## PIDLab - Mac OS

PIDLab calculates PID tuning parameters based on process gain. Tuning aggression is changed using a slider. A built in simulator allows you to see how the process/controller reacts to the tuning parameters. The program also allows you to enter you're own tuning parameters and see the result in the simulator. This is a good way to learn PID tuning.

Tuning parameters are calculated using the IMC (Internal Model Control) method to calculate PID tuning parameters. I’ve tried a lot of tuning methods over the years and have found this one to be the best.

Tuning parameters are calculated using the IMC (Internal Model Control) method to calculate PID tuning parameters. I’ve tried a lot of tuning methods over the years and have found this one to be the best.

## PID Lab

The program calculates:

PID Parameters:

For process types

For controller types

Parallel (non-interacting)

c(s) = Kc (1 + 1/(Ti s) + Td s)

Series (interacting)

c(s) = Kc (Ti s + 1)/(Ti s)(Td s + 1)

For controller modes

You can either enter the process gain (Kp) directly by touching the entry field or enter the changes in the controlled variable (CV) and manipulated variable (MV). The process gain is calculated in engineering units (EU) and scaled to percent of range using the scaling parameters. Controller output is almost always in % (0 to 100%).

Tuning aggression is adjusted using the slider to set the closed loop time constant to the process time constant ratio (λ/Ƭ).

The closed loop time constant (λ) is the time the controller is expected to reach set point (plus the dead time (ϴ)). Setting the closed loop time constant to process time constant ratio (λ/Ƭ) to 1.0 will make the MV change to its final value and allow the process to settle out to the setpoint. Setting (λ/Ƭ) greater than 1.0 will give a slower responce. Setting (λ/Ƭ) less than 1.0 will cause the MV to make a larger change and then reduce to its final value. Tight tuning would be to set the close loop time constant to the dead time.

Use the Integrating Process type (Ƭ = ∞) for both integrating processes or processes with long time constants. These processes use the maximum slope as the process gain. Tuning aggression for these processes is determined by setting the closed loop time constant to the dead time ratio (λ/ϴ). Once again, setting the closed loop time constant to the dead time gives tight control.

Glossary

Controlled Variable (CV): the variable we are trying to control (the process output).

Manipulated Variable (MV): the output from the controller we are using to control the process. This is the imput to the process.

Process Value (PV): the same as the CV. This is the output from the process.

Process Time Constant (Ƭ): the time it takes for the process to reach 63% of its altimate value after stepping its input (MV). If the process only has one lag (time constant). this is the first time constant (Ƭ1).

Second Time Constant (Ƭ2): Second time constant for a second order process. This is the secondary lag and is usually smaller than the first time constant.

Deadtime (ϴ): The time delay before any change in PV appears.

Closed Loop Time Constant (λ): Tuning parameter for IMC (Lamda) tuning. This is the desired time for the process to reach its set point (plus the deadtime and second lag)

Closed Loop to Open Loop Time Constant (λ/Ƭ): The ratio of the closed loop time constant to the open loop (process) time constant. Setting the value to 1.0 causes little or no overshoot in the PV response. Setting the value less than 1.0 gives tighter control. Setting the value greater than 1.0 gives looser control.

References:

“Probably the test simple PID tuning rules in the World,” Sigurd Skogestad, Jounal of Process Control, July 3, 2001

“Consider the generalized IMC-PID method for PID controller tuning of time-delay processes,” Y. Lee, S. Park, M. Lee, Hydrocarbon Processing, January 2006

PID Parameters:

- Controller Gain (Kc)
- Integral Time (Ti)
- Derivative Time (Td)

For process types

- First Order with Dead Time (FO)
- Second Order with Dead Time (SO)
- Integrating or Long Time Constant with Dead Time (I)

For controller types

Parallel (non-interacting)

c(s) = Kc (1 + 1/(Ti s) + Td s)

Series (interacting)

c(s) = Kc (Ti s + 1)/(Ti s)(Td s + 1)

For controller modes

- PID
- PI

You can either enter the process gain (Kp) directly by touching the entry field or enter the changes in the controlled variable (CV) and manipulated variable (MV). The process gain is calculated in engineering units (EU) and scaled to percent of range using the scaling parameters. Controller output is almost always in % (0 to 100%).

Tuning aggression is adjusted using the slider to set the closed loop time constant to the process time constant ratio (λ/Ƭ).

The closed loop time constant (λ) is the time the controller is expected to reach set point (plus the dead time (ϴ)). Setting the closed loop time constant to process time constant ratio (λ/Ƭ) to 1.0 will make the MV change to its final value and allow the process to settle out to the setpoint. Setting (λ/Ƭ) greater than 1.0 will give a slower responce. Setting (λ/Ƭ) less than 1.0 will cause the MV to make a larger change and then reduce to its final value. Tight tuning would be to set the close loop time constant to the dead time.

Use the Integrating Process type (Ƭ = ∞) for both integrating processes or processes with long time constants. These processes use the maximum slope as the process gain. Tuning aggression for these processes is determined by setting the closed loop time constant to the dead time ratio (λ/ϴ). Once again, setting the closed loop time constant to the dead time gives tight control.

Glossary

Controlled Variable (CV): the variable we are trying to control (the process output).

Manipulated Variable (MV): the output from the controller we are using to control the process. This is the imput to the process.

Process Value (PV): the same as the CV. This is the output from the process.

Process Time Constant (Ƭ): the time it takes for the process to reach 63% of its altimate value after stepping its input (MV). If the process only has one lag (time constant). this is the first time constant (Ƭ1).

Second Time Constant (Ƭ2): Second time constant for a second order process. This is the secondary lag and is usually smaller than the first time constant.

Deadtime (ϴ): The time delay before any change in PV appears.

Closed Loop Time Constant (λ): Tuning parameter for IMC (Lamda) tuning. This is the desired time for the process to reach its set point (plus the deadtime and second lag)

Closed Loop to Open Loop Time Constant (λ/Ƭ): The ratio of the closed loop time constant to the open loop (process) time constant. Setting the value to 1.0 causes little or no overshoot in the PV response. Setting the value less than 1.0 gives tighter control. Setting the value greater than 1.0 gives looser control.

References:

“Probably the test simple PID tuning rules in the World,” Sigurd Skogestad, Jounal of Process Control, July 3, 2001

“Consider the generalized IMC-PID method for PID controller tuning of time-delay processes,” Y. Lee, S. Park, M. Lee, Hydrocarbon Processing, January 2006