Rockwell Automation Publication ICSTT-RM448J-EN-P - April 2018
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Glossary
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.
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.
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.
