GE Industrial Solutions AF-300E$ - Manual (Page 124)

11-3
Feedback: The element of a control system that provides an
actual operation signal for comparison with the set point to
establish an error signal used by the regulator circuit.
Filter: A device that passes a signal or a range of signals
and eliminates all others.
Floating Ground: A circuit whose electrical common point is
not at earth ground potential or the same ground potential
as circuitry it is associated with. A voltage difference can
exist between the floating ground and earth ground.
Flux: The electro-magnetic field created by passing current
through a conductor. For motors, the magnetic field cre-
ated by energizing the motor windings.
Flux Vector: The mathematical represenation of flux indicat-
ing both filed strength and orientation.
Force: The tendency to change the motion or position of an
object with a push or pull.
Four-Quadrant Operation: The four combinations of forward
and reverse rotation and forward and reverse torque of which
a regenerative drive is capable. The four combinations are:
1. Forward rotation/forward torque (motoring)
2. Forward rotation/reverse torque (regeneration)
3. Reverse rotation/reverse torque (motoring)
4. Reverse rotation/forward torque (regeneration)
Full-Load Torque: The full-load torque of a motor is the torque
necessary to produce rated horsepower at full-load speed.
GTO: Gate turn-off power semiconductor device.
Harmonics: A sinusoidal component of a periodic wave or
quantity having a frequency that is an integral multiple of
the fundamental frequency.
Head: A measurement of pressure, usually in feet of water.
Horsepower: A measure of the amount of work that a motor
can perform in a given period of time. Refer to power for
KW equivalent.
Hunting: Undesirable fluctuations in motor speed that can
occur after a step change in speed reference (either accel-
eration or deceleration) or load.
Hysteresis Loss: The resistance offered by materials to be-
coming magnetized results in energy being expended and
corresponding loss. Hysteresis loss in a magnetic circuit is
the energy expended to magnetize and demagnetize the
core.
IGBT (Insulated Gate Bi-polar Transistor): Semi-conductor
devices used for power circuits that are capable of high
power output that operate at carrier frequencies of 20KHz
or more. IGBT’s have a faster rate of rise resulting in high
di/dt that occurs when the device is turned off.
Induction Motor: An alternating current motor in which the
primary winding on one member (usually the stator) is con-
nected to the power source. A secondary winding on the
other member (usually the rotor) carries the induced cur-
rent. For a squirrel cage induction motor there is no physi-
cal electrical connection to the secondary winding, it’s cur-
rent is induced.
Interposing Relay: A relay that accepts control signals of one
logic level in order to provide isolated contact signals in a
circuit operating a different logic level.
Inertia: A measure of a body’s resistance to changes in ve-
locity, whether the body is at rest or moving at a constant
velocity. The velocity can be either linear or rotational. The
moment of inertia (WK
2 ) is the product of the weight (W) of
an object and the square of the radius of gyration (K 2 ). The
radius of gyration is a measure of how the mass of the ob-
ject is distributed about the axis of rotation. WK
2 is usually
expressed in units of lb-ft 2 .
Instability: A situation where the output of a system does
not track the input. For closed loop systems, the control
system error is either increasing or oscillating.
Intermittent duty (INT): A motor that never reaches equilib-
rium temperature (equilibrium), but is permitted to cool down
between operations. For example, a crane, hoist or ma-
chine tool motor is often rated for 15 or 30 duty.
Inverter: A term commonly used for an AC adjustable fre-
quency drive. An inverter is also a term used to describe a
particular section of an AC drive. This section uses the DC
voltage from a previous circuit stage (Intermediate DC cir-
cuit) to produce an AC current or voltage having the de-
sired frequency.
Isolation Transformer: A transformer that electrically sepa-
rates the drive from the AC power line. An isolation trans-
former provides the following advantages:
1. It guards against inadvertent grounding of plant power
lines through grounds in the drive.
2. Enhances protection of semiconductors from line volt-
age transients.
3. Reduces disturbances from other solid state control
equipment such as Drives without isolation transformers,
time clock systems, electronic counters, etc.
Jogging: Jogging is a means of accomplishing momentary
motor movement by repetitive closure of a circuit using a
single pushbutton or contact element.
Kinetic Energy: The energy of motion possessed by a body.
Linearity: A measure of how closely a characteristic follows
a straight line function.