View Single Post
Unread 08-14-2011, 09:07 PM   #2
woodpelletsmoker
is One Chatty Farker
 
Join Date: 03-29-11
Location: Beijing,China
Downloads: 0
Uploads: 0
Default

How does PID works

It collects history data, speed of blower, and temperature of pit.
It considers history performance, present performance and predicted future performance to determine speed of blower.

Say you set pit temperature at 220 F.
When pit temperature is 180F, it will control blower running at peak speed,
When pit temperature reaches to 200F, blower may run at 50% of its normal speed.
When temperature reaches to 215F, blower may run at 10% of its normal speed
When temperature reaches to 219F, the blower may stop running.
Even then pit temperature will continue to rise.
When temperature reaches to 220F, the blower may begin to run again at 10% of normal speed.

Different pit may have different weighing factors of past, present and future, i.e. different value of P, I and D.
By trial and error, you will find best matching data of P,I.D, and your pit temperature fluctuation will keep within 1 F.

Many other controller, cheaper or much more expensive, their output is electrical relay or contacter. It simply turns on or off the blower.
Say you set pit temperature at 220F.
When pit temperature is 180F, the blower will run at its peak speed.
When pit temperatures to 200F, the blower will run at its peak speed.
When pit temperatures to 215F, the blower will run at its peak speed.
When pit temperatures to 219F, the blower STILL run at its peak speed.
When pit temperatures to 220F, the blower will STOP running.
But the pit temperature will CONTINUE to rise, it may rise to as high as 230F or even 240F, then it begins to drop
When pit temperature drops below 220F, the blower will run again at its peak speed.
But the pit temperature will CONTINUE to drop, it may drop to as low as 210F or even 200F, then it begins to rise.
Temperature fluctuation may be as high as 20F or even 40F.
woodpelletsmoker is offline   Reply With Quote