Industrial Controls/PLC

Question 1

What is the difference between control power and main electrical feed power

Answer 1

Main electrical feed power is fed from disconnects and circuit breaker’s they also feed sections of a motor control center(MCC)
Control power is the electrical supply that feeds things such as control consoles, solenoid valves, photocells etc.

Question 2

What are the decision-making devices of electrical control systems?

Answer 2

Logic devices

Question 3

What are some examples of electrical control inputs?

Answer 3

Mechanical movement, pressure, temperature, speed, light, float level

Question 4

What is a switch?

Answer 4

It is a device designed to make and break an electrical circuit

Question 5

What are some different types of switches

Answer 5

Pressure switches, temperature switches, emergency stop switches, interlock switches

Question 6

What did temperature switch is frequently contain?

Answer 6

Bimetallic element

Question 7

What are some process control and monitoring switches

Answer 7

Limit switches, pressure switches, liquid level switches, photocells, flow switches proximity switches

Question 8

What is a control output

Answer 8

The device that changes a small electrical signal current into useful work
Some examples are pilot lights ,numeric displays, solenoid valves, servo valves, motor starters

Question 9

What is a relay

Answer 9

Uses low-voltage to switch to higher voltage. They have an electromagnetic coil and they make or break contact with the fixed contacts when power supply to the coil

Question 10

How are released typically specified?

Answer 10

By the number of poles and numbers of throws

The number of poles is the number of inputs and the number of throws is the number of possible outputs

Question 11

What are some different types of relays?

Answer 11

Latching relays, time delay relay’s, counters, solid-state relays

Question 12

What is a latching relay?

Answer 12

It remains in the switched state, until current is reversed to force another switch. It will not automatically switch back when power is removed

Question 13

What are the two types of time delay relay’s?

Answer 13

TDD-time delay de-energize

TDE-Time delay energize

Question 14

What is a solid state relay?

Answer 14

No mechanical linkage, no moving parts, so it will not arc when switching under load, can be used for high amps (1200 amps)

Question 15

How is logic performed in a circuit?

Answer 15

Relays are connected in special ways by creating conditions to be met to get an output

Question 16

What are the two types of logic available?

Answer 16

Hard wired logic, and programmable logic

Question 17

What are the three types of relay logic?

Answer 17

The and, or, and not functions

Question 18

What is the “and” function?

Answer 18

One relay controls a foot pedal, and one controls a limit switch. It could be wired that foot pedal “and” limit switch must both be made to activate solenoid

Question 19

Describe the “or” function used with relays

Answer 19

A foot pedal relay, “or” a limit switch relay must be made to activate solenoid

Question 20

What is a sealed in relay

Answer 20

Once it has been given a momentary on signal, it can be wired to stay on until the circuit is broken by another device

Question 21

How are ladders always shown?

Answer 21

In the de-energized state

Question 22

What does a time delay and a pressure switch look like?

Answer 22

Both look like a single pole on off switch. The time delay will have an arrow up or down for TDD or TDE. The pressure switch will have a semi-circle

Question 23

What does a normally open relay look like?

Answer 23

• –| |—- normally open

- –||— normally closed

Question 24

What is a master control relay?

Answer 24

It is used as an emergency stop in a ladder system

Question 25

What are the components of a control system in a Plc?

Answer 25

Input devices, output devices, processor

Question 26

How is a PLC selected?

Answer 26

Usually selected on the number of input and output points

Question 27

What are the major hardware components to a PLC system?

Answer 27

Chassis and backplane, power supply, processor, I/O modules

Question 28

What power supply should be used for the PLC?

Answer 28

Always use the recommended power supply device, or you risk damaging the plc

Question 29

What concepts do all PLC units run on?

Answer 29

The binary concept

Question 30

What is the basic principles of a Plc logic circuit?

Answer 30

A signal comes from an input device. It is interpreted by the processor and the set of rules programmed. The processor outputs a signal to the output module, which then sends a signal to the output device.

Question 31

What is the ROM?

Answer 31

It is the PLC program, and is non volatile memory

Question 32

What is the difference between the indicator lights on an input and output module?

Answer 32

The indicator light comes on when the input is made (limit switch activated). The output light comes on when the signal is sent, but there is no feedback to say output device is actually operating (cut wire)

Question 33

What is the examine if closed symbol?

Answer 33

—-] [—-
The XIC is true when the bit is on one
Symbol is backwards from a relay

Question 34

What is the examine if open symbol?

Answer 34

—-]/[—-
The xio instruction is true when the bit is 0
Opposite of a open relay symbol

Question 35

What is an output energize symbol look like?

Answer 35

—-( )—–

Question 36

What is the truth table for the and function?

Answer 36

Input A.    Input B.    Motor A
True.         True.         True
True.          False.        False
False.         True.         False
False.         False.        False

Question 37

What is the truth table for the or function?

Answer 37

Input A.    Input B.    Motor A
True.         True.         True
True.          False.       True
False.         True.        True
False.         False.        False