1. The purpose of the control transformer in machine control systems is to
a) lower the line voltage to a safe level.
b) add reliability to the controls circuitry.
c) prevent the controls circuit form affecting the power line.
d) allow the controls to operate at a faster rate.
2. A delay-on (TON) relay has a preset of 5.0 seconds. If the coil terminals are energized for8.0 seconds, how long will its contacts be actuated?
a) 0 sec.
b) 3.0 sec
c) 5.0 sec
d) 8.0 sec
e) always
3. If a delay-on (TON) relay with a preset of 5.0 seconds is energized for 3 seconds, how longwill its contacts be actuated?
a) 0 sec.
b) 3.0 sec
c) 5.0 sec
d) 8.0 sec
e) always
4. If a delay-off (TOF) relay with a preset of 5.0 seconds is energized for 1.0 second, how longwill its contacts be actuated?
a) 0 sec.
b) 1.0 sec
c) 5.0 sec
d) 6.0 sec
e) always
5. Select the ladder diagram rung that will cause relay CR4 to be ON when relay CR1 is ON,CR2 is OFF, and CR3 is OFF.
6. Which of the following is NOT an I/O module?
a) Triac
b) Relay
c) TTL
d) Processor
e) Analog
7. What are the two steps the PLC must perform during operation?
a) solve the ladder, stop
b) run, stop
c) read input, send outputs
d) solve the ladder, I/O update
8. What is the purpose of the programming unit?
a) stores the program that is running
b) displays the programming help manual
c) allows programs to be modified and debugged
d) translates mnemonic code between different PLC brands
9. What is the Output Image Register?
a) a backup copy of the output
b) a place to store data to be output during next I/O update
c) a list of the devices connected to the outputs
d) a graphic image of the output terminals
10. What common devices operate the same as coils and contacts in ladder logic?
a) sensors
b) fuses
c) relays
d) switches
e) transformers
11. When a relay coil is energized, what is the condition of its normally closed contacts?
a) closed
b) open
12. In a PLC program, the number of contacts a particular relay can have depends on the
a) number of inputs.
b) number of outputs.
c) speed of the processor.
d) size of the processor memory.
13. How is the state of a relay coil represented inside the PLC?
a) as an analog voltage
b) as an analog current
c) as a digital bit
d) as an optical signal
14. If a particular coil is to be an output of the PLC, when is the state of the coil transferred to the output terminal?
a) during I/O update
b) as it solves the ladder
c) during a processor interrupt
d) after a power up delay
15. For the ladder diagram below, if all three inputs IN1, IN2, and IN3 are ON, what is the state of OUT1?
a) on
b) off
16. In an edge-triggered D flip flop, if the D input is ON when the Trigger input switches ON, the Q output will_____.
a) switch ON
b) switch OFF
c) remain in its last state
17. In a JK flip flop, if the J is ON and the K is OFF, then when the Trigger switches on, the Q will_____.
a) switch ON
b) switch OFF
c) remain in its last state
d) toggle
18. A level-triggered D flip flop can be made edge-triggered by
a) swapping the D and Trigger inputs
b) inverting the D input
c) inverting the trigger input
d) adding a one-shot
19. In ladder logic, all counters have a reset.
a) True
b) False
20. In most PLC timers, the standard time increment is _____ second.
a) 0.001
b) 0.01
c) 0.1
d) 1.0
21. Mnemonic programming code is mainly used
a) to make programming easier.
b) to make the PLC run faster.
c) to use less PLC program memory
d) with handheld programmers.
22. Of the mnemonic commands below, which one will combine elements already on the stack?
a) STO OUT1
b) OR CR1
c) AND LD
d) AND CR2
23. The mnemonic PLC code sequence for the ladder diagram below is______.
a)
LODN IN1
AND INS
OR IN2
ANDN IN3
OR LD
STO OUT1
b)
LODN IN1
AND IN2
LD IN2
ANDN IN3
OR LD
STO OUT1
c)
LOD IN1
ANDN IN2
OR IN2
ANDNIN3
STO OUT1
d)
LOD IN1
AND IN2
LDN IN2
ANDN IN3
OR LD
STO OUT1
24. In mnemonic PLC programming code, the stack operates as a
a) first in, first out
b) last in, first out
c) last in, last out.
