Augment the Safety Aspect: How Process Control Becomes a Plant Safety Cornerstone

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EDL Anlagenbau Gesellschaft mbH

ProMinent GmbH

Siemens AG Industry Sector

It evaluates the setpoint, process value and manipulated variable of a PID controller in a moving time frame. The Control Performance Index (CPI) describes the variance of a variable relative to a reference (benchmark).

In a steady-state process operating mode the determined stochastic characteristics are compared with reference values, which were evaluated e.g. during commissioning. As stochastic characteristics are irrelevant for setpoint steps, they are temporarily frozen while monitoring characteristics, such as settling time and step response overshoot, are automatically activated.

Fine-Tuning the Safety Aspects

“A message indicates if the control performance falls below a defined limit, thus allowing operators to react with specific procedures at an early stage,” Dr. Pfeiffer continues. “In many cases, controller re-tuning requires active plant tests, where the integrated PID tuner provides outstanding support.”

This tool is suitable for optimizing PID, PI and P controllers. Based on a mathematical process model that calcualted using experimental data, the tuner calculates controller parameter settings for optimum disturbance compensation or tracking performance. Optimization can be carried out in manual or automatic mode. Typical controller signals (setpoint, process value and manipulated variable) are recorded using a trend function. Before downloading the parameters, the closed-loop control behavior can be evaluated using simulation runs.

Cloud Computing for Process Safety

In contrast to the Con Per Mon function block monitoring, the cloud-based data service “Control Performance Analytics” assesses all control loops at a glance. Stochastic and deterministic parameters are computed, and the results presented in a performance report.

Loops with poor performance can be analyzed in detail, and if desired, Siemens experts can also provide a consulting service. If re-tuning is required, new control parameters based on historical data are suggested.

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