PID tuning


 
C

Christopher Vance

New member
Hello all,

I started my first HeaterMeter test with my 22.5" WSM this weekend. Here's the graph:

iT2A2ns.png


At midnight (during the lid open event) I added a significant amount of fuel and left it running overnight. At around 10:00am I changed the PID settings to 0, 8, .005, 8 and that resulted in the oscillation that you see. Could someone please jumpstart me with their PID settings for their WSM or help me tune mine. I spend some time with the wiki, but was unsuccessful. The fuel ran out at around 5:00pm.
 
Looking at that graph it seems there might be too much air getting in. The fact that after you added fuel it took almost 4 hours for the temperature to come back down means it is running without the HeaterMeter doing it's thing.
 
Hello Bryan! Let me show you some pictures I've got of the HeaterMeter's connection to the WSM:

JgpkPNy.jpg


RNVjQ8d.jpg


As you can see, the can is affixed to a single vent with four toggle bolts (and aluminum foil to protect the beautiful finish). What I suspect happened was that the vent was wide open to accommodate the toggle bolts during installation. As we discussed in another post, I suppose air was coming in unimpeded from the fan. I have since twisted the vent closed, so now it is about 1/3 open and the temperatures are much improved. I am still having some problems maintaining temperature. A graph follows:

1koePbh.png


It is much improved from before but I would like to get the oscillations down a bit if possible. The PID parameters are as follows: B=0, P=5, I=.002, D=5.

Thanks in advance for your input.
 
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Christopher, you're not doing yourself any favors by changing more than one parameter at a time. You've got a HUGE wind-up happening there. I'd suggest you run the blower in manual until figure out how to configure your vents to get you in the ball park, and use a higher pit temp setpoint until you are able to dial things in a bit. Also, don't try to make radical changes in setpoint until you get things figured out, or you'll do nothing but chase your tail. You should be able to see what changes you need to make within three oscillations. If you don't understand how to know what changes to make, just ask.
 
Stated another way, you might want to experiment with where things tend to run with the blower set to different manual setpoints until you get a feel for things. Otherwise, you're flying blindfolded and turning knobs and hoping you auger it into the ground. It's important to have a sense of what temp your pit is going to naturally settle at for different blower settings, so that you can recognize incipient overshoot and be able to make PID changes on the fly without having to watch it bobble for hours and hours.
 
Use your blower at a lower Max Speed try very low like 20% and slowly bring it up until you see a change. Once you see a change then that's your max you want to stay at, you may go a little higher or lower, but not much.
 
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