There is no use to know Algorithm inside the PID controller .Any controller in any software platform contains some basic function.For samples, there are plenty of discussed samples and you can find them by searching!

Hi Edwin,

Gladly enough Step7 has a function which takes care of the PID control. So it's not nessecary to create your own function so you don't really need to have the algorithm to set up the PID controller. Now offcourse I'm glad you ask for the algorithm because it's essential to understand how the PID controller works.

Can you please mention which PLC you are using, is it a S7-1500, 1200 or 300, 400?

The reason I ask is because the PID blocks for the S7-300/400 are different from the S7-1500/1200.

For S7-300/400;Depending on the application you can chose between:

- TCONT_C:The CONT_C instruction is used on SIMATIC S7 automation systems to control technical processes with continuous input and output variables.

- TCONT_CP:The instruction TCONT_CP is used to control temperature processes with continuous or pulsed control signals.

For S7-1200/1500:

- PID-compact: provides a continuous PID controller with integrated tuning. You can alternatively configure a pulse controller. Both manual and automatic mode are possible.

- PID-3step:provides a PID controller with tuning for valves or actuators with integral response.

I advice if you want to set up a PID controller take a good look at the manuals, the tia portal help-function also contains a lot of useful information.

If you have a 300/400 and you are going to use TCONT_CP, this is the algorithm behind it:

Where:
LMN_Sum(t) the manipulated variable in the controller's automatic mode
ER (0) is the step height of the normalized control deviation
GAIN is the controller gain
TI is the integration time
TD is the derivative action time
D_F is the derivative factor

You can find more info here :Description TCONT_CP
As you can see the standard PID algorithm is used here.

If you are using a 1200/1500 here is an example how to set up a PID-compact, done step by step:
http://www.youtube.com/watch?v=haww2NyllRc

Also chech out this thread by Pegaia:
/tf/WW/en/Posts/52322#253011

Hope this helped

Kind regards,
Jens

In my point of view an algorithm is more complex than a formula in time domain.An PID algorithm consists of

• Mode of operation like restart,manual mode,auto mode
• Peripheral data (input/output)handling
• error calculation and error manipulation such as deadband functions
• Switches for P_Part,I_Part and D_Part
• Calculate each part separately
• Summing the result from P_Part,I_Part and D_Part and form output
• Limit output or a linear mapping in case of actuator safety is required

Please note, the core calculation of an algorithm is finding P_Part,I_Part and D_Part and I am sure there is no formula to find the result.All iterative neumerical calculation with some concerns with each part for proper operation the whole.

I still believe , my concise description is still Valid! No need to know inside PID and search for samples!

Have Fun!

Hamid Hosseini