A–4

Glossary

Appendix A

Frequency Setting

While frequency has a broad meaning in electronics, it typically

 

refers to motor speed for variable-frequency drives (inverters). This

 

is because the output frequency of the inverter is variable, and is

 

proportional to the attained motor speed. For example, a motor with

 

a base frequency of 60 Hz can be speed controlled with an inverter

 

output varying form 0 to 60 Hz. See also Base Frequency, Carrier

 

Frequency, and Slip.

Harmonics

A harmonic is a whole number multiple of a base of fundamental

 

frequency. The square waves used in inverters produce high-

 

frequency harmonics, even though the main goal is to produce

 

lower-frequency sine waves. These harmonics can be harmful to

 

electronics (including motor windings) and cause radiated energy

 

that interferes with nearby electronic devices. Chokes, line reactors,

 

and filters are sometimes used to suppress the transmission of

 

harmonics in an electrical system. See also Choke.

Horsepower

A unit of physical measure to quantify the amount of work done per

 

unit of time. You can directly convert between horsepower and

 

Watts as measurements of power.

IGBT

Insulated Gate Bipolar Transistor (IGBT) – A semiconductor

 

transistor capable of conducting very large currents when in satura-

 

tion and capable of withstanding very high voltages when it is OFF.

 

This high-power bipolar transistor is the type used in Hitachi invert-

 

ers.

Inertia

The natural resistance a stationary object to being moved by an

 

external force. See also Momentum.

Intelligent Terminal

A configurable input or output logic function on the Hitachi invert-

 

ers. Each terminal may be assigned one of several functions.

Inverter

A device that electronically changes DC to AC current through an

 

alternating process of switching the input to the output, inverted and

 

non-inverted. A variable speed drive such as the Hitachi L100 is

 

also called an inverter, since it contains three inverter circuits to

 

generate 3-phase output to the motor.

Isolation Transformer

A transformer with 1:1 voltage ratio that provides electrical isola-

 

tion 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.