242 Glossary
Trident Planning and Installation Guide
DCS Distributed control system.
DDE Dynamic data exchange (DDE) is an interprocess communication mechanism
provided by Microsoft
Windows. Applications running under Windows can use
DDE to send and receive data and instructions to and from each other.
debug Act of locating and correcting faults: 1) one of the normal operations in software
development; such as editing, compiling, debugging, loading, and verifying; or 2)
the identification and isolation of a faulty physical component, including its
replacement or repair to return the system to operational status.
DI Module Digital Input Module.
DO Module Digital Output Module.
dual module Digital Output Module which is optimized for safety-critical environments where
low cost is more important than maximum availability. A dual module is equipped
with one parallel or series signal path and applies the 2-out-of-3 voting process
individually to each switch. While quadruplicated output circuitry provides
multiple redundancy for all critical signal paths, dual circuitry provides just enough
redundancy to ensure safe operation.
environment Stimuli at an interface (or interfaces) of the system.
error Element of a system resource assumes an undesired state. Such a state is then
contrary to the specification of the resource or the expectation (requirement) of the
user.
event State change of a discrete aliased variable which has been designated for event
logging. An event is said is to occur if such a variable changes from the normal
state. If the variable later changes back to the normal state, another event is said to
have occurred.
event logger Program that logs, displays and/or prints critical events in real time, based on state
changes of discrete variables in the program. Proper use of an event logger warns
users about dangerous conditions and printouts of events can help identify the
sequence of events that led to a trip.
event variable Discrete memory variable or discrete input point that has been assigned to an SOE
block.
external host Computer, such as a mainframe, minicomputer, workstation, or PC that
communicates with the controller over an Ethernet open network.
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