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Bartleby Sitemap - Textbook Solutions

All Textbook Solutions for Understanding Motor Controls

Refer to the circuit shown in Figure 3311. You are to construct this circuit on the job. Would it be possible to use an 11 pin control relay for 4CR?1RQ 2RQ 3RQ 4RQ 5RQ 6RQ 7RQ When using a mechanical clutch, what determines how fast a load can be accelerated and the amount of initial torque applied to the load?What is the primary advantage of an eddy current clutch over a mechanical clutch? How is the speed of an eddy current clutch controlled?1RQ Why is this component used instead of a diode?What is a freewheeling or kickback diode?Name two methods of sensing the current flow through the shunt field. 5RQ What unit controls the voltage applied to the armature?What device is often used to sense motor speed? 8RQ 1RQ 2RQ If an alternator is used to provide variable frequency, how is the output voltage of the alternator controlled?What solid-state device is generally used to produce variable frequency in drives designed to control motors up to 500 HP?Why are SCRs used to construct a bridge rectifier in many solid-state variable frequency drives?What is the main disadvantage of using SCRs in a variable frequency drive? How are junction transistors driven into saturation and what is the advantage of driving a transistor into saturation? What is the disadvantage of driving a junction transistor into saturation? 9RQ In variable frequency drives that employ IGBTs, how is the output voltage to the motor controlled? What type of motor is generally used with IGBT drives? 12RQ What is a thyristor?After an SCR has been turned on, what must be done to permit it to turn off again?15RQ 1RQ 2RQ A ¾ HP, single-phase squirrel cage motor is connected to 240-volt AC line. What is the full load current rating of this motor and what is the minimum size NEMA and IEC starters that should be used? 4RQ A 125 HP, synchronous motor is connected to a 230-volt, three phase AC line. The motor is intended to operate at 80 percent power factor. What is the full load running current of this motor? What is the minimum size NEMA and IEC starters that should be used to connect this motor to the line?6RQ 7RQ 8RQ 9RQ 10RQ 11RQ 12RQ If dual-element time delay fuses are to be used as the short circuit protective device, what size fuses should be used to protect the circuit in question #12? Five 5 HP, three-phase motors with NEMA code B are connected to a 240-volt line. The conductors are copper with type THWN insulation. What size conductor should be used to supply all of these motors? A 75 HP, three-phase squirrel cage induction motor is connected to 480 volts. The motor has a NEMA code D. What is the starting current for this motor?A 20 HP, three-phase squirrel cage induction motor has a NEMA code E. The motor is connected to 208 volts. What is the starting current for this motor? What industry first started using programmable logic controllers?Name two differences between PLCs and common home or business computers.Name the four basic sections of a programmable logic controller. 4RQ What device is used to program a PLC? What device separates the central processing unit from the outside world?What is opto-isolation? 8RQ 9RQ 10RQ What is the purpose of the key switch located on the front of the CPU in many programmable logic controllers? What is a software switch? Why are NEMA symbols such as push buttons, float switches, or limit switches not used in programmable logic controller schematics?2RQ Why are normally closed components such as STOP push buttons programmed normally open instead of normally closed when entering a program into the memory of a PLC?4RQ 5RQ List four basic rules for developing a program for a PLC.A PLC requires that times be programmed in 0.1-second intervals. What number should be entered to produce a time delay of 3 minutes?When programming in Boolean, what statement should be used to connect components in series?When programming in Boolean, what statement should be used to connect components in parallel?In a control circuit, it is imperative that a coil energize before another one. How can this be done when entering a program into the memory of the PLC?What is the function of a watchdog timer? Explain the difference between digital inputs and analog inputs. Why should signal wire runs be kept as short as possible? When signal wiring must cross power wiring, how should the wires be crossed? Why is shielded wire used for signal runs?What is the brute-force method of grounding?Explain the operation of the differential amplifier.To answer the following questions refer to the circuit in Figure 416. The pressure switch is shown as: a. Normally open b. Normally closed c. Normally open held closed d. Normally closed held open To answer the following questions refer to the circuit in Figure 416. When the pressure switch closes, which starter will energize first, 1M or 2M? Explain your answer.3RQ To answer the following questions refer to the circuit in Figure 416. What is the purpose of timer TR in this circuit?To answer the following questions refer to the circuit in Figure 416. What is the purpose of the rotary switch connected after the pressure switch?6RQ To answer the following questions refer to the circuit shown in Figure 41–10. Assume that the third speed push button is pressed. Explain the sequence of operation for the circuit. To answer the following questions refer to the circuit shown in Figure 4110. Assume that the third speed push button is pressed and the motor starts in its first or lowest speed. After a delay of 3 seconds, the motor accelerates to its second speed, but never accelerates to its highest or third speed. Which of the following could cause this problem? a. CR coil is open. b. Coil 2TR is open. c. Coil 1TR is open. d. Coil 1S is open.9RQ 10RQ To answer the following questions refer to the circuit shown in Figure 4114. Temperature switch TS1 is shown as: a. Normally open b. Normally closed c. Normally open held closed d. Normally closed held open 12RQ Is timer TR an on-delay or off-delay timer? 