Ruslan124
Member
- Messages
- 19
- Grill(s) owned
- RT-680
I have seen this discussed many times, so creating a thread explaining the issue might be useful.
PID controllers are quite complex, and given it is unlikely Recteq makes their own, it is possible the support rep you speak to might not fully understand the theory of PID adjustments.
Auger Motors – An auger motor turns at a fixed speed. A 3RPM motor will dump twice as many pellets into the burn pot as a 1.5RPM (although they don’t seem to exist, it makes the math easy).
More pellets in the pot mean higher temperatures. If you set your controller to the max, the auger will run continuously and add lots of fuel to the pot, causing more extensive fire and higher temperatures.
The lowest temp is determined by how few pellets you can put in the pot without causing a flame out.
PID Controller – Cannot adjust the speed of the auger, it can simply turn it on and off. The minimum feed rate determines the lowest amount of time it can run the auger. The highest amount of time is continuous (Max on your dial). The controller can use any setting in between.
It is a sophisticated device that uses samples from the RTD to predict when it should turn on the auger and for how long. It controls the temperature using time, i.e., turn on the auger for x seconds. The time obviously determines how much pellet volume drops into the pot.
It uses an algorithm to predict how much fuel (pellets) is needed to reach the set temperature. Actually not the number of pellets but the time needed to generate the appropriate volume of pellet dump based on previous experience). The actual temperature is compared with the set temp. A significant difference will result in the auger running longer, resulting in fast temperature increases. As the gap reduces, smaller timings minimize the pellet feed into the pot. Once it gets to temp, it tries to maintain the temp using as few pellets as possible. The minimum feed rate determines the smallest fuel that can be fed into the burn pot.
How does that relate to temperature swings?
Imagine the PID controller has calculated that the set temp is close but needs several pellets to get there. It checks the minimum feed rate and dumps the minimum number of pellets.
However, you have your minimum feed rate set high. The number of pellets fed is multiples of what is needed. Once they are in the pot, they have to burn so the temperature surges causing an overshoot. Eventually, the fire burns down, and the temperature drops. The controller now knows that the minimum feed rate will cause a large spike, so it lets the temperature drop quite far below the set point. The temp will bounce wildly above and below the set point for a while before settling down (as the controller learns).I don't know if the controller has writable memory but I suspect not. If it doesn't that means it cannot use multiple cooks to learn.
Because the minimum feed rate causes a large spike, it cannot maintain a steady temp, so it will typically swing between a few degrees above-set temp and many degrees below.
So your goal is to allow it to minimize the number of pellets by setting the minimum feed rate as low as possible without flameout.
This setting will be influenced by how well your smoker holds temp. That is influenced by environmental conditions. It will also be influenced by pellet conditions and BTU. So although you should be able to set it and forget it, if you live in an area with a diverse climate, your pellets are damp or you change pellets for a different quality with different burn specifications, you will probably need to make adjustments. It is also possible the length of the pellets will have an effect. Shorter pellets are more concentrated in the auger than longer pellets.
I have a 3RPM Auger that quickly reaches over 700 degrees with the MFR set at 5. After 5 minutes of reaching the set point, the temperature rarely exceeds a +/- 3-degree range. I also live in FL so cold weather is not something I have to deal with.
Edit - Ensure your heat diffuser, drip tray, and grates are installed when tuning your grill. They all affect the air flow.
PID controllers are quite complex, and given it is unlikely Recteq makes their own, it is possible the support rep you speak to might not fully understand the theory of PID adjustments.
Auger Motors – An auger motor turns at a fixed speed. A 3RPM motor will dump twice as many pellets into the burn pot as a 1.5RPM (although they don’t seem to exist, it makes the math easy).
More pellets in the pot mean higher temperatures. If you set your controller to the max, the auger will run continuously and add lots of fuel to the pot, causing more extensive fire and higher temperatures.
The lowest temp is determined by how few pellets you can put in the pot without causing a flame out.
PID Controller – Cannot adjust the speed of the auger, it can simply turn it on and off. The minimum feed rate determines the lowest amount of time it can run the auger. The highest amount of time is continuous (Max on your dial). The controller can use any setting in between.
It is a sophisticated device that uses samples from the RTD to predict when it should turn on the auger and for how long. It controls the temperature using time, i.e., turn on the auger for x seconds. The time obviously determines how much pellet volume drops into the pot.
It uses an algorithm to predict how much fuel (pellets) is needed to reach the set temperature. Actually not the number of pellets but the time needed to generate the appropriate volume of pellet dump based on previous experience). The actual temperature is compared with the set temp. A significant difference will result in the auger running longer, resulting in fast temperature increases. As the gap reduces, smaller timings minimize the pellet feed into the pot. Once it gets to temp, it tries to maintain the temp using as few pellets as possible. The minimum feed rate determines the smallest fuel that can be fed into the burn pot.
How does that relate to temperature swings?
Imagine the PID controller has calculated that the set temp is close but needs several pellets to get there. It checks the minimum feed rate and dumps the minimum number of pellets.
However, you have your minimum feed rate set high. The number of pellets fed is multiples of what is needed. Once they are in the pot, they have to burn so the temperature surges causing an overshoot. Eventually, the fire burns down, and the temperature drops. The controller now knows that the minimum feed rate will cause a large spike, so it lets the temperature drop quite far below the set point. The temp will bounce wildly above and below the set point for a while before settling down (as the controller learns).I don't know if the controller has writable memory but I suspect not. If it doesn't that means it cannot use multiple cooks to learn.
Because the minimum feed rate causes a large spike, it cannot maintain a steady temp, so it will typically swing between a few degrees above-set temp and many degrees below.
So your goal is to allow it to minimize the number of pellets by setting the minimum feed rate as low as possible without flameout.
This setting will be influenced by how well your smoker holds temp. That is influenced by environmental conditions. It will also be influenced by pellet conditions and BTU. So although you should be able to set it and forget it, if you live in an area with a diverse climate, your pellets are damp or you change pellets for a different quality with different burn specifications, you will probably need to make adjustments. It is also possible the length of the pellets will have an effect. Shorter pellets are more concentrated in the auger than longer pellets.
I have a 3RPM Auger that quickly reaches over 700 degrees with the MFR set at 5. After 5 minutes of reaching the set point, the temperature rarely exceeds a +/- 3-degree range. I also live in FL so cold weather is not something I have to deal with.
Edit - Ensure your heat diffuser, drip tray, and grates are installed when tuning your grill. They all affect the air flow.
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