© Tony Simmons 2010
Select the first letter of the word from the list above to jump to appropriate section of the glossary. If the term you are looking for starts with a digit or symbol, choose the '#' link.
Glossary of Automation & Control Engineering Terms
Scientific Apparatus Manufacturers Association of America. The SAMA Standard PMC 22.1-1981 Functional Diagramming of Instrument and Control Systems is the basis for the symbols used to depict the detail of modulating control loops.
SIL - Safety Integrity Level is a term introduced in IEC 61508 to set the different levels of integrity needed of a safety system.
SCADA
Supervisory Control and Data Acquisition system
SCSI
Small Computer Systems Interface (SCSI).
Security
The protection of computer hardware and software from accidental or malicious access, use, modification, destruction, or disclosure. Security also pertains to personnel, data, communications, and the physical protection of computer installations.
A graphical language for depicting sequential behaviour of a control system. It is used for defining control sequences that are time - and event - driven. It is defined by IEC Standard 848 and IEC 61131-3, and used in ISA S88 Part 2.
See also GRAFCET
Serial Link
A serial link is a simplistic reference to a communication link in which instead of using discrete input or output channels to communicate information to the process control system, data is transmitted serially over a pair of wires. In order for this to happen special software is required at both the sending and receiving ends of the link. This software must be able to recognise the data format used and an agreed communication protocol must be defined. Because there are many different protocols and variants serial communications require careful engineering and testing. Serial links are slow and able to communicate over relatively short distances. Because many data points can be transmitted over a serial link it is often assumed to be a cheap option to connect two pieces of equipment. It is not, because all such points may need to be processed as if they were real I/O points.
In the OSI communications model a service is a set of operations that a communications layer provides to the layer above it and defines what operations the layer is prepared to perform on behalf of its users. It does not define how these operations are implemented which is the job of the protocol. A service relates to an interface between two layers, with the lower layer being the service provider and the upper layer the service user.
Session Layer
One of the protocol layers in the OSI seven layer model. The session layer allows users on different machines to establish sessions between them. A session allows ordinary data transport, as does the transport layer, but it also provides some enhanced services useful in some applications. A session might be used to allow a user to log into a remote time-sharing system or to transfer a file between two machines. Related session services are token management and synchronisation.
Semantics
Semantics concerns the meaning and relationships of signs and symbols in a programming language and with what they represent. It is the principles that determine the truth- values of the formulas in a logical system.
SI
Systems Integrator or Systems Integration.
Simulation
The representation of selected characteristics of the behaviour of one physical or abstract system by another system. In a digital computer system, simulation is done by software. Typically simulation is used during software testing to replicate the actions of field devices such as on/off valves and motor contactors by writing extra software to simulate the receipt of input signals when an output condition is true.
SMS
Short Message Service
Software
The intellectual creation comprising the programs, procedures, rules and associated documentation pertaining to the operation of a programmable electronic system. It includes operating systems, firmware, and application programs.
Software Development Methodology
A term used to describe a set of procedures to be followed from the original conception of a system, through the specification, design, implementation, operation and evolution of the software in that system. A methodology includes technical methods to assist in the critical tasks of specification, documentation, analysis, design, coding, testing and configuration management. But just as important, it also includes procedures to control the development process and the deployment of technical methods.
Software diversity
The use of two or more dissimilar sets of software in parallel.
Software Specification
In order to be able to maintain software it is necessary for the engineer to understand how the application software has been structured and how data has been named. The Software Specification provides application specific information about how the software has been programmed. It lists what timers and flags have been used, records their values. It defines how parameters have been stored and which can be changed by the programmer and which by the user. If summarised file names and naming conventions. Read in conjunction with the code listing and annotations it provided the maintainer with information on how to make software changes.
Software System
Source Code
An original computer program expressed in human-readable form (programming language), which must be translated into machine-readable form before it can be executed by the computer.
Stage
One of the activities within the system project life cycle. (May also be referred to as a life cycle "phase").
The stage products (deliverables) represent the points along the development path where there is a clear change of emphasis, where one viewpoint or model of the emerging product is established and used as the basis for the next. As such the stages form natural milestones of the development progression and offer objective visibility of progress.
A state matrix is a table of information defining the states of plant devices (valves, drives, loop set points) for each of the procedural steps that must be executed to achieve the required functionality. States are usually represented by on/off, fast/slow and the like, and set points by the desired values. The matrix is an end product of requirements analysis once the physical and procedural models have been defined.
State Transition Diagram
A state transition diagram (STD) is a diagrammatic way of describing event driven functionality of a piece of equipment, for example. Any item of plant takes up a variety of "states" in order to function. Such states might be "shutdown", "available", "running", "filling", and so on. The change from on state to another takes place because some event happens. It may be a manual action such as opening a filling valve or more often a process variable reaching some pre-set limit. The STD documents all states and these transitions. Because what happens to cause a transition is often complicated, Sequence Function Charts (SFC) are used to document what goes on at each transition between states. See State Matrix and SFC.
Structural Testing
Examining the internal structure of the source code. Includes code inspection. Looks for dead code.
Structured Text (ST)
A high level textual language similar to PASCAL that encourages structured programming.
Sub-system
A term used to describe a part of the overall hardware or software system. A sub-system could be a software "mechanism" forming part of the overall system software. A sub-system might, in turn, comprise one or more software "modules" which might have common features and be re-used in other sub-systems or systems.
Examples of software sub-systems might be:-
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database
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graphic displays
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event logging
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process interlocks
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SUT
SUT - Abbreviation for Software Under Test.
Syntax
Syntax is systematic statement of the rules governing a programming language.
The term given to overall combination hardware and software which when operating together comprise the system. In the simplest of terms a system comprises:-
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system hardware
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system software
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application software
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peripherals
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interconnecting cabling
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documentation
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System software
The software within a programmable electronic system that manages the PES hardware and communication with external devices and internal resources.
Systematic Failure
Failures due to errors in specification, design, construction or use of a system which cause it to fail under particular combinations of inputs or under some environmental condition.
