SCADA System Terms and Definitions used for Engineers

SCADA systems are an essential component of modern industrial automation and process control. SCADA stands for Supervisory Control and Data Acquisition, and it is a system of computers, communication networks, and remote terminal units (RTUs) that allow operators to monitor and control a range of operations in real time. In this article, we’ll explain what SCADA is, the types of data it deals with, and the components that make up a SCADA system.

SCADA System Terms & Definitions

At its most basic, SCADA systems are designed to monitor and control remote processes and machines. They are used in a variety of industries including energy, oil and gas, water and waste water, telecommunications, and manufacturing. SCADA systems are composed of a number of components, including:

Address: An identifying name, label, or number for a data terminal, source, or storage location calculation.
Analog data: Data represented by scalar values.
Application Account: The account name used to run applications as either a service or a background process.
Application Software: The software written specifically to perform functional requirements for an individual plant when standard software packages cannot be configured to meet the requirements.
Availability: The percent of time a system or component remains on line and performs as specified.
Bidirectional: Providing for information transfer in both directions between master and remote terminals (of a communication channel).
Binary digit: A character used to represent one of the two digits in the binary number system and the basic unit of information in a two-state device.
Buffer: A device in which data are stored temporarily in the course of transmission from one point to another.
Call Up Time: The time between when the operator initially enters a display request and when all objects, lines, values (good or invalid), trends, and other parts of the display have been fully presented to the operator
Command: Commands sent by operators or by applications. Commands can be binary or analog (set-point).
Communication channel: A facility that permits signaling between two terminals.
Communications Subsystem: The hardware and software that performs the transmitting and receiving of digital information.
Configurable: The capability to select and connect standard hardware modules to create a system, or the capability to change functionality or sizing of software functions by changing parameters without having to modify or regenerate software.
Console: A collection of one or more workstations and associated equipment such as printers and communications devices used by an individual to interact with the SCADA system.
Cycle: The scanning of inputs, execution of algorithms and transmission of output values to devices.
Cyclic Polling (data request): The process by which a data acquisition system selectively requests data from one or more of its RTUs.
Dead Band: The range through which an input signal may be varied without initiating an action or observable change in output signal.
Flag: A character that signals the occurrence of some event. Usually, a field of 1 bit.
Faceplate: A graphic element that mimics the front panel of an analog controller instrument, hardwired push-button or switch.
Fail-Over: Occurs automatically without user intervention, transparent to the user.
Intelligent Electronic Devices (IED): An intelligent electronic device that perform specific control and/or data gathering function.
Logs: Files or printouts of information in chronological order.
Master Station: Server or servers and software responsible for communicating with the field equipment (RTUs, PLCs, etc.), and then to the HMI software running on workstations in the control room, or elsewhere.
Operating System: Software that runs on computers and manages the computer hardware and provides common services for execution of application software.
Protocol: A strict procedure required to initiate and maintain communication with the RTU or a PLC.
Redundant Configuration: A system and/or subsystem that provides for a standby module with automatic switchover from the primary unit to the standby module, in the event of a failure, without loss of a system function.
Report-by-Exception: The reporting of data (e.g., from RTU to master station) only when the data either changes state (e.g., for a status or digital input point) or exceeds a predefined dead-band (e.g., for an analog input point).
Round Trip Delay (latency): The time required for a packet of data to travel from a specific source to a specific destination and back again.
Security code: A group of data bits calculated by a transmitting terminal from the information within its message by use of a prearranged algorithm.
Self-Diagnostic: The capability of an electronic device to monitor its own status and indicate faults that occur within the device.
Supervisory control: A telemetry based process control command initiated from a Master Central Station either manually by operator or automatically by an application.
Tag: A collection of attributes that specify either a control loop or a process variable, or a measured input, or a calculated value.
Tag ID: The unique alphanumeric code assigned to inputs, outputs, equipment items, and control blocks.
Transaction: A sequence of messages between cooperating terminals to perform a specific function.

SCADA systems provide a critical link between the automation of industrial processes and the monitoring and control of those processes. They allow for the efficient and effective management of remote operations, and the collection and analysis of data from those operations. SCADA systems are used in a wide range of industries and are becoming increasingly important as the automation of industrial processes continues to grow.

SCADA System Terms & Definitions

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