DEFINITIONS RELATED TO FLOWCHART DIAGRAM SYMBOLOGY

برگشت به منوی اصلی

برگشت به منوی قبلی

DEFINITIONS RELATED TO FLOWCHART DIAGRAM SYMBOLOGY

See statement of permission

General

For the purpose of understanding the ISA S5.1 standard (now ANSI/ISA-5.01.01), the following definitions and terminologyapply. For a more complete treatment, see ISA-S51.1 and the ISA-S75 series of standards. Terms italicized within a definition are also defined in this clause.

Definitions Related to Flowsheet Symbology

Accessible

A feature of a discrete device function or feature of an interactive shared system function or feature that can be used or seen by an operator for the purpose of performing control operations, such as setpoint changes, auto-manual transfer, or on–off operations.

Alarm

An indicating instrument that provides a visible and/or audible indication if and when the value (or rate of change value) of a measured or initiating variable is out of limits, has changed from a safe to an unsafe condition, and/or has changed from a normal to an abnormal operating state or condition.

a) Actuation may be by binary switch or function or analog transmitter or function.

b) Indication may be by annunciator panel, flashing light, printer, buzzer, bell, horn, siren, and/or shared graphic display systems.

Analog

A signal or device that has no discrete positions or states and changes value as its input changes value. When used in its simplest form, as in “analog signal” as opposed to “binary signal,” the term denotes a continuously varying quantity.

Application software

Software specific to a user application that is configurable and in general contains logic sequences, permissive and limit expressions, control algorithms, and other code required to control the appropriate input, output, calculations, and decisions. See also software.

Assignable

A system feature permitting channeling or directing of a signal from one device to another without the need for changes in wiring either by means of patching, switching, or via keyboard commands to the system.

Auto-manual station

A manual loading station or control station that also provides switching between manual and automatic control modes of a control loop. See also manual loading station.

Balloon

An alternative term for the circular symbol used to denote and identify the purpose of an instrument or function that may contain a tag number. See preferred term, bubble.

Behind the panel

A location that, in a broad sense, means “not normally accessible to an operator,” such as the rear of an instrument or control panel, an enclosed instrument rack or cabinet, or an instrument rack room within an area that contains a panel.

Binary

A signal or device that has only two discrete positions/ states and, when used in its simplest form, as in “binary signal” as opposed to “analog signal,” the term denotes an “on–off ” or “high–low” state.

Board

A freestanding structure consisting of one or more sections, cubicles, or consoles that has groups of discrete (individual) instruments mounted on it, houses the operator–process interface, and is chosen to have a unique designation. See panel.

Bubble

The preferred term for the circular symbol used to denote and identify the purpose of an instrument or function that may contain a tag number. See alternative term, balloon.

Communication link

A wire, cable, or transmitter network or bus system that connects dedicated microprocessor- based and computer-based systems so that they share a common database and communicate according to a rigid protocol in a hierarchical and/or peer-to-peer relationship. See also data link.

a) Wires or cables may be of twisted pair, coaxial, telephone, or fiber optic construction.

b) Transmitters may be radio, telephone, and/or microwave devices.

Computer control system

A system in which all control action takes place within a control computer, such as a mainframe computer or minicomputer, which may be single or redundant.

Computing device

Preferred term for a device that performs one or more calculations or logic operations, or both, and transmits one or more resultant output signals. See also computing relay.

Computing function

A hardware or software function that performs one or more calculations or logic operations, or both, and transmits one or more resultant output signals.

Computing relay

Alternative term for a device that performs one or more calculations or logic operations, or both, and transmits one or more resultant output signals. See also computing device.

Configurable

A term for devices or systems whose functional or communication characteristics can be selected or rearranged through setting of program switches, application software, fill-in-the-blank forms, pull-down menus, entered values or text, or other methods other than rewiring as a means of altering the configuration.

Controller

A device having an output that varies to regulate a controlled variable in a specified manner that may be a self-contained analog or digital instrument or may be the equivalent of such an instrument in a shared-control system.

a) An automatic controller varies its output automatically in response to a direct or indirect input of a measured process variable.

b) A manual controller, or manual loading station, varies its output in response to a manual adjustment; it is not dependent on a measured process variable.

c) A controller may be an integral element of other functional elements of a control loop.

