Rockwell Automation Publication ICSTT-RM448M-EN-P - February 2021 137
Glossary
The following terms and abbreviations are used throughout this manual. For
definitions of terms not listed here, refer to the Allen-Bradley Industrial
Automation Glossary, publication AG-7.1
.
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.
actuator A device which cause 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 T9904. Used in pairs.
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.
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