Glossary: Terms and Abbreviations

Terms and abbreviations are listed in alphabetical order.

Term/Abbreviation In full Standard/Specification

Cat. Category
Basis for determining the performance level (PL) of a safety-related controller EN ISO 13849-1

Cross-circuit detection A "cross circuit" is an unintentional, incorrect connection between redundant circuits.
Possibly, the Safety PLC or safety-related I/O device provides clock outputs as an aid for detecting such a cross circuit. For example, if two differently clocked signals are routed back to two inputs along two channels via an emergency-stop control device, a cross circuit can definitely be detected in this emergency-stop circuit: in the event of a cross circuit, the same clock signal would be present at both inputs, instead of two different ones.
If available, the cross-circuit detection may be activated for the relevant inputs in the device parameterization editor of the involved device.

Further Info
Also take the corresponding information on implementing cross-circuit detection, which is found in the User Manual, into account.

-/-

Edge-triggered and state-controlled inputs A function block only evaluates the signals of edge-triggered inputs for changes in levels.
By contrast, a function block processes the signals of state-controlled inputs continuously, not only when there are changes in signal levels. -/-

EDM External Device Monitoring
Safety-related function block for monitoring the initial state and the switching behavior of contactors connected to the safety-related controller -/-

ESPE ElectroSensitive Protective Equipment IEC 61496-1

Exchange variable An exchange variable results when mapping a variable of the standard PLC and to a standard variable of the Safety PLC. This role mapping has to be done in the 'Data List' of the PLC or the Safety PLC. Exchange variables enable the communication between the standard controller and the Safety PLC (if included in your project).
General rules for the data exchange between the safety-related and the standard application are defined in the "Software Architectural Model" of the PLCopen TC5 Safety Specification. PLCopen TC5 Safety Specification

FVL/LVL A Full Variability Language (FVL) has no limitations and provide all possibilities of modern programming. For example, the full functional range of the IEC 61131-3 languages IL (Instruction List), or ST (Structured Text) as well as of C/C++ are provided.
In contrast to a FVL, a Limited Variability Language (LVL) is restricted regarding its functional range. This restriction is intended to help avoiding programming errors due to a high code complexity and to improve the code clarity.
The sector standard of the EN/IEC 61508 as well as the EN ISO 13849-1 recommend the use of a LVL as implemented in PLCnext Engineer. EN ISO 13849-1
and EN/IEC 62061

FBD/LD Graphical programming languages according to the IEC 61131-3 standard:
FBD = Function Block Diagram
LD = Ladder Diagram IEC 61131-3

NOLD NOLD (Network Oriented Ladder) code worksheets, programmed with the network-oriented graphic editor.
NOLD and FBD/LD use the same syntax and objects. Exception: connectors are not allowed in NOLD.
The NOLD editor prescribes the code layout (automatic network arrangement) thus supporting a very easy handling also via the keyboard. -/-

OSSD Output Signal Switching Device
Part of the ESPE, which can be connected to the machine control system and switched off via a safety request -/-

PL Performance Level
Value for the average probability of dangerous failure of safety-related machine control systems. The category (» Cat.) and the probability-related properties of the components used form the basis for determining the PL.
The target PL results in binding, safety-related design principles, which aim to minimize the risk of a malfunction. EN ISO 13849-1

PLC Programmable Logic Controller. -/-

Redundancy Redundancy refers generally to the presence of additional components/elements/units used to increase operational reliability and safety.
Examples:

Two mutually independent processing units (paths) in the Safety PLC (signal redundancy)

Two mutually independent circuits/power supplies

Pairs of contacts and signal lines for a safety-related control device or for an actuator

-/-

Restart inhibit When a restart inhibit is active, all safety-related outputs of the function block are in the defined safe state. This ensures that a machine/system cannot be restarted inadvertently.
If a restart inhibit is active, a reset signal is required to remove it and enable the machine/system to function. -/-

Risk analysis Statement, based on scientific facts and predefined criteria (e.g., risk graphs, defined in various standards, depending on the field of application), on the probability of possible risks occurring and on the damaging effects they would have during operation of a machine or system which requires protection.
The result of the risk analysis is classified as a category, level or performance level (depending on the relevant standard, i.e., area of application).
The result of the risk analysis can be used to directly derive the architecture of the safety-related system and to make statements as regards error detection and fault avoidance measures. -/-

Safety-related logic Safety-related logic refers to the safety-related code networks, consisting of safety-related functions, function blocks, FBD/LD code elements, and connecting lines, which are developed in the graphical SNOLD code editor.
The Safety PLC evaluates the connected safety-related sensors/control devices in accordance with the configured safety-related logic and switches the output signals accordingly, to control the connected actuators. -/-

SIL Safety Integrity Level
Value for assessing electrical/electronic/programmable electronic systems in terms of the reliability of their safety functions.
The target SIL results in binding, safety-related design principles, which aim to minimize the risk of a malfunction. IEC 61508

SILCL SIL Claim Limit, maximum SIL value for a subsystem. EN/IEC 62061

SNOLD SNOLD (Safety Network Oriented Ladder) code worksheets, programmed with the safety-related network-oriented graphic editor. Basically, the SNOLD editor works like the NOLD editor but provides additional safety-related features. -/-

ST Textual programming language Structured Text. IEC 61131-3

Startup inhibit When a startup inhibit is active, all safety-related outputs of the function block are in the defined safe state. This ensures that a machine/system cannot be started up inadvertently.
If a startup inhibit is active, a reset signal is required to remove it and enable the machine/system to function. -/-

State-controlled inputs See "Edge-triggered inputs". -/-

Stop category Stop categories in accordance with DIN EN 60204:

Stop category 0: an uncontrolled stop resulting from immediate removal of power to the machine drive units

Stop category 1: a controlled stop with power left available to the machine drive units in order to achieve the stop. The power is only removed when the stop has been achieved.

Stop category 2: a controlled stop with power left available to the machine drive units

DIN EN 60204