Temp sensor in a fireplace?

[JonR]

Hi all,

We're installing a masonry heater with a bake oven in our new home and it would be nice if we could use a temperature sensor inside to measure the temperature in the oven. This may be a tall task, however, and if so it's probably not worth it. A masonry heater is a high-efficiency fireplace with a sealed combustion chamber where the manufacturer claims the temperature can reach 1,500F or higher. The bake oven is a cavity (also with a sealed door) located directly above the firebox where items can be cooked. The bake oven is connected to the firebox by a slot through the middle.

The way these things work is to load a "charge" of wood into them and burn it up fast and hot, driving the heat into the thick masonry walls where it then slowly radiates into the living space over the next 6 - 12 hours. For baking, foods likely wouldn't be inserted into the oven until the fire was out and the temperature had cooled off to a useful level. It would be nice to be able to measure the heat decay inside the oven to help us figure out how long the temperature holds in a given range, how long it takes to get down to certain levels, etc. The alternative is lots of manual measurements and trial and error.

So, is there a way to do this? A wireless sensor would certainly be easiest to install (the doors are glass) but there might be a way to get a wire inside without causing problems. (This thing isn't entirely sealed with mortar - some joints are filled with a felt-like material to allow the parts to expand and contract.)

Is this a worthy challenge to the collective wisdom of CocoonTech?

JonR

 

[politics123]

Well, you can always use an Infrared temperature gun. Not sure how to connect it to anything, though

 

[hucker]

Thermocouples can measure that range:

http://www.omega.com/prodinfo/Thermocouples.html

Looks like a K or an E might work for you.

Chuck

 

[BraveSirRobbin]

Thermocouples can measure that range:

http://www.omega.com/prodinfo/Thermocouples.html

Looks like a K or an E might work for you.

Chuck

Problem with a thermocouple is their voltage output vs temp measured isn't a simple linear relationship. I.E. you need to refer to a look up table. Also, I believe it needs a reference temperature at it's terminal strip/junction.

Also, note the small millivolt change can represent a large temperature change, so measuring this with something like an 8-bit elk analog input would be a challenge.

This can be done, but I'm thinking you will also have to purchase a data logger made to measure this type of sensor.

 

[TonyNo]

This device should work well, has cold-junction compensation, and seems reasonably priced.

 

[nsisman]

JonR,

I think I saw something like your fireplace years ago up here in a fireplace shop.

I likely have it spellled wrong but is was somethng like "Kakkle offen" ? German or Swedish maybe ?

It took a charge of wood and then heated up a bunch of ceramic tiles and was supposed to be very efficient and put out heat for days !

Neil

 

[JonR]

nsisman,

That's the same kind of fireplace - they go by different names but all have their origins in Europe, particularly Scandinavia, from the period when the forests started to get used up and more efficiency was needed in fireplace design. This fireplace is supposed to be able to heat about 2000 sq. ft. as the primary heat source and they claim it's about 90% efficient and very clean. We've been told that operating ours twice a day will probably be enough to keep a nice consistent heat all day.

Most of these are custom built on-site although we found a kit from Temp-Cast that our mason was able to assemble quite nicely without having any prior experience with it. We're eager to see how well it performs in reality!

JonR

 

[hucker]

Also, note the small millivolt change can represent a large temperature change, so measuring this with something like an 8-bit elk analog input would be a challenge.

This can be done, but I'm thinking you will also have to purchase a data logger made to measure this type of sensor.

Nobody said anything about using 8bits to measure a 1500 degree temperature

Thermocouples and IR sensors can measure this range. If it needs to work with the limited hardware and software resourses (for this app, no flames please) of an Elk then I'd look for a device that streams or talks RS232 in some way.

You might look at products for pottery kilns (that is why I know TC's work).

Chuck

 

[TonyNo]

The unit in the link I posted has a serial port, but it's looking like you need their software to do anything with it.

Here is a better, general-purpose serial unit for a bit more ($180)...

http://www.eautomationpro.com/us/product/modl_1-1TW0YO.aspx