Control Systems Technology

Objectives and Syllabus

Develops an understanding of the functional capability of modern control systems. Topics covered are - system architecture; evolution of computer control, DCS, PLCs, SCADA, MIS & CIM systems: communications; telemetry, networks & highways: open systems; definition, influence of standards on Fieldbus & operating systems: real-time system software; interrupts, OS design, multi-tasking, real-time database design, specification of tasks: configuration; IEC 61131-3 functions & function blocks, signal conditioning & control algorithms, configuration tools: integrated alarm environments: system layout; signal distribution, segregation policy, power & air supply: intrinsic safety; hazardous area classification, barriers: reliability; terminology, availability and mean times, proof testing, series and parallel arrangements, redundancy, voting systems: hazard analysis; FMEA, common mode, CHAZOP: layers of safety; passive & active safety systems, alarm trip & interlock systems, EEMUA categories: protection system design; PES guidelines, IEC 61508, risk and demand rate, safety integrity levels (SIL), qualitative approach: safety equipment; TUV approval, logic technologies, special purpose PES: human factors; psychological model, anthropometrics.

Case studies relating to specific installations are used to reinforce the syllabus content.

Aims

To develop an understanding of the functionality of the hardware and configurable software of control systems and of the design of protection systems with particular reference to IEC standards.

Objectives

• To develop an appreciation of the technology of control systems in terms of their architecture, communications and system software design. 
• To provide an in depth understanding of the functionality of input and output channels. 
• To develop a feel for the functionality of configurable software in relation to the IEC 61131 standard with an emphasis on continuous control. 
• To understand ‘good practice’ regarding human factors in the design of display systems, alarm handling and abnormal situation management. 
• To provide a quantitative grounding in reliability and hazard analysis and in the design of protection systems in relation to IEC 61508 and 61511 standards.

Phasing

It is desirable, but not essential, that students have completed (or have some familiarity with the material covered in) the Instrumentation and Measurement (CME 8366) module before doing this one.

Study Modes

This module is of one week's full-time intensive study consisting of a variety of formal lectures, group work and case studies based upon typical industrial control systems.  It is followed by an assignment to be carried out in the student’s own time.

Assignment

The assignment typically consists of a technical review of part of an industrial control system to which the students have access (or have access to its design) in the course of their normal employment.  The review will focus on aspects of the system's design, such as its requirements from a reliability and safety point of view.

Recommended Texts

• Andrews J D & Moss T R,  Reliability and Risk Assessment,  Professional Engineering Publishing,  2002 
• Goble W M,  Control System safety Evaluation and Reliability,  2nd Edition,  ISA,  Carolina,  1998. 
• Lewis R W,  Programming Industrial Control Systems using IEC 1131-3,  IEE,  London,  Revised Edition,  1998. 
• Love J,  Process Automation Handbook,  Springer,  2007
• Lister A M & Eager R D,  Fundamentals of Operating Systems,  MacMillan,  5th Edition,  1998. 
• Smith D J,  Reliability, Maintainability and Risk,  5th Edition,  Butterworth Heineman,  1997.

Topics Included

Systems architecture:  Evolution of computer control.  Differences between integrated (ICS), distributed control systems (DCS) and programmable logic controllers (PLC).  Overview of use of ICS, DCS and PLCs for continuous and sequence control.  Concepts of supervisory control and data acquisition (SCADA), management information systems (MIS) and computer integrated manufacture (CIM).  Communications: networks and highways.  Telemetry and remote terminal units (RTU).  Wireless technology: satellite, radio and telephone links.

Open systems:  Driving forces: access and interoperability.  Integration of control and information systems.  Standards and enabling technologies.  Impact on architecture.  Data objects and linking: object linking and embedding (OLE) and OLE for process control (OPC).  Security aspects: access and firewalls.  Awareness of threats and risks to data infrastructure.  API 1164 and the ISO 17799 standard on information security management.

System software:  Review of concepts and functionality of real-time and multi-tasking operating systems.  Prioritisation of tasks.  Overview of commercial off-the-shelf  (COTS) software packages and application tools.  Categorisation of system vs application software and configurable vs procedural software.  Demonstration of proprietary development environment.

Operator interface:  Access.  Display systems: groups, mimics, trends and status.  Good practice.  Integrated alarm environments: integration of control and alarm functions.  Alarm handling: annunciation and acknowledgement.  Alarm lists and alarm limits.  Alarm logging, report generation and management.  Human factors: operator’s role, psychological model, anthropometrics.  Abnormal situation management (ASM) systems.

Configuration:  the IEC 61131 standard (Part 3).  Functions and function blocks.  Signal conditioning and control algorithms.  Connectivity and function block diagrams.  Functionality of typical configurable control packages.  Configuration tools.  Database structure and operations.  Blocks and slots.  Processing of typical analogue and discrete I/O signals.  Case study on continuous control.  Ladder logic.  Contacts, coils and rungs.  Ladder execution.  Integration of sequence and continuous control.  Timers and counters.  Demonstration of the functionality of proprietary PLCs.

Hardware aspects:  Memory types.  Peripheral devices.  Operator stations.  Card and rack organisation.  Plant input and output interfaces.  Mechanical interfaces.  Consideration of typical analogue and discrete I/O channels.  

Hazard analysis and quantification: cause and consequence.  HAZOP, CHAZOP and COOP studies.  Failure mode effect analysis (FMEA).  Fault tree analysis.  Cut sets and fault tree evaluation.  Calculation of demand rate.

Systems reliability:  Rep airable vs unrepairable systems.  Definition of terminology: eg failure rate, reliability, MTBF, and availability.  Proof testing.  Series and parallel elements.  Common cause failure and common mode effects.  Voting and standby systems.  Protection systems.  Definition of terminology: PFD, hazard and demand rates, risk and consequence.  Random hardware vs systematic failures.  Redundancy vs diversity.  Worked examples based on shut-down systems.  Fail-safe design.  Spurious failures.  Reliability data.
Layers of safety:  Distinction between control and protection systems.  Historical perspective: HSE Guidelines on programmable electronic systems (PES).  EEMUA categories.  Passive, active and control.  Pressure relief & venting systems.  Alarm, trip and interlock systems.  Programmable emergency shut-down systems (ESD).  Fire and gas (F&G) detection.

Protection systems:  Risk and ALARP.  Safety methodology.  Interpretation of the IEC 61508 and 61511 standards (and ISA SP84).  Safety integrity levels (SIL).  Quantitative approach to calculating required SIL.  Qualitative approach to SIL and use of hazardous event severity matrix.  Worked example.  Layers of protection analysis (LOPA).  Protection system design and independence.  TUV approvals and use of risk graph.  Failure modes: de-energise to trip, overt and covert.  Safety equipment technologies: electromagnetic relay logic, DC coupled logic, dynamic logic, special purpose PES.