VFD Multiple Choice Questions :-
1) VFD stands for what?
A. Very Fine Dog
B. Variable Air Volume
C. Variable Frequency Drive
D. Variable Frequency Motor
Ans: C
2) VAV stands for what?
A. Value After Vortex
B. Variable Air Volume
C. Variable Frequency Drive
D. Value After Value
Ans: B
3) The Vapor Side of a system is the
A. High Side
B. Low Side
C. Middle Side
D. Suction Line
Ans: B
4) The Liquid Side of a system is the
A. High Side
B. Low Side
C. Middle Side
D. Liquid Line
Ans: A
5) What are 2 ways of controlling valves, dampers, ect. in a commercial building?
A. Pneumatic (Missed)
B. Low Voltage
C. Electronically (Missed)
D. High Voltage
Ans: A, C
6. Low voltage units are typically designed for use with motors rated to deliver 0.2 kW or 1/4 ________ (hp) up to several megawatts.
A. Fuel oil
B. Shoe size
C. Horsepower
D. ISO/IEC 646
Ans: C
7. An embedded ________ governs the overall operation of the VFD controller.
A. Reduced instruction set computer
B. Central processing unit
C. 64-bit
D. Microprocessor
Ans: D
8. As new types of ________ switches have been introduced, these have promptly been applied to inverter circuits at all voltage and current ratings for which suitable devices are available.
A. Condensed matter physics
B. Quantum mechanics
C. Physics
D. Semiconductor
Ans: D
9. The main microprocessor programming is in ________ that is inaccessible to the VFD user.
A. BIOS
B. Read-only memory
C. Firmware
D. Operating system
Ans: C
10. Introduced in the 1980s, the ________ (IGBT) became the device used in most VFD inverter circuits in the first decade of the 21st century.
A. Insulated-gate bipolar transistor
B. Bipolar junction transistor
C. Power MOSFET
D. Power semiconductor device
Ans: A
11. Much of the same logic contained in large, powerful VFDs is also embedded in small ________ such as those commonly used in computer fans.
A. Electronic speed control
B. Brushless DC electric motor
C. Induction motor
D. Electric motor
Ans: B
12. In addition to this simple volts per hertz control more advanced control methods such as vector control and ________ (DTC) exist.
A. Electrical generator
B. Linear motor
C. Direct torque control
D. Electric motor
Ans: C
13. This starting method typically allows a motor to develop 150% of its rated ________ while the VFD is drawing less than 50% of its rated current from the mains in the low speed range.
A. Torque
B. Energy
C. Force
D. Angular momentum
Ans: A
14. Thus the ________ of volts per hertz must be regulated to a constant value (460/60 = 7.67 V/Hz in this case).
A. Percentage
B. Divisor
C. Ratio
D. Reason
Ans: C
15. A small amount of braking torque is available to help ________ the load a little faster than it would stop if the motor were simply switched off and allowed to coast.
A. Acceleration
B. Kinematics
C. Speed
D. Force
Ans: A
16. Variable Frequency Drives work with which of the following motors?
A. Single-Phase AC Motors
B. Three-Phase AC Motors
C. DC Motors
D. B and C are correct but not A.
E. A, B and C are all correct.
Ans: B
17. The setting for the speed of a VFD is known as which of the following:
A. Setpoint
B. Control Point
C. Reference
D. Speed Point
E. All of the above are common names for the speed setting.
Ans: C
18. Assuming no friction losses, if a VFD is operating a fan at 30Hz, ½ the full speed, which
of the following is the correct power consumption?
A. 50% power consumption
B. 33% power consumption
C. 25% power consumption
D. 12.5% power consumption
E. 6.7% power consumption
Ans: D
19. Limits are very important for a VFD operating a fan. Which of the following are the most commonly used limits for a fan?
A. 18Hz Minimum speed; 60Hz Maximum speed
B. 6Hz Minimum speed; 60Hz Maximum speed
C. 18Hz Minimum speed; 90Hz Maximum speed
D. 6Hz Minimum speed; 90Hz Maximum speed
E. 0Hz Minimum speed; 120Hz Maximum speed
Ans: B
20. Inside the VFD, acceleration, is also known as which of the following:
A. Increase Speed
B. Increase Setpoint
C. Speed UP
D. Run-Up
E. Ramp-Up
Ans: E
VFD Objective Questions Pdf Free Download ::
21. One external switch is attached to the VFD. This switch is for starting and stopping the VFD. A potentiometer is also wired to the VFD and it changes the speed of the motor. This type of control arrangement is known as which of the following?
A. Local or Hand Control
B. Remote Control
C. Cascade Control
D. Master/Slave Control
E. Closed Loop Control
Ans: B
22. If an RS-485 connection is wired between a VFD and a DDC controller, this control arrangement is known as which of the following:
A. Remote Control
B. Closed Loop Control
C. Master/Slave Control
D. Cascade Control
E. Serial Communications
Ans: E
23. If a single VFD operates 3 motors, which of the following must be remembered?
A. It must be connected in a Master/Slave arrangement.
B. The VFD must use a Cascade Controller Card.
C. An RS-485 connection must be made between the VFD and motors.
D. Each of the 3 motors must have overload protection.
E. All of the above are required.
Ans: D
24. A fan, using a VFD, is described as a Closed Loop control arrangement. Which of the following must always be programmed in the VFD?
