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CLS200 Series User’s Guide
173
D
DAC
See Digital-to-Analog Converter.
Data Logging
A method of recording a process variable
over a period of time. Used to review process
performance.
DC
See Direct Current.
Deadband
The range through which a variation of the input
produces no noticeable change in the output.
In the deadband, specific conditions can be
placed on control output actions. Operators
select the deadband. It is usually above the
heating proportional band and below the
cooling proportional band.
Default Parameter Settings
The values that the user adjustable parameters
have when a controller ships from Watlow or
after the user programmed setting are cleared.
Derivative Control (D)
The last term in the PID algorithm. Action that
anticipated the rate of change of the process,
and compensates to minimize overshoot
and undershoot. Derivative control is an
instantaneous change of the control output in
the same direction as the proportional error.
This is caused by a change in the process
variable (PV) that decreases over the time of the
derivative (TD). The TD is in units of seconds.
Deutsche Industrial Norms (DIN)
A set of technical, scientific and dimensional
standards developed in Germany. Many DIN
standards have worldwide recognition.
Deviation Alarm
Warns that a process has exceeded or fallen
below a certain range around the setpoint.
Digital-to-Analog Converter (DAC)
A device that converts a numerical input signal
to a signal that is proportional to the input in
some way.
Direct Action
An output control action in which an increase in
the process variable, causes an increase in the
output. Cooling applications usually use direct
action.
Direct Current (DC)
An electric current that flows in one direction.
Distributed Zero Crossing (DZC)
A form of digital output control in which the
output on/off state is calculated for every ac
line cycle. Power is switched at the zero cross,
which reduces electrical noise. See also Zero
Cross.
E
Earth Ground
A metal rod, usually copper, that provides an
electrical path to the earth, to prevent or reduce
the risk of electrical shock.
EIA/TIA
See Serial Communications.
Electrical Noise
See Noise.
Electromagnetic Interference (EMI)
Electrical and magnetic noise imposed on a
system. There are many possible causes, such
as switching ac power on inside the sine wave.
EMI can interfere with the operation of controls
and other devices.
Electrical-Mechanical Relays
See Relay, Electromechanical.
Emissivity
The ratio of radiation emitted from a surface
compared to radiation emitted from a blackbody
at the same temperature.
Engineering Units
Selectable units of measure, such as degrees
Celsius and Fahrenheit, pounds per square inch,
newtons per meter, gallons per minute, liters per
minute, cubic feet per minute or cubic meters
per minute.
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