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4th Year Electrical > PLC’s > Flashcards

PLC’s Flashcards

1
Q

The XIC instruction is true when the external input device that controls it ________ (provides/does not provide) voltage.

A

Provides

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2
Q

The examine if off instruction is true when the external input device that controls it _______ (provides/does not provide) voltage.

A

Does not provide

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3
Q

What binary bit will be represented when the XIO instruction is false?

A

1

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4
Q

If a normally closed push button (which is not pressed) is wired to a PLC as a stop button, a logic _______ (true/false) condition will exist at the corresponding XIO ladder logic instruction.

A

False

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5
Q

List the 4 major sections of a PLC system

A

Input
CPU
Programming
Output

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6
Q

List 3 main reasons PLC’s are preferred over other control sections

A

Flexibility; easy to add control sections
Reliably; no moving parts
Accuracy; timers are more accurate than conventional

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7
Q

List three types (categories) of devices that can be wired to an input

A

Discrete; PB’s, limit switches, float switches
Analogue; potentiometer, rheostat
Pulse; shaft encoder

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8
Q

What are the two main types of PLC memory?

A

RAM; executive, factory set, non volatile
ROM; user, volatile

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9
Q

List two factors that should be taken into account regarding the physical environment for a PLC installation

A

Temperature
Humidity
Dust
Shock and vibration

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10
Q

List two devices that can be used for programming a PLC

A

PC
Laptop
Handheld programmer

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11
Q

Name the device that is used in both input and output module circuitry to provide electrical isolation

A

OPTO isolator (coupler)

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12
Q

What is the best practice for grounding a single shielded cable?

A

Ground/bond at one end only (controller)
NO SHIELD IN THE FIELD

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13
Q

List the three main PLC programming instructions used with relay ladder logic

A

XIC; examine if closed
XIO; examine if open
OTE; output energize

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14
Q

What is the difference between an internal dummy relay instruction and a real output energize instruction?

A

There is no physical field connection. It only exists in the logic program

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15
Q

While in run mode, a Micrologix 1000 PLC will allow an instruction to be changed from XIC to XIO. (T/F)

A

False

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16
Q

While in run mode, a PLC will allow a timers preset value to be changed. (T/F)

A

True

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17
Q

A “single scan test” mode is a convenient way of testing the logic and function of your program while you are still offline. (T/F)

A

False

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18
Q

Output modules having ‘dry contacts’ may switch both AC and DC loads. (T/F)

A

True

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19
Q

The user memory (program) will normally be retained in memory on the PLC’s in our lab if the normal AC power supply is lost. (T/F)

A

True

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20
Q

An on-delay timer’s address could be O:0/1. (T/F)

A

False

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21
Q

An output thats addressed B:0/2 can be wired to an indicating light in the field. (T/F)

A

False

22
Q

Why would it not be considered good practice to wire a normally open stop button to an XIO.

A

Its not fail safe. It wont stop if PB fails or a loose wire occurs

23
Q

A sinking type input module will ______ (send/receive) current from/to the input field device.

A

Receive

24
Q

What is an MCR sometimes used for?

A

Low voltage protection

25
Q

The CPU of a PLC has three main jobs. What are they?

A

Read inputs
Solve logic
Write outputs

26
Q

What could happen if a PLC’s battery were to become depleted?

A

Loss of user data

27
Q

What is meant by discrete I/O?

A

On/off only

28
Q

What should be considered when running wires to inputs?

A

Use shielded wire
Tie ground to one end only (controller)

29
Q

Does a latching relay provide low voltage protection?

A

No. It will remain latched after restoration of power

30
Q

When would you not want to use a master control relay in conjunction with a PLC?

A

Where low voltage protection in not desirable

31
Q

Other than analogue inputs, what other type of inputs are available?

A

Discrete
Pulse

32
Q

Of all the advantages of PLC’s, which is the most important?

A

Maintainability

33
Q

Give a brief description of the CPU section.

A

Its the brain of the PLC
Includes: processor, power supply, memory

34
Q

What is a bit?

A

0 or 1

35
Q

What is a byte?

A

8 bits

36
Q

What is a word?

A

16 bits

37
Q

Which type of memory is used as a form of non-volatile memory?

A

RAM

38
Q

Which type of memory deals with the status of field devices?

A

ROM

39
Q

Which type of memory deals with the user program and data?

A

ROM

40
Q

Which type of memory is not changed by the user?

A

RAM

41
Q

How is the memory size required for a PLC system determined?

A

Determined by the size of the program and the number of inputs and outputs

42
Q

List three types of backup non-volatile memory for the PLC user memory

A

EEPROM
UVPROM
NOVRAM

43
Q

List three types of programming language for PLC’s

A

Ladder logic
Boolean
Structured text
Function block

44
Q

What is a one shot?

A

An instruction that will only stay on for one operating cycle (scan)

45
Q

What type of timers are available with the PLC we used in the lab?

A

TON (on delay)
TOF (off delay)
RTO (retentive on delay)

46
Q

What type of counters are available with the PLC used in the lab?

A

CTU (count up)
CTD (count down)

47
Q

List five different functions that PLC application software provides

A

Program ladder logic
Upload and download programs
Document ladder programs
Edit or modify logic programs
Change or modify controller operation

48
Q

What does the programming section do?

A

Program entry
Documentation
Ability to initiate run mode

49
Q

What does the output section do?

A

Switches outputs on or off
Provides surge protection and electrical isolation

50
Q

Describe a PLC

A

Its a solid state control system that monitors the status of devices connected as inputs. Based upon a user written program, stored in memory, it controls the status of devices connected as outputs

51
Q

Where could you find the status of each input?

A

Data table

52
Q

Whats an I/O update?

A

Reading inputs and writing to outputs based on the program

4th Year Electrical (8 decks)

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