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All Textbook Solutions for Industrial Motor Control
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: a. Normally closed float switch b. Normally open held closed float switch c. Normally open float switch d. Normally closed held open float switchThe symbol shown is a(n)
iron core transformer.
auto transformer.
current transformer.
air core transformer.
The symbol shown is: a. Normally open pressure switch b. Normally open flow switch c. Normally open float switch d. Normally open temperature switchThe 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 2–22, what type of push button would you use for the silence button?
Normally closed
Normally open
Referring to the circuit in Figure 222, 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?Pushpull buttons are generally used because a. they are smaller in size than standard push buttons. b. they contain larger contacts that can withstand more current than standard push buttons. c. they can perform more than one function while only requiring the space of one single-function push button. d. they are larger in size than standard push buttons, making them more visible to an operator.What device is generally used by lighted push buttons to reduce the voltage applied to the lamp?
Series resistor
Transformer
Series capacitor
Series inductor
13RQA single-phase, 120 volt motor is controlled by a manual motor starter. The motor is not running, and the switch handle on the starter is found to be in the center 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 2 to 3 minutes after it has tripped?
6RQ7RQ8RQHow many overload sensors are required by the NEC 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 eight-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?6RQWhat 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 type of pressure switch is generally used to sense small changes in low pressure systems?2RQA 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?
6RQ7RQDescribe the sequence of operations required to (a) pump sumps and (b) fill tanks.
Draw the normally open and normally closed contact symbols for a float switch.What type of float switch does not have a differential setting?
What is the advantage of the bubble type system for sensing liquid level?
Assume 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?Refer to the circuit shown in Figure 9-5. Assume that the warning buzzer sounds and the warning light is on. It is discovered that pump 2 is running and pump 1 is not. When the reset button is pressed the warning buzzer turns off and the warning light remains on. Which of the follow could not cause this condition?
The contacts of float switch FS1 did not close.
The contacts of float switch FS2 did not close.
The coil of starter 1M is defective.
The overload contact connected to starter 1M is open.
Refer to the circuit shown in Figure 9-5. It is discovered that the tank is overflowing but the warning buzzer and warning light are not turned on. Both pumps are running. Which of the following could cause this condition?
The warning buzzer is defective.
Float switch FS4 contacts did not close.
Control relay CR is defective.
The reset button is shorted.
What are typical uses of flow switches?
Draw a line diagram to show a green light that glows when liquid flow occurs.Draw a one-line diagram showing a bell that rings in the absence of flow. Include a switch to turn off the bell manually.
What is a transducer?
What is the most common output current for flow sensors?What is Faradays Law concerning conductors moving through a magnetic field?What type of flow sensors use Faradays Law as their principle of operation?What is the operating principle of the solid-state airflow sensor described in this text?
Refer to the circuit shown in Figure 10-6. When the pressure switch closes the lube oil pump starts, but the compressor motor does not. The red indicator light, however, does go out. Which of the following conditions could NOT cause this problem? A. The compressor contactor coil is open. B. The lube oil overload contact (LOP OL) is open. C. The pressure switch contact is defective. D. The compressor overload contact (COMP OL) is open.Refer to the circuit shown in Figure 10-6. When the pressure switch closes, neither the lube oil pump nor the compressor start. Upon further examination of the circuit, it is discovered that the red indicator light is not lit. Pressing the reset button has no effect on the state of the circuit. Which of the following could NOT cause this condition? A. The control transformer fuse is blown. B. CR relay is defective. C. The emergency stop button contacts are open. D. The lube oil overload contacts are open.What 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 11–11. 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 closed.
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 11–11. Assume that the platform is located on the lower floor. When the UP push-button is pressed, the platform raises. 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?
The solenoid valve opened when limit switch LS1 opened.
The UP push-button is shorted.
Limit switch LS1 did not open its contacts.
Limit switch LS2 contacts did not re-close when the platform began to rise.
5RQ1RQNEMA-rated motors are designed to operate at what percentage of their rated voltage?3RQWhat is meant by the statement that solenoid valves are digital devices?
Why is it important that the inlet and outlet ports on a two-way valve not be reversed?
What type of valve is generally used to supply air pressure to a double-acting cylinder?4RQWhat type of switch is generally used to ensure that a motor-operated valve is tightly seated?Should a metal bar be heated or cooled to make it expand?
2RQ3RQWhy 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?
