Good day all. It was suggested that I start up a PID controller tutorial thread. Sounded like a good idea to me so, here I am.
What is a PID in the first place?
P - Proportional
I - Integral
D - Derivative
These parameters describe gain formulas. Gain determines how fast and how hard your controlled device will turn on.
What are gain, error and setpoint?
Gain is the multiplication of the error that causes the circuit to start a correction. Error is the difference between the setpoint and the feedback from your sensor. In this case, the sensor is a thermocouple. Setpoint is the point at which you want the PID to regulate. (i.e. 250 F)
Proportional gain is a straight forward multiplication of feedback error times circuit gain. For example; if I had 1 volt of error on a proportional gain stage with a gain (Av) of 10, the output of the error amplifier would be 10 volts. Proportional gain will get you close to your set point regulation but it is sloppy when used alone for regulation.
Integral gain is an integration of error over time. Integral gain will smooth out your proportional peaks and valleys and will hold tight regulation if set correctly. PI regulation is good for most analog thermal control applications.
Derivative gain will push your PI hard in one direction or the other depending on the trending temperature. For example, if you open the smoker door, the sudden loss of heat will trigger your controller to turn full on faster with a derivative gain function than if only a PI loop were used.
How is heat controlled in the smoker?
In an electric smoker, heat is generated by a resistive element usually over 1000 watts. To control 1000 watts at 120 VAC, you need to control 8.333 Amps of current. To switch this much power, you need a relay or silicon switch capable of handling the voltage and current needed by the element.
Solid State Relays or SSRs are inexpensive and readily available silicon switches for DC control of AC switching.
Charcoal smoker:
The amount of air pushed through the fire box controls the internal temperature of the charcoal smoker. Regulation is achieved by using a fan that blows into the fire box and partially starving the smoker for air when the fan is off. Fans can be of AC or DC design but usually DC fans are easier to obtain in the size needed for controlling a smoker cabinet. Fans are turned on and off using a relay or silicon switch like an NPN transistor or N-MOSFET which are wired to pull the fan negative lead to ground when the device gate is energized.
Next discussion will cover how a PID is wired for use in controlling a smoker.
JC
What is a PID in the first place?
P - Proportional
I - Integral
D - Derivative
These parameters describe gain formulas. Gain determines how fast and how hard your controlled device will turn on.
What are gain, error and setpoint?
Gain is the multiplication of the error that causes the circuit to start a correction. Error is the difference between the setpoint and the feedback from your sensor. In this case, the sensor is a thermocouple. Setpoint is the point at which you want the PID to regulate. (i.e. 250 F)
Proportional gain is a straight forward multiplication of feedback error times circuit gain. For example; if I had 1 volt of error on a proportional gain stage with a gain (Av) of 10, the output of the error amplifier would be 10 volts. Proportional gain will get you close to your set point regulation but it is sloppy when used alone for regulation.
Integral gain is an integration of error over time. Integral gain will smooth out your proportional peaks and valleys and will hold tight regulation if set correctly. PI regulation is good for most analog thermal control applications.
Derivative gain will push your PI hard in one direction or the other depending on the trending temperature. For example, if you open the smoker door, the sudden loss of heat will trigger your controller to turn full on faster with a derivative gain function than if only a PI loop were used.
How is heat controlled in the smoker?
In an electric smoker, heat is generated by a resistive element usually over 1000 watts. To control 1000 watts at 120 VAC, you need to control 8.333 Amps of current. To switch this much power, you need a relay or silicon switch capable of handling the voltage and current needed by the element.
Solid State Relays or SSRs are inexpensive and readily available silicon switches for DC control of AC switching.
Charcoal smoker:
The amount of air pushed through the fire box controls the internal temperature of the charcoal smoker. Regulation is achieved by using a fan that blows into the fire box and partially starving the smoker for air when the fan is off. Fans can be of AC or DC design but usually DC fans are easier to obtain in the size needed for controlling a smoker cabinet. Fans are turned on and off using a relay or silicon switch like an NPN transistor or N-MOSFET which are wired to pull the fan negative lead to ground when the device gate is energized.
Next discussion will cover how a PID is wired for use in controlling a smoker.
JC
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