Watlow 8LS Controller - Manual (Page 137)

Glossary
8LS User’s Guide 129
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.
Reflection Compensation Mode
A control feature that automatically corrects the
reading from a sensor.
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 con-
trol.
Solid State Relay (SSR) — A switching
device with no moving parts that com-
pletes or interrupts a circuit electrically.
Reset
Control action that automatically eliminates off-
set or droop between setpoint and actual process
temperature.
See also Integral.
Automatic Reset — The integral function of a
PI or PID temperature controller that adjusts the
process temperature to the setpoint after the sys-
tem stabilizes. The inverse of integral.
Automatic Power Reset — A feature in latch-
ing limit controls that
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.
S
Serial Communications
A method of transmitting information between
devices by sending all bits serially over a single
communication channel.
RS-232 — An Electronics Industries of America
(EIA) standard for interface between data termi-
nal equipment and data communications equip-
ment for serial binary data interchange. This is
usually for communications over a short distance
(50 feet or less) and to a single device.
RS-485 — An Electronics Industries of America
(EIA) standard for electrical characteristics of
generators and receivers for use in balanced digi-
tal multipoint systems. This is usually used to
communicate with multiple devices over a com-
mon cable or where distances over 50 feet are
required.
Setpoint (SP)
The desired value programmed into a controller.
For example, the temperature at which a system
is to be maintained.
Shield
A metallic foil or braided wire layer surrounding
conductors that is designed to prevent electro-
static or electromagnetic interference from exter-
nal sources.
Signal
Any electrical transmittance that conveys infor-
mation.
Solid State Relay (SSR)
See Relay, Solid State.