Response Speed Of Stoker vs Guru...


 
D

D Arita

TVWBB Fan
I'm not very computer savy, but I've done a lot of reading here and elsewhere on both the Stoker and Guru products. There's been mention that the Stoker may not respond as quickly or appropriately as the Guru, to changes in pit temps. Can anyone who knows both programs, explain the differences in how they work?
I'm really not trying to knock the Stoker...it's obviously a great product. In my lack of computer knowledge, I am only trying to understand how these things work and what differences there may be in their programs.
 
That's a tough question. If an ATC is truly "intuitive" it should anticipate swings and respond accordingly. I have the Stoker and have never seen the blower come on before the LCD hits the set temp (no intuition).
I think the proof is in the stability of control. If you stay at temp, responsiveness is a non issue (it's also the variable that must be working to keep you at temp). Again, given other cook variables, unless you do a side by side you'll never know.
I believe we have a few mathletes here that can explain the algorithms in detail though.
 
I am confident no one knows the real answer because these are such variable systems. Even if you did side-by-side comparisons, with the fire acting differently you wouldn't able to know which is better.

Theoretically, the algorithm can be optimized for speed of response, how much it overshoots the target and how much it oscillates. Speed alone is not the right single figure of merit as it might with high overshoot.

Fortunately we are talking about cooking meat which is a pretty forgiving thing when it comes to temp fluctuations.
 
I know it's a tough question to answer. I also have pellet burners and can see differences in the way they operate. Some can hold temps to 3 degree swings, while others have big swings, but produce more smoke. Stoker and Guru will never divulge their programs, but I have to believe that they each operate differently to hold temps to target. Just wish I understood how each does it, so that I might adapt what I am doing to the ATC or get the ATC that fits what I already do.
 
I guess my thought is that a unit that works to 90% efficiency is effectively no better than a unit that works to 85% when cooking something as simple as meat also affected by many outside variables.
If we were processing plutonium though, I think the differential would be relevant
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KIS(S)- temp too low turn on fan. Temp too high turn off fan.

Fancy - develop an algorithm that can anticipate when the temperature might go below your threshold and turn on the fan before that happens. Since the temperature incoming up turn off the fan before the temperature is reached so you don't overshoot your temperature.

It seems that the KIS(S)keep it simple (stupid) principle - is more likely the scenario with ATC's.
 
Originally posted by James Harvey:
I guess my thought is that a unit that works to 90% efficiency is effectively no better than a unit that works to 85% when cooking something as simple as meat also affected by many outside variables.
If we were processing plutonium though, I think the differential would be relevant
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I'm sure you're right, but this being my hobby, I'm sure I obsess over it. To me, that's part of the fun of it...I can get as into it as I want or not.
 
Originally posted by Russell Y:
KIS(S)- temp too low turn on fan. Temp too high turn off fan.
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Too complicated to explain in simple terms but that scheme does not work. This is a feedback system and is liable to get stuck in loops without some sort of "filtering."

Imagine if the temp was below target. You turn on the fan and as soon as the air hits the fire, it causes the temp to jump up above target for an instant. This logic would say to turn the fan off then. As soon as you do, the temp is below target again. So you turn it back on and the process repeats.

Fancy - develop an algorithm that can anticipate when the temperature might go below your threshold and turn on the fan before that happens. Since the temperature incoming up turn off the fan before the temperature is reached so you don't overshoot your temperature.
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This is too fancy
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. Predicting the future is a difficult thing. In this case, with the variability of the fire makes it darn impossible.

So instead of that, we rely on ways to keep the above oscillations at bay, but at the same time, not filter too much of the system response as to make it too slow to achieve the target, or overshoot. This is the foundation of the PID algorithm. You can read about it on the Wiki: http://en.wikipedia.org/wiki/PID_algorithm

It seems that the KIS(S)keep it simple (stupid) principle - is more likely the scenario with ATC's.
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Stoker generates diagnostic information that tells me it has PID style control. It clearly accumulates data over time before acting.
 
By the way, I worked with the software developer for the stoker to allow the PC app (stokerlog) to implement this feature so that it could be customized. He went ahead and put his part in, I have been too lazy to implement my end of it
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.

The trick here is that we can't do all the control in the PC as if you shut off the PC, you would lose control. So the PC needs to provide high level control and the stoker, low level and continue to run in a fail safe mode even if the PC is not responding.
 
Imagine if the temp was below target. You turn on the fan and as soon as the air hits the fire, it causes the temp to jump up above target for an instant. This logic would say to turn the fan off then. As soon as you do, the temp is below target again. So you turn it back on and the process repeats.
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As a Guru owner your description above sounds how the Guru puffs every 5-10 seconds when it reaches temperature.

Even fancier would be a variable speed fan that could adjust accordingly.
 
The controller made by Auber Instruments is PID based. It does operate differently than simple ON when temp is below set point/OFF when it reaches set point as it intisipates temp changes and reacts acts accordingly.
The Savannah Stoker which is an aftermarket controller for the Traeger Wood Pellet Grill used a PID with Fuzzy logic. If you are not familur with the operation of a pellet grill, the fuel is feed to the fire along with air flow. A pellet grill is much more difficult to control the temperature than a charcoal/lump/wood pit.
 
Originally posted by Amir:
By the way, I worked with the software developer for the stoker to allow the PC app (stokerlog) to implement this feature so that it could be customized. He went ahead and put his part in, I have been too lazy to implement my end of it
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.

The trick here is that we can't do all the control in the PC as if you shut off the PC, you would lose control. So the PC needs to provide high level control and the stoker, low level and continue to run in a fail safe mode even if the PC is not responding.
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Are you talking about the scoket commands?
 
Fuzzy Logic is a fancy term for the system learning and is an advanced control technique. Personally, as a Process Control Engineer, it's overkill.

The basic job of a pit temperature controller is to 'stoke' the fire with additional airflow when the measured temperature drops too far below setpoint. You need to understand what a given flow of air will do to the fire in order to raise the temperature at the grate.

So, the proprietary knowledge of the Stoker would be how they determine when the fan should come on and for how long. You need to account for ash blowing around and all that kind of stuff.

Kevin at Rock's told me that the algorithm they use is in fact a PID On/Off. In controls terminology that is a GAP controller.

A deadband is defined around your setpoint and the on or off signal is sent to the blower depending on the measured temperature.

The (P)roportional or Gain, (I)ntegral action and (D)erivative action are the three tuning factors in a PID control algorithm. The P affects the initial reaction or kick, Integral amongst other things is used to reduce the offset between the resulting measured value and setpoint. Derivative is used typically to anticipate the rate of change but is seldom used in industry due to its reputation for causing instability in the response.

Now, these tuning factors can be programmed in three ways, first to react very quickly to the disturbance, but your offset will be greater and you'll need more integral to reduce it, but too much integral can lead to instability as well.

The second way is to react more slowly, be more stable andhave a smaller offset, but over a longer time period. Less integral is required and a more stable response is seen.

The third way is somewhere in between.
 
Having run the two side by side on an identical rib cook in two WSM I can say we couldn't tell much of a difference with the exception of I think the Guru display only lists in increments of 5 degrees and Stoker will show you 225.3 for example. Maybe a Guru owner can confirm this. Reason this would be important is that you could be 4.9 degrees +/- and display would read 225. Not that 5 degrees is going to make a difference either way.

For what its worth, my buddy who's Guru is shown in this picture sold it in favor of a Stoker.

 
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