AS IEC 61131.6:2014 – Programmable controllers Part 6: Functional safety.
[SOURCE: IEC 62061:2005, 3.2.6, modified]
Note Ito entry: An element may comprise hardware anaor software.
[SOURCE: IEC 61508-4:2010, 3.4.5, modified]
element safety function
that part of a safety function which Is implemented by an element
[SOURCE: IEC 61508-4:2010, 3.5.3. modified]
embedded SW embedded software embedded firmware
software controlling the operation of the FS-PLC or one of its subsystems
Not. 1 to entry: Th, embedded is supplied by the FS-PLC manufacturer in$ICII,d .n me 1i. user hae no direct access to embedded software The FS-PLC manufacturer develop, or writes embedded sofiware to control his FSPLC. This may. for ekaniple, control the communication subsyst.m or the interpretation of the program developed by the user in the engineering tools.
Note 2 to entry: Another term for embedded software.
Note 3 to entry: Frrmware can be either safety related or non-safety related.
engineering tools
software for developing the application program
EXAMPLE. The engineering tools software is supplied by the FS-PLC manulacturer to be Instelled on a personal computer workstation Within this SW package the user develops or wntes his application program to control his process. This application program is then downloaded into the FS-PLC, where it determines control 01 the user’s FS.PLC. attached equipment and thui process.
Note Ito entry: Application programs and software can be either safety related or non-safety related.
equipment under control
equipment. machinery, apparatus or plant used for manufacturing, process, transportation. medical or other activities
Note Ito entry: The EUC control system is separate and distinct trom the EUC.
[SOURCE: IEC 61508-4:2010, 3.2.1]
equipment under test
representative configuration(s), as defined by the manufacturer, used for type tests
termination of the ability of a functional unit to provide a required function or operation of a functional unit in any way other than as required
Note Ito entry: This is based on IEC 60050-191:1990, 191 -04-01 with changes to include ystemafic failures due to, for example, deficiencies in specification or SOftwSre,
SEE. Figute 2 for the relationship between Vaults and failures.
random hardware failure
failure, occurring at a random time, that results from one or more of the possible degradation mechanisms in the hardware
Note t to entry: Ther. ate many degradation mechanisms occurring at diftw.nt rates I different components and. Since manufacturing tolerances cause component, to ta due to these mechanisms alter ditterent times In Operation failures of equipment compnsing many components occur at predictabl, rates but at unpredictable (i.e. random) timeS.
Note 2 to entry: A major distinguishing feature between random hardware tailures and systematic failures (see 3.56). is that system failure rates (or other appropriate measures). anaing horn random hardware failures, can be predicted with reasonable accuracy but Systematic failures, by their very nature, cannot be accuratly predict.d. That is. system failure rates arising trom random hardware tailumes can be quanttied with reasonable accuracy but tho,e ansing from systematic failures cannot be accurately statistically quantified because the events leading to them cannot easity be predicted.
(SOURCE: IEC 61508-4:2010, 3.6.5)
probability that a specific product will operate for a specific durationitime (() without a failure
Note I to entry’ For a complex product liii. a programmable controller. the average failure rate approximates a constant tailure rate with an exponential reliability lunclion: R(S) — e ‘‘ — e
Note 2 to entry: If the time (S( in the last .quation is the MTBF, th, equation yields a reliability ot 0,368 meaning that only 36.8 % of a specific product wll operate without a failure for their MTBF.
combination of the probability of occurrence ol harm and the severity of that harm
(SOURCE: ISO/IEC Guide 51 :1999, definition 3.2)
Note Ito entry. For more discussion on this Concept, see Annex Aol IEC 61508-52010.
(SOURCE: IEC 61508•4:2010, 31.6].