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Author Topic: Revelations about PID controllers  (Read 1726 times)

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okie smokie

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Revelations about PID controllers
« on: July 29, 2019, 08:25:39 PM »

Revelations about the PID controllers. 
 It is apparent that when set to a specific temp like 225 and then people report that the pit then gets to 225 and stays there. (plus/minus 2-3 degrees). You are being misled.  The temp actually may swing up and down 6 to 10 degrees, but the PID brain averages it out for us.  Actually making minor alterations in pellet feed as it goes.  However, the end result is the same--you get the average temp of 225 over the whole cooking period. 
I did a temp check with my Maverick pit probe and noted the temp swings even tho the RecTec control read 225* the whole time. Maverick went as high as 232 and as low at 221.  SOO, no complaint there, just FYI. Actually that is very very tight control.
I wondered why they would program them that way?  Just to make us feel good? Or just to keep us from worrying about trivial things? Maybe one of our engineers would comment.
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BigDave83

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Re: Revelations about PID controllers
« Reply #1 on: July 29, 2019, 08:43:58 PM »

I didn't read your whole post but from what I did read you have a Rec Tec. Those guys are always going on about how it is set at 225 and the temp never moves off of 225 for 30 hours straight. I think the RT controller has it built in to not really bounce around because people would complain if it moved 10 or 20 degrees like it does. when I had mine I watched the grate temps move around. It also depends on what you load it with, Ribs and flatter product had more stable temps than whole turkeys or chickens I figure that is just because of the air disruption.

 My GMG has PID I can watch it move on the display 5 or 10 degrees. I stopped checking cooker temps long ago unless I think there is an issue with something I cooked being done to soon or taking longer than I had thought.
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wilpark

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Re: Revelations about PID controllers
« Reply #2 on: July 29, 2019, 09:39:24 PM »

Im my opinion no need to worry about exact temp.  Not every piece of meat is the same.  If you want to do precision cookery get a sous vide machine. 

Sent from my SM-G975U using Tapatalk

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pmillen

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Re: Revelations about PID controllers
« Reply #3 on: July 29, 2019, 10:04:50 PM »

I wondered why they would program them that way?  Just to make us feel good? Or just to keep us from worrying about trivial things? Maybe one of our engineers would comment.

I'm not an engineer but I was a Product Manager for a Fortune 500 company.  In our company the engineers were a valuable part of the Product Team but the decisions were the Product Manager’s alone (the PM's pay was based on product profitability).

Here’s how I would have thought through the question–
  • The temperature swings are inconsequential
  • Option One  We could program the display to not expose the small temperature deviations
         a.  Discuss this with legal to ensure that there are no misleading statements in company material or employee job aids
         b.  Customers will use their own equipment to monitor actual temperatures
                   i.  they will report it as a problem to our Customer Service Department
                           ●  product reputation will suffer through social media
                  ii.  my product will be charged with the loaded costs of handling these calls
                           ●  profitability will suffer
                                     ○  my bonus will suffer
  • Option Two  We could display the temperature swings
         a.  Devote a small section on inconsequential temperature swings in the Quick Start document and Owner’s Manual
                   i.  some customers will ignore the written material and report it as a problem to our Customer Service Department
                           ●  Cust. Svc. will rapidly diffuse the situation
                  ii.  my product will be charged with the loaded costs of handling these calls
                           ●  profitability will suffer
                                     ○  my bonus will suffer
I think Option Two, displaying the temperature swings, is the ethical and straightforward way to conduct business.  It would have been my choice.
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Paul

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okie smokie

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Re: Revelations about PID controllers
« Reply #4 on: July 29, 2019, 10:40:49 PM »

All above are good analyses.  I would bet that none of us or our readers have called the company to inquire or complain. It is what I called it--FYI.  For me just an interesting observance and perhaps a chance to gain knowledge that I had missed. Being old, unemployed and curious can be a serious problem.  But I feel better now. Thanks all.  :clap:
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Canadian John

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Re: Revelations about PID controllers
« Reply #5 on: July 30, 2019, 08:23:22 AM »


 My thinking goes back to the early days, the advent of digital controllers, a major step up from the smoke/med/high or 3 speed controller..The early digitals had massive swings. People didn't accept them

and tried all kinds of things to even out the temperatures. As a result, 3RD party controllers were developed. For the most part they solved the problem at a cost not affordable to all..With new companies

evolving, competition demanded a better mousetrap thus better controllers..There have been astronomical advancements in pellet pit technology since the advent of Joe Traeger's first pits, controllers being

just one.
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bregent

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Re: Revelations about PID controllers
« Reply #6 on: July 30, 2019, 12:19:27 PM »

>I wondered why they would program them that way?

Memphis also uses Roanoke controllers and work pretty much the same. It's really similar to how many modern ovens with digital displays work. You set the temp and the display starts to increase while it's preheating. Once it reaches temp, the display just shows the set temp, even though WE know that inside the temp is really fluctuating. Oven temps have always fluctuated, and nobody really cared. Pellet grills will always have temp swings, as long as it's displaying the average temp that's all that matters.


Another thing I've noticed about the Memphis and may also be true for RecTec; If you increase the temp, the display immediately starts to increase, even though we know it can't possibly change that fast. Again, that's similar to ovens I've used.

I think the bottom line is that they want it to function like a modern oven. The problem is that BBq'ers have all kinds of temp monitoring devices, and I know some folks get bent out of shape (not you personally) when the display doesn't match the temp as read by a 3rd party thermometer, but that's comparing instantaneous readings to averaged.
« Last Edit: July 30, 2019, 12:23:04 PM by bregent »
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pmillen

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Re: Revelations about PID controllers
« Reply #7 on: July 30, 2019, 01:05:26 PM »

I think the bottom line is that they want it to function like a modern oven. The problem is that BBq'ers have all kinds of temp monitoring devices, and I know some folks get bent out of shape (not you personally) when the display doesn't match the temp as read by a 3rd party thermometer, but that's comparing instantaneous readings to averaged.

 :)
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Paul

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okie smokie

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Re: Revelations about PID controllers
« Reply #8 on: August 01, 2019, 10:25:06 AM »

I like it averaged.  That is the bottom line for the long cooks.  Only reason I checked it out with the Maverick is to make sure the set temp is what you are actually getting. I actually had to adjust the "offset" to get the correct temp at the middle of the grates. Of course I had to watch the Maverick fluctuate up and down, and then when it was reasonably stable, I averaged it out and made my adjustment. One of the few controls that allows you to adjust the readout to match the actual temp.  (the error was more than 15*).  Not much, and I could also understand just making allowances for it, but hey! easy to do so I did it!  Picking nits is my specialty.
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pmillen

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Re: Revelations about PID controllers
« Reply #9 on: August 01, 2019, 11:49:51 AM »

Picking nits is my specialty.

Nit picking is worth doing, in two ways.

1.  The search for excellence.
2.  Literally—they're unborn and/or immature lice.
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Paul

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