Bartleby Sitemap - Textbook Solutions

All Textbook Solutions for Understanding Motor Controls

When installing a motor control system, list four major factors to consider concerning the power system. 2RQIs the National Electrical Code a law?Explain the difference between manual control, semiautomatic control, and automatic control. 5RQExplain the difference between jogging and inching.7RQWhat agency requires employers to provide a workplace free of recognized hazards for its employees?What is meant by the term ramping? What is the most important function of any control system?1RQThe symbol shown is: Normally closed float switch Normally open held closed float switch Normally open float switch Normally closed held open float switch The symbol shown is: a. Iron core transformer b. Auto transformer c. Current transformer d. Air core transformerThe symbol shown is: Normally open pressure switch Normally open flow switch Normally open float switch Normally open temperature switch The symbol shown is: a. Double acting push button b. Two-position selector switch c. Three-position selector switch d. Maintained contact push buttonIf you were installing the circuit in Figure 233, what type of push button would you use for the silence button? a. Normally closed b. Normally openReferring to the circuit in Figure 2–33, should the float switch be connected as a normally open or normally closed switch? 8RQ9RQWhen reading a schematic diagram, are the control components shown as they should be when the machine is turned off or de-energized, or are they shown as they should be when the machine is in operation?A manual motor starter controls a single phase 120 volt motor. The motor is not running, and theswitch handle on the starter is found to be in thecenter position. What does this indicate?2RQ3RQA push button manual starter has tripped on overload. Explain how to reset the starter so themotor can be restarted.What is meant by the term line voltage on some pilot sensing devices? Explain the difference between manual motor starters that provide low voltage release and those that do not. 7RQ8RQRefer to the circuit shown in Figure 310. When would the amber pilot light be turned on? a. When the manual/automatic switch is set in themanual position. b. When the float switch contacts are closed. c. Anytime the manual starter is turned on. d. Only when the manual/automatic switch is setin the manual position.10RQ1RQ2RQ3RQ4RQWhy is it necessary to permit a solder melting type of overload relay to cool for two to three minutes after it has tripped? 6RQ7RQ8RQHow many overload sensors are required by the National Electrical Code to protect a direct current motor?A large motor has a full load current rating of 425 amperes. Current transformers with a ratio of 600:5 are used to reduce the current to the overload heaters. What should be the full load current rating of the overload heaters? 1RQ2RQExplain the difference between auxiliary contacts and load contacts. 4RQWhat is optoisolation and what is its main advantage?What pin numbers are connected to the coil of an 8-pin control relay? An 11-pin control relay contains three sets of single-pole double throw contacts. List the pin numbers by pairs that can be used as normally open contacts. What is the purpose of the shading coil? Refer to the circuit shown in Figure 5-29. Is the thermostat contact normally open, normally closed, normally closed held open, or normally open held closed? Figure 5-29 The contactor contains both load and auxiliary contacts. What is the difference between a motor starter and a contactor? A 150-horsepower motor is to be installed on a 480-volt three-phase line. What is the minimum size NEMA starter that should be used for this installation?What is the minimum size IEC starter rated for the motor described in question 11? When energizing or de-energizing a combination starter what safety precaution should always be taken?14RQRefer to the circuit shown in Figure 5-29. In this circuit, the HR contactor is equipped with five contacts. Three are load contacts and two are auxiliary contacts. From looking at the schematic diagram, how is it possible to identify which contacts are the load contacts and which are the auxiliary contacts? Figure 5-29 The contactor contains both load and auxiliary contacts.What is the operating voltage of most magnetic control systems?How many primary windings do control transformers have?3RQ4RQWhy are two of the primary leads crossed control transformer? Refer to the circuit shown in Figure 7-10. If wire number 11 were disconnected at the normally open auxiliary M contact, how would the circuit operate? Figure 7-10 Numbers are placed beside all components.Assume that when the START button is pressed M starter does not energize. List seven possible causes for this problem. a. _____________ b. _____________ c. _____________ d. _____________ e. _____________ f. _____________ Explain the difference between a motor starter and a contactor. Refer to the schematic in Figure 7-10. Assume that when the START button is pressed, the control transformer fuse blows. What is the most likely cause of this trouble? Figure 7-10 Numbers are placed beside all components. Explain the difference between load and auxiliary contacts.6RQIn a schematic diagram, what does a dashed line drawn between two components indicate?1RQ2RQThe two STOP push buttons in Figure 8–2 are connected in series with each other. What would be the action of the circuit if they were to be connected in parallel as shown in Figure 8–6? 