Control station

A manual loading station that also provides switching between manual and automatic control modes of a control loop. See also auto-manual station.

a) The operator interface of a distributed control system may be referred to as a control station.

Control valve

A device, other than a common, handactuated process block valve or self-actuated check valve, that directly manipulates the flow of one or more fluid process streams.

a) The designation “hand control valve” shall be limited to hand-actuated valves that, when used for process throttling, require identification as an instrument or control device.

Converter

A device that receives information as one form of an instrument signal and transmits an output signal as another form, such as a current to pneumatic signal converter.

a) An instrument that changes a sensor’s output to a standard signal is properly designated as a transmitter and not a converter. Typically, a temperature element (TE) connects to a transmitter (TT) and not to a converter (TY).

b) A converter is sometimes referred to as a transducer, a completely general term not recommended for signal conversion.

Data link

A wire, cable, or transmitter network or bus system that connects field located devices with dedicated microprocessors so that they share a common database and communicate according to a rigid protocol in a hierarchical or peer-to-peer relationship to other such devices and/or compatible microprocessorbased systems. See also communication link.

a) Wire or cable may be of twisted-pair, coaxial, telephone, or fiber optic construction.

b) Transmitters may be radio, telephone, or microwave devices.

Detector

A device that is used to detect the presence of something, such as flammable or toxic gases or discrete parts. See also primary element and sensor.

Device

A piece of instrument hardware that is designed to perform a specific action or function, such as a controller, indicator, transmitter, annunciator, or control valve.

Digital A signal or device that generates or uses binary digit signals to represent continuous values or discrete states.

Discrete

A term used to describe the following:

a) Signals that have any number of noncontinuous distinct or defined states or positions. Binary signals are a subset. See binary.

b) Instruments or devices that have separate or individual entities, such as a single-case controller or recorder.

Distributed control system Instrumentation,

input/output devices, control devices, and operator interface devices that, in addition to executing stated control and indication functions, permits transmission of control, measurement, and operating information to

and from single- or multiple-user specifiable locations, connected by single or multiple communication links.

Field instrument

An instrument that is not mounted on a panel or console or in a control room but commonly in the vicinity of its primary element or final control element. See local instrument.

Final control element

A device, such as a control valve, that directly controls the value of the manipulated variable of a control loop.

Function

The purpose of, or the action performed by, a device or application software.

Identification The sequence of letters or digits, or both, used to designate an individual instrument, function, or loop.

Instrument

A device used for direct or indirect measurement, monitoring, or control of a variable.

a) Includes primary elements, indicators, controllers, final control elements, computing devices, and electrical devices such as annunciators, switches, and pushbuttons.

b) Does not apply to an instrument’s internal components or parts, such as receiver bellows or resistors.

Instrumentation

A collection of instruments or functions or their application for the purpose of measuring, monitoring, controlling, or any combination of these.

Local instrument

An instrument that is not mounted on a panel or console or in a control room but commonly is in the vicinity of its primary element or final control element. See field instrument.

Local panel

A panel that is not a central or main panel and is commonly located in the vicinity of plant subsystems or subareas (sometimes called a local instrument panel).

a) The term local panel instrument should not be confused with local instrument or local instrument panel.

Loop

A combination of two or more instruments or control functions arranged so that signals pass from one to another for the purpose of measurement indication or control of a process variable.

Manual loading station

A device or function that has a manually adjustable output and may also have indicators,lights, and/or other functions that are used to actuate or modulate one or more devices. It does not provide switching between auto-manual modes of a control loop.

Measurement

The determination of the existence or magnitude of a process variable.

Monitor

A general term for an instrument or instrument system used to measure or sense the status or magnitude of one or more variables for the purpose of deriving useful information. This sometimes means an analyzer, indicator, or alarm.

Monitor light A light that indicates which of a number of normal (but not abnormal) conditions of a system or device exists. See also pilot light.

Multifunction devices

Devices (controllers) that receive one or more input signals and send out two or more output signals or perform two or more functions.

