PLC Session 1

Question 1

Name 4 main parts to a PLC

Answer 1

1. Power Supply
2. CPU
3. Input Module
4. Output Module

Question 2

Name 5 Advantages of a PLC

Answer 2

• Smaller physical size than hard-wire solutions
• Easier and faster to make changes
• PLC’s have integrated diagnostics and override functions
• Applications can be immediately documented
• Applications can be duplicated faster and less expensive

Question 3

Name 5 things about PLC Inputs and outputs

Answer 3

Basic PLC Operation

Inputs and Outputs

• Inputs can be discrete or analogue
• Outputs can be discrete or analogue (discrete- triac, transistor or relay)
• Inputs and Outputs must be addressed
• Discrete inputs and outputs are simply on or off, true or false.
• Typical analogue signals are 0-10 Volts, 0-20 mA, and 4-20 m

Question 4

What do Sensors do in a PLC?

Answer 4

Sensors provide input to the plc; the sensor will receive an actual physical condition and
convert that to an electrical signal for the plc to interpret. A sensor can be as simple as a
push button or as complex as ultrasonic’s.

Question 5

What do Actuators do in a PLC?

Answer 5

Actuators convert an electrical signal from the PLC into a physical condition. Actuators
are connected to the PLC output. A motor starter is one example of an actuator that is
connected to the PLC output. Depending on the output PLC signal the motor starter will
either start or stop the motor

Question 6

What does the CPU do in a PLC?

Answer 6

The central processor unit (CPU) is a microprocessor system that contains the system
memory and is the PLC decision making unit. The CPU monitors the inputs and makes
decisions based on instructions held in the program memory. The CPU performs,
counting, timing, data comparison, and sequential operation

Question 7

What programming type language are we using with PLC’s?

Answer 7

Ladder Logic