3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in OPC 10000-1, OPC 10000-3, OPC 10000‑4, OPC 10000-6 and the following apply.
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3.1.1 Common terms and definitions
3.1.1.1 Cyclic Redundancy Check
<method> procedure used to calculate the redundant data
3.1.1.2 error
discrepancy between a computed, observed or measured value or condition and the true, specified or theoretically correct value or condition
3.1.1.3 failure
termination of the ability of a functional unit to perform a required function or operation of a functional unit in any way other than as required
3.1.1.4 fault
abnormal condition that may cause a reduction in, or loss of, the capability of a functional unit to perform a required function
3.1.1.5 message
<information theory and communication theory> ordered sequence of characters (usually octets) intended to convey information
3.1.1.6 performance level
discrete level used to specify the ability of safety-related parts of control systems to perform a safety function under foreseeable conditions
3.1.1.7 residual error probability
probability of an error undetected by the SCL safety measures
3.1.1.8 residual error rate
statistical rate at which the SCL safety measures fail to detect errors
3.1.1.9 safety communication layer
communication layer above the OPC UA communication stack that includes all necessary additional measures to ensure safe transmission of data in accordance with the requirements of IEC 61508
3.1.1.10 safety function response time
worst case elapsed time following an actuation of a safety sensor connected to a fieldbus, until the corresponding safe state of its safety actuator(s) is achieved in the presence of errors or failures in the safety function
3.1.1.11 safety integrity level
discrete level (one out of a possible four), corresponding to a range of safety integrity values, where safety integrity level 4 has the highest level of safety integrity and safety integrity level1 has the lowest
3.1.1.12 safety measure
measure to control possible communication errors that is designed and implemented in compliance with the requirements of IEC 61508
3.1.1.13 safety PDU
PDU transferred through the safety communication channel
3.1.2 Additional terms and definitions
3.1.2.1 fail-safe
ability of a system that, by adequate technical or organizational measures, prevents from hazards either deterministically or by reducing the risk to a tolerable measure
3.1.2.2 fail-safe substitute values
values which are issued or delivered instead of process values when the safety function is set to a fail-safe state
3.1.2.3 flag
one-bit value used to indicate a certain status or control information
3.1.2.4 Globally Unique Identifier
128-bit number used to identify information in computer systems
3.1.2.5 MonitoringNumber
means used to ensure the correct order among transmitted safety PDUs and to monitor the communication delay
3.1.2.6 Non-safety-
predicate meaning that the respective object is a “standard” object and has not been designed and implemented to fulfil any requirements with respect to functional safety
3.1.2.7 OPC UA Mapper
non-safety-related part of the implementation of this document which maps the SPDU to the actual OPC UA services
3.1.2.8 process values
input and output data (in a safety PDU) that are required to control an automated process
3.1.2.9 qualifier
attribute (bit or Boolean), indicating whether the corresponding value is valid or not (e.g. being a fail-safe substitute value)
3.1.2.10 SafetyAutomationComponent
communication partner in a unidirectional safety link
3.1.2.11 SafetyConsumer
entity (usually software) that implements the data sink of a unidirectional safety link
3.1.2.12 SafetyData
application data transmitted across a safety network using a safety protocol
3.1.2.13 SafetyProvider
entity (usually software) that implements the data source of a unidirectional safety link
3.1.2.14 SafetyBaseID
randomly generated authenticity ID which is used to safely authenticate SafetyProviders having the same SafetyProviderID
3.1.2.15 SafetyProviderID
user-assigned, locally unique identifier which is used to safely authenticate SafetyProviders within a certain area
3.1.2.16 standard transmission system
part of the transmission system (implemented in hardware and software) that is not implemented according to any safety standards