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Glossary
Appendix A
A–4
Isolation
Transformer
A transformer with 1:1 voltage ratio that provides electrical isolation between its primary and
secondary windings. These are typically used on the power input side of the device to be
protected. An isolation transformer can protect equipment from a ground fault or other
malfunction of nearby equipment, as well as attenuate harmful harmonics and transients on the
input power.
Jogging
Operation
Usually done manually, a jog command from an operator’s panel requests the motor/drive
system to run indefinitely in a particular direction, until the machine operator ends the jog
operation.
Jump Frequency A jump frequency is a point on the inverter output frequency range that you want the inverter to
skip around. This feature may be used to avoid a resonant frequency, and you can program up
to three jump frequencies in the inverter.
Line Reactor A three-phase inductor generally installed in the AC input circuit of an inverter to minimize
harmonics and to limit short-circuit current.
Momentum The physical property of a body in motion that causes it to continue to remain in motion. In the
case of motors, the rotor and attached load are rotating and possess angular momentum.
Multi-speed
Operation
The ability of a motor drive to store preset discrete speed levels for the motor, and control
motor speed according to the currently selected speed preset. The Hitachi inverters have 16
preset speeds.
Motor Load In motor terminology, motor load consists of the inertia of the physical mass that is moved by
the motor and the related friction from guiding mechanisms. See also inertia.
NEC The National Electric Code is a regulatory document that governs electrical power and device
wiring and installation in the United States.
NEMA The National Electric Manufacturer’s Association. NEMA Codes are a published series of
device ratings standards. Industry uses these to evaluate or compare the performance of devices
made by various manufacturers to a known standard.
Open-collector
Outputs
A common logic-type discrete output that uses an NPN transistor that acts as a switch to a
power supply common, usually ground. The transistor’s collector is open for external connec-
tion (not connected internally). Thus, the output sinks external load current to ground.
Orientation When using the expansion card SJ-FB with encoder feedback, the orientation feature is avail-
able. Also called home search in motion terminology, you can specify a search direction and a
stop position. Typically the orientation procedure is necessary after each inverter powerup.
Power Factor A ratio that expresses a phase difference (timing offset) between current and voltage supplied
by a power source to a load. A perfect power factor = 1.0 (no phase offset). Power factors less
than one cause some energy loss in power transmission wiring (source to load).
PID Loop Proportional-Integral-Derivative – a mathematical model used for process control. A process
controller maintains a process variable (PV) at a setpoint (SP) by using its PID algorithm to
compensate for dynamic conditions and varies its output to drive the PV toward the desired
value. See also error.
Process 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.
PWM 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 (pulse-width-modulat-
ing), the average voltage is controlled. The chopping frequency is sometimes called the carrier
frequency.