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P
rocess Variable
A physical property of a process that is of interest because it affects
the quality of the primary task accomplished by the process. For an
industrial oven, temperature is the process variable. See also
PID
Loop
and
Error
.
P
WM
Pulse-width modulation: A type of AC adjustable frequency drive that
accomplishes frequency and voltage control at the output section
(inverter) of the drive. The drive output voltage waveform is at a
constant amplitude, and by “chopping” the waveform (pulsewidth-
modulating), the average voltage is controlled. The chopping
frequency is sometimes called the
Carrier Frequency
.
R
eactance
The impedance of inductors and capacitors has two components. The
resistive part is constant, while the reactive part changes with
applied frequency. These devices have a complex impedance (complex
number), where the resistance is the real part and the reactance is
the imaginary part.
R
ectifier
An electronic device made of one or more diodes that converts AC
power into DC power. Rectifiers are usually used in combination with
capacitors to filter (smooth) the rectified waveform to closely
approximate a pure DC voltage source.
R
egenerative
B
raking
A particular method of generating reverse torque to a motor, an
inverter will switch internally to allow the motor to become a
generator and will either store the energy internally, deliver the
braking energy back to the main power input, or dissipate it with a
resistor.
R
egulation
The quality of control applied to maintain a parameter of interest at a
desired value. Usually expressed as a percent (±) from the nominal,
motor regulation usually refers to its shaft speed.
R
everse Torque
The torque applied in the direction opposite to motor shaft rotation.
As such, reverse torque is a decelerating force on the motor and its
external load.
R
otor
The windings of a motor that rotate, being physically coupled to the
motor shaft. See also
Stator.
Saturation Voltage
For a transistor semiconductor device, it is in saturation when an
increase in input current no longer results in an increase in the
output current. The saturation voltage is the voltage drop across the
device. The ideal saturation voltage is zero.
Sensorless Vector
Control
A technique used in some variable-frequency drives (featured in some
other Hitachi inverter model families) to rotate the force vector in the
motor without the use of a shaft position sensor (angular). Benefits
include an increase in torque at the lowest speed and the cost savings
from the lack of a shaft position sensor.
A6
Appendix A
A 6
Appendix A