7RQ8RQ9RQ10RQ11RQ12RQHow 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?3RQ4RQWhy does a magnetic field not have to be moving or changing to produce an output voltage in the Hall generator?
Proximity detectors are basically _____________
__________________________________________.
What is the basic principle of operation used with detectors designed to detect only ferrous metals?3RQWhat type of electric circuit is used to increase the sensitivity of a metal detecting proximity detector?What type of proximity detector uses an oscillator that operates at radio frequencies?
6RQ7RQHow 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 angle, at what angle must the receiver be mounted?How much voltage is produced by a silicon solar cell?
10RQWhat are the two major types of control circuits?2RQRefer to the schematic shown in Figure 184. What type of switch is the thermostat? a. Normally open temperature switch b. Normally closed temperature switch c. Normally open, held closed temperature switch d. Normally closed, held open temperature switchRefer to the schematic shown in Figure 184. What type of switch is the low water switch? a. Normally open float switch b. Normally closed float switch c. Normally open held closed float switch d. Normally closed held open float switchWhat generally characterizes a three-wire control circuit?Explain the function of a holding contact.7RQDefine a schematic diagram.
Define a wiring diagram.Referring to circuit 1 (Figure 19–2A), explain the operation of the circuit if pressure switch PS is connected normally closed instead of normally open.
4RQ1RQExplain the operation of circuit 2 (Figure 20–1) if relay coil TR2 is burned out.
Refer to circuit 2, shown in Figure 20–1. Assume that both times are set for a delay of 5 seconds. When the START button is pressed, motor 1 starts running immediately. After a delay of 10 seconds, motor 3 starts running, but motor 2 never starts. Which of the following could cause this problem?
The TR1 coil is open.
The M2 starter coil is open.
The TR2 coil is open.
The OL2 contact is open.
Refer to circuit 2, shown in Figure 201. Assume that the timers are set for a delay of 5 seconds. When the START button is pressed, nothing happens. No motors start running for a period of 1 minute. Which of the following could not cause this problem? a. The M1 holding contacts did not close. b. The STOP push button is open. c. The OL1 contact is open. d. The M2 coil is open.(Refer to circuit 211.) 1. Explain the operation of the circuit shown in Figure 211 if float switch FS were connected normally closed instead of normally open.Explain the operation of the circuit shown in Figure 211 if relay coil M1 were burned out.Why are numbers used when developing a wiring diagram from a schematic diagram?The float switch in Figure 22–1 is:
normally closed
normally open
normally closed, held open
normally open, held closed
The circuit in Figure 22–1 is designed to sound an alarm if the liquid level rises to a high enough level. What change would have to be made in the circuit so that it would sound an alarm if the liquid level dropped below a certain point?
Referring to the circuit shown in Figure 23–1, would it be possible to change the components that have been numbered with an 8 to a number 9, and the components that have been numbered with a 9 to a number 8, without affecting the operation of the circuit?
Are numbering systems other than the one described in this text used to develop wiring diagrams from schematic diagrams?
Refer to Figure 251 to answer the following questions. When switch HOA SW 122 is in the OFF position, which contacts have connection between them?Refer to Figure 25–1 to answer the following questions.
How much voltage will be applied to coil 1CR when it is energized?
Refer to Figure 25–1 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 251 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 25–1 to answer the following questions.
In what position must switch HOA 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 26–1. Should float switch FS2 be wired as normally open or normally closed? Explain your answer.
What does the dashed line between the two float switch contacts labeled FS1 indicate?Refer to the circuit shown in Figure 272. Would it be possible to replace the hand-off-auto switch in this circuit with a hand-off-auto switch that contained a common terminal and center Off position like the HOA switch shown in Figure 271? Explain your answer.Refer to the circuit shown in Figure 27–2. Would the temperature have to increase or decrease to permit the fan to turn on?
Refer to the circuit shown in Figure 27–2. Which starter controls the holding contacts connected in parallel with the start push button?
