Hey all! I am new to Arduinos but already want to say that it is a great product and the forum support looks awesome!
With that said I am trying to find a temp sensor so I can build an automated propane smoker heat controller. I am unsure where this should be posted, sorry if it is in the wrong category.
The temp sensor will tell the servo how far to open or close the valve to keep the optimum smoking temp for LONG durations. Is a thermocoupler the right way to go on this? if so i was horribly confused how to get one of these hooked up to the arduino. Anyone have any inexpensive ideas for the sensor?
maybe u can observe the temperature (of the gas flame?) somehow?
then u might be able to use a LM35 (150°C (max))...
maybe u can use a piece of metal near the flame?
The temp probe looks like it would work but at $169 :o ! it is beyond my budget for this one, was thinking what really needs to be taken is the temperature of the air at the top of the smoker. Would a k type thermo coupler work to get the air temp?
ok - if u can deduce the burner temperature from the exhaust air, u can just measure the exhaust air, too...
what temperature do u expect? if it is clearly below 150°C (300°F) u can use a LM35... it is cheap and quite accurate...
yes, u can use an analog pin for that... at 5V reference u had a resolution of 0.5K (take care to use a stabilized, temperature compensated power supply; maybe that regulator on the arduino board is sensitive to ambient temperature changes)... analogReference() - Arduino Reference
The optimum smoking temp is 200f to 225f, however since it is a smoker with a large flame at the bottom I have seen it exceed 350f by accident. The analog gauge that came with it goes to 600+ but I have never seen it get above 300 on purpose. :-/
I figured a sketch that sampled every 10 seconds and limited the flame adjustment amount to small increments so it doesn't run out of control would do. The servo throw will also be limited so it doesn't turn off the propane and doesn't set the flame above medium either.
I could place the probe at the same point as the pre-existing gauge which seems to be a good local about 2/3 up the smoker. It sounds like I could just use the LM35 since I am trying to stay below 300f?
if u want to use it for making food,
then the sensor should be outside of the food compartment...
maybe at the outside of the food compartment?
i guess there will be some insulation (an air filled space) and then a stone wall?
right?
just specially licensed devices may have contact to food, i think...
i saw it in TV: they stuck a metal stick with a sensor inside a big piece of meat, before they closed the compartment...
they made the smoke by pressing special wood on a rotating piece of metal...
is that what u mean with "smoker"?
oh
ok
above the food in the exhaust air stream might be safe, 2...
ur safety measures (like limiting the gas flow...) sound good...
maybe a second LM35 at a different place would be fine, 2?
(just in case the primary LM35 got too hot)
is there a fail safe valve?
i heard that nuclear power plants have 3 independent valves in series, if they want to be sure, that the flow stops, when they want it to stop...
i have that for my fresh air duct:
when the power fails, a relay falls off, which turns on a fan (battery powered)...
(i have that twice... just to be safe in case i dont wake up from the alarm toot..)
Essentially the smoker is a metal box with a propane flame at the bottom, with some wood chips and water in containers right above the flame. The sensor would measure the air the meat would be great to sample but that is another matter and sounds like it would be a mess.
What would happen to an LM35 exposed to say 350 degress? would it melt or just max out the voltage it is sending to the arduino (a fuse might be handy to protect things)? I can look for a propane safety valve I am sure they are out there. I think I will move the smoker from my deck to the driveway for any test runs just in case it gets out of hand :-?
i think above 300°F the LM35 will loose accuracy...
and somewhen it will fail (permanently)...
the datasheet
insinuates,
that u can use it up to 175°C
(on page 5)...
i like the version in a metal case, but it is rather expensive...
the epoxy case wont burn, iirc
but maybe it produces bad chemicals...
but the air flows away from the food, doesnt it?
Personally, if I were doing this (sounds like a fun project - something I could use for my propane-fired smoker!), I would use digital BBQ temperature probes, one for the smoker itself (situated somewhere in the middle-upper 2/3rds of the smoker), and one for the meat, and sample/adjust for both. The digital probes are fairly cheap (~$20.00 US), and are made for the task. The only issue might be with figuring out if they have a linear or logarithmic response curve.
The only thing left after that would be some kind of automated hopper mechanism to feed in wood chips for the smoke!
While a part of me likes this project, another part tells me it would take all the fun out of sitting outside, enjoying a beer (or other beverage), and tending the smoker during the long cooking journey of raw meat to tender lovin' perfection...
maybe the fun comes back, when arduino makes
a clicking sound that denotes the temperature deviation
and
beeping noises that denote the actions taken...
I think the fun will come back with not having to get up out of the chair to constantly check what is going on (it takes alot of energy to get out of the chair ) So I am thinkg the k-type thermocoupler is the way to go with the control will this work? http://www.virtualvillage.com/thermocouple-with-1-4-x-4-type-k-probe-003820-031.html
the only thing inside would be the probe everything else would be outside the smoker and protected from the heat!
that thermocouple on ur URL looks similar to that one in TV... all silverish metal with a wire...
the temperature range is good, 2...
the costs (thermocouple + interface) r higher than the costs for 2 LM35-s,
but the LM35 is possibly not suited for this task
(mainly because of fumes that might come out of LM35's case...)...
i just had another idea (sorry if it is distracting):
a pyrometer targetted on the outside of the food containing compartment might be a nice alternative?
I'd just use a t'couple then you don't have any of the heat issues mentioned. Have a look at the MAX6675, it's a k-type amp with the cold junction Richard mentioned. I haven't used one yet (just about to) but it lools like t'couple on one side and SPI on the other, very simple.
just to be safe in case i dont wake up from the alarm toot..)
) So I am thinkg the k-type thermocoupler is the way to go with the control will this work?