Chapter 10 Homework
PLC timers
are output instructions and provide the same function as electromechanical timing relays
The receiver of a 4 to 20 mA current loop
interprets and reacts to the 4-20 mA signal
Which of the following PLC timers would is used to delay the start of a machine process?
on delay timer
Which of the following would not be considered a VFD program parameter?
Type of enclosure
Inverter outputs can be classified as
all of these
__________ is the ability of a VFD to increase or decrease the voltage and frequency to an AC motor gradually.
ramping
VFDs cannot operate as motor protection devices along with their role of motor speed controllers.
f
Which of the following motor nameplate data may be programmed into a VFD?
All of these
PLCs were originally designed as replacements
relay control panels
Derating may be required when a drive is installed at high altitude.
t
Flux vector control is popular for applications that need better speed regulation and/or optimum torque, especially at lower frequencies.
t
The DC Bus voltage is calculated by taking the RMS value of the line voltage and multiplying it by
1.414
A 4-20 mA transmitter has an input range of 0-200 °F. If the loop current is 12 mA the temperature indicated would be
100 f
Which of the following VFD braking systems redirects energy back to the AC supply?
Regenerative braking
Which of the following types of program parameters can be change or adjusted while the drive is running or stopped?
Tunable on the fly
The power source of a 4 to 20 mA current loop
powers the transmitter
A motor attached encoder device may be used to provide feedback on the motors
all of these
An adjustable speed drive may be used to control _______ of a motor
all of these
Low frequency voltage boost
all of these
PLC input modules
all of these
Which of the following devices would be considered to be digital in nature?
all of these
Which of the following should be taken into consideration when determining the location for a VFD?
all of these
A flux vector drive controls the ________of the magnetic flux in an AC induction
direction and magnitude wrong- sspeed and direction
The speed of a DC motor is ________________ proportional to the armature voltage and _____________ proportional to the field current.
directly, inversely
A variable frequency drive cannot be used to operate a 3-phase motor from a single-phase AC supply.
f
Analog signals are represented by two distinct amplitudes.
f
The addressing format used for PLCs is the same for all manufacturers.
f
VFDs are not required to have a disconnecting means capable of disconnecting all power supplied to the drive.
f
VFDs increase motor speed in steps.
f
Non-configurable alarms can be enabled or disabled by the operator.
false
The programming device must always be connected to the PLC to run the program.
false
For an input module, where is the problem most likely to reside, if the status indicator and ladder instructions agree, but not with the sensor condition?
field device or wiring
A VFD reactor is basically an ___________ installed on the input or output of the drive.
inductor
Flux vector VFDs are classified as ________ types
open loop or closed loop
The transmitter of a 4 to 20 mA current loop
converts the signal into 4- 20 mA
An open loop VFD operates without benefit of any feedback signals.
true
Most manufacturers require that a shielded power cable be used for the electrical connection between the VFD and the motor.
true
PLCs are the most widely used process control technology.
true
Programming parameters associated with DC drives are like those associated with AC drives.
true
Sensorless open-loop vector control involves calculating an estimate of the motor's magnetic flux and torque based on the measured value of __________of the motor.
voltage and current
Use of which of the following will increase the distance that the motor can be located from the drive?
load reactor
The central processing unit or processor of a PLC
looks at the inputs, makes the decision provided by the program, and sets the status of the outputs
From a safety standpoint, only ____________ pushbuttons should utilized for motor stop buttons.
normally closed
Which of the following DC drive parameter sets the time it takes to change speeds from one setting to another?
Acceleration time
The ___________ of a variable frequency drive acts to filter out any AC.
DC Bus circuit
An inverter is used to convert current from
DC to AC
Which of the following changes state whenever the accumulated value of the PLC timer reaches the preset value?
Enable bit
Which of the following VFD refinements compensates for power losses that occur at low speeds?
Low frequency voltage boost
Which of the following is not a function of the PLC programming device?
To run the user program
A PID controller in a VFD automatically corrects the error between the actual motor speed and the desired set point speed by calculating the __________ between the two and then outputting a corrective action.
difference
A free-wheeling __________ is connected across and IGBT to protect the transistor by conducting current when it turns off.
diode
For an input module, where is the problem most likely to reside, if the status indicator and sensor condition agree, but not with the ladder instructions?
input module
The ___________-duty motor is designed for optimized performance to operate in conjunction with a VFD.
inverter
Excessive energy is generated when the __________ drives the motor during deceleration.
load
The power supply required to operate the PLC processor and I/O modules units is
low-voltage dc
The sensor of a 4 to 20 mA current loop
measures the value of the process variable
For an output module, where is the problem most likely to reside, if the field device condition and status indicator agree but the output instruction does not?
output module
An overhauling load
results in generator action and occurs whenever the inertia of the load is more than that of the motor rotor.
To change the direction of rotation of a DC motor you
reverse either the armature or field polarity
A 4-20 mA current loop is more immune to noise than a 0-10 V signal.
t
A speed control potentiometer would be classified as an analog input.
t
A watchdog timer is used to monitor the scan process of a PLC.
t
Derating a VFD means using a larger than normal drive in the application.
t
In addition to the safety aspect, proper grounding of a VFD system reduces electromagnetic interference.
t
PLC output modules convert signals from the CPU that are used to control output field devices.
t
The Relay Ladder Logic (RLL) programming language is based on electromagnetic relay control.
t
The flux vector method of VFD speed control provides more precise control of motor speed and torque.
t
The inverter circuit of a VFD acts to switch the DC Bus voltage on and off at specific intervals.
t
The load characteristics of the driven machinery must be taken into consideration when selecting a variable frequency drive for a particular application.
t
The term hard-wired refers to logic control functions that are determined by the way the devices are interconnected.
t
Tuning the PID controller involves gain and time adjustments.
t
With VFD speed control the voltage to the motor must be decreased as the frequency is decreased to prevent overheating of the motor.
t
