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