Watlow Series D8 - Manual (Page 219)

Series D8 User’s Guide Glossary
Doc. 0600-3120-2000 Watlow Anafaze 201
The item or substance that is to be heated or cooled.
Low Deviation Alarm
Warns that the process has dropped more than a cer -
tain amount belo w set point. It can be used as either
an alarm or control function.
Low Alarm
A signal that is associated with a set minimum v alue
that can be used as either an alarm or boost control
function.
M
Manual Mode
A selectable mode that has no automatic control
aspects. The operator sets output levels.
Manual Reset
A parameter that allows the user to eliminate offset or
droop between set point and actual process tempera-
ture. See also Integral.
Milliampere (mA)
One thousandth of an ampere.
N
Noise
Unwanted electrical signals that usually produce sig-
nal interference in sensors and sensor circuits. See
also Electromagnetic Interference.
Noise Suppression
The use of components to reduce electrical interfer -
ence that is caused by making or breaking electrical
contact, or by inductors.
O
Object
An object is a softw are programming concept in
which data and functionality are associated with vir -
tual objects. DeviceNet objects consists 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 v ariable 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 dif-
fers from the set point by more than the hysteresis.
Open Loop
A control system with no sensory feedback.
Optical Isolation
Two electronic netw orks 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 dif ference
between set point and process variable.
Output Type
The form of control output, such as time proportion-
ing, distributed zero crossing, Serial D AC or analog.
Also the description of the electrical hardw are that
makes up the output.
Overshoot
The amount by which a process v ariable exceeds the
set point before it stabilizes.
P
PID
Proportional, Inte gral, Deri vative. A control mode
with three functions: Proportional action dampens the
system response, inte gral corrects for droops, and
derivative prevents overshoot and undershoot.
Polarity
The electrical quality of ha ving tw o opposite poles,
one positive and one negative. Polarity determines the
direction in which a current tends to fl w.
Process Input
A v oltage 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,
fl w, fluid l vel, 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° belo w the set point, the heat propor -
tioned effort is 50 percent. The lower the PB v alue,
the higher the gain.