Integrating Safety and Control Systems
Authors: Ewens A.J. , Laffey S.M. 
Published: October 2008

A paper examining the feasibility of combining safety, detection and process control systems into one functional and physical system. It is set within the contextual boundaries of technological advancements and increasing legislative concerns. The technological evolution of control systems is described and a review taken of some systems available in the market. The cases for and against integration of these systems is made and a conclusion reached.

INTRODUCTION

The need for greater flexibility, economy and efficiency in the volatile world of the oil and gas industry increases daily. Coupled with this, the rapid evolution of technology employed, in monitoring control and safety systems has led to increasing pressures to integrate these systems into a single package. The degree to which systems are integrated can vary greatly. This paper will give some examples of the types of integrated systems to demonstrate the options available.

An overview of the evolution of technology in this field is given with examples of how the needs of the various control systems have been dealt with in the past; followed by an appraisal of functional requirements of the various systems and some examples of the technological solutions vendors commonly offer to meet these requirements.

The advantages and disadvantages of the integration approach are listed, a summary given and a conclusion to the discussion offered.

TECHNOLOGICAL EVOLUTION 0F CONTROL SYSTEMS

The pressures behind integration will be examined later but one such pressure is the convergence of the technology used in process control and safety systems. Essentially, the technology is based around the application of computer systems.

EARLY HISTORY

Before the introduction of computers for industrial process control applications, the standard industrial control system consisted of a large number of either pneumatic or electronic single loop analogue controllers. This equipment provided, and still provides, excellent control of industrial processes. The main disadvantages of stand-alone controllers are that they are not easily reconfigured but they cannot easily communicate with other plant computers or systems.

The first practical digital computer control system was designed by the Hughes Aircraft Company for the US Air force. It used a computer called the DIGITACTM and controlled an airplane in flight by computed set point changes to an analogue-based automatic pilot. It was first flown successfully in 1954.

The losing company in the competition for the US Air Force contract marketed their computer as a process control computer which was a turning point in the early history of process computers. It is interesting to note that computer control developed not from process or manufacturing industries initiatives but through the efforts of computer and electronics vendors to expand their markets beyond the military segment.

The first industrial installation of a computer system was made by the Daystrom Company at the Louisiana Power and Light plant in Sterlington, Louisiana. It was a supervisory data monitoring system, rather than a closed loop control system.