Rockwell Automation AADvance Controller Safety Manual - Manual (Page 124)

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6-8 Document: 553630
ICSTT-RM446K-EN-P Issue: 10 _C
Safety Manual (AADvance Controller)
safety accuracy
The accuracy of an analogue signal within
which the signal is guaranteed to be free of
dangerous faults. If the signal drifts outside
of this range, it is declared faulty.
safety-critical state
A faulted state which prevents the
execution of a process demand.
sensor
A device or combination of devices that
measure a process condition. Examples are
transmitters, transducers, process switches
and position switches.
sequential function chart
An IEC 61131 language that divides the
process cycle into a number of well-defined
steps separated by transitions. See 'limited
variability language'.
SFF
Safe Failure Fraction. Given by (the sum of
the rate of safe failures plus the rate of
detected dangerous failures) divided by (the
sum of the rate of safe failures plus the rate
of detected and undetected dangerous
failures).
SIF
Safety Instrumented Function. A form of
process control that performs specified
functions to achieve or maintain a safe state
of a process when unacceptable or
dangerous process conditions are detected.
SIL
Safety Integrity Level. One of four possible
discrete levels, defined in IEC 61508 and IEC
61511, for specifying the safety integrity
requirements of the safety functions to be
allocated to a safety-related system. SIL4 has
the highest level of safety integrity; SIL1 has
the lowest.
The whole of an installation (of which the
AADvance system forms a part) must meet
these requirements in order to achieve an
overall SIL rating.
SNCP
SNCP (Safety Network Control Protocol) is
the Safety Protocol that allows elements of
an AADvance System to exchange data.
SNCP is a SIL 3 certified protocol which
provides a safety layer for the Ethernet
network making it a "Black Channel".
SNTP
Simple Network Time Protocol. Used for
synchronizing the clocks of computer
systems over packet-switched, variable-
latency data networks.
structured text
A high level IEC 61131-3 language with
syntax similar to Pascal. Used mainly to
implement complex procedures that cannot
be expressed easily with graphical languages.
synchronous
A data communications term describing a
serial transmission protocol. A pre-arranged
number of bits is expected to be sent across
a line per second. To synchronise the
sending and receiving machines, a clocking
signal is sent by the transmitting computer.
There are no start or stop bits.
T
TA
See 'termination assembly'.
target
An attribute of a 'configuration' which
describes characteristics of the AADvance
controller on which the configuration will
run. Includes characteristics such as the
memory model and the sizes of variable
types for the controller.
TCP
Transmission control protocol. One of the
core protocols of the Internet Protocol
suite. It provides reliable, ordered delivery
of a stream of bytes from a program on one
computer to another program on another
computer. Common applications include the
World Wide Web, e-mail and file transfer
and, for an AADvance controller, Modbus
communications over Ethernet.