The programmable Logic Control, shortly called as PLC, was first designed by an American Mechanical engineer Dick Morley on January 1st of 1968. PLC were first developed to reduce the work load of an employee in automobile industry, since then they have been used in all other harsh environments. PLC were designed to replace the hard-wired relay logic systems. Hard-wired relay system made it difficult for design engineers to alter the process. There is a chance to fail the control systems because usually PLC run constantly on harsh environments which leads to various consequences like production line and process stopping.
Here I’m trying to give a brief idea about the main reasons of why PLC system fails:
• Ground Integrity
Correct grounding is very essential for the safe of PLC as well its maintenance crew. A well grounding also helps to reduce the electrical white noise from outside. The maintenance engineer can check the earth bonding point to make sure there is no damage on earthing cable or any loose connections. They can check it by using multimeter.
• Power supply issues
The PLC must need a steady, uninterrupted flow of power for the better performance. Power supply issues can be occurred due to the breakage of cable, loose connections and failure of power supply. In most of the companies have backup power source to avoid the possibilities of power failure like uninterrupted power supplies (UPS). By using this type of secondary power source, user can at least save the processed data and shut down the system properly if need. Nowadays, in market the PLC with inbuilt battery is available. This way data can be saved properly before the system went off.
• Input output Modules & Field Devices
The main failure of PLC occurred due to the failure of field devices or power supply issues. Usually when this error occurs, either the sudden stop of system or irregularity of performance. Each of this issue denies the required signals to run the process. To resolve this issue, maintenance team will go through the system software to find the issue, normally its because of I/O point. By identifying the input output point, the engineer can trace the problem. This is may be because of the error in configuration of PLC, tripped circuit breaker, loose of terminal block, failure of 24 VDC supply or wiring issue
• Loss of Network Connection
Almost all the PLC systems have connection with peripheral devices like Human Machine Interfaces, commonly called as HMIs, and other devices to function properly. Usually we use ethernet cables to connect the PLC system with other devices. The devices cannot perform their function if any outage happened between the devices for whatever reasons. It also may lead to immediate downtime of company.
• Heat
We know that excess heat is the one of the major problem for the life of electronic equipment. The system will fail If we didn’t safeguard the PLC system properly. All the equipment should keep below the threshold temperature specified by the manufacturer. Otherwise the PLC system or peripheral system fails. The system will fail on high humidity too. There is a chance for the formation of condensation on electrical components due to high humidity. Can be avoided to an extent by providing proper air circulation techniques or HVAC systems and keep away the PLC system from the devices generating high heat.
• Electrical Noise Interference
Companies need to reduce various electrical noises like Electromagnetic interference (EMI) and Radio frequency interference (RFI) as much as possible. There are so many methods to reduce the downtime of a PLC system due to electrical noises by relocating the sensitive equipment, adding barriers, covering the sensitive equipment.