8 Steps to PLC Commissioning

After learning how to program a PLC, putting your very own program into a Programmable Logic Controller and actually connecting the input and output devices into it may be exciting, but you actually have to follow some basic precautions before the thrill carries you away.

In this post, you will learn about the basics of PLC Commissioning: What PLC Commissioning is, Why you should do PLC Commissioning, and How you can do PLC Commissioning.

What is PLC Commissioning?

PLC Commissioning is a series of careful examinations done in a PLC control system to ensure that the controller, program, input and output devices, and associated wiring conform to the specifications of the design.
Before you start PLC commissioning, it is important that you eliminate the possible hazards in your workspace first.

This means that actuators, especially ones that produce powerful movements such as motors or valves must be disconnected from the programmable logic controller.

With that out of the way, here are the steps to get you started with PLC Commissioning.

Steps in PLC Commissioning

PLC Commissioning Basics
PLC Commissioning: Header Image

1. Cable connections must meet standards

All cable connections between the PLC, the input devices, the power supply, the output devices, and the programming device must be checked thoroughly as they are the media that the PLC uses to communicate between each of the devices.

All cables must meet the required specifications according to the standards, it should even meet the local standards set for the specific hardware.

2. Check the power supply

The power supply of the PLC must match the voltage setting of the PLC.

The voltage setting of the power supply must also conform to the voltage ratings of the input and output devices, otherwise, one of the two must be replaced by another device.

3. Check indicator lights of the PLC

The indicator lights on the PLC should determine if the PLC will work properly.

If the power is properly applied, the power indicator of the PLC should turn on. Fault indicators are usually installed on PLCs, so ensure that the fault light is not turned on at this point.

4. Put PLC in a test mode.

The PLC must be put in a mode that prevents it from sending an output voltage or current to the output devices.

This can either be called “Disable” or “Continuous test” mode depending on the PLC manufacturer.

In this mode of operation, the outputs will be de-energized, so you are assured of your safety when testing.

5. Check protective devices

In this step, you must ensure that the protective devices of the PLC are set to their proper trip settings.

6. Check emergency stop buttons

The emergency stop buttons, usually normally closed push buttons, must be checked thoroughly because these buttons are the ones that will stop ALL PLC operations in an emergency event.

7. Check connection points of input and output devices

In this step, the connection points of all input and output devices must be double-checked.

Make sure that each device is connected to the proper address according to the program present in the PLC memory.

If you fail to do this step, you may encounter issues such as the output being turned on at inappropriate times (usually because of the wrong sensor being activated).

So, pay extra attention to this step.

8. Test the software

After all of the previous steps have been performed, it is now time to load the program into the PLC and start testing the software.

Testing the software is relatively easy as most PLCs contain software-checking programs already.

Even though this step checks the program for incorrect device addresses, it is always important to do the preceding step (Checking connection) in order to save time.

The PLC provides a printout of the input and output points that were used, along with the counter presets, timer settings, with the errors that it has encountered.

If you already did a great job in the preceding steps, doing this only serves as a “proofread” for all the things that you have performed.

Testing the Input and Output Devices

In testing the input and output devices during the PLC commissioning process, you must check them one at a time to ensure that each device works properly according to specifications.

That may sound tedious, but it is actually worth the time.

In project management, or in any step-oriented work, there is a rule of thumb that must be followed, that is “The later you catch a mistake, the harder it is to correct”.

Just imagine if you missed a tiny detail that caused several hours of downtime in your system: More time would be spent troubleshooting the system, and you would have to perform PLC Commissioning again, anyway.

Input Devices

PLC Commissioning: Input Devices (Photo from Siemens)
PLC Commissioning: Input Devices (Photo from Siemens)

In testing the input devices, you should be able to manually check each device by using pilot lights at the output side of the Programmable Logic Controller.

Because input devices are usually in the form of switches, the pilot lights at the output side of the PLC can suffice to represent the switching conditions of the input devices.

You should obviously have to learn about the different input devices for the PLC before you start testing them: just the knowledge of activating them and knowing what each input device should be used for may already be enough, but that shouldn’t stop you from learning more about it!

Of course, because the devices are being tested one at a time, then you must connect each device to the same input terminal at the I/O side of the PLC.

Output Devices

PLC Commissioning: Output Devices - Solenoid
PLC Commissioning: Output Devices – Solenoid

In testing the output devices, make sure that you disconnect every single device from the PLC.

Testing the output devices requires that you use the appropriate source for that output device and make sure that it runs according to specifications.

Similar to input devices, the testing must be done one device at a time.

Simply put, testing output devices not only allows you to check whether each device is working or not, but it also allows you to check if it still performs accordingly.


PLC Commissioning is a process that involves doing each and every detail of setting up a PLC system with a safety precaution in mind. Also, it is a good investment of your time because it lessens the possibility of failures in the future.

Thank you for reading!