PLC (Definitions From ISA )

Question 1

Accessible :

Answer 1

A term applied to a device or
function that can be used or be seen by an operator for the purpose of performing control actions, e.g., set point changes, auto-manual transfer, or on-off actions.

Question 2

Alarm :

Answer 2

A device or function that signals the existence of an abnormal condition by means of an audible or visible discrete change, or both, intended to attract attention.

Question 3

Assignable:

Answer 3

A term applied to a feature permitting the channeling (or directing) of a signal from one device to another without the need for switching, patching, or changes in wiring.

Question 4

Auto-manual station:

Answer 4

Synonym for control station

Question 5

Balloon:

Answer 5

Synonym for bubble.

Question 6

Behind the panel:

Answer 6

A term applied to a location that is within an area that contains (1) the instrument panel, (2) its associated rack-mounted hardware, or (3) is enclosed within the panel. Behind the panel devices are not accessible for the operator’s normal use, and are not designated as local or front-of-panel-mounted. In a very broad sense, “behind the panel” is equivalent to “not normally accessible to the operator.”

Question 7

Binary:

Answer 7

A term applied to a signal or device that has only two discrete positions or states. 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, i.e., one which does not represent continuously varying quantities.

Question 8

Bubble:

Answer 8

The circular symbol used to denote and identify the purpose of an instrument or
function. It may contain a tag number. Synonym for balloon.

Question 9

Computing device:

Answer 9

A device or function that performs one or more calculations or logic operations, or both, and transmits one or more resultant output signals. A computing device is sometimes called a computing relay.

Question 10

Configurable:

Answer 10

A term applied to a device or system whose functional characteristics can be selected or rearranged through programming or other methods. The concept excludes rewiring as a means of altering the configuration.

Question 11

Controller:

Answer 11

A device having an output that varies to regulate a controlled variable in a specified manner. A controller may be a self-contained analog or digital instrument, or it may be the equivalent of such an instrument in a shared-control system.
An automatic controller varies its output automatically in response to a direct or indirect input of a measured process variable. A manual controller is a manual loading station, and its output is not dependent on a measured process variable but can be varied only by manual adjustment.

A controller may be integral with other functional elements of a control loop

Question 12

Control station:

Answer 12

A manual loading station that also provides switching between manual and automatic control modes of a control loop. It is also known as an auto-manual station. In addition, the operator interface of a distributed control system may be regarded as a control station.

Question 13

Control valve:

Answer 13

A device, other than a common, hand-actuated ON-OFF valve or self-actuated check valve, that directly manipulates the flow of one or more fluid process streams.
It is expected that use of the designation “hand control valve” will be limited to hand-actuated valves that (1) are used for process throttling, or (2) require identification as an instrument.

Question 14

Converter:

Answer 14

A device that receives information in one form of an instrument signal and transmits an output signal in another form.

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

A converter is also referred to as a transducer; however, “transducer” is a completely general term, and its use specifically for signal conversion is not recommended.

Question 15

Digital:

Answer 15

A term applied to a signal or device that uses binary digits to represent continuous values or discrete states.

Question 16

Distributed control system:

Answer 16

A system which, while being functionally integrated, consists of subsystems which may be physically separate and remotely located from one another.

Question 17

Final control element:

Answer 17

The device that directly controls the value of the manipulated variable of a control loop. Often the final control element is a control valve.

Question 18

Function:

Answer 18

The purpose of, or an action performed by, a device.

Question 19

Identification:

Answer 19

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

Question 20

Instrument:

Answer 20

A device used directly or indirectly to measure and/or control a variable. The term includes primary elements, final control elements, computing devices, and electrical devices such as annunciators, switches, and pushbuttons. The term does not apply to parts (e.g., a receiver bellows or a resistor) that are internal components of an instrument.

Question 21

Instrumentation:

Answer 21

A collection of instruments or their application for the purpose of observation,
measurement, control, or any combination of these.

