Digital Cat Probe

Just so I understand completely, the front of the cat is the inlet? That seems very odd to me, as -- aside from some radiation -- I'd expect temps to be fairly cool on the inlet side of the cat.

It is surprising the two different probes read very differently, but it sounded like you have a few readings that agree with the thermocouple, and they all disagree with the old mechanical Condar. Are you sure that one is not just wrong?

The thermocouples never go past 1000 degrees, while the 6" Condar bi-metallic probe will read up into the 1700's while the cat is active. That to me says the probe is correct, but how is it reading those temps and the thermocouples do not?

Your cat is likely peaking at 1700F if your wood is good, but I also would not be surprised that the temperature on the inlet side of the cat is closer to 1000F. Could the Condar probe be somehow falsely compensated, if it is designed specifically for measuring on the input side of the cat?

I'm trying to think of some way that you could test your probes, but nothing accessible in the household comes to mind, that runs a known temperature above 1000F.

I do not think it is anything special, Condar mentions temperatures behind the cat for the bi-metallic probes as well.

http://www.condar.com/cat_meters_woodstoves.html

One of the differences is they use copper for the probes, not sure if they have copper in the thermocouples or not.

The thermocouples are usually manufactured from stainless tubing, for good reason. You need very poor thermal conductivity down the length of the probe, to get a reading at the tip only. It's a matter of aspect ratios, with much surface and minimal transmission depth thru the tip, versus much transmission length and minimal cross section down its length.

Are you sure you're set up for Fahrenheit and not Celsius? 1000 degrees C = 1832 degrees F.. Also if your temperature is set up for Fahrenheit have you tried adjusting your offset to reflect what you think your temp is at that time?

To check your setup place the thermocouple in boiling water it should read 212 degrees F or 100 degrees C.

Ray

So I did some tests over the weekend to test accuracy of the thermocouple vs the bi-metallic, thinking that one HAD to be wrong, well as the pics will show, both are pretty close to each other.

Tested the Thermocouple in the oven set at 550. It reads 554, close enough and verified.


I however could not do this test with the probe due to it was reading over 2000 degrees with it put on the same place in the rack in the oven, I discounted this result as the probe tip should be the only thing receiving that kind of heat and it throws off the bi-metallic if the whole probe is put in the oven.

Test the thermocouple over high heat on the range:


Test the bi-metallic probe over high heat on the range:


As you can see both read about the same temperature, so either both are off or both are correct in high heat, I don't have a way to verify the results are correct, but find it interesting that both read the same temperatures. I did get both of them cherry red before reading the final results, I must say my hands were pretty hot holding that bi-metallic, it takes A LOT longer to get up to temp.


So this brings me full circle to my issue, if BOTH are reading temperatures correctly then why am I getting two very different results from reading my catalytic combustor at the same exact spots?

hah! Very frustrating, indeed. Is it possible the shaft of one is contacting more stove body metal than the other, where it penetrates the outer casing of your stove, thus cooling the probe body?

This picture is not correct, but this past weekend I put the whole damn 6" thermocouple IN one of the cat cells, it was just small enough to fit, as pictured I tried doing it in the middle but the damper when open would push it back out. With it inserted into the cell it reads about the same temps as usual, hovers around 800-980 F during peak burns, However if an active flame hits the cat the results jump up into the 1000 range.

I'm really surprised the wire/probe junction holds up to those sort of temperatures. Typically, that part of the probe body is rated much lower.

At this point I don't care if it holds up or not, it is a last ditch effort to see what works. I too am at a loss as to why it won't read correctly when inserted directly into a cell on the cat.

I will shoot a message to BK and Woodstock and see if they can direct me to someone that can explain why this is not working.

Might also be good to forward a link to this thread over to the folks at Omega engineering. If someone knows a thing or three about thermal measurement, it's them.

I have given up on this project for my Appalachian 52 Bay Insert, none of the manufacturers know how to make this work from the front and default back to the Condar bi-metallic probe as the solution, Buck included. I am not about to drill a hole through the thick top plate of this insert just to find out if the thermocouple will work from behind the cat, that is the only way to access it.

All the manufacturers seem to be happy with just offering bi-metallic probes, no one seemed to like the idea, which I find odd.

I ruined the 6" thermocouple by cutting it thinking maybe making it shorter would be better.

Maybe someone down the road will read this thread and have the solution.

Sorry to hear that!

Me? I'd probably drill the top. It's an insert... who will see it?

Problem being it is an insert, I would have to drill through the top plate, and then there is 2" of space for the air jacket that goes over the top of the firebox, then drill into the top of the firebox.

IF it was only drilling out the top plate then I would consider it.