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4th Year Electrical > PLCs > Flashcards

PLCs Flashcards

1
Q

How are PLCs usually selected?

A

According to the number of input and output points they can service.

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2
Q

What side of an I/O point are switches and sensors connected to on a PLC?

A

Input

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3
Q

What might be connected to the output of an IO point within a PLC?

A

Pilot lights

Contactors and relays

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4
Q

True or false: the programming, memory, and communication requirements on a PLC remain the same regardless of size.

A

False. In larger systems, these requirements increase.

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5
Q

How many IO points could you expect to see in a “Large” system?

A

120 000

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6
Q

What devices comprise a control system?

A

Input devices
Controller
Output devices

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7
Q

What device receives information from an input device and decides upon a response?

A

Controller

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8
Q

What device of a control system would a solenoid be? (In/out/control)

A

Output device

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9
Q

What device in the control system would a thermostat be? (In/out/control)

A

Input

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10
Q

What are the advantages of using PLCs?

A

Lower overall cost
Programmability
Reliability
Expandability

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11
Q

What factors contribute to the cost advantages of a PLC? (Vs. Control panels using relays)

A
  • less maintenance (no mechanical parts wearing out)
  • troubleshooting is easier and reduces down time
  • physically smaller
  • smaller energy requirements
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12
Q

What factors contribute to the programmability of PLCs?

A
  • using software increases level of process automation
  • can be updated without changes in hardwiring
  • program can be revised while system in operation
  • one program can be used for several identical processes
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13
Q

What factors contribute to the reliability of PLCs?

A

solid state technology

   - able to operate in many environments
   - static electronic switching (no movingparts)
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14
Q

What is a communication data highway?

A

A link between two PLC systems (as in adding another system to expand, and linking the two with a communication data highway)

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15
Q

What are the major hardware components of a modular PLC system?

A

Power supply
Backplane
Processor (CPU)
I/O modules

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16
Q

What type of power is supplied to the PLC and its components?

A

DC power

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17
Q

Which specific devices does the power supply feed power to? Which devices does it NOT?

A

Supplies power to the processor (CPU) and I/O modules.

Does NOT supply power to field I/O devices

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18
Q

True or false:

I/O devices are electrically isolated from backplane, and CPU but connected to I/O modules and PLC power supply

A

False. electrically isolated from backplane, CPU, and PLC power supply

Connected to IO modules

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19
Q

What is the function of a backplane?

A

1) Allows communication btwn CPU and and other components

2) Distributes power for internal operation of processor and IO modules

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20
Q

What hardware component is the power and communication bus for PLC components?

A

Backplane

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21
Q

If the PLC does not have a chassis, how is the continuity of the backplane maintained?

A

By connectors on the sides of the modules and at the end plates which snap together.

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22
Q

What kind of PLC is not designed to be readily taken apart and replaced?

A

Shoebox PLC

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23
Q

What is a common application of shoebox PLCs?

A

Often used to replace small relay control systems.

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24
Q

What makes a shoebox PLC unique?

A

Do not have separate power, processor, or I/O modules

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25
Q

What are the primary functions of a PLC processor?

A

1) read and store status of all input devices
2) execute user program by solving programs logic
3) update status of all the outputs

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26
Q

What a processor scan?

A

The sequence by which a processor carries out its functions

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27
Q

what are the types of memory used in PLCs?

A

RAM, ROM, EEPROM

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28
Q

What type of memory requires backup battery supply to keep stored data or to keep programs in tact when power is removed?

A

Volatile

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29
Q

Which type of memory is considered permanent?

A

Non-volatile

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30
Q

Which type of memory is easily altered to update or change programs?

A

Volatile

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31
Q

What does RAM stand for?

A

Random access memory

32
Q

What kind of memory is RAM memory?

A

Volatile (usually)

33
Q

What type of RAM memory is provided a memory chip with a self-contained battery within the package

A

Non-volatile RAM

34
Q

What does ROM stand for?

A

Read only memory

35
Q

What type of memory is ROM?

A

Non-volatile

36
Q

(RAM/ROM) systems cannot be altered or written to by a user. Ie. Program fixed at manufacture.

A

ROM

37
Q

The basic input/output system is stored in ________ (RAM/ROM). Why?

A

ROM. so the PLC recognizes its components when it is first turned on.

