LLCCA_PID Function Block

Overview

The LLCCA_PID function block implements a PID (Proportional-Integral-Derivative) controller with step tuning functionality. It is designed for use in Siemens S7-1200 and S7-1500 PLCs.

Features

• Support for S7-1200 and S7-1500
• Chien–Hrones–Reswick and Ziegler-Nichols step tuning
• Runs in Siemens PLC-simulator
• Source code can be accessed and modified
• Overall simpler design then Siemens PID_Compact

Known Issues

• The step tuning only works if the process (input) is very stable.
• An abort mechanism is needed to stop tuning if the process is or becomes unstable.

Process Value Simulator

A process value simulator function has been added to facilitate easier testing and simulation of the PID controller.

GUI for Easy Testing

A TP1200 Comfort project has been added so that the functionality can be easily tested and compared with Siemens PID_Compact.

Usage Instructions

Please refer to the LLCCA_PID Quick Start Manual.

Installation

• Open the .zap19 file in Siemens TIA Portal 19.

Installation SCL-files

1. Open a Siemens TIA Portal 19 project.
2. Place the SCL files under "External source files."
3. Execute the "Generate blocks from source" menu item.

Code Overview

The file LLCCA_PID_x_y_z.scl contains the SCL (Structured Control Language) code for the LLCCA_PID function block. The code includes:

• Input Variables: Setpoint, Input, ManualValue, Reset
• Output Variables: Out, Terms (structure with p, i, d components)
• In-Out Variables: ioMode, ioKp, ioTi, ioTd
• Internal Variables: Various static and temporary variables for calculations and state management

Functionality

The code implements the following functionality:

• Modes: Inactive, Step tuning, Reserved, Automatic, Manual
• Step Tuning: Calculates PID parameters based on the process response to a step change in the output.
• PID Control: Calculates the output based on the error between the setpoint and the input, using the configured PID parameters.
• Filtering: Includes input filtering and derivative filtering to improve control performance.
• Anti-Integral Windup: Prevents the integral term from becoming too large, which can cause instability.

Additional Notes

• The code is well-structured and includes comments to explain the functionality.
• The terminology of some variables and functions is taken from the Siemens PID_Compact controller.
• The code is optimized for access and visibility.

License

LCC Automation AB / (c)Copyright 2024. Released under the MIT License.