14RQ To answer the following questions refer to the circuit shown in Figure 41–14. Assume that contact TS1 closes and the air injection blower motor starts operating, but the high-pressure pump motor does not start. What could cause this problem? Temperature switch TS3 is open. Coil 2M is open. Flow switch FL1 is defective and did not close. Coil TR is open. What are the three main electrical test instruments used in troubleshooting? What is the advantage of a plunger type voltage tester?A motor is tripping out on overload. The motor nameplate reveals a full load current of 68 amperes. When the motor is operating under load, an ammeter indicates the following: Phase #1 = 106 amperes, Phase #2 = 104 amperes, and Phase #3 = 105 amperes. What is the most likely problem with this motor?A motor is tripping out on overload. The motor nameplate reveals a full load current of 168 amperes. When the motor is operating under load, an ammeter indicates the following: Phase #1 = 166 amperes, Phase #2 = 164 amperes, and Phase #3 = 225 amperes. What is the most likely problem with this motor? 5RQ Refer to the circuit shown in Figure 42–17. Assume that the motor is running in the forward direction. When the revers e push button is pressed, the motor continues to run in the forward direction. Which of the following could cause this problem? The normally open side of the reverse push button is not making a complete circuit when pressed. R contactor coil is open. The normally closed side of the reverse push button is not breaking the circuit when the reverse push button is pressed. There is nothing wrong with the circuit. The stop push button must be pressed before the motor will stop running in the forward direction and permit the motor to be reversed. 7RQ Refer to the circuit shown in Figure 4221. Assume that the THIRD SPEED push button is pressed. The motor starts in second speed, skipping first speed. After 5 seconds, the motor accelerates to third speed. Which of the following could cause this problem? a. S1 contactor coil is open. b. CR1 contactor coil is open. c. TRl timer coil is open. d. S1 load contacts are shorted.9RQ Refer to the circuit shown in Figure 42–21. Assume that a fused jumper is connected across terminals 1 and 3 of TR2 timer. What would happen if the jumper were left in place and the FIRST SPEED push button pressed? The motor would start in its lowest speed and progress to second speed, but never increase to third speed. The motor would start operating immediately in third speed. The motor would not start. The motor would start in second speed and then increase to third speed. 11RQ 12RQ What are the disadvantages of low-speed, directly coupled induction motors?2RQ What three alignment checks should be made to ensure satisfactory and long service for directly coupled and belt-coupled power transmissions?4RQ Induction motors should not be used below a certain speed rpm. What is this speed?What is the primary reason for using a pulley drive?How tightly should V-belts be adjusted?Refer to Figure 436 and assume the motor is to rotate in the opposite direction. How can the belt slack be maintained on top?A machine delivered for installation has a 2-inch pulley on the motor and a 6-inch pulley on the load. The motor nameplate reads 180 rpm. At what speed in rpm will the driven machine rotate? 1RQ The atoms of a material used as an insulator generally contain ___________ valence electrons. The two materials most often used to produce semiconductor devices are ____________ and ____________. 4RQ 5RQ How is an N-type material made?Which type of semiconductor material can withstand the greatest amount of heat? All electronic components are formed from P-type and N-type materials. What factors determine the kind of components formed?1RQ Draw the schematic symbol for a diode. 3RQ Explain the difference between the conventional current flow theory and the electron flow theory. 5RQ Explain how to test a diode with an ohmmeter. How is a zener diode connected in a circuit as compared to a common junction diode? What is the primary use of a zener diode?A 5.1-volt zener diode is to be connected to an 8-volt power source. The current must be limited to 50 milliamperes. What value of current-limiting resistor must be connected in series with the zener diode?4RQ In a zener diode circuit, the current-limiting resistor limits the total circuit current to 150 milliamperes. If the load circuit is drawing a current of 90 milliamperes, how much current is flowing through the zener diode?1RQ 2RQ What is the average forward voltage drop of LED? What does the arrow pointing away from a diode symbol indicate? 5RQ When used as a photovoltaic device, how much voltage is generally produced by a photodiode?When used as a photovoltaic device, how much voltage is generally produced by a photodiode?1RQ Explain how to test an NPN transistor with an ohmmeter.Explain how to test a PNP transistor with an ohmmeter. What polarity must be connected to the collector, base, and emitter of an NPN to make it forward biased? What polarity must be connected to the collector, base, and emitter of a PNP transistor to make it forward biased? Explain the difference between an analog device and a digital device. 1RQ How many layers of semiconductor material are used to construct a UJT?Briefly explain the operation of the UJT.Draw the schematic symbol for the UJT.5RQ 1RQ 2RQ 3RQ How many layers of semiconductor material are used to construct an SCR? SCRs are members of a family of devices known as thyristors. What is a thyristor? Briefly explain why thyristors have the ability to control large amounts of power. What is the average voltage drop of an SCR when it is turned on?Explain why an SCR must be phase shifted.1RQ Draw the two schematic symbols used to represent the diac.3RQ When a diac first turns on, does the voltage drop, remain at the same level, or increase to a higher level?1RQ 2RQ Which family of devices does the triac belong to?Briefly explain why a triac must be phase shifted. What electronic component is frequently used to phase shift the triac?6RQ 1RQ 2RQ 3RQ 4RQ 5RQ 6RQ 7RQ 8RQ 9RQ 10RQ 1RQ 2RQ 3RQ 4RQ 5RQ 6RQ Name two effects of negative feedback.Refer to Figure 548. If resistor R1 is 200 ohms and resistor R2 is 10 kilohms, what is the gain of the amplifier? Figure 548 Noninverting amplifier connection.Refer to Figure 54–9. If resistor R1 is 470 ohms and resistor R2 is 47 kilohms, what is the gain of the amplifier? Figure 54-9 Inverting amplifier connection. What is the purpose of the hysteresis loop when the op amp is used as an oscillator?

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