38
Q

What does EEPROM stand for?

A

Electrically erasable programmable memory

39
Q

Is EEPROM considered volatile or non-volatile?

A

Non-volatile

40
Q

What’s an example of a type of EEPROM?

A

Flash memory cards or USB drives

41
Q

Processors utilizing EEPROM memory ____ (can/cannot) be reprogrammed

A

Can, even though it is considered to be non-volatile.

42
Q

What must happen before a new program is loaded on an EEPROM processor?

A

Memory chip must be erased

43
Q

TRUE OR FALSE: One start button could be used to operate a number of motors or other equipment

A

True

44
Q

TRUE OR FALSE: The voltage for the input signals is provided by the controller

A

False; is provided by a separate source.

45
Q

How is the signal voltage isolated from the controllers processor?

A

Optoisolators or

Small relays and filter circuitry

46
Q

What is the processor itself isolated from?

A

Voltage transients or

Magnetic interference

47
Q

What kinds of controls are special I/O modules used for?

A 
Position control
High speed counters
Temperature control
Proportional integral derivative control 
Fuzzy logic control
Identification sensors
Cam positioners 
Analogue I/O
48
Q

What is the advantage remote IO modules offer?

A

Reduce wiring btwn PLC and input/output devices. Requires only one cable back to PLC instead of individual cables from each IO device.

49
Q

What is a data highway?

A

Local area network cabling that connects a number of PLCs, or PLCs and personal computers, allowing them to exchange programs and data.

50
Q

What allows one PC to change programs of several PLCs?

A

Data highway

51
Q

What is the difference between the terms “discrete” and “analogue” with regards to PLCs?

A 
Discrete = device is on or off
Analogue = device operates over a range of values of voltage or current
52
Q

How does an optoisolating device operate?

A

Changes the input from a discrete device (to an input module) into a light beam

Light beam electrically isolates I/O modules from signal circuits

Protects PLC from high voltage of discrete input circuit

53
Q

What is a solid state electronic switch called for dc? Ac?

A 
DC = transistor
AC = triac
54
Q

What is the function of a solid state electronic switch?

A

Activated by a light (signal from processor) and closes the circuit to a discrete output device

55
Q

When would an interposing relay be used?

A

For output circuits that require larger currents.

56
Q

What are the two most common methods of sending an analogue signal?

A

1) proportional voltage

2) proportional current

57
Q

What device must be used in order for a PLC to receive an analogue signal?

A

Special analogue input card

58
Q

What is the most common analogue voltage standard?

A

0V to 10V dc
0V = 0%
10V = 100%

59
Q

What is the most common analogue current standard?

A

4mA to 20mA

60
Q

Why is the min mA analogue signal NOT 0A?

A

Allows PLC to tell the difference between a zero % signal and a broken wire condition

61
Q

What kind of output card is used to achieve proportional control?

A

Analogue output card

62
Q

What is the most common type of cable used in analogue PLC applications?

A

Shielded twisted pair

63
Q

What size conductor would you expect to see in analogue cables?(large/small)

A

Small. As small as 22AWG. (Current levels are small)

64
Q

What is used to prevent electrical interference and distortion of analogue signals?

A

SHIELDED cable

65
Q

How do you ensure the shield acts as a “drain”?

A

Ground only one end of the shield.

66
Q

What is the common programming device?

A

PCs

67
Q

What are the 5 main types of languages used for programming PLCs? Which are graphic-based, and which are text-based?

A 
Graphic:
Ladder diagrams (LD)
Function block diagrams (FBD)
Sequential functions (or flow) chart (SFC)
Text:
Structured test (ST)
Instruction lists (IL)
68
Q

Which language is most often used to program PLCs?

A

Ladder diagram

69
Q

Which language resembles a schematic diagram?

A

Ladder diagrams

70
Q

What language is typically used in Europe?

A

FBD function block diagrams

71
Q

How is each function block labelled in function block diagrams?

A

Based on boolean logic

72
Q

What language is used for large-process controls where several complex functions take place in sequence?

A

Sequential function chart (SFC)

73
Q

Which language is similar to BASIC language?

A

Structured text

74
Q

Which language is more closely related to machine code used to make a microchip function?

A

Instruction lists

75
Q

Which language is similar to assembler language programs?

A

Instruction lists

4th Year Electrical (24 decks)

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