Siemens ST PCS 7 manual Libraries, PID Tuner

© Siemens AG 2007

Engineering system

ES software

Standard engineering software

I&C libraries

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Examples of editable OS standard displays (faceplates) from the PCS 7 library

Preconfigured and tested blocks, faceplates and symbols are organized in I&C libraries and form the basic elements for the graphic configuration of automation solutions. The use of these library elements plays a major role in minimizing the engineering input and project costs.

The comprehensive range of blocks can be categorized as fol- lows:

•Simple logic and driver blocks

•Technological blocks with integral operation and signaling functions such as PID controllers, motors or valves

•Blocks for integration of PROFIBUS field devices in accor- dance with PROFIBUS PA profile 3.0 (including standardized evaluation of the process value status)

•Blocks with more advanced control algorithms for Advanced Process Control (APC) functions

Advanced Process Control (APC) functions

The APC functions concentrated in separate blocks expand the PID-based control functions of SIMATIC PCS 7 by more ad- vanced control algorithms, e.g.:

• Model-based multi-variable controller

The use of a multi-variable controller is recommendable for com- plex processes where several variables which are mutually de- pendent have to be controlled. Separate control of the individual variables, e.g. using PID controllers, has the disadvantages that interactions result in different effects on the respective variables.

The model-based ModPreCon multi-variable controller inte- grated in SIMATIC PCS 7 separately analyzes the response of up to four mutually dependent variables over a longer period of time. A parameter matrix is calculated from the results, and used by the ModPreCon for optimum control of the variables.

Note:

The ModPreCon makes great demands on memory and processing time of the designated automation system. For that reason, please check the resources of the designated automation system before use. We recom- mend the use of an automation system of type AS 416 or higher.

• Setting of control parameters dependent on working point

The GainSched block has been designed for variable setting of controller parameters depending on the working point in non-lin- ear controlled systems. The block functions similar to the poly- gon block, and can derive three separate output variables from the response of an input variable, and apply these as control pa- rameters for a linked controller block. The GainSched block then adjusts the control parameters of the combined controller de- pending on the response of the actual value.

The faceplate of the GainSched block can be called from the faceplate of the associated controller.

• Monitoring of control quality

The ConPerMon block can be used to monitor the quality of a controller block according to a patented procedure. The set- point, actual value and manipulated variable of the controller block (e.g. PID controller) are connected to the ConPerMon block which determines the control quality using these online values. The block can trigger a warning or alarm depending on the deviation from a reference value, e.g. the control quality de- termined during commissioning.

The faceplate of the ConPerMon block can be called from the faceplate of the associated controller. OS displays can be gen- erated during engineering which list all deviations in the control quality of a plant or unit. The plant operator can use these dis- plays to recognize problems early, and to analyze and specifi- cally eliminate such before they result in serious deficiencies or a production failure.

PID Tuner

The PID Tuner is a function integrated in the CFC for optimization of the CTRL_PID and CTRL_S software controllers. The optimum parameters for a control loop can then be determined for PID, PI and P control modes in defined steps.

The tool is suitable for optimizing controlled systems with or with- out an integral component. Optimization can be carried out in manual or automatic mode. The transient response of the con- trollers with the determined parameters can be checked by de- fining jumps. The controller parameters can be saved, and re- called as required.

During determination of the controller parameters, the typical controller values (actual value, setpoint, manipulated variable) are recorded by a trend function.

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Siemens ST PCS 7 · November 2007