Programmable Logic Controller Introduction

PLC (Programmable Logic Controller) is one of electronic equipments. It was called “Sequence Controller” before. It was named “Programmable Logic Controller (PLC)” by NEMA (National Electrical Manufacture Association) in 1978 and defined as electronic equipment. The operation of PLC is explained in the following steps:

Step 1

Read the external input signal, such as the status of keypad, sensor, switch and pulse.

Step 2

Using microprocessor to execute the calculations of logic, sequence, timer,counter and formula according to the status and the value of the input signal read in the step 1 and pre-write programs saved inner to get the corresponding output signal, such as open or close of relay, operation of controlled machine or procedure to control automatic machine or procedure of manufacture. PLC also can be used to maintain and adjust of production program by editing or modifying the peripheral equipments (personal computer/handheld programming panel). The common program language of PLC is ladder diagram. There are stronger functions in PLC with the development and application requirements of electronic technology, such as position control, network and etc. Output/Input signals are DI (Digital Input), AI (Analog Input), PI (Pulse Input), DO (Digital Output), AO (Analog Output) and PO (Pulse Output). Thus PLC plays an important role in the feature industry.

In todays environment of automation, the importance of PLC has rapidly increased. With growing demand for training in this area, Different companys has introduced several packages for PLC training. The standard package consists of PLC module, power supply, programming and operating software and PC/PPI cable. An optional accessory includes digital and analog expansion modules.

PLC Performs following functions.

• PLC performs relay equivalent functions
• PLC performs ON/OFF control
• Ladder diagram programming
• Designed for industrial environment

PLC INPUT Wiring:

• Push buttons
• Selector Switches
• Limit Switches
• Level Switches    
• Photoelectric Sensors
• Proximity Sensors 
• Motor Starter Contacts 
• Relay Contacts 
• Thumb wheel Switches 

PLC OUTPUT wiring 

• Valves 
• Motor 
• Starters 
• Solenoids 
• Control 
• Relays
• Alarms 
• Lights 
• Fans 

Internal Structure of PLC  

 

Selecting PLC hardware

•       Inputs/Outputs

–      Type,

•       AC, DC, sourcing, sinking, etc.

–      Number of

•       10, 16, 20, 32, 156

•       Memory

–      Type

•       Flash or Battery backed

–      Size

•       1k, 6k, 12k, 16k, 64k

•       Functions required

–      Instruction set

•       Messaging

•       PID

•       PTO, PWM

–      Arithmetic

–      Communications

•       DeviceNet, Ethernet

•       Remote I/O, DH+

–      Report generation

PLC application  

•       Solenoid 1

–      On  = Sol 3 is off, and Motor is off, and Sensor 2 is off, and Auto Switch is on

–      Off  = Sol 3 is on, or Motor is on, or Sensor 2 is on

•       Solenoid 2

–      On  = Sol 3 is off, and Motor is off, and Sensor 2 is on

–      Off  = Sol 3 is on, or Motor is on, or Sensor 1 is on

•       Motor

–      On  = Sensor 1 is on, and Solenoid 2 is off, and Solenoid 1 is off

–      Off  = Solenoid 3 on

•       Solenoid 3

–      On  = Sol 1 is off, and Sol 2 is off, and Motor has run for 30 sec.

–      Off  = Solenoid 3 has been on for 60 sec.

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Basic PLC Ladder Programming Example 14

Basic PLC Ladder Programming Training Example 14 : 24 Hour clock using Counter PLC Ladder Program 

Basic PLC Ladder Programming Training Examples for Beginners. Hi Friends here we are starting a series of Free Training on PLC Ladder Programming. These PLC Ladder Programs are important to get basics of Ladder Programs

PLC Ladder Practice Problem:

•  Using 3 counters together with the flag of M1013 (1s clock pulse) to operate a 24-hour clock. 

Topics Covered in this example is use of Counter in PLC Program  

Number of PLC Counter Required 

C0 - count per second

C1- count per minute

C2 - count per hour 

Number of PLC internal memory flag Required

M1013 - 1s clock 

PLC Ladder Programming:

PLC Ladder Programming Description: 

.

• The key of operating a 24-hour clock is to use M1013 (1s clock pulse). When the program is executed, C0 will count once per second. When the counted number reaches 60(1 minute), C0 = ON. C1 will count once, and C0 will be reset at the same time; similarly, when the counted number in C1 reaches 60(1 hour), C1 = ON. C2 will count once, and C1 will be reset at the same time. Furthermore, when the present value in C2 reaches 24, C2 will be reset, and the 24-hour counting process will start again.

• The 24-hour clock operates by using C0 to count “second”, C1 to count “minute” and C2 to count “hour.” In this clock, the value of “second”, “minute” and “hour” can be read by C0, C1 and C2 correspondingly. When the set value of C2 is 12, the clock will be a 12-hour clock.  

See More Examples here

PLC Ladder Programming Example 1

PLC Ladder Programming Example 2

PLC Ladder Programming Example 3

PLC Ladder Programming Example 4

PLC Ladder Programming Example 5

PLC Ladder Programming Example 6

PLC Ladder Programming Example 7

PLC Ladder Programming Example 8

PLC Ladder Programming Example 9

PLC Ladder Programming Example 10

PLC Ladder Programming Example 11

PLC Ladder Programming Example 12

PLC Ladder Programming Example 13

PLC Ladder Programming Example 14

PLC Ladder Programming Example 15

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