Added PID controller to my SmokinTex 1400

[ctimmer]

Almost completed:

Results are encouraging, complete information can be found here:

http://therockbottom.net/BBQ/SmokinTexMod/smokintexmod.html

Curt

 

[deltadude]

Yo Curt,

Now that is how you document a Mod, excellent,  the web page clearly shows everything that needs to be done, the resources, excellent, excellent.  If you owned a MES I would add you to the MES HOT MOD collection and give you a MES Ownerscertificate of appreciation.

Great post, very excellent work...

Of course I am assuming that is your web page, if not it is still a great write up.

 

[ctimmer]

Of course I am assuming that is your web page, if not it is still a great write up.

This is my web page and I will be updating it as I learn more about PID temperature control. I'm looking for feedback on anything that is not clear or missing.

Thanks for the encouragement,

Curt

 

[fencesitter]

Ahhh... I finally have the chance to post from a computer with a real browser. This site doesn't seem to like my phone's browser.

I'm sure your PID controller could be tuned better- even a 10 degree temperature swing seems way too much. Mine is only +/-1 degree and that's with rough numbers from memory since my controller's dynamic self tune feature really screwed things up after the initial auto tune. 

You can try to tweak your settings yourself. Your manual recommends increasing the Integral time. Or you can run the auto tuning again. I know with my brand of controller, it was best to start it with the default P, I, and D control values, whatever they were. You might need to experiment a bit. Probably auto tune with something in the smoker. If not a hunk of meat, at least a brick or a covered pot of water.

Was the PV reading on the controller actually steady or did it follow the graphs from your Stoker? In other words, the Stoker indicates the smoker never really came up to the temp you set it at, but I find it hard to believe the controller was cutting out too early.

It's also interesting to note that with a steadier temperature, the heat within the smoker was more even. Rather, it's not that the back was consistently 15 degrees warmer than the front, it almost like it was one third of the temperature swing hotter. I'm sure it's not quite like that, but I've only got two data points to work with.... Okay, the other data point would be at room temperature, so a straight 15 degree delta would be pretty hard to achieve then.

Can you use your Stoker for measuring the food temperature? With some creative wiring you might be able to get the Stoker to put the smoker in a hold mode where the temp is reduced.

Finally, on your site you're worried about driving the smoker too hot- in industrial applications, there is a separate limit alarm box to warn when things get too hot. The PID controller can be set to trigger one of the alarm outputs if things get too hot. If you want, you can put a relay on the SSR control line to turn it off when the alarm is triggered, however, a friend told me that the failure mode of SSRs is to short closed, so turning it off probably wouldn't work. Instead, think about putting a relay on the high voltage side of the SSR. If the alarm triggers, the relay would hopefully cut power to the heater.

 

[fencesitter]

PS- How thick is the stainless panel of your smoker? I've wanted to put a switch like you did in step 1, but I've had problems drilling through stainless in the past, so I don't want to burn through a few bits to make a sloppy hole.

 

[justpassingthru]

Thank you ctimmer for the info, I'm wanting to install a PID controlled heater strip in my GOSM, this helps me to understand it more clearer (I'm not a electronics person).

Fencesitter, I've had good success with drilling stainless up to 1/4" by making an indentation using a center punch and turning my bit at a slow speed.

Gene

 

[ctimmer]

I just started a smoke. 3 racks of baby backs.

As soon as the temperature reaches 200 or so I will start the PID controller and run the auto-tune.

You can watch the temperatures at:

http://curttimmerman.net/logger/bbqmonitor.html

Just click on 'Start Monitor', it will automatically refresh every 3 minutes.

Curt

 

[ctimmer]

Fencesitter - lots to think about here!
 

even a 10 degree temperature swing seems way too much

Agreed, after adjusting the set point to 250F yeilding a stoker temperature of about 220F the swing settled down quite a bit. Because the SmokinTex is fairly well insulated it does not respond as quickly when the power is shut off. Setting the smoker temperature higher seems to support this.

Probably auto tune with something in the smoker

I finally figured this out. This PID controller will probably work better in the winter when the smoker/ambient temperature is much greater.

the Stoker indicates the smoker never really came up to the temp you set it at, but I find it hard to believe the controller was cutting out too early.

This opens up a real can of worms about definitions. What is the definition of 'oven temperature'? If you put multiple probes in different places in a smoker you will most likely get multiple readings that could vary greatly. By putting the PID sensor next to the smoker sensor I am measuring roughly the same reading as the stock smoker but not necessarily what the smoker sees as the proper oven temperature.

the front was one third of the temperature swing hotter

This could have been caused by sensors being different distances from the food.

on your site you're worried about driving the smoker too hot- in industrial applications

I was really thinking about operator error. Even with the stock set up the thermostat could short out sending the temperatures through the roof. I'm looking into an independent set up to shut everything down at some pre-set temperature.

