GE Industrial Solutions AF-300E$ - Manual (Page 126)

11-5
PLC (Programmable Logic Controller): Solid-state control
logic for machines and processes where a sequence of
operations can be changed easily with programming
(software).
Pull-up Torque: The torque required to accelerate the load
from standstill to full speed (where breakdown torque oc-
curs), expressed in percent of running torque. It is the torque
required not only to overcome friction, windage and prod-
uct loading but also to overcome the inertia of the machine.
The torque required by a machine may not be constant
after the machine has started to turn. This load type is
characteristic of fans, centrifugal pumps and certain ma-
chine tools.
PWM (Pulse Width Modulated): A type of AC adjustable fre-
quency drive that accomplishes frequency and voltage con-
trol at the output section (inverter) of the drive. The drive’s
output voltage is always a constant amplitude and by “chop-
ping” (pulse width modulating) the average voltage is con-
trolled.
Reactance: Any force that opposes changes in current volt-
age. The inertia of electrons causes them to oppose sud-
den changes in current flow or voltage.
Rectifier: A device that transforms alternating-current to di-
rect-current.
Regeneration: The characteristic of a motor to act as a gen-
erator when the rotor synchronous frequency is greater than
the applied frequency.
Regenerative Braking: The technique of slowing or stopping
a drive by regeneration.
Regenerative Control: A regenerative drive contains the in-
herent capability and/or power semi-conductors to control
the flow of power to and from the motor.
Regulation: The ability of a control system to hold a speed
once it has been set. Regulation is given in percentages of
either base speed or set speed. Regulation is rated upon
two separate sets of conditions:
A. Load Regulation (speed regulation) is the percentage of
speed change with a defined change in load. Assuming all
other parameters to be constant.
B. Line Regulation is the percentage of speed change with
a given line voltage change, assuming all other parameters
to be constant.
Resolution: The smallest distinguishable increment into which
a quantity can be divided (e.g. position or shaft speed). It is
also the degree to which nearly equal values of a quantity
can be discriminated. For encoders, it is the number of
unique electrically identified positions occurring in 360 de-
grees of input shaft rotation.
SCR (Silicon Control Rectifier): A solid state device that has
an anode, a cathode, and gate which controls when it al-
lows conduction.
Service Factor: When used on a motor nameplate, a num-
ber which indicates how much above the nameplate rating
a motor can be loaded without causing serious degrada-
tion (i.e. A motor with 1.15 S.F. can produce 15% greater
torque than one with 1.0 S.F.). When used in applying mo-
tors or gearmotors, it is a figure of merit which is used to
adjust measured loads in an attempt to compensate for
conditions which are difficult to measure or define.
Set Speed: The desired operating speed.
Shock Load: The load seen by a clutch, brake or motor in a
system which transmits high peak loads. This type of load
is present in crushers, separators, grinders, conveyors,
winches and cranes.
Slewing: Slewing is an incremental motion of the motor shaft
or machine table from one position to another at maximum
speed without losing position control.
Slip: The difference between rotating magnetic field speed
(synchronous speed) and rotor speed of AC induction mo-
tors. Usually expressed as a percentage of synchronous
speed.
Speed Range: The speed minimum and maximum at which
a motor must operate under constant or variable torque
load conditions. A 10:1 speed range for a motor with top
speed of 1800 RPM means the motor must operate as low
as 180 RPM and still remain within regulation specifications.
Controllers are capable of wider controllable speed ranges
than motors because there is no thermal limitation, only
electrical. Controllable speed range of a motor is limited by
the ability to deliver 100% torque below base speed with-
out additional cooling.
Speed Regulation: The numerical measure in percent, of how
accurately the motor speed can be maintained. It is the
percentage of change in speed between full load and no
load.
Stability: The ability of a drive to operate a motor at con-
stant speed (under varying load), without “hunting” (alter-
nately speeding up and slowing down). It is related to both
the characteristics of the load being driven and electrical
time constants in the drive regulator circuits.
Surge Protection: The process of absorbing and clipping
voltage transients on an incoming AC line or control circuit.
MOV’s (Metal Oxide Varistors) and specially designed R-C
networks are usually used to accomplish this.