Omron MX2 User Manual page 281

Glossary
Slip
Squirrel Cage
Stator
Tachometer
Thermal Switch
Thermistor
Three-phase power
Torque
Transistor
Trip Event
Watt Loss
The difference between the theoretical speed of a motor at no load (deter-
mined 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.
A "nick-name" for the appearance of the rotor frame assembly for an AC
induction motor.
The windings in a motor that are stationary and coupled to the power input of
the motor. See also Rotor.
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.
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.
A type of temperature sensor that changes its resistance according to its tem-
perature. The sensing range of thermistors and their ruggedness make them
ideal for motor overheating detection. Omron inverters have built-in thermistor
input circuits, which can detect an overheated motor and shut off (trip) the
inverter output.
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.
Therefore, the Neutral connection is theoretically zero. This is why inverters
that generate 3-phase power for motors do not generally have a Neutral con-
nection to the motor. However, the Earth Ground connection is important for
safety reasons, and is provided.
The rotational force exerted by a motor shaft. The units of measurement con-
sist of the distance (radius from shaft center axis) and force (weight) applied
at that distance. Units are usually given as pound-feet, ounce-inches, or New-
ton-meters.
A solid state, three-terminal device that provides amplification of signals and
can be used for switching and control. While transistors have a linear operat-
ing range, inverters use them as high-powered switches. Recent develop-
ments in power semiconductors have produced transistors capable of
handling high voltages and currents, all with high reliability. The saturation
voltage has been decreasing, resulting in less heat dissipation. Omron invert-
ers use state-of-the-art semiconductors to provide high performance and reli-
ability in a compact package. See also IGBT and Saturation Voltage.
An event that causes the inverter to stop operation is called a "trip" event (as
in tripping a circuit breaker). The inverter keeps a history log of trip events.
They also require an action to clear.
A measure of the internal power loss of a component, the difference between
the power it consumes and what its output delivers. An inverter's watt loss is
the input power minus the power delivered to the motor. The watt loss is typi-
cally highest when an inverter is delivering its maximum output. Therefore,
watt loss is usually specified for a particular output level. Inverter watt loss
specifications are important when designing enclosures.
Section A-1
259