Watlow Controls 8LS, Руководство пользователя

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Glossary
130 8LS User’s Guide
Span
The difference between the lower and upper lim-
its 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 out-
put 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 thermo-
couple. 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 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).
TI (Timed Integral)
The Integral term.
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 desir-
able when long lead or extension wires produce
unacceptable signal degradation.
U
Upscale Break Protection
A form of break detection for burned-out thermo-
couples. Signals the operator that the thermocou-
ple has burned out.
Undershoot
The amount by which a process variable falls
below the setpoint before it stabilizes.
V
Volt (V)
The unit of measure for electrical potential, volt-
age or electromotive force (EMF).
See Voltage.
Voltage (V)
The difference in electrical potential between two
points in a circuit. It’s the push or pressure behind
current flow through a circuit. One volt (V) is the
difference in potential required to move one cou-
lomb 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 current (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