How to maintain a PLC (Programmable Logic Controller)

Updated: March 2020

Why is PLC Maintenance Important?

PLCs (programmable logic controllers) are such an integral part of the automation world, and in turn a major contributor to the industrial market. Downtime can be incredibly costly, and finding parts for legacy units can be difficult and time consuming. (MRO Electric sells many legacy and discontinued automation components, from top brands) Therefore, properly maintaining your PLC can avoid unnecessary headaches and get the most life out of your units.

Pre-Maintenance Checklist

Before starting preventative maintenance on your PLC, make sure to do the following:

  1. Back up your PLC program prior to getting your hands dirty (it’s also a good idea to always keep a master copy of operating programs on hand).
  2. Follow proper lockout/tagout procedures.
  3. Remove power from the system. Power should always be off and unplugged during maintenance.
  4. Audit all parts in use.

PLC Maintenance Procedures

This is a good guidebook to use when performing preventive PLC maintenance:

  1. Check environmental factors / operating conditions. Humidity, temperature and other factors play an important role in the longevity and proper operation of your components. Be sure that these factors are consistently within the range of your PLCs optimal operating conditions.
  2. Clear debris, dust, and buildup from your units. A clean working environment for your PLC is a great way to prevent downtime. Also, dust getting to the circuit boards could cause a catastrophic short circuit.
  3. Clean or replace all filters installed in enclosures. This allows your PLC to get the maximum airflow and ensures consistency.
  4. Check all your connections for a tight fit, especially I/O modules. This is a very simple way to make sure everything is working smoothly. Also, a loose connection may cause lasting damage to your components.
  5. Inspect I/O devices for proper adjustments.
  6. Check LED battery indicators on the RAM memory module in the CPU. If the OK LED is on or flashing, replace the battery ASAP.

Other Things to Keep in Mind

  1. Calibrate circuit cards with process control analogs every 6 months.
  2. Service devices such as sensors every month.
  3. Never place other pieces of equipment that produce lots of noise or heat close to your PLC.

How to maintain a PLC (Programmable Logic Controller)

As many of us know, PLCs (programmable logic controllers) are staples in the factory automation world. In order to have them running optimally and as efficiently as possible, routine maintenance is imperative. Generally, manufacturers produce PLCs to endure strenuous, unsterilized environments. By adhering to an adequate maintenance schedule, PLCs operating timeframe can be lengthened.

Protect your PLC

Always be on the lookout for corrosive and conductive contaminants that have the potential to become a detriment to a PLCs’ components. By completing visual inspections for black dust and blowing airborne particles from the PLC’s vicinity, you are lowering the likelihood of contamination.

Is power flowing?

A PLC will not operate correctly without adequate power. To avoid any operation bugs, remain vigilant of any surges or shorts.

Calibrate Analog Components

Always refer to the preventative maintenance schedule for any analog input device. Analog inputs need to be cleaned regularly and calibrated as accurately as possible.

Take EMI into consideration

EMI (electromagnetic interference) is known to cause horrible issues for PLCs without clearly indicating what the specific issue is or how to go about fixing it. To remain ahead of the game, many perform an audit of the local wiring to pinpoint potential EMI sources before they interfere with the operation of your PLC. Lower-level components and high-current wires often interfere with each other, which wiring designs must take into consideration.

Additional PLC Maintenance Tips

By creating a PLC maintenance checklist and adhering to it strictly, operating errors can likely be avoided. The space between the PLC and the machine it’s controlling should be minimal.

MRO Electric and Supply has new and refurbished Modicon PLC parts available here. We also offer repair pricing. For more information, please call 800-691-8511 or email

Updated on May 14, 2020 by David Link

Joe Kaminski

Joe Kaminski is an industrial automation specialist at MRO Electric. He has a background in industrial engineering and supply chain management. Joe has worked in the automation industry for over 10 years providing support to some of the largest companies in the world. For more info, visit

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