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LLCCA_PID_QuickStartGuide.md

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LLCCA_PID Quick Start Manual

This manual provides a quick guide to using the LLCCA_PID function block for Siemens S7-1200/1500 PLCs. This function block implements a PID controller with step tuning capabilities.

1. Function Block Interface

The function block has the following inputs, outputs, and parameters:

Inputs:

  • Setpoint: The desired value for the process variable. (Real)
  • Input: The current value of the process variable. (Real)
  • ManualValue: The output value when in manual mode. (Real)
  • Reset: A boolean signal to reset the integral term and filters. (Bool)

Outputs:

  • Out: The calculated output value of the PID controller. (Real)
  • Terms: A structure containing the individual PID terms:
    • p: Proportional term (Real)
    • i: Integral term (Real)
    • d: Derivative term (Real)

In-Out Parameters:

  • ioMode: The operating mode of the controller. (USInt)
    • 0: Inactive
    • 1: Step tuning
    • 2: Reserved
    • 3: Automatic
    • 4: Manual
  • ioKp: Proportional gain. (Real)
  • ioTi: Integral time in seconds. (Real)
  • ioTd: Derivative time in seconds. (Real)

2. Operating Modes

The LLCCA_PID function block supports the following operating modes:

  • Inactive (0): The controller output is set to 0.
  • Step Tuning (1): The controller automatically determines PID parameters based on the process response to a step change in the output. This mode requires a stable process.
  • Automatic (3): The controller operates in automatic mode using the configured PID parameters.
  • Manual (4): The controller output is set to the ManualValue input.

3. Step Tuning

To perform step tuning:

a. Set `ioMode` to 1.
b. Ensure the process is stable.
c. The controller will automatically initiate a step change in the output and analyze the process response to calculate PID parameters.
d. Once tuning is complete, the controller will revert to the previous mode and the calculated `ioKp`, `ioTi`, and `ioTd` values will be updated.

4. Automatic Mode

In automatic mode:

a. Set `ioMode` to 3.
b. Provide the desired `Setpoint`.
c. The controller will calculate the output based on the configured `ioKp`, `ioTi`, and `ioTd` values.

5. Manual Mode

In manual mode:

a. Set `ioMode` to 4.
b. Provide the desired output value in `ManualValue`.

6. Tuning Rules

The step tuning function uses predefined tuning rules to calculate PID parameters. You can select the desired rule by setting the statAdvanced.tuningRule parameter:

  • 0: Chien–Hrones–Reswick (CHR) with 0% overshoot
  • 1: CHR with 20% overshoot
  • 11: Ziegler-Nichols (ZN) fast
  • 12: ZN normal
  • 13: ZN slow

7. Additional Parameters

The function block also provides additional parameters for advanced configuration:

  • statAdvanced.outMax: Maximum output value.
  • statAdvanced.outMin: Minimum output value.
  • statAdvanced.inputFilter: Time constant for the input filter.
  • statAdvanced.derivateFilter: Time constant for the derivative filter.

8. Example Implementation

// Instance of the LLCCA_PID function block
myPID(Setpoint := 100.0, 
      Input := processValue, 
      ManualValue := 50.0, 
      Reset := false, 
      ioMode := 3, 
      ioKp := 2.5, 
      ioTi := 10.0, 
      ioTd := 1.0, 
      Out => controlOutput, 
      Terms => pidTerms);