Watlow CLS - Manual (Page 173)

Glossary
165
Default Parameters
The programmed instructions that are perma-
nently stored in the microprocessor software.
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 under-
shoot. 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. Similar to burst
fire.
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.
Electrical Noise
See Noise.
Electromagnetic Interference (EMI)
Electrical and magnetic noise imposed on a sys-
tem. 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 Cel-
sius and Fahrenheit, pounds per square inch,
newtons per meter, gallons per minute, liters per
minute, cubic feet per minute or cubic meters per
minute.
EPROM
Erasable Programmable, Read-Only Memory
inside the controller.
Error
The difference between the correct or desired
value and the actual value.
F
Fahrenheit
The temperature scale that sets the freezing point
of water at 32
º F and its boiling point at 212 º F at
standard atmospheric pressure. The formula for
conversion to Celsius is:
º C=5/9 ( º F-32 º F).
Failed Sensor Alarm
Warns that an input sensor no longer produces a
valid signal. For example, when there are thermo-
couple breaks, infrared problems or resistance