25. For the ladder rung below, what would be the first 4 lines of mnemonic PLC code?
a)
LODN CR2
AND CR5
OR CR6
ANDN CR7
b)
LODN CR7
AND CR6
OR CR2
AND CR5
c)
LOD CR6
ANDN CR7
LOD CR2
AND CR5
d)
LOD CR2
AND CR5
LODN CR7
AND CR6
26. The main difference between a dc opto-isolated input and an ac/dc opto-isolated input on a PLC is that the ac/dc input_____.
a) contains 2 LEDs in parallel
b) is capacitor coupled
c) has a 60Hz band-pass filter
d) responds faster
27. A limitation in using a PLC's internal power supply to provide power for the PLC inputs is_____.
a) its voltage cannot be varied
b) it has a low current capacity
c) it switches on/off with the PLC
d) all of the above
28. Comparing relay outputs and solid state outputs, relay outputs_____.
a) have no moving parts
b) are more reliable
c) can switch any polarity signal
d) have no contact bounce
(chatter)
29. Of the two types of transistor output configurations (PNP and NPN), which is sourcing and which is sinking?
a) PNP is sourcing, NPN is sinking
b) NPN is sourcing, PNP is sinking
30. If one terminal of a lamp is connected directly to the negative terminal of the power supply, what kind of transistor output unit will be required to allow the PLC to light the lamp?
a) sourcing
b) sinking
31. What is the voltage resolution of a 10-bit unipolar 5 volt analog input?
a) 2.44 mV
b) 4.88mV
c) 9.77mV
d) 4.995V
32. A 10 volt unipolar analog input has a voltage resolution of 78.125 mV. The bit resolution is____ bits.
a) 7
b) 8
c) 9
d) 10
33. A 10-bit bipolar ?10 volt analog input has ?4.35 volts applied to the input terminals. Whatwill be the converted value in decimal format?
a) 222
b) 445
c) 734
d) 1469
34. To measure a voltage that ranges for -1 to +5.5 volts, the best choice for an analog inputrange would be
a) 5 volts unipolar
b) 5 volts bipolar
c) 10 volts unipolar
d) 10 volts bipolar
35. An 8-bit 10 volt unipolar analog input on a PLC is not operating correctly. We connect acomputer to the PLC and setup our monitoring software. Upon doing some measurements onthe system, we find that if we input zero volts dc, the PLC indicates 000001012, and if weinput 8 volts dc, the PLC indicates 110111002. What do you suspect is wrong with thesystem?
a) constant voltage offset
b) percentage offset
c) noisy signal
d) cannot be determined
36. An inductive proximity sensor has a specified range of 5mm. If the sensor is sensing brass(derating factor of 0.40), maximum range?
a) 2mm
b) 4.6mm
c) 5.4mm
d) 12.5mm
37. An inductive proximity sensor is needed that will sense a stainless steel (derating factor 0.85) target object that is 7.5 mm from the face of the sensor. We should therefore specify a sensor with what minimum range?
a) 6.375mm
b) 6.65mm
c) 8.35mm
d) 8.82mm
38. In addition to sensing no-metallic objects, capacitive proximity sensors will sense metal objects as well as inductive proximity sensors. So why use inductive proximity sensors?
a) fewer wires to connect
b) lower cost
c) smaller
d) more available variety
39. Ultrasonic proximity sensors are not used for sensing close-range objects because they
a) overheat
b) have a deadband
c) are inaccurate at close range
d) will break the target object
40. When the beam of a retro-reflective NPN-output dark-off optical sensor is interrupted by a target object, it's output signal will be
a) high
b) low
Chapter 9
41. Platinum has a resistance change of +0.385 ohms/degree C. A 200 ohm platinum RTD measures 222 ohms. What is its temperature in degrees Celsius?