I've had problems drilling through stainless in the past

The center punch is a good idea. Sometimes drilling a small hole, then the full size helps. You can also use a slightly smaller bit than needed and finish up with a hand grinder.

Thanks for all the feedback,

Curt

 

[fencesitter]

Don't worry about the insulation nor the reaction time of the heater (both in turning on and off), the PID controller should take that all into account, so long as you tune it under similar conditions (with a thermal mass in the smoker).

Overheat protection: Me, I don't really have that problem- when trying to roast a turkey last Thanksgiving, I was having trouble trying to maintain 325 with the heater running constantly at maybe 65F outside temp. Your smoker is pretty darn similar construction. While it has 40% more power than mine (200 watts), it's also a bit larger, so I wouldn't really worry too much about overheating to the point of destroying the smoker. You might even want to experiment and see how hot you can get your smoker. I assumed that the regular glass mat insulation was good up to regular oven temperatures so even reaching 450F wouldn't be bad for mine, but that may be a flawed assumption.

In looking at some other setups, I was reminded that some devices have thermal fuses to cut power to the heater. If you really are paranoid, you could either go for that or, actually wire your built in thermostat in series with the heater and set it at the maximum temperature. Note that this may not work all that well- my Cookshack SM-008 smoker's thermostat maxed out at 250 and would even kick in at 235, so I had to bypass it. Your SmokinTex's thermostat looks similarly limited.

I might actually be more worried about overheating your PID controller since it's mounted above the smoker, but at least you do have it stood off from the surface. Also it looks like you've got your SSR heatsink in a well sealed box- you might want to think about air cooling it a bit better. That said, my SSR's heatsink doesn't get that hot, but it is dealing with less power and it's also mounted to my aluminum case which dissipates heat better than your plastic enclosure.


Quote:

Originally Posted by ctimmer  


Agreed, after adjusting the set point to 250F yeilding a stoker temperature of about 220F the swing settled down quite a bit. Because the SmokinTex is fairly well insulated it does not respond as quickly when the power is shut off. Setting the smoker temperature higher seems to support this.

Okay, so the heat isn't really even- somewhat directly above the heater where you have the PID input is hotter than the front or rear Stoker sensors.

This opens up a real can of worms about definitions. What is the definition of 'oven temperature'? If you put multiple probes in different places in a smoker you will most likely get multiple readings that could vary greatly. By putting the PID sensor next to the smoker sensor I am measuring roughly the same reading as the stock smoker but not necessarily what the smoker [Do you mean Stoker?] sees as the proper oven temperature.

This could have been caused by sensors being different distances from the food.

Yeah, that reminds me, I should really put a thermometer in near the food or put my PID's sensor farther from the heater. I may have such long smokes because the air temp near the food is a lot lower than what the PID controller thinks the oven temp is.

edit:

That's an interesting way to put the ribs in- I might need to try that instead of putting them in flat. How well does it work for you? I'm worried about the meat falling off the bone- either while smoking or when trying to take the rib out.

I also like the probes in the ribs. Everyone here seems to like to do them by time, but I like to get mine to 195. I guess that's also because my smoker recommends starting a smoke with a cold unit, so you have to add some time coming up to temp. Even then, my ribs take twice as long as what others smoke theirs for.

Do all those meat probes go to your Stoker?

 

[ctimmer]

The PID controller worked better this time. The temperatures were a little erratic because I was testing different temperature settings.

I might actually be more worried about overheating your PID controller since it's mounted above the smoker,

Because of the insulation the top just gets slightly warm.

your SSR heatsink in a well sealed box

The specifications indicate that I am well below the requirement for a heat sink. If it gets to be an issue I will mount a small PC fan on the back of the enclosure to pull air through the heat sink.

By putting the PID sensor next to the smoker sensor I am measuring roughly the same reading as the stock smoker but not necessarily what the smoker [Do you mean Stoker?] sees as the proper oven temperature.

Actually I referring to the smoker control. The simple on/off control doesn't really care what the actual temperature reading is as long as the thermostat is calibrated to yield to proper oven temperature. I learned something here. I need to set the PID offset to produce the same desired temperature or move the PID sensor to a more realistic measuring position in the smoker oven.

That's an interesting way to put the ribs in- I might need to try that instead of putting them in flat. How well does it work for you?

Works good, I stared doing this when I had different smoke times for ribs on different shelves. I've never had any problems with the ribs falling off, the small edge of the ribs will only slide in about an inch or so. Getting them out can be a bit of a challenge.

Do all those meat probes go to your Stoker?

Yes - I placed a food probe with an attached oven sensor in one of the center ribs and the other set in the ribs closest to the door (4 total sensors). The set up has a somewhat Dr Frankenstein look about it.

Curt

 

[srisinger]

And, unfortunately, ctimmer's website didn't survive the last five years. Anybody have any leads?

 

[smokin phil]

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[redheelerdog]

Here's a simple PID setup with some good info: http://www.smokingmeatforums.com/t/91229/just-the-beginning-of-my-fridge-smoker-project