Rockwell Automation WebPak 3000 DC Drive Application Workbook Version 1.1 - Manual (Page 93)

Glossary Glossary-1
G
LOSSARY
automatic field weakening (spillover control) - A speed control method that allows
the motor to operate throughout the entire constant-torque and constant-horsepower
ranges with only one speed control. The field current regulator is controlled by
armature voltage. When armature voltage is between zero and 85% of rated voltage,
field current is maximum. As armature voltage increases from 85 to 100%, field
current is automatically reduced to provide maximum motor speed. Small speed
changes can be made quickly because field strength is varied as a function of
armature voltage.
base speed - The manufacturer’s nameplate rating where the motor will develop rated
horsepower at rated load and voltage. It is commonly the point where full armature
voltage is applied with full rated field excitation.
cascade control - A control strategy in which the output of one loop is the input for
another loop. Synonymous with series control.
closed-loop system - A regulator circuit in which the actual value of the controlled
variable (e.g., speed) is sensed and a signal proportional to this value (feedback
signal) is compared with a signal proportional to the desired value (reference signal).
The difference between these signals (error signal) causes the actual value to change
in the direction that will reduce the difference in signals to zero.
CML - Current minor loop. See loop.
constant horsepower - A designation for variable speed motors used for loads
requiring the same amount of horsepower regardless of their motor speed during a
normal operation.
constant horsepower range - A range of motor operation where motor speed is
controlled by field weakening. In this range, motor torque decreases as speed
increases. Since horsepower is speed times torque (divided by a constant), the value
of horsepower developed by the motor in this range is constant.
constant torque - Refers to loads with horsepower requirements that change linearly
at different speeds. Horsepower varies with the speed, i.e., 2/1 HP at 1800/900 RPM
(seen on some two-speed motors).
constant torque range - A speed range in which the motor is capable of delivering a
constant torque, subject to cooling limitations of the motor.
control types:
• position control - Position control is used to coordinate speed and/or tension
between adjacent sections of a process line. The position feedback can be a
potentiometer or transducer connected to a position-sensing roll. Web tension is
established by loading the position-sensing roll.