getting to know your oven, but when experienced you'll hardly ever use or need them.

Last edited by david s; 06-04-2013 at 02:52 AM. Reason: Typos again
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  #13  
Old 06-04-2013, 03:54 AM
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Default Re: how many thermocouples?

I love being the odd duck. I like and use my thermocouples all the time and don't find them incongruous at all. But then again I built my oven for bread and not pizza. I also do large batches of bread on a single firing so I need to know that I have enough stored energy to do that.

If all I was doing was pizza and a few loaves of bread I agree that thermocouples are not necessary. But still, if your a bit of a geek and like gadgets and need precise heating numbers thermocouples are cool.
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  #14  
Old 06-04-2013, 06:25 AM
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Default Re: how many thermocouples?

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Originally Posted by Faith In Virginia View Post
I love being the odd duck.

But still, if your a bit of a geek and like gadgets and need precise heating numbers thermocouples are cool.
Faith, I'll be geeky duck with you.......if that's ok
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  #15  
Old 06-04-2013, 07:32 AM
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Default Re: how many thermocouples?

KB,

I'm also in the geek club. I bought a digital thermometer on-line for $40- (nice big display because my eyes aren't getting any better as I get older!) It takes 2 type K thermocouples and you can easily switch to read either one. It came with 2 cheap thermocouples but I went ahead and bought 2 high temperature (1000 degrees centigrade) thermocouples on line with extra long leads for about $30. So I was $70 out the door with exactly what I needed. I can post of photo of the meter after I get home if it would help.

Neil
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Old 06-04-2013, 06:52 PM
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Default Re: how many thermocouples?

KB

here is my digital thermometer.

I am currently using it to monitor my (daily) small curing fires to ensure I don't get too much heat too soon.

I stuck the end of the thermocouple near the fire I could get a nice high temperature reading!

It has a differential temperature capability (T1-T2) so I was wondering if I could somehow use that to ensure that I don't get thermal expansion (cracking) problems....

Sorry, "you can take the man out of the engineer but you can't take the ..." or something like that!

Neil
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  #17  
Old 06-04-2013, 08:00 PM
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Post Re: how many thermocouples?

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Originally Posted by boerwarrior View Post
KB

here is my digital thermometer.

I am currently using it to monitor my (daily) small curing fires to ensure I don't get too much heat too soon.

It has a differential temperature capability (T1-T2) so I was wondering if I could somehow use that to ensure that I don't get thermal expansion (cracking) problems....

Neil
Neil,
That is a neat inexpensive set you have there, $40 bucks you can't beat that. Where did you get?

It looks to me that the meter has three selection options. T1 or T2 and differential read out T1-T2. I'm sure you could better monitor a thermal temperature difference with the meter, and also calculated a differential expansion of some sort. The calculation is above my expertise but maybe along your line of work. I’m sure we can figure out something. Having some experience with temperature instrumentation and it uses, but far from being an expert. I’ll take a WAG. I would think that placement of T1 and T2 would be the first challenge. Where is the most likely place the greatest temperature difference would be found and would create thermal stresses during curing? I would think the top dead center of the dome would be the higher of the two. Where to place the second I’m not sure.

I’m thinking as stated by others that insulation would have the greatest overall benefit to keep these thermal stresses in check. The more I think about how to monitor these temperature differences is making my head spin. I’ll throw in the old BS excuse I have be known to use, and that works pretty well at work. As in most endeavors cost is an issue. “The cost to benefit ratio” a excuse that keeps me as busy as I want to be. They trusted I know what I’m talking about when I don’t have a clue. I hope they never call me out on it.
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Last edited by kbartman; 06-05-2013 at 02:02 AM.
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  #18  
Old 06-05-2013, 03:20 AM
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Default Re: how many thermocouples?

Ok, here is some very brief research on the associated cost and my 2 cents.

