Watlow CPC400 - Manual (Page 214)

Glossary CPC400 Series User’s Guide
200 Watlow Anafaze Doc. 0600-2900-2000
S
Serial Communications
A method of transmitting information between
devices by sending all bits serially over a single
communication channel.
Set Point (SP)
The desired value of the process variable. 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.
Span
The difference between the lower and upper lim-
its of a range expressed in the same units as the
range.
Stability
The ability of a device to maintain a constant out-
put with the application of a constant input.
T
Thermistor
A temperature-sensing device made of semicon-
ductor material that exhibits a large change in
resistance for a small change in temperature.
Thermistors usually have negative temperature
coefficients, although they are also available with
positive temperature coefficients.
Thermocouple (T/C)
A temperature sensing device made by joining
two dissimilar metals. This junction produces an
electrical voltage in proportion to the difference
in temperature between the hot junction (sensing
junction) and the lead wire connection to the
instrument (cold junction).
Thermocouple Extension Wire
A grade of wire used between the measuring
junction and the reference junction of a thermo-
couple. Extension wire and thermocouple wire
have similar properties, but extension wire is less
costly.
Transmitter
A device that transmits temperature data from
either a thermocouple or RTD by way of a two-
wire loop. The loop has an external power supply.
The transmitter acts as a variable resistor with
respect to its input signal. Transmitters are
desirable when long lead or extension wires pro-
duce unacceptable signal degradation.
U
Undershoot
The amount by which a process variable falls
below the set point before it stabilizes.
V
Volt (V)
The unit of measure for electrical potential, volt-
age or electromotive force (EMF). See also Volt-
age.
Voltage (V)
The difference in electrical potential between two
points in a circuit. It is the push or pressure
behind current flow through a circuit. One volt
(V) is the difference in potential required to move
one coulomb of charge between two points in a
circuit, consuming one joule of energy. In other
words, one volt (V) is equal to one ampere of cur-
rent (I) flowing through one ohm of resistance
(R), or V = IR.
Z
Zero Cross
Action that provides output switching only at or
near the zero-voltage crossing points of the ac
sine wave.