# Extreme High Temperature Measurment

Discussion in 'General Electronics Discussion' started by Robo_Pi, Jun 2, 2017.

1. ### Robo_Pi

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Oct 5, 2015
Hi, I don't post here a lot but I'd like to get some ideas for the following project.

I'm thinking about building a furnace for melting aluminum. I've watched a lot of YouTube videos for ideas on how to build the actual furnace, and there are certainly many different ways of doing that. I'll be using wood as a fuel source which is a lesser used fuel, but there are actually quite a few wood-fired furnace examples on YouTube. The problem is that I'm not really thrilled with any of them as they seem to fairly random in the way they are used. Some people have furnace that just barely melt the aluminum other have actually produce wood heat that far exceeds the temperatures needed. And that's actually not good for the Aluminum.

In fact, this is the reason that I would like to monitor the temperature. I'd like to be able to control the blower so I get just the right temperature to cast the aluminum without over-heating it unnecessarily. So I thought I'd post the project here as a question to get ideas.

I have come up with some ideas already on my own. In fact, the best idea I've come up with thus far is to employ the use of a small steel bar maybe 1/2" in diameter that transverses the furnace wall, Then attach a high-heat-tolerant resistor to the end outside the furnace. Then just monitor the temperature of this steel rod and "extrapolate" from there to calculate how hot the hotter end must be. I could probably calibrate this over time to work, assuming the idea works at all.

Another idea I had, but I'm not sure how to implement it, is to have a sensor that "looks" through a hole in the furnace at the internal flames and reports the frequency of light received, and then calculate the temperature from the flame wavelength. Like I say, at this point it's just an idea and I'm not sure how I would actually implement it.

One thing I would like to add is that it's imperative that this is an extremely low-cost project. I have plenty of Arduino boards, and I'm willing to program one for this project. But I can't be paying out several hundred dollars for a commercial temperature reader. So this needs to be a DIY electronic project that can be done for peanuts.

It doesn't even need to be electronic if anyone has any other suggestions. But I'm thinking a nice electronic readout would be cool. In fact, if I'm using an Arduino to measure the termp, I could then also program the Arduino to control the furnace blower and that would even be better yet. That way it would be a totally automated furnace that monitors and keeps precisely the right temperature all on its own.

I can figure out the part of getting the Arduino to control the blower, what I need is a dependable temperature sensor.

Anyway, I'm just looking for ideas, so all input is welcome. Thanks.

