Wanna build a PID temp controller.. help?

[scottlindner]

I want to build a PID temp controller for my GOSM. I BBQ'd for a party with a bunch of friends two weeks ago and they thought I was crazy to check the temp every 20-30 minutes for a 3 hour smoke. I told them I really felt I needed to. I'm sure over time I'll get better and need to check less frequently. So.. I figure I'll dive into the PID solution. I have read about people doing it. Does anyone have any details so I'm not figuring everything out from scratch?

Cheers,
Scott

 

[walleye1]

Hi Scott

Here is a great write up on building a PID controller from scratch.
http://www.susanminor.org/forums/sho...?p=504#post504

Auber Instruments seems to be where a lot of people by the controllers from. I've built 2 of them and used their products. They were great to deal with as well. Auber also makes a Plug and Play unit, here's a link to few of these as well.
http://auberins.com/index.php?main_p...e0947ea706a3a4

Mike

Opps....
I just realized this is on the "Propane Smokers" Board... I was referring to PID controllers for electric smokers....

 

[ddave]

You might try a Maverick ET-73 thermometor instead

http://www.ikitchen.com/maresmth.htm...S_010=maresmth

and just set the high and low temp alarms. Gives you one probe for smoker temp and another probe for meat temp. No need to check the temp unless the Maverick is beeping. I use this on my SnP (which was converted to propane) and it works very well. Once a gas smoker is stabilized, there should be very little temp change anyways unless something changes like the wind coming up, smoke wood catching fire, or some other strange happening.

Oh . . . and checking your smoker every 30 minutes for a 3 hour smoke is not that excessive in my opinion. Sounds like you need to withhold the Q from your friends until they develop a proper appreciation for your dedication.

Dave

 

[scottlindner]

He mounted it inside the smoker? Wouldn't the heat become a problem?


I was about to say, something is missing in that PID.

Scott

 

[scottlindner]

That's not a bad suggestion, but my vision is for smoking turkeys through the night. I suppose I could relocate the baby monitor next to the smoker. Not sure how the wife would feel about that.

Scott

 

[ddave]

No need to put the baby monitor next to the smoker. The ET-73 has a transmitter attached to the temp probes that would be by the smoker and a separate receiver unit that can go in the house. The alarms beep on the receiver unit.

I've used mine to do overnight smokes and it works really well.

Some things that come to mind though . . . when you were checking the temp throughout the smoke, did you find that it changed much? What was your target temp range? I wouldn't think a propane smoker would wander that much unless it was in the wind. I know once my SnP gets settled in, it will go between 235° and 250° for hours on end unless the wind comes up. And the SnP is an offset. I would think a cabinet smoker like the GOSM would be even more stable.

Dave

 

[walleye1]

Scott

That is a smoke generator but the heating plate that burns the wood is located in the main tower of the smoker. A number of people have installed them this way as there really is no heat at that location. I myself prefer it built into a project box, that way it is more portable.

Sorry for the confusion as I'm a watt burner with limited knowledge on propane units.

Mike

 

[scottlindner]

It changes a lot. We get a lot of wind here.

Scott

 

[scottlindner]

Wow.. that's cool. I had no clue you could do that. Do you think it would work in a propane smoker as well, or does that trick work mostly with electric?

Cheers,
Scott

 

[ddave]

Hmm . . . seems like a tall order for a PID controller to overcome. If it ramps up the flame and the wind dies down or shifts, the temp rise may be more that the burner can compensate for and still stay lit. If you are turning off the burner and relighting, you have a whole host of other programming and safety features to try to build into the logic of the controller Might I suggest a windbreak.



Or, if you are adventurous and have the time, build a UDS. If you have a good sealing lid, wind doesn't affect them at all. Great for overnight cooks.

Sorry, I am not providing much help with your original question though. If you do decide to pursue the PID project, keep us posted.

Dave

 

[scottlindner]

I'm not that familiar with PIDs but I have programmed many PLCs in the past. I was planning on addressing those issues with the program itself. I was considering either adding something to reignite the flame on a set interval like every second, or using another thermometer to detect if the flame blows out to reignite. As for the wild temps, too aggressive of a program will cause overcorrection. I don't know how PIDs are programmed, maybe that's my misunderstanding. Maybe I should use a microcontroller instead to best address the issues?

Cheers,
Scott

 

[ddave]

I have had some experience in tuning PID loops for dry kiln controllers and a wood fired boiler control system when I used to work for a sawmill. My brother was actually the head electrician and he did lots of PLC programming.

