Test Run with UDS and 4.3 HM and RD3

Here is a shot of my first test run. This is on a homemade UDS with HM 4.3 and RD3. The RD3 in using a 1" inlet. No other inlets are open aside from the 2" outlet on top of the UDS.

Temp seems to waver over about 10-15 degrees. I started out with default PID settings. At about 9am I changed the "fan on above" to 99% to simulate fan on at 100% only as per a post or two I read. That seemed to cause some strange things to happen. Changed it back to default at 10:30.

At 11am I changed PID to 7, 0.01, 4 as per another post but it didn't seem to change much.

My UDS has always been a fickle thing but are there any suggestions for a smoother, more stable temp?

Thanks

Dave

It looks like you need to do some PID tuning of your HM, but there are a couple other things you might want to check first.
First of all, the easiest way to achieve a flat temp line is to allow both the damper and fan to run the full range of the HM output, so I suggest you start out with the blower set on above 0% and Min 0%, and set the servo to fully open at 100%.

From there you need to get a grasp on the air flow requirements of your pit and adjust the top vent and MAX blower settings appropriately. PID tuning will be easier if you have your vent and blower speeds dialed in first, sometimes a tweak to the blower MAX or top vent setting can smooth out a bumpy graph like that on its own.

Finally, sometimes people get a bumpy graph like that because the air is skipping right by the fire and shooting up in the cooking chamber, so the inrush of cool air makes the pit probe reading drop rapidly. You want to make sure your air inlet is configured so it is directly stoking the fire, ideally from below. You want to make sure your MAX blower speed isn't so high that it fills the pit with cold air rapidly. You also want to situate your pit probe so it is not in a position were there is high air flow. This is different on every pit, but for example near the outer wall of the grill where the air rushes around a heat deflector or water bowl. It's a good idea to run a cook with a bunch of probes placed in various spots in the grill and watch them to see what position gives you the most stable and accurate temp, then put your pit probe there.

So that's a long winded bunch of general information for you, soak that in and see if any of that applies. After that you probably want to read the section in the HM wiki about PID tuning, where you look at the oscillations as seen in your graph and make some calculations to determine what your PID settings should be.

Thanks Ralph. I will try to implement that in my next trial run. Really appreciate the response.

Just wanted to say thanks again, Ralph, for the awesome RD3 and for the above advice. Did a rib cook today and used the advice you gave above along with some other threads I read here and had a very successful cook. Here is my graph:



The four "lid open" events are me spraying the ribs. UDS recovered to set point every time just as the "lid open" time ended. Very happy with the control of the HM (Thanks Bryan!!!) and the RD3 (Thanks Ralph!)

...oh, and the ribs were very tasty!!!

Glad to help, looks like you made a nice improvement. I've seen flatter graphs but a little ripple is no big deal, your consistent recovery without overshoot after lid openings is nice, that's pretty important...

what did you change?

Would be nice to see an entire cook. You're displaying just over 5 hours. A lot can go awry on a 16 hour cook. Not saying your settings are bad, but give it a cook, add some meat, and see how it goes.

Would be nice to see a bigger cook. You're displaying just over 5 hours. A lot can go awry on a 16 hour cook. Not saying your settings are bad, but give it a long cook, add some more meat, and see how it goes.