AC Electronic Drives Study Guide
a _______ is a feedback device that uses a Glass lens with lines on it n a light source to create electrical pulses
Encoder
the three common modes for stopping a motor
coast, ramp, DC brake
the simplest method of stopping a motor is the ______ method
coasting
the final step before starting production with a new system is referred to as ______
commissioning
motor torque is directly related to the amount of ______ supply to the motor
current
torque control of an AC induction motor is done by controlling the applied______
current
analog input signal are normally ____ or ____ representing the range of 0 to 100%
0-10 VDC, 4-20 mA
using a 4 - 20 mA analog input and a motor that has a running speed of 1750 RPM a 12 mA signal would cause the motor to run at _____ RPM
875
the method of quickly stopping a motor by injecting a DC current into the motor windings is called
DC braking
what are the two common vfd failure symptoms
Drive does not run, Drive does not run at correct speed
the inverter section of a VFD typically uses _____ for switching to create the output PWM signal
IGBTs
most general-purpose drives use transistors or _____ and they're rectifier circuits to ramp up the current to the DC bus on power up
SCRs
the relationship of voltage and frequency in an AC induction motor is defined by the ______ ratio
Volts per Herts
____ breaking uses energy fed back from the motor when acting as a generator to assist and stopping the motor
dynamic
vector drives differ from general purpose drives because they use a ____ or _____ for feedback from the motor to control the process
encoder, resolver
the number of permanent magnets on the rotor of a servo motor is _______ to the number of poles in the stator
equal
AC servo drives compare ____ to set points to determine if the actual condition is equal to the set point
feedback
a general-purpose drive does not require any type of _____
feedback
when working on VFDs you should wait a minimum of _____ for the DC bus voltage to dissipate after powering down
five minutes
applying a DC current to the motor stator to build up the magnetic field prior to starting is referred to as
fluxing
speed of an AC induction motor can be varied by changing the number of poles or the applied ______
frequency
an SCR is a unidirectional semiconductor similar to the diode except it has a third leg called a _____ that controls when the SCR turns on
gate
name the three major categories of vfd's
general purpose, vector, servo
vector drives use special AC induction motors which can withstand _____ caused by the drive output
heating
name three sources of power failure
incoming power failure, DC bus voltage failure, I/O control power failure
the widening of a PWM signal causes the current to _____
increase
the inductive reactance of a motor increases as the frequency _____
increases
servo drives are used for ____ control which requires a high degree of precision
motion
servo motors use a feedback device to determine the rotor _____ and _____ so the controller knows which stator windings to switch on and off
position, speed
what are the three types of feedback AC servo drives use to achieve precision position, speed, and torque?
position, speed, current
the rectifier section of a vfd takes the DC bus voltage and converts it into a signal called _____
pulse-width modulation
the term used for controlling the acceleration and deceleration time is called _____
ramping
what are the four main sections of a vfd
rectifier, DC circuit, inverter, main control board
if a drive does not run at the correct speed it could be due to an incorrect or missing ____ signal
reference
the ______ is a 3 coil transformer with a rotating winding and to fix position windings feedback device mounted to the motor shaft
resolver
three common servo motor feedback devices
resolver, encoder, hall effect
to avoid running at a speed which causes high vibration most VFDs have _____ parameters
skip frequency
variable frequency drives are used to control _____ and _____ of an AC induction motor
speed, torque
a troubleshooting device used to measure a digital input is a_____
voltmeter
acceleration time is the time it takes for the drive to go from _____ to _____ speed
zero, maximum