Programmable Logic Controllers

Question 1

it is a special form of microprocessor-based
controller that uses programmable memory to
store instructions and to implement functions
such as logic, sequencing, timing, counting, and arithmetic in order to control machines and processes

Answer 1

programmable logic controller (PLC)

Question 2

when did PLC began?

Answer 2

1970s

Question 3

this is the component that provides power to a PLC CPU and I/O. The power supply must convert the line voltage to around 5VDC for the PLC to use.

Answer 3

power supply

Question 4

what are the types of power supply?

Answer 4

24 volts DC
100 - 240 volts AC
110/220 volts AC

Question 5

this is the component that processes information and carries out instructions in a PLC. This is also known as the processor or controller

Answer 5

central processing unit (CPU)

Question 6

types of input module

Answer 6

DC -12 volts
DC -24 volts
110/220 volts AC

Question 6

the component where output devices are
physically connected to a PLC. The input
module transfer signals from the internal relay

Answer 6

output module

Question 6

types of output module

Answer 6

Transistor type (24 VDC)
Relay/Contact Type(24 VDC/220 VAC)
TRIAC Type (110/220 VAC)

Question 6

the component where input devices are
physically connected to a PLC. The input
module transfer signals to the internal relay.

Answer 6

input module

Question 7

this provides a path to supply common (sinking-sourcing concept)

Answer 7

sinking

Question 8

this provides a path to supply source (sinking-sourcing concept)

Answer 8

sourcing

Question 9

What are the two major types of PLC?

Answer 9

• fixed/integrated/compact
• modular

Question 10

this type of PLC is one of the earliest types used back in the 1970s and is very compact with a simplistic design and is the least expensive of PLC types on the market.

Answer 10

fixed

Question 11

what are the advantages of fixed type PLC?

Answer 11

• Less scanning time
• Usually small, have less memory so cost is less
• Less troubleshooting time so less downtime

Question 12

what are the disadvantages of fixed type PLC?

Answer 12

• Limited number of inputs and outputs
• Not suited for future expansion
• If part of unit fails, the entire unit may need
  replacement

Question 12

this type of PLC allows multiple expansions of the PLC system through the use of modules, hence the term “modular”. Modules give the programmable logic controller additional features like
increased number of I/O units, and they are usually easier to use because each component is independent of each other.

Answer 12

modular

Question 12

what are the advantages of modular type PLC?

Answer 12

• The main advantage is that the number of input and output terminals can be expanded to cope with the changes to the hardware system
• Modules can be easily installed or removed without affecting other
  modules