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Home / Technical Articles / 4 Steps To Follow During Commissioning of a PLC System

PLC programs are never final…

Yes, PLC programs are never final, it is always possible to make corrections and subsequent adaptations to new system according the customer requirements. Even during commissioning, program changes are often necessary.

4 Steps To Follow During Commissioning of a PLC System (photo credit:

The commissioning of a system can be divided into four steps:

  1. Checking the hardware
  2. Transferring and testing the software
  3. Optimization of the software
  4. Commissioning of the entire system

1. Checking the hardware

Each sensor, switch and button is connected to a specific input and each actuator to an output. During engineering process addresses and wires must not be mixed up. Also, the sensors and actuator placing should be checked (that they are where they have to be in the automated system).

During checking procedure, the outputs are set in a test mode. The actuators must then meet the specified requirements (functions). If changes are made, then the documentation (allocation list, drawings, etc) must also be updated to respond to reality.

PLC hardware
PLC hardware (photo credit: BR Automation)

1.1 Testing inputs and outputs

Input devices, e.g. switches, can be manipulated to give the open and closed contact conditions and the corresponding LED on the input module observed. It should be illuminated when the input is closed and not illuminated when it is open.

Failure of an LED to illuminate could be because the input device is not correctly operating, there are incorrect wiring connections to the input module, the input device is not correctly powered or the LED or input module is defective. For output devices that can be safely started, push buttons might have been installed so that each output can be tested.

Go back to Steps ↑

2. Transferring and testing of software

Prior to commissioning, all available off-line and virtual PLC program testing tools should be used intensively to find program faults. For example, such test tool is in STEP 7 as subprogram S7-PLCSIM. It simulates the work of a PLC (virtual PLC) and allows the user written PLC program to be tested.

Following this, the program is transferred to a central processing unit in the virtual PLC. The entire program is executed without using the real PLC.

The user has to simulate the input signal changes and verify how the outputs react to it. Some PLCs offer simulation in a real PLC: the entire program is executed in a PLC without the real inputs and outputs being connected. Processing of the PLC outputs thus only takes place in the PLC image table. The physical PLC I/Os are not updated to/from the PLC I/O images.

Therefore this eliminates the risk of damaging machines or system parts.

After this, the individual user program parts and system functions are tested: manual operation, setting, individual monitoring programs etc. and finally the interaction of the program parts with the help of the main program.

The system can and should be commissioned step-by-step. Important aspects of commissioning and fault detection are the test functions of the programming system, such as the single-step mode or the setting of stop points. The single-step mode in particular is of importance, whereby the program in the PLC memory is executed line-by-line or step-by-step. In this way, any program faults which may occur in the program can be immediately localized.

Go back to Steps ↑

3. Optimization of the software

User programs can almost always be improved after the first test run. It is important that any corrections or modifications are made not just in the PLC user program, but are also taken into account in the documentation.

4. Commissioning of the entire system

This already occurs in part during the testing and optimization phase. Once the final status of the PLC user program and the documentation is established, all the controller functions (in accordance with the automation task) need to be executed step-by-step again.

If no faults occur by the entire system commissioning, then the system is ready to be handed over to the customer.

PLC panel during commissioning
PLC panel during commissioning (photo credit:

Go back to Steps ↑

References //

  • Application of PLC industrial automation – AutoMatic
  • Programmable Logic Controllers by W. Bolton

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More Information

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. Mallay Festus Bangura
    Nov 13, 2020

    Am seriously benefiting from your valuable information and hope to be able to share this with other colleagues in the engineering discipline

  2. Shumon
    Oct 27, 2020

    Everything is very open with a very clear clarification of the issues. It was definitely informative. Your site is extremely helpful. Thanks for sharing!

  3. Vijay Panchal
    Jul 03, 2019

    I take type of drive and servo motor for repairing purpose. I want to its data book and service book

  4. Abba Babagana
    Jul 03, 2019

    Dear Mr Edvard Csanyi, I find your posting very interesting and useful and yet simple. Please kindly avail me some good specific Auto-cad and LV/MV design softwares for possible use in my designs in buildings and industries.
    I am writing from Nigeria west Africa.

  5. Ryan Pereira
    Feb 15, 2017


    We recently loss our electrical engineer. Which he wrote all our programs for our hydraulic press. Quite recently there have been a lot of plc’s coming back to us with the problem of them losing their memory due to battery going dead. We have records of all our presses, and I think I know how to up load then. But I am not sure how to test to make sure it will works. As they just send over the plc’s and we send it back to them as the companies could be anyway in the world.

    Ryan Pereira
    Production Manager

    FXD Engineering PTY LTD
    10 Christable Way
    Landsdale W.A Perth 6065
    Phone: +61 8 9303 4466
    Mobile: +61 423 458 872
    Email: [email protected]

    • I want to help you out
      Apr 27, 2017

      Can you send me sample program & details so I will check

  6. subodh arya
    Sep 22, 2015

    It’s really a good experience reading things on electrical engineer portal about automation . I recently started working on automation taking a training to work on different plc , hmi and scada .

  7. Touy
    Aug 25, 2015

    It very helpful to study about electrical engineer

  8. Calvin-huy103
    Aug 16, 2015

    Can you send me link to download 2 book :
    Application of PLC industrial automation – AutoMatic
    Programmable Logic Controllers by W. Bolton

    • Prince Daniel Ikenna Paul
      Jul 02, 2019

      I really like everything I’m seeing here. Please have can I get your books and a video copy of everything.

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