<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
