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7 Appendix
7.1 Abbreviations
Table 2: Abbreviations Related to Functional Safety
Abbrevia-
tions
Reference
Description
B
10d
Number of cycles until 10% of the components have a dangerous failure (for pneumatic and
electromechanical components).
Cat.
EN ISO 13849-1
Category, level “B, 1–4”
CCF
Common cause failure
DC
Diagnostic coverage divided into Low, Medium, and High.
FIT
Failure in time: 1E-9/hour
HFT
EN IEC 61508
Hardware fault tolerance: HFT = n means that n+1 faults could cause a loss of the safety func-
tion.
MTTFd
EN ISO 13849-1
Mean time to failure - dangerous. Unit: Years are divided into Low, Medium, and High.
PFH
EN IEC 61508
Probability of dangerous failures per hour. Consider this value if the safety device is operated
in high demand or continuous mode of operation, where the frequency of demands for oper-
ation made on a safety-related system is greater than 1 per year.
PFD
EN IEC 61508
Average probability of failure on demand, value used for low demand operation.
PL
EN ISO 13849-1
Discrete level used to specify the ability of safety-related parts of control systems to perform a
safety function under foreseeable conditions. Levels divided into a to e.
PLr
Required performance level (the required performance level for a particular safety function).
SIL
EN IEC 61508
EN IEC 62061
Safety integrity level
STO
EN IEC 61800-5-2 Safe Torque Off
SS1
EN IEC 61800-5-2 Safe Stop 1
SRECS
EN IEC 62061
Safety-related electrical control system
SRP/CS
EN ISO 13849-1
Safety-related parts of control systems
PDS/SR
EN IEC 61800-5-2 Power Drive System (safety-related)
7.2 Conventions
Numbered lists indicate procedures.
Bulleted and dashed lists indicate listings of other information where the order of the information is not relevant.
Bolded text indicates highlighting and section headings.
Italicized text indicates the following:
Cross-reference.
Link.
Footnote.
Parameter name.
AQ313340186453en-00101 / 130R0544
22 | Danfoss A/S © 2021.03
Appendix
Safe Torque Off
Operating Guide