8. Glossary
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It's the CPU that is not in the active state (controlling the system) or in the stand-by state (overseeing the
Active CPU). It can’t assume control of the system.
Half-cluster (PLCA or PLCB) which is momentarily in any state other than Active (Stand-by, Inactive, Not-
configure or Starting).
Variables that are not shared between PLCA and PLCB in a redundant application. These variables
correspond to diagnostic or private command to each half-cluster (PLCA or PLCB).
POU from the program type, created automatically, which should be completed by the user. It is executed
in two PLCs (PLCA and PLCB), and used for actions and private variables management of each PLC
(PLCA and PLCB), such as switchovers diagnostics and management due to not vital failures.
Eight bits group numbered from 0 to 7.
Elements on which the instructions work. They may represent constants, variables or set of variables.
Type of communication where two nodes on a network exchange data and/or warnings without relying on
a master.
Acronym for programmable logic controller.
Denomination of one of the two controllers composing a redundant PLC. The other is called PLCB.
Denomination of one of the two controllers composing a redundant PLC. The other is called PLCA.
Program Organization Unit or Unit Program Organization, is a subdivision of the application program that
can be written in any of the available languages.
A group of rules and conventions used for a program creation.
Also called PLC. Equipment which executes a control under the applicative program command. It’s
composed by a CPU, a power supply and a I/O structure.
Part of the project corresponding to the source code.
The PLC project as a whole, composed by the project archive (source code) and by the applicative
project (executable code).
Rules of procedures and standard formats that through control signals, allow the establishment of a data
transmission and error recovery between equipment.
Acronym for random access memory. It’s where all the memory addresses can be accessed directly at
random and at the same speed. It is volatile, thus, its contents are lost when the device is powered down,
unless you have a battery for retaining values.
System that contains reserve elements or doubled to perform a certain task, which can tolerate certain
types of failure without damaging the task execution.
Corresponds to the other system CPU, e.g. the CPU1 in relation to CPU2 and vice versa.
Set consisting on a cluster (PLCA and PLCB), PX2612 control panel, and remote I/O systems.
Relays language and
Altus blocks
Group of instructions and variables that allow an applicative program edition to be used in a PLC.
Ripple present in DC supply voltage.
It is a standard for serial data exchange between two points (point to point)
It is a standard for serial data exchange between two or more points (point to point full duplex)
It is a standard for serial data exchange between two or more points (point to point half duplex).
Acronym used to indicate serial reception.
Supervisory Control and Data Acquisition. Supervisory system used for the plant control and operation.
Stands for screened twisted pair. Even UTP cable, but all pairs of wires are surrounded by a metal foil or
a metal braid screen, in order to minimize radiation and susceptibility to external noise. It is also known
for SUTP (Screened Unshielded Twisted Pair) or FTP (Foil Twisted Pair).
A device interface that transfers data in serial mode.
Equipment connected to a communication network that transmits data only if requested by another
device called the master.
Simple Network Time Protocol. Protocol for network time synchronization.
Sequence Of Events. Service to monitor the variation of pre-configured digital inputs, saving the date /
time of the change and its new state.
Computer programs, procedures and rules related to the operation of a data processing system.
Device on which integrated circuits or other components fit, making it easier to replace them and
simplifying the maintenance.
In a redundant system, it’s the CPU that oversees the Active CPU, not executing the system control, but
being ready to take control in case of failure on the Active CPU.
Half-cluster (PLCA or PLCB) which is momentarily in Stand-by state.
Procedure for final clearance of the control system when the programs of all stations and remote CPUs
are run together, having been developed and verified individually.
Segment of a communication network that interconnects a group of devices (nodes) in order to isolate the
local traffic or use different protocols or physical layer.
Equipment connected to a PLC or instrumentation network in order to monitor or control the process
variables.
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