By the way I haven't built the actual furnace yet, so when I do build it I can include whatever hardware is required for this sensor to work properly.

~~~~~

I just had another idea as I was typing this. What if I put a steel bar trough the furnace so it sticks out both sides. Then attach wires to that rod and run a small current through it. Does the resistance of steel change with temperature? Maybe I could just use the steel rod as the actual "thermistor"? I actually like that idea if it would work.

2. ### davennModerator

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Sep 5, 2009
melting point of aluminium is 660 C
so this would cover your needs, it goes to 700 C .....

http://www.ebay.com.au/itm/Digital-...103319?hash=item235f158d57:g:2NMAAOSwHPlWcnr5

you may find ways to interface it with other electronics

Dave

3. ### Robo_Pi

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Oct 5, 2015
Thanks Dave. I didn't realized they had devices like this that are so affordable. That's certainly an option to be sure. It's hardly an electronic "project" though. More like an electronic product.

I guess I'm really thinking about incorporating an Arduino into this picture for a total self-controlled blower. Even with the hand-held device I would need to monitor the temperature and control the heat source myself. That's certainly doable. But an automated Arduino project would be more fun.

Also I have about 25 Arduino boards laying around so I'd kind of like to put some of them to use.

But I do thank you for pointing this device out. I didn't know they were that inexpensive. It's nice to know that these are available.

4. ### davennModerator

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Sep 5, 2009
trying to do high temp reading any other way would be extremely difficult ... mainly cuz of the problem of finding sensors that
can operate at those temperatures, hence why non-contact is the way to go.
I used one of these handheld ones out on the hot lava in Hawaii to make sure I was walking in the safe areas

the project part for you is to discover how to interface one of those units with your processor to do your other things
There's really no need to re-invent the wheel as far as the actual temp sensor/readout goes

Dave

5. ### Robo_Pi

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Oct 5, 2015
"the project part for you is to discover how to interface one of those units with your processor to do your other things"

I was reading over the product you pointed to and I don't see where that gun offers any outputs other than the actual LCD readout.

I do appreciate the suggestion though, and I may end up purchasing one of these anyway.

I just thought I'd post this here in case someone else has had experience with a similar situation. You can never go wrong with asking for ideas. There's always more than one way to skin a cat as they say.

6. ### davennModerator

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Sep 5, 2009
it probably doesn't ( on the outside) I didn't expect it to
the fun part is to get one and open it up and see what can be done with the electronics inside

7. ### Bluejets

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Oct 5, 2014
I do my own castings for the miniature 4 stroke engines I build and to me, any temp measuring device would just get in the way and create a safety hazard. I use a high kw gas burner and firebrick enclosure with the appropriate crusibles and clamps for dispensing. Never found precise temp of the aluminium to be an issue. If you must, then would the handheld infrared units have a high enough range?

8. ### Robo_Pi

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Oct 5, 2015
I'm not going to take a manufactured lazer gun apart and try to figure out how it works. In fact, I've found that in modern day equipment like this it's often impossible to even figure out how they work. They often use unmarked chips, and who knows what kind of programming they might have in their microcontroller. Not only this but they often even build them in a way that makes them extremely difficult, if not impossible, to disassemble without breaking them entirely.

In any case, I found what I need a lot cheaper on YouTube just now:

In case anyone else is interested here's a temperature probe for about \$6 that will measure up to 2200 F directly.

I should have just search YouTube from the get go.

9. ### Robo_Pi

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Oct 5, 2015
Most of the YouTube videos I've watched on casting aluminum don't bother measuring the temperature. And the vast majority of them also use gas which tends to produce consistent heat anyway. Maybe that's the reason they don't need to worry about the temp so much.

I'm going to be melting aluminum with wood heat, and this presents additional problems because different types of wood burn at different temperatures. In fact, even a single species of wood may burn at quite different temperatures depending on how dry, cured, or green it is. In fact, this is why most people who cast metals don't bother with wood because they see it as being too problematic.

I have no problem using the wood fuel, especially because in my case it's totally free. Can't pass that up in my financial situation. I have a sawmill, so I have literally tons of scrap wood laying around. I'm not going to go out an pay for gas when I have free wood.

But the wood does present the additional "problem" of being more difficult to control for consistent heat. It's not really a "problem" if a person is prepared to deal with it. It's only a problem if the person who is using wood for fuel isn't aware that it requires special attention.

And so this is why I would like to monitor the temperature of my wood-fired furnace.

I've seen people on YouTube casting aluminum using wood fires. But often times they do it extremely crudely and they aren't doing anything to control the heat. So they often end up with molten aluminum that's either too cold and doesn't poor well, or too hot which often cause the casting to have air pockets, etc, from the excessively hot metal.

So it's using wood as fuel that is the special case here. If I were going to heat with gas temperature most likely wouldn't be much of an issue at all.

hevans1944 and davenn like this.
10. ### duke37

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Jan 9, 2011
Many, many years ago I used an ORP12 photoresistor looking down a ceramic tube to control temperature.
Chromel/alumel (K type) thermocouples will work at the temperatures you want.

Have you thought about using charcoal as a more consistent fuel?

11. ### Irv

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Jun 7, 2017
There's a 380 degree C sensor for arduino for \$14.50 at Amazon.

12. ### davennModerator

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Sep 5, 2009

nowhere near high enough !

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Oct 5, 2015
14. ### davennModerator

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Sep 5, 2009
Jennifer Thornton likes this.
15. ### Jennifer Thornton

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Aug 10, 2017
It is a great deal.

16. ### Jennifer Thornton

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Aug 10, 2017
In general for really hot things you measure the emission spectrum at a exact wavelength and then find how much broadening there is due to the doppler effect. This is directly related to temperature as long as the energy distribution is a maxwellian.

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Aug 10, 2017