Automating Manufacturing Systems - Process Control and ...

plc glossary - 35.9
35.4 D
daisy chain - allows serial communication of devices to transfer data through each (and every) device
between two points.
darlington coupled - two transistors are ganged together by connecting collectors to bases to increase the
gain. These increase the input impedance, and reduce the back propagation of noise from loads.
DARPA (Defense Advanced Research Projects Agency) - replaced ARPA. This is a branch of the US
department of defence that has participated in a large number of research projects.
data acquisition - refers to the automated collection of information collected from a process or system.
data highway - a term for a communication bus between two separated computers, or peripherals. This term
is mainly used for PLC’s.
data link layer - an OSI model layer
data logger - a dedicated system for data acquisition.
data register - stores data values temporarily in a CPU.
database - a software program that stores and recalls data in an organized way.
DARPA (Defense Advanced Research Projects Agency) -
DC (Direct Current) - a current that flows only in one direction. The alternative is AC.
DCA (Defense Communications Agency) - developed DDN.
DCD (Data Carrier Detect) - used as a handshake in asynchronous communication.
DCE (Data Communications Equipment) - A term used when describing unintelligent serial
communications clients. An example of this equipment is a modem. The complement to this is
DTE.
DCE (Distributed Computing Environment) - applications can be distributed over a number of computers
because of the use of standards interfaces, functions, and procedures.
DDN (Defense Data Network) - a group of DoD networks, including MILNET.
dead band - a region for a device when it no longer operates.
dead time - a delay between an event occurring and the resulting action.
debounce - a switch may not make sudden and complete contact as it is closes, circuitry can be added to
remove a few on-off transitions as the switch mechanically bounces.
debug - after a program has been written it undergoes a testing stage called debugging that involves trying to
locate and eliminate logic and other errors. This is also a time when most engineers deeply regret
not spending more time on the initial design.
decibel (dB) - a logarithmic compression of values that makes them more suited to human perception (for
both scaleability and reference)
decision support - the use of on-line data, and decision analysis tools are used when making decisions. One
example is the selection of electronic components based on specifications, projected costs, etc.
DECnet (Digital Equipment Corporation net) - a proprietary network architecture developed by DEC.
decrement - to decrease a numeric value.
dedicated computer - a computer with only one task.
default - a standard condition.
demorgan’s laws - Boolean laws great for simplifying equations ~(AB) = ~A + ~B, or ~(A+B) = ~A~B.
density - a mass per unit volume.
depth first search - an artificial intelligence technique that follows a single line of reasoning first.
derivative control - a control technique that uses changes in the system of setpoint to drive the system. This
control approach gives fast response to change.
design - creation of a new part/product based on perceived needs. Design implies a few steps that are ill
defined, but generally include, rough conceptual design, detailed design, analysis, redesign, and
testing.
design capture - the process of formally describing a design, either through drafted drawings, schematic
drawings, etc.
design cycle - the steps of the design. The use of the word cycle implies that it never ends, although we must
at some point decide to release a design.
design Variables - are the parameters in the design that describe the part. Design variables usually include
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