Watlow CAS200 - Manual (Page 123)

CAS200 User’s Guide Glossary
Watlow Anafaze 111
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 tempera-
ture coefficient sensor only, while the ther-
mistor 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
output. 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 sin-
gle communication channel.
EIA/TIA-232—An Electronics Industries of
America (EIA) standard for interface between
data terminal equipment and data communi-
cations equipment for serial binary data inter-
change. This is usually for communications
over a short distance (50 feet or less) and to a
single device.
EIA/TIA-485—An Electronics Industries of
America (EIA) standard for electrical charac-
teristics of generators and receivers for use in
balanced digital multipoint systems. This is
usually used to communicate with multiple
devices over a common cable or where dis-
tances over 50 feet are required.
Setpoint (SP)
The desired value programmed into a control-
ler. For example, the temperature at which a
system is to be maintained.
Shield
A metallic foil or braided wire layer surround-
ing conductors that is designed to prevent elec-
trostatic or electromagnetic interference from
external sources.
Signal
Any electrical transmittance that conveys
information.
Solid State Relay (SSR)
See Relay, Solid State.
Span
The difference between the lower and upper
limits of a range expressed in the same units
as the range.
Spread
In heat/cool applications, the +/- difference
between heat and cool. Also known as process
deadband.
See deadband.
Stability
The ability of a device to maintain a constant
output with the application of a constant
input.
T
T/C Extension Wire
A grade of wire used between the measuring
junction and the reference junction of a ther-
mocouple. Extension wire and thermocouple
wire have similar properties, but extension
wire is less costly.
TD (Timed Derivative)
The derivative function.
Thermistor
A temperature-sensing device made of semi-
conductor material that exhibits a large
change in resistance for a small change in tem-
perature. Thermistors usually have negative
temperature coefficients, although they are
also available with positive temperature coeffi-
cients.
Thermocouple (T/C)
A temperature sensing device made by joining
two dissimilar metals. This junction produces
an electrical voltage in proportion to the differ-
ence in temperature between the hot junction
(sensing junction) and the lead wire connection
to the instrument (cold junction).