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 for 8.0 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 long will 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 long will its contacts be actuated?
a) 0 sec.
b) 1.0 sec
c) 5.0 sec
d) 6.0 sec
e) always
5. Which of the following is NOT an I/O module?
a) Triac
b) Relay
c) TTL
d) Processor
e) Analog
6. 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
7. 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
8. 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
9. What common devices operate the same as coils and contacts in ladder logic?
a) sensors
b) fuses
c) relays
d) switches
e) transformers
10. When a relay coil is energized, what is the condition of its normally closed contacts?
a) closed
b) open
11. 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.
12. 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
13. 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
14. 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
15. 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
16. 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
16. In ladder logic, all counters have a reset.
a) True
b) False
17. In most PLC timers, the standard time increment is _____ second.
a) 0.001
b) 0.01
c) 0.1
d) 1.0
18. 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.
19. 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
20. 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
20. 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
21. 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)
22. 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
23. 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
24. 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
25. 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
26. A 10-bit bipolar ±10 volt analog input has ±4.35 volts applied to the input terminals. What will be the converted value in decimal format?
a) 222
b) 445
c) 734
d) 1469
27. To measure a voltage that ranges for -1 to +5.5 volts, the best choice for an analog input range would be
a) 5 volts unipolar
b) 5 volts bipolar
c) 10 volts unipolar
d) 10 volts bipolar
28. An 8-bit 10 volt unipolar analog input on a PLC is not operating correctly. We connect a computer to the PLC and setup our monitoring software. Upon doing some measurements on the system, we find that if we input zero volts dc, the PLC indicates 000001012, and if we input 8 volts dc, the PLC indicates 110111002. What do you suspect is wrong with the system?
a) constant voltage offset
b) percentage offset
c) noisy signal
d) cannot be determined
29. 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
30. 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
31. 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
32. 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
33. 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
34. 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
35. An integrated circuit temperature probe is rated at 0-10 volts dc over a 0-175C range. What is 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
36. 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
36. 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
37. 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
38. 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
39. What is the main effect that an increase in the derivative gain Kd has on a closed loop PID system?
a) slows the response
b) causes oscillation
c) reduces long-term error
d) reduces "hunting"
40. 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"
41. What is the main effect that an increase in the integral gain Ki has on a closed loop PID system?
a) slows the response
b) causes oscillation
c) reduces long-term error
d) reduces "hunting"
42. Cite one disadvantage in using excessive integral gain Ki
a) slows the response
b) causes oscillation
c) reduces long-term error
d) reduces "hunting"
43. An AC induction motor is rated at 1750 rpm with a line frequency of 60Hz. If the motor is operated on a 50 Hz line, what will be its approximate speed in RPM?
a) 29.17
b) 35
c) 1, 458
d) 2,100
44. An AC induction motor is rated at 1175 rpm, 480V, 60 HZ 3-phase. If we reduce the motor speed by reducing the line frequency to 25 HZ, what should be the line voltage?
a) 3.125V
b) 200V
c) 490V
d) 1152V
45. In a motor starter, the auxiliary contacts operate at the same time as the
a) main contacts
b) overloads
c) overload contacts
d) spindle
46. In a motor starter, the spindle ratchet directly operates the
a) main contacts
b) auxiliary contacts
c) overload contacts
d) coil
47. A pulse width modulator dc motor controller has an input voltage of 10 volts dc. If it is operating at 45% duty cycle, the average output voltage will be
a) 0.45V
b) 4.5V
c) 10V
d) 45V
48. NEMA and IEC enclosure ratings classify enclosures according to
a) environmental and safety issues
b) temperature and ventilation
c) size
d) weight
49. Select the best IEC IP number for an electrical box used in a textile mill. It must be dust tight and be able to withstand an occasional water hosedown by the cleaning crew.
a) 55
b) 56
c) 65
d) 66
50. Convert the IEC rating IP64 to the nearest equivalent NEMA rating.
a) 1
b) 2
c) 3
d) 3S
51. 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
52. 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