4RQ5RQ6RQRefer to the circuit shown in Figure 272. Assume that the HOA switch is set in the Hand position. When the Start button is pressed, the red warning lamp lights. When the Start button is released, the light turns off, but the fan motor does not start. Each time the Start button is pressed, the warning lamp lights for as long as the Start button is held down, but it goes out each time the Start button is released, and the fan does not start. Which of the following could cause this condition? a. The Temp 1 switch is open. b. The M2 starter coil is open. c. The M1 starter coil is open. d. The Stop push button is open.1RQ2RQThe two stop push buttons in Figure 282 are connected in series with each other. What would be the action of the circuit if they were connected in parallel, as shown in Figure 286?4RQ1RQWhat is interlocking?Referring to the schematic shown in Figure 297, how would the circuit operate if the normally closed R contact connected in series with the F coil were connected normally open?What would be the danger, if any, if the circuit were wired as stated in question 3?5RQAssume that the circuit shown in Figure 29–7 were to be connected as shown in Figure 29–14. 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 30–8. 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 30–9. 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 is the purpose of sequence control?2RQAssume that all three motors shown in Figure 3114 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? a. The stop button is shorted. b. 2M contact between wire numbers 31 and 32 is hung closed. c. The 3M load contacts are welded shut. d. The normally open 3M contact between wire numbers 23 and 31 is hung closed.Referring to Figure 31–14, 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
The number 2 push button were pressed before the number 1 push button?
The number 1 push button were pressed first?
5RQ1RQ2RQExplain the physical difference between series field windings and shunt field windings.4RQ5RQ6RQ7RQ8RQ1RQWhy is direct current more difficult to interrupt than alternating current?Why are clapper-type contactors generally used to control DC devices?4RQHow is the inrush current to large DC motors often limited?
6RQHow is the FCR connected in relationship to the shunt field?8RQ9RQ1RQWhy 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?
8RQ1RQ2RQWhat does the term bifilar mean?Why do stepping motors have teeth machined in the stator poles and rotor?5RQ6RQ7RQ8RQList five common starting methods for three-phase squirrel-cage motors.
2RQA squirrel-cage motor produces 1100 pound-feet of torque at starting when full voltage is applied to the motor. If the voltage is reduced to 50% during starting, how much starting torque will the motor develop?What is the most common device used to disconnect the start winding of a resistance start single-phase motor that is intended to operate in the open air?
5RQ6RQ7RQ8RQ9RQ10RQ1RQWhat advantage does a reactor have when limiting inrush current that is not available with a resistor?Refer to the circuit shown in Figure 37–1. 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?
The Start button is shorted.
Timer coil TR is open.
Contactor coil R is open.
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 382. Assume that timer TR1 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 385. Explain the steps necessary for coil S2 to energize.9RQRefer to the circuit shown in Figure 38–5. 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 wyedelta starting.2RQ3RQRefer to the circuit shown in Figure 399. 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 one minute, the motor has not changed from wye to delta. Which of the following could cause this condition? a. TR timer coil is open. b. S contactor coil is open. c. 1M starter coil is open. d. The control transformer fuse is blown.Refer to the circuit shown in Figure 39–9. 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?
TR timer coil is open.
2M contactor coil is open.
S contactor coil is open.
1M starter coil is open.
6RQThe motor nameplate of a wye–delta starter 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 3914. What is the purpose of timer TR2?Refer to the circuit shown in Figure 39–14. When the Start button is pressed, the control transformer fuse blows immediately. Which of the following could not cause this problem?
Control Relay coil CR is shorted.
Starter coil 1M is shorted.
Contactor coil S is shorted.
Contactor coil 2M is shorted.
1RQ2RQ3RQWhat is a watchdog timer?
Refer to the circuit shown in Figure 405. When the Start button is pressed, the motor does not start. Which of the following could not cause this problem? a. The control transformer fuse is blown. b. Overload contact 2 is open. c. TR1 timer coil is open. d. Control relay coil CR is open.6RQ1RQ2RQWhat is the advantage of consequent pole motors over some other types of variable speed motors?
4RQRefer to the circuit shown in Figure 416. You are to install this control system. How many auxiliary contacts should starter 1L contain? List how many are normally open and how many are normally closed.Refer to the circuit shown in Figure 41–6. What is the function of contactor 2L?
Refer to the circuit shown in Figure 41–7. 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?
1L contactor coil is open.
H contactor coil is open.
PR relay coil is open.
2L contactor coil is open.
8RQRefer to the circuit shown in Figure 41–10. Explain the action of the circuit if coil 2CR is shorted and the 2ND speed push button is pressed.
Refer to the circuit shown in Figure 4110. You are to construct this circuit on the job. Would it be possible to use an 11-pin control relay for 4CR?1RQ2RQ3RQ4RQ5RQ6RQ