PLC programming

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Joseph Bundala
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#1

A programmable logic controller, PLC, or programmable controller is a digital computer used for automation of typically industrial electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many machines, in many industries.
https://en.wikibooks.org/wiki/Introduct ... rogramming

There are famous controllers like Allen-Bradley from Rockwell Automation and SIMATIC STEP 7 from Siemens. The architecture is the same LADDER language, but slightly differences in addressing the bits for the input, output, Latching/Unlatching, and Set/Reset the coil etc.

I have attached a book , and a website where you can practice your programming skills online by simulating your LADDER.

Try to program this:
Suppose we have an AC motor, and we want to control it by using push buttons (Start, Stop), write a program that will be "downloaded" to the controller to control the motor.
http://www.plcsimulator.net/

Note:
  • Start-button is a Normally Open button
  • Stop-button is a Normally Closed button
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Joseph Bundala
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#2

I tried to code and simulate two set ups in above problem, though my video had limited recording time, but we may have an idea about programming PLC to perform the task above.

Note: RSLogix Emulator in Allen-Bradley and STEP 7 Emulator have different ways on addressing I/O.

The idea about contacts in ladder is the same as taking into account how logic gates are behaving in AND, OR etc.
Start button==>Normally Open contact has bit '0' ,when activated has bit '1'
Stop button==>Normally Closed contact has bit '1', when activated has bit '0'
Image

In the second set up, i observed the following which may need adjustments in the code.

1. Start the motor--> The motor runs
2. Stop the motor--> The motor stops
But, when i release this stop button the motor runs again, because Start button was pressed previously . In a real practice, its not a good idea to have this connection. We may need a set up(Set Reset) which detects the rising edge of the motor to invoke reset when stop button is pressed and released. We may also add a timer to control this scenario. Imagine, the motor is running, stop button is pressed and then abruptly start button is pressed. Are we gonna kill the motor?
Video



Try this
Write the same problem, just use one push button (The Start and Stop buttons are in the same button)
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Eli
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#3

I will slowly start learning PLC programming then, thank you for your post Simulink, it is great indeed!
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