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How Do I Convert PID Parameters From Gain to Time?

Primary Software: LabVIEW Toolkits>>PID and Fuzzy Logic Toolkit
Primary Software Version: 8.6.1
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem:
I am using the PID Control Toolkit. The PID Gains input is asking for Gain, Integral Time, and Derivative Time. I am familiar with Proportional Gain, Integral Gain, and Derivative Gain. What is the difference between these two formats and how do I convert between them?

Solution:
There are no industry wide standards for PID algorithms as different manufacturers use different PID algorithms. The three major classifications of PID controller algorithms are ideal, parallel, and series. The ideal and the parallel forms are most relevant and flexible for tuning algorithms and are both widely used in the industry.

 

The series representation essentially consists of a PI and PD controller in series and made early analog controllers easier to build. As shown in the equations below, Kp, Kc are gain parameters; Ti and Td are integral and derivative time respectively.

 

 
  • Integral term or Reset
    The proportional term make changes to the output that is proportional to the current error value.

              The proportional gain may also be expressed as proportional band (PB)

              So a proportional band of 50% is equivalent to a proportional gain of 2.

  • Integral term or Reset
    The integral term is proportional to both the magnitude and the duration of the error. Increasing integral time makes the output respond slower to an error, which is opposite of the effect of increasing integral gain. The integral gain in the parallel PID is equal to the overall gain divided by integral time in the ideal PID.

  • Derivative term or Rate
    The derivative term demonstrates the rate of change of the process error by determining the slope of the error over time. The derivative gain in the parallel PID is equal to the overall gain times derivative time in the ideal formulation.


For a complete explanation of the implementation to the PID algorithm in the PID Control Toolkit see Chapter 2 of the PID Control Toolkit User Manual.



Related Links:
Developer Zone Community: PID, Fuzzy Logic, and Real-Time Control Seminar
Product Manuals: PID Control Toolkit User Manual
Developer Zone Tutorial: PID Theory Explained
LabVIEW 8.6 Help: Control Design and Simulation Module
KnowledgeBase 4B2AGDGH: Control Design Toolkit 2.1.2 with LabVIEW 8.5

 



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Report Date: 03/05/2004
Last Updated: 05/29/2009
Document ID: 374DUJOH

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