4RQFollowing the procedure discussed in Chapter 7, place wire numbers on the schematic in Figure 8–7. Place corresponding wire numbers on the components shown in Figure 8–8. 1RQWhat is interlocking?Referring to the schematic shown in Figure 97, how would the circuit operate if the normally closed R contact connected in series with F coil were to be connected normally open?What would be the danger, if any, if the circuit were to be wired as stated in question 3? 5RQAssume that the circuit shown in Figure 97 were to be connected as shown in Figure 914. In what way would the operation of the circuit be different, if at all? Explain the difference between inching and jogging. What is the main purpose of jogging?Refer to the circuit shown in Figure 108. In this circuit, the jog button has been connected incorrectly. The normally closed section has been connected in parallel with the run push button and the normally open section has been connected in series with the holding contacts. Explain how this circuit operates.Refer to the circuit shown in Figure 109. In this circuit the jog push button has again been connected incorrectly. The normally closed section of the button has been connected in series with the normally open run push button and the normally open section of the jog button is connecting in parallel with the holding contacts. Explain how this circuit operates. What are the two basic classifications of timers? Explain the operation of an on-delay relay. 3RQ4RQHow are pneumatic timers adjusted? Name two methods used by electronic timers to obtain their time base. What is the purpose of sequence control?2RQAssume that all three motors shown in Figure 12–14 are running. Now assume that the STOP button is pressed and motors #1 and #2 stop running, but motor #3 continues to operate. Which of the following could cause this problem? STOP button is shorted. The 2M contact between wire numbers 31 and 32 is hung closed. The 3M load contacts are welded shut. The normally open 3M contact between wire numbers 23 and 31 is hung closed. Referring to Figure 1214, assume that the normally open 2M contact located between wire numbers 23 and 29 is welded closed. Also assume that none of the motors are running. What would happen if: a. The number 2 push button was to be pressed before the number 1 push button? b. The number 1 push button was to be pressed first?5RQ What type of pressure switch is generally used to sense small changes in low pressure systems? 2RQ A pressure switch is to be installed on a system with pressures that can range from 1500 PSI to 1800 PSI. What type of pressure switch should be used? A pressure switch is to be installed in a circuit that requires it to have three normally open contacts and one normally closed contact. The switch actually has one normally open Contact What must be done to permit this pressure switch to operate in this circuit? What is a piezoresistor? 6RQ7RQWhen using a rod type float switch, how is the amount float movement required to open or close the contacts adjusted?What type of float switch does not have a differential setting? What is the advantage of the bubbler type system for sensing liquid level?4RQAssume that a pipe has an inside diameter of 1 square inch. How much air pressure would be required to bubble air through 25 feet of water? What is the common name for an air flow switch?What type of switch is contained on most flow switches? Refer to the circuit shown in Figure 15-2. Why is there an overload contact symbol shown in series with the compressor contactor but not the condenser fan contactor or evaporator fan contactor? Refer to the circuit shown in Figure 15-6. The STOP button is shown to be an emergency STOP button. What does the symbol used for the STOP button actually represent? Refer to the circuit shown in Figure 15-6. If an overload should occur on the compressor motor and the overload contact open, would it affect the operation of the lube oil pump?Refer to the circuit shown in Figure 15-6. If the circuit is in operation and an overload should occur on the lube oil pump and the overload contact open, would it affect the operation of the compressor? 7RQWhat is the primary use of a limit switch?Why are the contacts of a micro switch spring loaded?Refer to the circuit shown in Figure 16-11. Assume that the platform is located on the bottom floor. When the UP push button is pressed the pump motor does not start. Which of the following could not cause this problem? The contacts of limit switch LS1 are open. The contacts of limit switch LS2 are open. Motor starter coil M is open. The overload contact is open. Refer to the circuit shown in Figure 16-11. Assume that the platform is located on the lower floor. When the UP push button is pressed, the platform rises. When the platform reaches the upper floor, however, the pump does not turn off but continues to run until the overload relay opens the overload contacts. Which of the following could cause this problem? a. The solenoid valve opened when limit switch LS1 opened. b. The UP push button is shorted. c. Limit switch LS1 did not open its contacts. d. Limit switch LS2 contacts did not reclose when the platform began to rise.5RQShould a metal