28 Introduction to the manual
STO Safe torque off (EN/IEC 61800-5-2). In this manual, this term is used in
two different contexts:
• the STO circuit in the drive (the drive STO function)
• the STO safety function in the FSO module.
Safety functions in the FSO module (eg, STO, SSE, SS1 and POUS)
activate the drive STO function, that is, open the drive STO circuit. In
addition, some safety functions can activate the STO safety function in
the FSO module, which in turn opens the drive STO circuit. See section
Dependencies between safety functions on page 193.
Stop category There are three categories of stop functions:
• stop category 0: an uncontrolled stop where power to the machine
actuators is removed immediately
• stop category 1: a controlled stop where the machine actuators have
power for stopping, after which the power is removed
• stop category 2: a controlled stop where the machine actuators
continue to have power.
Stop category 0 and 1 definitions also apply to Emergency stop
categories.
T1 Proof test interval (IEC 61508). T1 is a parameter used to define the
probabilistic failure rate (PFH or PFD
avg
) for the safety function or
subsystem. Performing a proof test at a maximum interval of T1 is
required to keep the SIL capability valid. The same interval must be
followed to keep the PL capability (EN ISO 13849) valid. See also
section Proof tests on page 512.
T
m
See Mission time.
TP Test pulse. Term diagnostic pulse is used in this manual.
TWCDT Total worst-case delay time
Validation Confirmation by, for example, analysis that the safety system meets the
functional safety requirements of the specific application.
Verification Confirmation by, for example, testing that the safety system meets the
requirements set by the specification.
WCDT Worst-case delay time
WD Watchdog
ZCU-
xx Drive control unit type (xx = version number)
Zero speed Speed limit where a ramp stop safety function is considered to be
completed and drive STO is activated. The acknowledgement of the
safety function becomes possible when this speed is reached.
Zero speed limit is given with parameter FSOGEN.51 Zero speed
without encoder on page 408 or, when an encoder is used, FSOGEN.52
Zero speed with encoder on page 408.
λ
d
Dangerous failure rate
λ
du
Dangerous failure rate, undetected failures
Term /
Abbreviation
Description
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