Question 22

Local:

Answer 22

The location of an instrument that is neither in nor on a panel or console, nor is it mounted in a control room. Local instruments are commonly in the vicinity of a primary element or a final control element. The word “field” is often used synonymously with local.

Question 23

Local panel:

Answer 23

A panel that is not a central or main panel. Local panels are commonly in the vicinity of plant subsystems or sub-areas. The term “local panel instrument” should not be confused with “local instrument.”

Question 24

Loop:

Answer 24

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

Question 25

Manual loading station:

Answer 25

A device or function having a manually adjustable output that is used to actuate one or more remote devices. The station does not provide switching between manual and automatic control modes of a control loop (see controller and control station). The station may have integral indicators, lights, or other features. It is also known as a manual station or a manual loader.

Question 26

Measurement:

Answer 26

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

Question 27

Monitor:

Answer 27

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. The term monitor is very unspecific — sometimes meaning analyzer, indicator, or alarm. Monitor can also be used as a verb.

Question 28

Monitor light:

Answer 28

Synonym for pilot light.

Question 29

Panel:

Answer 29

A structure that has a group of instruments mounted on it, houses the operator-process interface, and is chosen to have a unique designation. The panel may consist of one or more sections, cubicles, consoles, or desks. Synonym for board.

Question 30

Panel-mounted:

Answer 30

A term applied to an instrument that is mounted on a panel or console and is accessible for an operator’s normal use. A function that is normally accessible to an operator in a shared-display system is the equivalent of a discrete panel-mounted device.

Question 31

Pilot light:

Answer 31

A light that indicates which of a number of normal conditions of a system or device exists. It is unlike an alarm light, which indicates an abnormal condition. The pilot light is also known as a monitor light.

Question 32

Primary element:

Answer 32

Synonym for sensor.

Question 33

Process:

Answer 33

: Any operation or sequence of operations involving a change of energy, state, composition, dimension, or other properties that may be defined with respect to a datum

Question 34

Process variable:

Answer 34

Any variable property of a process. The term process variable is used in this standard to apply to all variables other than instrument signals

Question 35

Program:

Answer 35

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

Question 36

Programmable logic controller:

Answer 36

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

Question 37

Relay:

Answer 37

A device whose function is to pass on information in an unchanged form or in some modified form. Relay is often used to mean computing device. The latter term is preferred.

The term “relay” also is applied specifically to an electric, pneumatic, or hydraulic switch that is actuated by a signal. The term also is applied to functions performed by a relay.

Question 38

Scan:

Answer 38

To sample, in a predetermined manner, each of a number of variables intermittently. The function of a scanning device is often to ascertain the state or value of a variable. The device may be associated with other functions such as recording and alarming.

Question 39

Sensor:

Answer 39

: That part of a loop or instrument that first senses the value of a process variable, and that assumes a corresponding, predetermined, and intelligible state or output. The sensor may be separate from or integral with another functional element of a loop. The sensor is also known as a detector or primary element.

Question 40

Set point:

Answer 40

An input variable that sets the desired value of the controlled variable. The set point may be manually set, automatically set, or programmed. Its value is expressed in the same units as the controlled variable.

Question 41

Shared controller:

Answer 41

A controller, containing preprogrammed algorithms that are usually accessible, configurable, and assignable. It permits a number of process variables to be controlled by a single device.

Question 42

Shared display:

Answer 42

The operator interface device (usually a video screen) used to display process
control information from a number of sources at the command of the operator.

Question 43

Switch:

Answer 43

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

Question 44

Test point:

Answer 44

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

Question 45

Transducer:

Answer 45

A general term for a device that receives information in the form of one or more physical quantities, modifies the information and/or its form, if required, and produces a resultant output signal. Depending on the application, the transducer can be a primary element, transmitter, relay, converter or other device. Because the term “transducer” is not specific, its use for specific applications is not recommended.

Question 46

Transmitter:

Answer 46

A device that senses a process variable through the medium of a sensor and has an output whose steady-state value varies only as a predetermined function of the process variable. The sensor may or may not be integral with the transmitter.