Hitachi L2002 A Appendix

A–3

L2002 Inverter

DC Braking	The inverter DC braking feature stops the AC commutation to the
	motor, and sends a DC current through the motor windings in order
	to stop the motor. Also called “DC injection braking,” it has little
	effect at high speed, and is used as the motor is nearing a stop.
Deadband	In a control system, the range of input change for which there is no
	perceptible change in the output. In PID loops, the error term may
	have a dead band associated with it. Deadband may or may not be
	desirable; it depends on the needs of the application.

Digital Operator Panel For Hitachi inverters, “digital operator panel” (DOP) refers first to the operator keypad on the front panel of the inverter. It also includes hand-held remote keypads, which connect to the inverter via a cable. Finally, the DOP Professional is a PC-based software simulation of the keypad devices.

Diode	A semiconductor device that has a voltage-current characteristic
	that allows current to flow only in one direction, with negligible
	leakage current in the reverse direction. See also Rectifier.
Duty Cycle	1. The percent of time a square wave of fixed frequency is ON
	(high) versus OFF (low). 2. The ratio of operating time of a device
	such as a motor to its resting time. This parameter usually is speci-
	fied in association with the allowable thermal rise for the device.
Dynamic Braking	For the L2002 inverter models, the braking unit and braking resistor
	are optional (external) components. The dynamic braking feature
	shunts the motor-generated EMF energy into a special braking
	resistor. The added dissipation (braking torque) is effective at
	higher speeds, having a reduced effect as the motor nears a stop.
Error	In process control, the error is the difference between the desired
	value or setpoint (SP) and the actual value of a the process variable
	(PV). See also Process Variable and PID Loop.
EMI	Electromagnetic Interference - In motor/drive systems, the switch-
	ing of high currents and voltages creates the possibility of generat-
	ing radiated electrical noise that may interfere with the operation of
	nearby sensitive electrical instruments or devices. Certain aspects of
	an installation, such as long motor lead wire lengths, tend to
	increase the chance of EMI. Hitachi provides accessory filter
	components you can install to decrease the level of EMI.
Four-quadrant	Referring to a graph of torque versus direction, a four-quadrant
operation	drive can turn the motor either forward or reverse, as well as decel-
	erate in either direction (see also reverse torque). A load that has a
	relatively high inertia and must move in both directions and change
	directions rapidly requires four-quadrant capability from its drive.

A Appendix