Technical information

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Glossary
Encoder Marker
A once-per-revolution signal provided by some incremental encoders to specify a reference point within
that revolution. Also known as Zero Reference signal or index pulse.
Encoder Resolution
A measure of the smallest positional change which can be detected by the encoder.
Explosion-proof
A enclosure classification that indicates an enclosure is capable of withstanding internal explosions without
bursting or allowing ignition to reach beyond the confines of the enclosure itself.
Fall Time
The time for the amplitude of system response to decay to 37 percent of its steady-state value after the
removal of a steady-state step input signal.
Feedback
A signal usually indicating velocity or position, which is transferred from the output back to the input for
use in a closed loop system.
Feed Forward
A technique used to pre-compensate a control loop for known errors due to motor, drive or lead
characteristics. Provides improved response.
Field Weakening
A method of increasing the speed of a wound field DC motor. Accomplished by reducing stator magnetic
field by reducing the field winding current.
Filter (Control Systems)
A transfer function used to modify the frequency or time response of a control system.
Flutter
An error of the basic cycle of an encoder per one revolution.
Following Error
Difference between the commanded position and actual position of the motor.
Form Factor
The ratio of RMS current to average current. This number is a measure of the current ripple in a PWM or
other switched mode type of controller. Since motor heating is a function of RMS current while motor
torque is a function of average current, a form factor greater than 1.00 means some fraction of motor current
is producing heat but not torque.
Four Quadrant
Refers to a motion system which can operate in all four quadrants, (i.e., velocity in either direction and
torque in either direction). This means that the motor can accelerate, run and decelerate in either direction.
Friction
A resistance to motion caused by surfaces rubbing together. Friction can be constant with varying speed
(coulomb friction) or proportional to speed (viscous friction) or present at rest (static friction).
Full Load Current
The delivered current to a motor operated at its full load torque and speed with rated voltage applied.