Archive | ISA Transactions

Fig. 1. Block diagram of a cascade control system.

Improving performance using cascade control and a Smith predictor

Abstract: Many investigations have been done on tuning proportional-integral-derivative (PID) controllers in single-input single-output (SISO) systems. However, only a few investigations have been carried out on tuning PID controllers in cascade control systems. In this paper, a new approach, namely the use of a Smith predictor in the outer loop of a cascade control system, […]

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Fig. 1. Input vector for TITO process.

Guidelines for the tuning and the evaluation of decentralized and decoupling controllers for processes with recirculation

Abstract: This paper gives guidelines for the pairing, the time response specification, and the tuning for processes with recirculation when decentralized controllers are used. This selection is based on the condition number, which is an indicator of the process directionality, and on the generalized dynamic relative gain (GDRG), which is a measure of the interaction. […]

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Fig. 1. Feedback control system with a gain phase margin tester.

Robust PID Tuning Strategy for Uncertain Plants Based on the Kharitonov Theorem

Abstract: In this paper, the Kharitonov theorem for interval plants is exploited for the purpose of synthesizing a stabilizing controller. The aim here is to develop a controller to simultaneously stabilize the four Kharitonov-defined vortex polynomials. Different from the prevailing works, the controller is designed systematically and graphically through the search of a non-conservative Kharitonov region […]

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Fig. 1. Experimental setup for control of temperature process by pulse width modulation

PID gain scheduling using fuzzy logic

Abstract: A simple, yet robust and stable alternative to proportional, integral, derivative (PID) gain scheduling is developed using fuzzy logic. This fuzzy gain scheduling allows simple online duplication of PID control and the online improvement of PID control performance. The method is demonstrated with a physical model where PID control performance is improved to levels […]

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PFDavg for 1oo2 voting devices with common cause

Viewpoint on ISA TR84.0.02 Simplified Methods and Fault Tree Analysis

Abstract: ANSI/ISA-S84.01-1996 and IEC 61508 require the establishment of a safety integrity level for any safety instrumented system or safety related system used to mitigate risk. Each stage of design, operation, maintenance, and testing is judged against this safety integrity level. Quantitative techniques can be used to verify whether the safety integrity level is met. […]

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The Century’s Greatest Contributions to Control Practice

Introduction: Flowing with the tide of reflection and forecasting as the century changes, I took the liberty to conduct a survey of the century’s most important contributions to the practice of “control.’  I quite enjoyed considering the importance of the past events, and forecasting which contributions will be important in this new century. So did […]

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