a) 0
b) 57.14
c) 85.14
d) 576.62
42. An integrated circuit temperature probe is rated at 0-10 volts dc over a 0-175C range. Whatis the temperature in degrees Celsius when the output voltage is 3.65 volts dc?
a) .0208
b) 63.88
c) 111.13
d) 479.45
43. A 0 to +500 psi pressure transducer has a calibration factor of 100psi/volt. What is the full scale output voltage of the transducer?
a) 0V
b) 5V
c) 10V
d) 100V
44. You have installed into a water pipe a turbine flow sensor that has a calibration factor of 60 pulses/gallon. When water is flowing in the pipe the sensor outputs 470 pulses/minute. What is the flow rate in gallons/minute?
a) 0.128
b) 7.83
c) 470
d) 28,200
45. A slotted disk and opto-interrupter ouputs pulses at 62 Hz. The disk has only one slot cut in it. What is the rotating speed of the disk in rpm?
a) 1.033
b) 62
c) 3,720
d) 223,200
46. In a closed loop system the process variable PV is 1.7 volts and the setpoint SP is 3.7 volts. What is the error voltage?
a) 0.66V
b) 1.51V
c) 2.00V
d) 9.30V
47. What is the main effect that an increase in the derivative gain Kd has on a closed loop PIDsystem?
a) slows the response
b) causes oscillation
c) reduces long-term error
d) reduces "hunting"
48. Cite one indication that the proportional gain Kp in a PID system is too low
a) fast response
b) oscillation
c) large long-term error
d) "hunting"
49. What is the main effect that an increase in the integral gain Ki has on a closed loop PIDsystem?
a) slows the response
b) causes oscillation
c) reduces long-term error
d) reduces "hunting"
50. Cite one disadvantage in using excessive integral gain Ki
a) slows the response
b) causes oscillation
c) reduces long-term error
d) reduces "hunting"
51. An AC induction motor is rated at 1750 rpm with a line frequency of 60Hz. If the motor isoperated on a 50 Hz line, what will be its approximate speed in RPM?
a) 29.17
b) 35
c) 1, 458
d) 2,100 12
52. An AC induction motor is rated at 1175 rpm, 480V, 60 HZ 3-phase. If we reduce the motorspeed by reducing the line frequency to 25 HZ, what should be the line voltage?
a) 3.125V
b) 200V
c) 490V
d) 1152V
53. In a motor starter, the auxiliary contacts operate at the same time as the
a) main contacts
b) overloads
c) overload contacts
d) spindle
54. In a motor starter, the spindle ratchet directly operates the
a) main contacts
b) auxiliary contacts
c) overload contacts
d) coil
55. A pulse width modulator dc motor controller has an input voltage of 10 volts dc. If it isoperating at 45% duty cycle, the average output voltage will be
a) 0.45V
b) 4.5V
c) 10V
d) 45V
56. NEMA and IEC enclosure ratings classify enclosures according to
a) environmental and safety issues
b) temperature and ventilation
c) size
d) weight
57. Select the best IEC IP number for an electrical box used in a textile mill. It must be dusttight and be able to withstand an occasional water hosedown by the cleaning crew.
a) 55
b) 56
c) 65
d) 66
58. Convert the IEC rating IP64 to the nearest equivalent NEMA rating.
a) 1
b) 2
c) 3
d) 3S
59. In a redundant PLC system, the PLCs are wired with
a) parallel inputs, parallel outputs
b) parallel inputs, series outputs
c) series inputs, parallel outputs
d) series inputs, series outputs
60. The advantage in a pullrope emergency switch is
a) it is inexpensive
b) one switch provides access to many people
c) it is easy to install and reliable
d) all of the above