Programmable Electronic Systems

With a PES the representation and operation of the plant is realized almost entirely via monitors. The basic setup of such a system is shown in Fig. 6.5. It is now briefly commented upon following [2]. 

In the input/output interface input signals are received and after processing in the PSE output to the final control elements (vid. Fig. 6.6). 

Binary signals stem from relays, limit monitors, pushbuttons and switches. They can be processed directiy and be output to contacts, switches or lamps. All measuring values are cyclically scanned and checked before processing as to their validity. The following distinctions are made. 

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Being excellent at discrete logic, PLCs are a potential candidate for implementing interlocks. Process interlocks are clearlv acceptable for implementation within a PLC. Implementation of safety interlocks in programmable electronic systems (such as a PLC) is not universally accepted. Many organizations continue to require that all safety interlocks be hard-wired, but implementing safety interlocks in a PLC that is dedicated to safety functions is accepted by some as being equivalent to the hard-wired approach. 

Software In some programmable electronic systems (PES), errors are much easier to detect and correct than in others. Using the term software, in the wider sense, to cover all procedures, as distinct from hardware or equipment, some software is much friendlier than others. Training and instructions are obvious examples. As another example, if many types of gaskets or nuts and bolts are stocked, sooner or later the wrong type will be installed. It is better, and cheaper in the long run, to keep the number of types stocked to a minimum, even though more expensive types than are strictly necessaiy are used for some applications. 

HSE 1987. Programmable Electronic Systems in Safety Related Applications. Part I, An Introductory Guide. Part II, General Technical Guidelines. Health Safety Executive, Her Majesty s Stationery Office, London. 

Maggioli, V. J., and G. FI. Stike, Jr. 1990. Programmable Electronic Systems and Safety in Today s Chemical Plants. 24th Annual Loss Prevention Symposium. August 19-22, San Diego, California. American Institute of Chemical Engineers, New York. 

Programmable Electronic System (PES) A system based on a computer connected to sensors and/or actuators in a plant for the purpose of control. 

The use of computers and microprocessors (also known as programmable electronic systems [PES]) in process control continues to grow. They have brought about many improvements but have also been responsible for some failures. If we can learn from these failures, we may be able to prevent them from happening again. A number of them are therefore described below. Although PES is the most precise descnption of the equipment used, I refer to it as a computer, as this is the term usually used by the nonexpert. 

Safety Related Instrument Systems for the Process Industries (Including Programmable Electronic Systems)", Publication No 160, The Engineering Equipment Manufacturers and Users Association (EEMUA), 14/15 Belgrave Square, London SW1X 8PS ... 

Since the 1970s, process controls have evolved from pneumatic analog technology to electronic analog technology to microprocessor-based controls. Electronic and pneumatic controllers have now virtually disappeared from process control systems, which are dominated by programmable electronic systems based on microprocessor technology. 

U.K. Ministry of Defence, Defence Standard 00-58 A Guideline for HAZOP Studies in Systems which include a Programmable Electronic System, MOD Directorate of Standardisation, Glasgow, U.K. 

One of the more influential documents on SIS was called "Programmable Electronic Systems in Safety Related Applications," which was published by the Health and Safety Executive (HSE) in the United Kingdom (Ref. 2 and 3). Early national standards for SIS include "Grundsatze fur Rechner in Systemen mit Sicherheitsaufgaben," published in Germany (Ref. 4 and 5) in 1990 and ANSI/ISA-84.01-1996, "Application of Safety Instrumented... 

List the advantages of using programmable electronic systems in safety applications as compared to solid state logic. 

Nevertheless in the context of the licensing procedure hardwired activation of safety functions is demanded in addition to PES activation, since it is still difficult to assess the reliability of computer programs. However, in [6] aspects are presented which have to be accounted for if electric/electronic/programmable electronic systems (E/E/PES) are used to realize safety functions. Below some general remarks are made following [7]. The corresponding mathematical and technical treatment is presented in Chap. 11. Since the requirements of [6] can be applied as well to other control systems than (E/E/PES) we speak in what follows of PCE equipment with the understanding that any of the above types of process control is meant. 

VDI/VDE-Richtlinien (Nov 2000). Safeguarding of industrial process plants by means of process control engineeringusing safety-related programmable electronic systems. 

Reliability prediction of programmable electronic systems in the automotive industry... 

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