Glossary
Appendix A
A–2
Glossary
Ambient Temperature
The air temperature in the chamber in which a powered electronic
unit resides. A unit’s heat sinks rely on a lower ambient temperature
in order to dissipate heat away from sensitive electronics.
Auto-tuning
The ability of a controller to execute a procedure that interacts with
a load to determine the proper coefficients to use in the control
algorithm. Auto-tuning is a common feature of process controllers
with PID loops. Hitachi inverters feature auto tuning to determine
motor parameters for optimal commutation. Auto-tuning is avail-
able as a special command from a digital operator panel. See also
digital operator panel.
Base Frequency
The power input frequency for which an AC induction motor is
designed to operate. Most motors will specify a 50 to 60 Hz value.
The Hitachi inverters have a programmable base frequency, so you
must ensure that parameter matches the attached motor. The term
base frequency helps differentiate it from the carrier frequency. See
also carrier frequency and frequency setting.
Braking Resistor
Some variable speed drives can cause the motor to develop deceler-
ating torque by switching motor wiring so the motor becomes a
generator, connected to an energy-absorbing resistor. See also four-
quadrant operation and dynamic braking.
Break-away Torque
The torque a motor must produce to overcome the static friction of a
load, in order to start the load moving.
Brushes
A sliding electrical connection between a fixed post inside the
motor housing and a ring on the motor shaft. Typically used in DC
motors or low-cost AC motors, brushes route current to windings on
the rotor. AC induction motors with a squirrel-cage design do not
have the need for brushes. See also commutation and squirrel cage.
Carrier Frequency
The frequency of the constant, periodic, switching waveform that
the inverter modulates to generate the AC output to the motor. See
also PWM.
CE
A regulatory agency for governing the performance of electronic
products in Europe. Drive installations designed to have CE
approval must have particular filter(s) installed in the application.
Choke
An inductor which is tuned to react at radio frequencies is called a
“choke,” since it attenuates (chokes) frequencies above a particular
threshold. Tuning is often accomplished by using a movable
magnetic core. In variable-frequency drive systems, a choke
positioned around high-current wiring can help attenuate harmful
harmonics and protect equipment. See also harmonics.
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