A. A sensor must be wired to the VFD monitoring the feedback signal.
B. The VFD must be given a setpoint.
C. A Derivative setting must always be programmed.
D. A and B are correct but not C.
E. All three answers, A, B and C are correct.
Ans: D
25. Multiple pumps are to be operated together to maintain the correct pressure in a hot water supply. When the demand increases beyond the capacity of the initial pump, which uses a VFD, separate fixed stages are enabled to start additional pumps. This control arrangement is referred to as which of the following:
A. Multi Motor Control
B. Master/Slave Control
C. Cascade Control
D. Serial Communications
E. Open Loop Control
Ans: C
26. If you are controlling the VFD from the keypad mounted 3m (10feet) away, this control arrangement is known as which of the following?
A) Local/ Hand Control
B) Remote/ Auto Control
C) Serial Control
D) Cascade Control
E) Closed Loop Control
Ans: A
27. A single VFD operates 3 fan motors, which of the following must be remembered?
A. It must be connected in a Master/Slave arrangement.
B. The VFD must use a Cascade Controller card.
C. An RS-485 connection must be made between the VFD and fans.
D. Each of the 3 fans must have overload protection.
E. All of the above are required.
Ans: D
28. Multiple pumps are to be operated together to maintain the correct pressure in a hot water supply. When the demand increases beyond the capacity of the initial pump, which uses a VFD, separate fixed stages are enabled to start additional pumps. This control arrangement is referred to as which of the following:
A. Multi Motor Control
B. Master/Slave Control
C. Cascade Control
D. Serial Communications
E. Open Loop Control
Ans: C
29. On a Closed Loop system using a VFD, the output starts to oscillate between minimum and maximum speed. Which of the following might correct the problem?
A. Increase Proportional Gain
B. Decrease Proportional Gain
C. Make Action Normal
D. Make Action Inverse
E. Turn Derivative
Ans: B
30. Which of the following control arrangements are identified by one VFD sending a 4-20mA signal out its AO (Analog output) to the AI (Analog Input) of the other VFD?
A) Local/ Hand Control
B) Remote/ Auto Control
C) Master/Slave
D) Serial Comm.
E) Multi-motor with Cascade Controller card.
Ans: C
31. A pressure transmitter is wired directly to a VFD and a DDC Controller from a BAS system only starts and stops the VFD. Which of the following is the correct connection?
A) An AO on the Controller is wired to an AI of the VFD.
B) An AI on the Controller is wired to an AO of the VFD.
C) A DI on the Controller is wired to a DO of the VFD.
D) An AI on the Controller is wired to an DO of the VFD.
E) A DO on the Controller is wired to a DI of the VFD.
Ans: E
32. A pressure transmitter (4-20mA) is needed to monitor the feedback going to a VFD, which is programmed for Closed Loop. To which of the following VFD control wire connections should the transmitter be attached for proper operation?
A. Analog Input
B. Digital Input
C. Analog/Digital Output
D. Relay Output
E. Both C and D are correct
Ans: A
33. A light is used to indicate when the VFD goes into an alarm condition. To which of the following VFD control wire connections should a 120Vac light be attached.
A. Analog Input
B. Digital Input
C. Analog/Digital Output
D. Relay Output
E. Both C and D are correct
Ans: D
34. Three VFDs are operating via Serial Communications with a Local Area DDC Controller. How many wire connections are needed on the VFD for serial communications?
A. 2 wire
B. 4 wire
C. 9 wire
D. 10 wire
E. It depends on how much information is desired between the VFDs and DDC Controller.
Ans: A
35. When discussing if a drive is 6,12 or 18 Pulse, which part of the drive is being discussed?
A. Inverter
B. DC Link
C. Rectifier
D. RFI Filter
E. Transmitter
Ans: C
36. Banks of large capacitors are the most prominent in which of the following parts of a drive?
A. Inverter
B. DC Link
C. Rectifier
D. RFI Filter
E. Transmitter
Ans: B
37. The main function of which of the following parts of an VFD is to change a high DC voltage into a pulsed AC voltage.
A. Inverter
B. DC Link
C. Rectifier
D. RFI Filter
E. Transmitter
Ans: A
38. If 480Vac is the incoming power to the VFD, which of the following is the expected voltage at the DC Link?
A. 240Vdc
B. 312Vdc
C. 480Vdc
D. 648Vdc
E. 800Vdc
Ans: D
39. IGBTs are found in which part of the drive?
A. Inverter
B. DC Link
C. Rectifier
D. RFI Filter
E. Transmitter
Ans: A
40. What type of application curve must be used inside a VFD to operate these Cooling Tower Fans correctly?
A) Constant Torque
B) Variable Torque
C) Constant Power
D) Variable Power
Ans: B