Hitachi L2002 manual 235

A–7

L2002 Inverter

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.
Three-phase power	An AC power source with three Hot connections that have phase
	offsets of 120 degrees is a 3-phase power source. Usually, Neutral
	and Earth Ground wires accompany the three Hot connections.
	Loads may be configured in a delta or Y configuration. A Y-
	connected load such as an AC induction motor will be a balanced
	load; the currents in all the Hot connections are the same. There-
	fore, the Neutral connection is theoretically zero. This is why
	inverters that generate 3-phase power for motors do not generally
	have a Neutral connection to the motor. However, the Earth Ground
	connection is important for safety reasons, and is provided.

A Appendix