Electronic Instrumentation for Control

Abstract

Advancements in the area of electronic devices, particularly the wonder chip “Micro-processor”, have indeed pushed electronic systems in process control, far ahead of other known and established systems. With increased reliability of the present day devices and provision of redundant systems of marginal extra cost, the confidence of the plant operator in electronic instrumentation is restored to the same level as with the conventional pneumatic systems. Intrinsic safety features limiting the energy at the field equipments at the minimum permissible level, have rendered electronic systems acceptable for the most hazardous plant environments.

The early electronic analog system on the low level current signal concept (4–20 Ma) is being fast replaced by digital systems with visual display units, the underlying emphasis being ergonomics or human engineering. In this system the process control components have been made functional by split architecture, wherein controllers are de-linked from display systems and operator control. Large control panels with analog instruments have been dispensed with and large process plants can now be operated from a small console with a couple of visual display units and operator key-board for command, together with the advantages of obtaining a fund of management information, plant review, process calculations, etc. which would otherwise could have been provided only by a computer.

Cost Analysis have shown that the digital systems are much cheaper than conventional analog systems. The added feature on digital systems is the easy hook up of a process computer for optimisation. Industry reports have indicated that investments on process computers have paid back in less than a year in terms of increased yield, product quality and reduced cost of utilises.

Distributed control systems should perhaps be the technology of the next decade in electronic instruments for process control with digital display system, analog controllers and pneumatic final control elements.

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Notes on contributors

R. Gopalakrishnan

R. Gopalakrishnan is presently the Manager, Central Engineering with Engineers India Limited. He has been associated with the design and engineering of instrumentation and control for various process plants which include oil refineries, petrochemical and fertiliser plants. He is also associated with the various National Committees for planning the policies with regard to instrumentation in the country. He has also served as a Member in the Advisory Committee for CSIR and CEERI.