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Wednesday, 9 September 2015

VFD(Variable Frequency Drive) Multiple Choice Questions And Answers

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

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