I guess if you had all of the correct components and the time and money, you could get either one to work. You're basically building an oven or furnace control system so you might talk to someone who is knowledgeable about those -- particulary the safety features of how to handle reignitng the burner. I saw somewhere on the internet where someone basically built an oven control system for a propane burner but I can't remember where I saw it.

If I have any luck digging it up, I'll post a link.

Dave

 

[richoso1]

A propane GOSM will drop cabinet temp when the water pan runs low, that is if you're using water/liquid. If you keep the water pan nearly full, the temps do stablize rather well. I experience this everytime the pan runs low, as soon as the added water heats back up again, temps rise. A quicker return to normal temps is to add hot water to the pan. I hope this helps.

 

[mgnorcal]

I had never heard of a PID, but I found some good info at the link below for anyone interested in temp controllers.

For a GOSM -type smoker, I'd say you are better off doing a cheap insulation and windbreak mod.

Aside from that, I can tell you I don't get more than a 10* variation in temp over an all-day cook with my gas smoker, and I haven't yet done any significant mods to it.
And actually, that variation is always the same - as the meat heats up, the smoker temp rises a bit.
I only need to add water once very 3 hours or so and wood chips if I want them.

Temperature Controller Basics Handbook

 

[ddave]

An excellent point . . . and another reason NOT to try to automate the process. If the cabinet temp drops due to the water pan running dry then the PID loop will increase the flame in an attempt to bring the temp back up. Not good with a dry water pan.

Now I know with a PLC you could add a sensor for water level and even program that logic into the sytem but then you'd have more $$$ into the control system than you would in the smoker. Or I guess you could use sand in the pan for temp stability but still there are many other complexities to overcome.

Agreed. More cost effective IMHO.

For better or worse, smoking meat is a participation sport. Well, with a UDS, you can run for pretty long periods unattended if there is nothing you need to do to the meat.

I have run mine for 6 hours at a time in a 16 hour smoke without touching or even looking at it. The Maverick ET-73 was on duty though in case the temp got out of range.

Dave

 

[jimr]

I'm no HVAC professional but wouldn't you need a thermocoupler w/electronic ignition to safely use a PID to control a propane burner??

 

[scottlindner]

It sounds like there are five independent variables that control two or three dependent variables.

Independent Variables are:
- inside temp
- outside temp
- wind velocity
- flame out?
- water out?

Dependent Variables are:
- propane rate (increase/decrease)
- ignite propane
- (optional) add water

This all sounds fairly easy to control. The things that make this tricky are:
- variable hysteresis due to the water quantity and temp

I haven't done control theory in a very long time, but my dusty brain cells tell me the hardest part is the mechanics of controlling temperature safely, rather than modeling the control theory.

A friend uses a different water pan so he never runs out of water. That could be an easy solution. I could put a gallon of water outside the smoker inverted with a dip tube into the water pan so it adds more water as it runs low. This would fix the water quantity and since it would replenish as it looses water the temp would be effectively fixed. Solving the hardest part of the control model.

It all sounds simple to me, other than finding reasonable parts to do it all. It sounds like something you guys don't do on this forum. Maybe it isn't necessary or it isn't cost effective?

Scott

 

[mgnorcal]

A little thought experiment might clarify.

(1) Suppose you do no modification to a GOSM, and you want to do a 9 hour cook. You'll set the flame initially and check it after about 10-30 minutes to ensure you're at the right temp. Then every 2-3 hours afterward you check the temp and smoke amount and water amount and make necessary adjustments. This requires a total of 4-5 visits, each averaging 2 minutes long. At worst, you will have "suffered" a temperature fluctuation by about 10* during one of the intervals.

(2) Suppose you create a programmed temp controller and a water-feeding modification. You'll still need to replenish wood chips every few hours and you'll probably want to look inside once during the cook to make sure everything is going fine. If successful, you will have maintained the temp within 1-2* for the duration of the smoke.


It remains to be shown that there is an advantage to scenario (2), much less an advantage that justifies the time, $, and trouble proposed here.

There are electric smokers made that are essentially set-it-and-forget-it for anyone who does not want to deal with tending the smoker.

 

[scottlindner]

It's the overnight turkey's I'm thinking of. It's sleep I'm after, not set and forget. I don't mind checking it every 20-30 minutes if I'm already awake. Plus, it gives me a reason to tell the wife I need to mop with a fresh beer each time I go out. ;)

Scott

 

[ddave]

I don't know of anyone that has done it but I have only been here a little over a year. Doesn't mean it is a bad idea. Just a fairly complex undertaking. Probably not cost effective. Necessary depends on your perspective.

Build a UDS. Elegant simplicity.

Dave