Quote:
Originally Posted by Faith In Virginia View Post
Here you go KB,

I have 6 thermocouples

Two in the floor one at 3/4 inch from the surface and one 4 inch from the surface.
Two in the walls mid way up the wall 3/4 inch from the surface,one left one right.
One in the wall midway up 4 inches from the surface.
One in the wall midway up between the oven and the insulation 7.5 inches from the surface.
Quote:
Originally Posted by RichC View Post
Well KBartman, I may actually put 1 or 2 in. Also how do you guys fit them so they're replaceable? Thermowells aren't very cheap or is there some sort if DIY thermowell or sleeve that's made out of copper pipe or something, what's the best thermowell to use?

Faith, you have some very nice highly accurate equipment but a bit above my price range. My goal is to impress my guests and get a fairly accurate temperature read out; at the same time have some techy fun along the way. I agree with the placement of your thermocouples and may throw in a few more for sh@ts and grins. Portability is not a concern of mine, I'm thinking of a permanent display. Not sure where to locate it, I don’t want to take away from the ambiance of the ancient oven.

I have to make a poke at davids on this.
Quote:
Originally Posted by david s View Post
It is rather incongruous to use electronic devices on an ancient oven. I find my stopwatch, observation…………
I’m sure you meant to say sand hour glass instead of a stopwatch……lol………That being said I’ll find a inconspicuous convenient location to mount my techy toys.

To make a long story short I’ll get to the point. I think RichC copper pipe is a good idea. I think a roll of 3\8 tubing will do fine in creating an inexpensive thermo well and facilitate easy replacement.

I found an inexpensive 1\16 din single loop controller for $67 it will make a perfect readout display and provide for more techy future toys. And it also can double as a temperature control on initial curing. Not my idea though, I read it somewhere here in the forum. Throw in a cheap $15 selector switch and some cheap homemade thermocouples I’ll have all the other tech geek’s envois. All done under a $100.

Warning my estimates tent to have cost over runs. Consider my bathroom remodel a few years back at $3500 ended up being $12,000. Also my WFO estimate I told the better half is well past the $1500 ok to start project agreement. She’s always a good sport though. She'll always end up with a better project then first conceived.
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  #19  
Old 06-05-2013, 04:01 AM
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Default Re: how many thermocouples?

Quote:
Originally Posted by kbartman View Post

To make a long story short I’ll get to the point. I think RichC copper pipe is a good idea. I think a roll of 3\8 tubing will do fine in creating an inexpensive thermo well and facilitate easy replacement.
I used a copper pipe for the sleeve for my thermometer probe on my mobile oven and wish I hadn't. The thermal conductivity of copper is k value 400 W/mk That of stainless steel 16. A metal tube connecting the inside of the oven to the outside will conduct a fair amount of heat away from the chamber.I now always use stainless if fitting one on an oven. Another little problem I had was that the pipe fitted too tightly in the wall of the dome so every time the oven heated up it would push the pipe out of the outer shell a few millimeters each time. I had to fix it by making the hole in the inner wall slightly oversized so it would not grip the tube. That was about 4 years ago and it is still functioning well.
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Old 06-05-2013, 05:35 AM
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Default Re: how many thermocouples?

Quote:
Originally Posted by david s View Post
I used a copper pipe for the sleeve for my thermometer probe on my mobile oven and wish I hadn't. The thermal conductivity of copper is k value 400 W/mk That of stainless steel 16. A metal tube connecting the inside of the oven to the outside will conduct a fair amount of heat away from the chamber.I now always use stainless if fitting one on an oven. Another little problem I had was that the pipe fitted too tightly in the wall of the dome so every time the oven heated up it would push the pipe out of the outer shell a few millimeters each time. I had to fix it by making the hole in the inner wall slightly oversized so it would not grip the tube. That was about 4 years ago and it is still functioning well.
All good info Dave. A little above my pay grade. I only install, repair, troubleshoot, operate and maintain the equipment. I try to leave the design and calculations up to the experts and learn from there mistakes. Usually the design team is long gone and we experiment to come up with solutions’ like your.

Ouch stainless tubing, you can now see the why my projects are plague with cost over runs.

Hope you didn’t mind the poke and hope you will be getting the hour glass out to impress the guest.
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Last edited by kbartman; 06-05-2013 at 07:43 AM. Reason: proof reading after posting
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