bar be heated or cooled to make it expand? What type of metal remains in a liquid state at room temperature? How is a bimetal strip made?Why are bimetal strips often formed into a spiral shape?Why should electrical contacts never be permitted to open or close slowly?What two factors determine the amount of voltage produced by a thermocouple?What is a thermopile?What do the letters RTD stand for? What type of wire is used to make an RTD?What material is a thermistor made of? Why is it difficult to measure temperature with a thermistor? If the temperature of a NTC thermistor increases, will its resistance increase or decrease?How can a silicon diode be made to measure temperature? Assume that a silicon diode is being used as a temperature detector. If its temperature increases, will its voltage drop increase or decrease? What type of chemical is used to cause a pressure change in a bellows type thermostat? What material was used to make the first Hall generator?What two factors determine the polarity of the output voltage produced by the Hall generator? What two factors determine the amount of voltage produced by the Hall generator? What is a reluctor? Why does a magnetic field not have to be moving or changing to produce an output voltage in the Hall generator?What is the function of a proximity detector? What is the basic principle of operation used with proximity detectors designed to detect ferrous type metals only? What is an oscillator?What is the basic operating principle of operation used with proximity detectors designed to detect all types of metal?What type of electric circuit is used to increase the sensitivity of a metal detecting proximity detector? Name two types of proximity detectors used to detect objects that are not made of metal.What is the maximum range at which most capacitive proximity detectors can be used to sense an object? How is it possible for an ultrasonic proximity detector to measure the distance to an object?List the three major categories of photodetectors. In which category does the solar cell belong? In which category do phototransistors and photodiodes belong? 4RQ5RQ6RQWhat is the advantage of a photodetector that uses a reflector to operate? An object is to be detected by reflecting light off a shiny surface. If the transmitter is mounted at a 60-degree angle, at what angle must the receiver be mounted?How much voltage is produced by a silicon solar cell?What determines the amount of current a solar cell can produce?11RQRefer to the circuit in Figure 2020. Assume that the door is being raised and something breaks the light beam. Will this cause the door to stop moving?13RQRefer to Figure 21–1 to answer the following questions. When switch HOA SW 122 is in the off position, which contacts have connection between them? Refer to Figure 211 to answer the following questions. How much voltage will be applied to coil 1CR when it is energized?Refer to Figure 211 to answer the following questions. Referring to switch (RS SW 123), in what position must the switch be set to make connection between terminals 3 and 4?4RQ5RQ6RQ7RQRefer to Figure 21–1 to answer the following questions. Assume that HOA SW 120 has been set in the auto position. List four ways by which coil CR-8 could be energized. Refer to Figure 21–1 to answer the following questions. In what position must switch SW 123 be set to make connection between terminals 3 and 4? 10RQ1RQWhen connecting a control system, what should be done each time a wire termination is made to any component?What should be done to each component to help identify it? What is the disadvantage of wiring components to a terminal strip? What is the main advantage of making connections at a terminal strip?Refer to the circuit shown in Figure 221. Should float switch FS2 be wired as normally open or normally closed? Explain your answer. Figure 221 Pump control circuit.What does the dashed line between the two float switch contacts labeled FS1 indicate? How is across-the-line starting accomplished?2RQ3RQ4RQ5RQ1RQWhat advantage does a reactor have when limiting in-rush current that is not available with a resistor?Refer to the circuit shown in Figure 241. Assume that timer TR is set for a delay of 10 seconds. When the START button is pressed, the motor starts in low speed. After a delay of 30 seconds the motor is still in its lowest speed and has not accelerated to normal speed. Which of the following could not cause this condition? a. The START button is shorted. b. Timer coil TR is open. c. Contactor coil R is open. d. Timed contact TR did not close after a delay of 10 seconds.4RQ5RQ1RQExplain the differences between open and closed transition starting.3RQRefer to the circuit shown in Figure 252. Assume that timer TR is set for a time delay of 10 seconds. When the START button is pressed, the motor does not start. After a period of 10 seconds, the motor starts with full line voltage applied to it. Which of the following could cause this condition? a. Timer TR coil is open. b. CR coil is open. c. Contactor S coil is open. d. Contactor R coil is open.5RQ6RQ7RQRefer to the circuit shown in Figure 255. Explain the steps necessary for coil S2 to energize.9RQRefer to the circuit shown in Figure 25–5. Assume that timer TR1 is set for a delay of 10 seconds and timer TR2 is set for a delay of 5 seconds. When the START button is pressed, the motor