Rockwell Automation AADvance Controller Solutions Handbook - Manual (Page 137)

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Document: 553631
(ICSTT-RM447J_EN_P) Issue: 09:
11-1
Glossary of Terms
A
accuracy
The degree of conformity of a measure to a
standard or a true value. See also
'resolution'.
achievable safe state
A safe state that is achievable.
Note: Sometimes, a safe state cannot be
achieved. An example is a non-recoverable
fault such as a voting element with a shorted
switch and no means to bypass the effect of
the short.
actuator
A device which causes an electrical,
mechanical or pneumatic action to occur
when required within a plant component.
Examples are valves and pumps.
AITA
Analogue input termination assembly.
alarms and events (AE)
An OPC data type that provides time
stamped alarm and event notifications.
allotted process safety time
The portion of the total process safety time
allotted to a sub function of that process.
application software
Software specific to the user application,
typically using logic sequences, limits and
expressions to read inputs, make decisions
and control outputs to suit the
requirements of the system for functional
safety.
architecture
Organizational structure of a computing
system which describes the functional
relationship between board level, device
level and system level components.
asynchronous
A data communications term describing a
serial transmission protocol. A start signal is
sent before each byte or character and a
stop signal is sent after each byte or
character. An example is ASCII over RS-
232-C. See also 'RS-232-C, RS-422, RS-485'.
availability
The probability that a system will be able to
carry out its designated function when
required for use — normally expressed as a
percentage.
B
backplane clip
A sprung, plastic device to hold together
two adjacent AADvance base units. Part
number 9904. Used in pairs.
base unit
One of two designs which form the
supporting parts of an AADvance controller.
See 'I/O base unit' and 'processor base unit'.
bindings
Bindings describe a "relationship" between
variables in different AADvance controllers.
Once a variable is "bound" to another
variable, a unique and strong relationships is
created between the two variables and the
SIL 3 Certified SNCP protocol is used to
ensure that the consuming variable is
updated with the data from the producing
variable.
black channel
A communication path whose layer (i.e.
cabling, connections, media converters,
routers/switches and associated
firmware/software, etc.) has no requirement
to maintain the integrity of safety critical
data transferred over it. Measures to detect
and compensate for any errors introduced
into the black channel must be implemented
by the safety critical sender and receiver (by
software and/or hardware means) to make
sure the data retains its integrity.
Glossary of Terms