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SJ200 Inverter
Appendix A
A–7
Sensorless Vector
Control
A technique used in variable-frequency drives 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. See
also Intelligent Sensorless Vector Control.
Setpoint (SP) The setpoint is the desired value of a process variable of interest.
See also Process Variable (PV) and PID Loop.
Single-phase power An AC power source consisting of Hot and Neutral wires. An Earth
Ground connection usually accompanies them. In theory, the
voltage potential on Neutral stays at or near Earth Ground, while
Hot varies sinusoidally above and below Neutral. This power source
is named Single Phase to differentiate it from three-phase power
sources. Some Hitachi inverters can accept single phase input
power, but they all output three-phase power to the motor. See also
Three-phase.
Slip The difference between the theoretical speed of a motor at no load
(determined by its inverter output waveforms) and the actual speed.
Some slip is essential in order to develop torque to the load, but too
much will cause excessive heat in the motor windings and/or cause
the motor to stall.
Squirrel Cage A “nick-name” for the appearance of the rotor frame assembly for
an AC induction motor.
Stator The windings in a motor that are stationary and coupled to the
power input of the motor. See also Rotor.
Tachometer 1. A signal generator usually attached to the motor shaft for the
purpose of providing feedback to the speed controlling device of the
motor. 2. A speed-monitoring test meter that may optically sense
shaft rotation speed and display it on a readout.
Thermal Switch An electromechanical safety device that opens to stop current flow
when the temperature at the device reaches a specific temperature
threshold. Thermal switches are sometimes installed in the motor in
order to protect the windings from heat damage. The inverter can
use thermal switch signals to trip (shut down) if the motor
overheats. See also Trip.
Thermistor A type of temperature sensor that changes its resistance according
to its temperature. The sensing range of thermistors and their
ruggedness make them ideal for motor overheating detection.
Hitachi inverters have built-in thermistor input circuits, which can
detect an overheated motor and shut off (trip) the inverter output.