starts. After 10 seconds the S1 contacts open and the motor continues to accelerate, but never reaches full speed. After a delay of about 30 seconds, the motor trips out on overload. Which of the following could cause this problem? TR1 coil is open. S2 coil is open. S1 coil is open. R coil is open. Name two requirements that must be met before a motor can be used for wye-delta starting.2RQ3RQRefer to the circuit shown in Figure 26–9. Assume that timer TR is set for a delay of 10 seconds. When the START button is pressed, the motor starts with its windings connected in wye. After a period of 1 minute, the motor has not changed from wye to delta. Which of the following could cause this condition? TR timer coil is open. S contactor coil is open. 1M starter coil is open. The control transformer fuse is blown. Refer to the circuit shown in Figure 269. Assume that timer TR is set for a delay of 10 seconds. When the START button is pressed, the motor does not start. After a delay of 10 seconds, the motor suddenly starts with its stator windings connected in delta. Which of the following could cause this problem? a. TR timer coil is open. b. 2M contactor coil is open. c. S contactor coil is open. d. 1M starter coil is open.6RQThe motor nameplate of a wye-delta started motor has a full load current of 287 amperes. What current rating should be used to determine the proper overload heater size? 8RQRefer to the circuit shown in Figure 2614. What is the purpose of timer TR2?Refer to the circuit shown in Figure 2614. When the START button is pressed, the control transformer fuse blows immediately. Which of the following could not cause this problem? a. Control relay coil CR is shorted. b. Starter coil 1M is shorted. c. Contactor coil S is shorted. d. Contactor coil 2M is shorted.1RQ2RQ3RQWhat is a watchdog timer?5RQ6RQ1RQWhat are the three basic types of direct current motors?3RQWhat type of armature winding is generally used for machines designed to operate on low voltage and high current? 5RQ6RQ7RQ8RQExplain the difference between cumulative and differential compounding. 10RQ11RQ1RQ2RQ3RQWhat is the advantage of a capacitor start induction run motor over a resistance start induction run motor?5RQ6RQWhat is synchronous speed?What two factors determine synchronous speed?9RQ10RQName three methods of braking a motor.How is the braking force of drum type brakes controlled? Why are mechanical brakes often used on cranes? What is the advantage of dynamic brakes over mechanical brakes? What is the disadvantage of dynamic brakes when compared to mechanical brakes?The amount of counter torque developed by a direct current generator is proportional to what? When using dynamic braking for a direct current motor, how is the braking time controlled? Name three factors that determine the amount of induced voltage. How is dynamic braking for direct current motors accomplished? How is the dynamic braking force of an alternating current motor controlled?How is a plugging stop accomplished?12RQ13RQ1RQ2RQA wound rotor induction motor has a stator that contains six poles per phase. How many poles per phase are in the rotor circuit? Name three factors that determine the amount of torque developed by a wound rotor induction motor. 5RQExplain why controlling the rotor current also controls the stator current.What is the function of a micro limit switch when used with a manual controller for a wound rotor motor?8RQWhat is rotor slip? 10RQ11RQ12RQRefer to the schematic diagram in Figure 318. Assume that the motor is not running. When the third speed push button is pressed, the motor starts in its lowest speed. After a delay of 3 seconds, the motor accelerates to second speed and 3 seconds later to third speed. After a period of about 1 minute, the fourth speed push button is pressed, but the motor does not accelerate to fourth speed. Which of the following could cause this problem? a. Control relay CR2 coil is open. b. S2 contactor coil is open. c. CR3 coil is shorted. d. S3 contactor coil is open.1RQWhat is an amortisseur winding and what function does it serve?3RQ4RQ5RQ6RQ7RQ8RQ9RQ10RQ1RQ2RQWhat is the advantage of consequent pole motors over some other types of variable speed motors? 4RQRefer to the circuit shown in Figure 33–6. You are to install this control system. How many auxiliary contacts should starter 1L contain and how many are normally open and how many are normally closed? Refer to the circuit shown in Figure 336. What is the function of contactor 2L?Refer to the circuit shown in Figure 33–7. When the low speed push button is pressed, the motor begins to run in low speed. When the high speed push button is pressed, the motor stops running. Which of the following could cause this problem? The 1L contactor coil is open. H contactor coil is open. PR relay coil is open. The 2L contactor coil is open. 8RQRefer to the circuit shown in Figure 33–11. Explain the action of the circuit if coil 2CR is shorted and the second speed push button is pressed. 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?1RQ2RQ3RQ4RQ5RQ6RQ7RQWhen 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?1RQWhy 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. 5RQWhat unit controls the voltage applied to the armature?What device is often used to sense motor speed? 8RQ1RQ2RQIf 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?
Page: [1][2]