D8 Series User’s Guide
166
N
Noise
Unwanted electrical signals that usually produce
signal interference in sensors and sensor
circuits. See also Electromagnetic Interference.
Noise Suppression
The use of components to reduce electrical
interference that is caused by making or
breaking electrical contact, or by inductors.
O
Object
An object is a software programming concept
in which data and functionality are associated
with virtual objects. DeviceNet™ objects consist
of data, called attributes and functions, called
services. Services are used to examine or
change attribute values.
Offset
The difference between the set point and the
actual value of the process variable. Offset is
the error in the process variable that is typical of
proportional-only control.
On/Off Control
A method of control that turns the output full on
until set point is reached, and then off until the
process differs from the set point by more than
the hysteresis.
Open Loop
A control system with no sensory feedback.
Optical Isolation
Two electronic networks that are connected
through an LED (Light Emitting Diode) and a
photoelectric receiver. There is no electrical
continuity between the two networks.
Output
Control signal action in response to the
difference between set point and process
variable.
Output Type
The form of control output, such as time
proportioning, distributed zero crossing, Serial
DAC or analog. Also the description of the
electrical hardware 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 adjusts
the output in proportion to the deviation from set
point, 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.
PV
See Process Variable.
