Watlow CPC400 - Manual (Page 213)

CPC400 Series User’s Guide Glossary
Doc. 0600-2900-2000 Watlow Anafaze 199
Optical Isolation
Two electronic networks that are connected
through an LED (Light Emitting Diode) and a
photoelectric receiver. There is no electrical conti-
nuity between the two networks.
Output
Control signal action in response to the differ-
ence between set point and process variable.
Output Type
The form of control output, such as time propor-
tioning, distributed zero crossing, Serial DAC or
analog. Also the description of the electrical hard-
ware that makes up the output.
Overshoot
The amount by which a process variable exceeds
the set point before it stabilizes.
P
PID
Proportional, Integral, Derivative. A control
mode with three functions: Proportional action
dampens the system response, integral corrects
for droops, and derivative prevents overshoot and
undershoot.
Polarity
The electrical quality of having two opposite
poles, one positive and one negative. Polarity
determines the direction in which a current tends
to flow.
Process Input
A voltage or current input that represents a
straight line function.
Process Variable (PV)
The parameter that is controlled or measured.
Typical examples are temperature, relative
humidity, pressure, flow, fluid level, events, etc.
Proportional (P)
Output effort proportional to the error from set
point. For example, if the proportional band is 20˚
and the process is 10˚ below the set point, the
heat proportioned effort is 50 percent. The lower
the PB value, the higher the gain.
Proportional Band (PB)
A range in which the proportioning function of
the control is active. Expressed in units, degrees
or percent of span. See also PID.
Proportional Control
A control using only the P (proportional) value of
PID control.
Pulse Input
Digital pulse signals from devices, such as optical
encoders.
PV
See Process Variable.
R
Ramp
A programmed increase in the temperature of a
set point system.
Range
The area between two limits in which a quantity
or value is measured. It is usually described in
terms of lower and upper limits.
Recipe
See Job.
Relay
A switching device.
Electromechanical Relay — A power
switching device that completes or interrupts a
circuit by physically moving electrical contacts
into contact with each other. Not recommended
for PID control.
Solid State Relay (SSR) — A switching
device with no moving parts that completes or
interrupts a circuit electrically.
Reset
See Automatic Reset, Manual Reset.
Resistance
Opposition to the flow of electric current, mea-
sured in Ohms.
Resistance Temperature Detector (RTD)
A sensor that uses the resistance temperature
characteristic to measure temperature. There are
two basic types of RTDs: the wire RTD, which is
usually made of platinum, and the thermistor,
which is made of a semiconductor material. The
wire RTD is a positive temperature coefficient
sensor only, while the thermistor can have either
a negative or positive temperature coefficient.
Reverse Action
An output control action in which an increase in
the process variable causes a decrease in the out-
put. Heating applications usually use reverse
action.
RTD
See Resistance Temperature Detector.