# Economical Smoke & Humidity Sensor That Can Handle Up To 350F - 500F degrees?

Hi Guys,

I'm looking to make a board that can read smoke and humidity at higher temperatures. If it can also read temp, that's a bonus. I've been using an MQ2, but don't think it can handle temps that high (I've not tested it above 225F which I think is already pushing the MQ2 sensor).

Minimum temp it would need to be able to handle would be 350F degrees, but prefer something that is stout enough to handle up to 500F. What are my options? Thanks!

Above 100C humidity is meaningless. If you want to measure the water content of a gas sample, draw it off in a tube and cool it down.

What property of the smoke are you measuring? I would guess that if everything is ouchy-burny-hot then there will be smoke.

I'm trying to measure the content of steam and smoke coming off a grill if that helps at all...

Any help is really, really appreciated...finding a sensor that can handle these things has stumped me for a long time. I've been able to get some basic LPG, CO, and Smoke readings from my MQ2 by doing some calculations based on the MQ2 nonlinear graph of each gas using a few points and the slope, and the sensor has worked when I placed it just beyond the chimney. If the MQ2 cant handle more than say 150 degrees for any extended time, I don't think I can use the MQ2. Maybe if I gave a project overview of precisely what I'm trying to do, and we could figure out a better way to do it...

[u]PROJECT OVERVIEW[/u]

Here's what I'm trying to do: I have a new pellet grill. I'll be smoking boston butts for extended periods of time - say 8-12 hours. The grill during that time will likely be set between 225-250F. All I'd like to do, is put some sensor that is compatible with the arduino on the chimney stack for the pellet smoker. From there, I want it to somehow give me a ballpark figure on humidity (doesn't have to be precise...but should be accurate enough to sound an alarm if the cooking chamber is dry air)...think the difference between 20% humidity, 50% humidity, and 80% humidity. Other than that, I want to get the smoke concentration coming off the chimney stack. The pellet smoker basically just burns sawdust that's been capsulated and that's it. So I'd like to get a reading on the amount of smoke coming off of the grill.

This sounds tough. First, in what units do you measure smoke? Maybe by opacity with some optical sensor. That way the sensor elements could be outside of the stack, and only a light beam would need to be in the smoke.

As for humidity, maybe somebody makes a sensor for measuring humidity at high temp, but I'll bet they charge an arm and a leg for it. Being an incurable experimenter, I would consider placing two metal plates vertically in the stack, with only a small gap between, and then use enough potential across them so that the water would be ionized and move charge across the gap. You would need some stainless steel, or better, to inhibit corrosion. But likely the other elements of the smoke might add to the charge transfer. Might work, might not. Just a thought.

Another idea. If you put a small cooled plate in the stack (Peltier technology), maybe you could condense water out of the smoke, and some volume of water per unit time (along with consideration of the plate temperature and smoke temperature) would give a rough estimate of humidity. If you got a gadget like this working at a reasonable cost, there would probably be a customer base.

If you do come up with a sensor, you have to figure out some way to calibrate it, so that you know roughly what it is measuring. That takes time and trials.

Then you have to learn how to interpret the sensor readings in order to get the result you want. That takes time and trials as well.

After all those trials, I think you will have figured out how the smoker works and won't need the sensors. Humans are pretty good at that sort of thing.

Ok - first off, I doubt you are going to be able to find a sensor that will do what you want while still being inexpensive. If one does exist, it probably works something like the oxygen sensor in an automobile - in other words is it probably an active sensor of some sort. Having a pellet smoker myself, I just can't see how you would be able to stick a sensor inside such a smoke-filled chamber and have it work for very long (as the condensate from the smoke would likely "gum it up" after a short while).

http://www.genuineideas.com/ArticlesIndex/dryasabone.html

The key statement is at the end:

Since it is hard to measure humidity directly or inexpensively under cooking conditions, measure the water loss rate, and use that as a surrogate humidity level.

This of course means using a pan (or something) of water, then somehow measuring the water loss. Even then, you wouldn't have a perfect measurement, because that would say nothing about what moisture the meat itself is giving off.

Perhaps you could do a wet-bulb/dry-bulb measurement with a couple of thermistors?

http://www.meatsandsausages.com/smokehouse-plans/smokehouse-humidity

High-temp thermistor probes are fairly easy to purchase; alternatively, you can use a thermocouple and amplifier. You'd have to figure out a way to keep the wet-bulb side wet, but that might be much easier (and cheaper) than a real high-temp humidity sensor.

http://meathaccp.wisc.edu/assets/wet_bulb.pdf

This guy:

http://www.tinkurlab.com/category/bbq-lab/

...is using this sensor:

https://www.sparkfun.com/products/9569

It's not really clear where he is measuring the humidity, given the max operating temp of the sensor (I'd have to guess at the stack, where the temp might be lower?)

Ultimately, my gut feeling (nothing objective here) is that the more you watch, the longer it takes to boil. In other words, maybe going to all of this trouble of checking, measuring, etc - you're ultimately doing yourself a disfavor? I understand that there is science behind cooking (and of course smoking), but I think pursuing the perfection, at least for myself, kinda takes the fun out of it.

What I've found works best - at least so far, with my trial-and-error methods:

1. Low and slow - I put my smoker on the lowest non-smoke setting (180 degrees), and let it run for 10-12 hours.

2. If I think I need or want extra moisture, I'll put a pan of water in with the meat.

3. Or, I might put a pan of "sauce" in with it, and baste on occasion until the sauce runs out, then move the meat to the pan to keep the humidity level up.

Really, though, my best results have been just to set it to 180, throw the meat on, close the lid, then walk away and don't peek at it until 10-12 hours have passed. But hey, if you manage to come up with a great automated monitoring system or solution, I'd love to hear about it. So keep experimenting; I'm not trying to stop ya!

Lastly - I'm going to leave a few more links; maybe you've seen them before, but if not - enjoy:

http://amazingribs.com/tips_and_technique/cooking_time.html

http://cooking.stackexchange.com/questions/35415/how-important-is-humidity-when-smoking-a-brisket

http://www.huffingtonpost.com/craig-goldwyn/physicist-cracks-bbq-mystery_b_987719.html

http://www.genuineideas.com/ArticlesIndex/sratlas.html