See multipoint and multivariable devices.

Multipoint devices Indicators or recorders that may be single or multivariable type and that receive input signals from two or more primary elements or transmitters.

See multifunction devices and multivariable devices.

Multivariable devices

Devices (indicators, recorders, or controllers) that receive two or more input signals and send one output signal. See multifunction and multipoint devices.

Panel

A freestanding or built-in structure, consisting of one or more sections, cubicles, consoles, or desks, in which groups of instrument hardware are mounted.

It could house the operator–process interface and is given a unique designation.

Panel-mounted

An instrument or other device that is mounted in a panel or console and is accessible for an operator’s normal use.

a) A function that is normally accessible to an operator in a shared-display system is the equivalent of a discrete panel-mounted device.

Pilot light

A light that indicates which of a number of normal conditions of a system or device exists. It is not an alarm light that indicates an abnormal condition. See also monitor light.

Primary element

An external or internal instrument, or a system element, that quantitatively converts the measured variable into a form suitable for measurement. See also detector and sensor:

a) An orifice plate is an external primary element.

b) The sensing portion of a transmitter is an internal primary element.

Process

Any operation or sequence of operations involving a change of energy, state, composition, dimension, or other properties that may be defined with respect to zero or some other defined initial value.

Process variable

Any measurable property of a process.

Used in this standard to apply to all variables other than instrument signals between devices in a loop.

Program

A repeatable sequence of actions that defines the state of outputs as a fixed relationship to the state of inputs.

Programmable logic controller

A controller, usually with multiple inputs and outputs, that contains an alterable program that is

a) Typically used to control binary and/or discrete logic or sequencing functions.

b) Also used to provide continuous control functions.

Relay

A device whose function is to pass on information in an unchanged form or in some modified form; often used to mean the preferred term, computing device.

a) Relay is a term applied specifically to an electric, pneumatic, or hydraulic switching device that is actuated by a signal, and to functions performed by a relay.

Scan

To sample or multiplex, in a predetermined manner, each of a number of variables periodically and/or intermittently.

a) A scanning or multiplexing device is often used to ascertain the state or value of a group of variables and may be associated with other functions such as recording and alarming.

Sensor

A separate or integral part, or function, of a loop or an instrument that first senses the value of a process variable. It assumes a corresponding predetermined and intelligible state and/or generates an output signal indicative of or proportional to the process variable.

See also detector and primary element.

Setpoint

An input variable that sets the desired value of the controlled variable manually, automatically, or by means of a program in the same units as the controlled variable.

Shared control

A feature of a control device or function that contains a number of preprogrammed algorithms that are user retrievable, configurable, and connectable. It allows user-defined control strategies or functions to be implemented and is often used to describe the control features of a distributed control system.

a) Control of multiple process variables can be implemented by sharing the capabilities of a single device of this kind.

Shared display

The operator interface device (such as video, light emitting diode, liquid crystal, or other display unit) used to display process control information from a number of sources at the command of the operator. It is often used to describe the visual features of a distributed control system.

Software

The programs, codes, procedures, algorithms, patterns, rules, and associated documentation required for the operation or maintenance of a microprocessor- or computer-based system. See also application software.

Software link

The interconnection of system components via communications networks or functions via software or keyboard instruction.

Supervisory setpoint control system

The generation of setpoint or other control information by a computer control system for use by shared control, shared display, or other regulatory control devices.

Switch

A device that connects, disconnects, selects, or transfers one or more circuits and is not designated as a controller, relay, or control valve. As a verb, the term is also applied to a function performed by a switch.

Test point

A process connection to which no instrument is permanently connected; it is intended for the temporary or intermittent connection of an instrument.

Transducer

A general term for a device, which can be a primary element, transmitter, relay, converter, or other device, that receives information in the form of one or more physical quantities, modifies the information or its form if required, and produces a

resultant output signal.

Transmitter

A device that senses a process variable through the medium of a sensor or measuring element and has an output whose steady-state value varies only as a predetermined function of the process variable.

The sensor can be an integral part, as in a direct connected pressure transmitter, or a separate part, as in a thermocouple-actuated temperature transmitter.