Programmable controllers are designed to be very easy to maintain so as to enhance maximum operation with little or no interruptions.
However, there are some aspects of maintenance that should be looked at once the system is implemented and is functioning.
There are some measures that can be taken regularly, so there will be less probability of failure in the system.
The following are some practices that should be followed to maintain the system in good operating condition this section explained.
Preventive Maintenance of PLC System
Essential elements of maintenance for the programmable controller systems are very limited that can dramatically lessen frequency of failure of system constituents.
It is recommended the preventive maintenance for the PLC system to be done together with the regular maintenance of the machine or equipment to minimize the time the equipment or the controller is off line.
However, they vary with the schedule of PLC preventive maintenance based on the condition of the environment in which the controller is installed and the worse the condition the more frequent the maintenance.
The following are guidelines for preventive measures:
- Regularly, clean or remove in occasions any filters put at enclosures in a pattern based on the dust intensity present. This filter should not be checked only when the machine is produced to be maintained, as this may cause a delay in the detection of any problem. This practice will help the clean air circulation to be available inside the enclosure.
- Make sure that you do not have dirt and dust settling all over the parts of the PLC; the central processing unit and the I/O system is not made dust proof. Dust accumulation on heat sinks and on the surface of the electronic circuitry may hinder heat from being expelled leading to a malfunction of the circuit. Additionally, if continue dust penetrates to the boards it makes a short circuit and can earlier cause the damage of the circuit board.
- The connections with the I/O modules should now and again be checked to confirm that all the plugs, sockets, terminal strips and the modules connect well. In addition, make sure that the module is properly integrated and fixed. Do this type of check more frequently in cases where the PLC system is installed in an area which is characterized by vibrations that could cause terminal connections.
- It should also be stated that heavy equipment that produces sound should not be placed near to the PLC.
- Ensure that all the objects that do not need to be in the equipment housed in the enclosure are excluded. Placing articles like drawings, installation manuals or any other article on the top of CPU rack or any other rack enclosure will hinder the airflow and result in hot spot formation, which can cause system malfunction.
- If the PLC system enclosure is installed where it is exposed to vibration, then an appropriate alarm/switch that connects to the PLC in advance should be fitted. This way, the programmable controller can be set to detect high levels of vibrations that often translates to loosening of connections.
Spare Parts of PLC System
A special stock of spare parts should be maintained since they may be required frequently.
This practice will reduce time that one has to spend because a particular component has developed a fault. In a failure situation, the right spare in place may be, at most, a matter of minutes whereas without it, it could be hours or even days.
Generally, it can be argued that the amount of a spare part to be stocked should be in the range of 10% of that part which is commonly used.
For anything used less than ten percent or any particular component of the product, then less than ten percent of that particular component can be stocked.
There should always be one spare for every component on the main CPU board, irrespective of the number of CPUs in as many as there are computers.
Each power supply; main or auxiliary, should also have a backup.
Some applications may call for a complete CPU rack as a spare and standby. This is extreme case when the downed system has to be brought to operation at the soonest possible time, no time has elapsed in order to try to identify which of the CPU boards has developed a failure.
Replacement of I/O Modules
When a given module requires to be replaced, the user should be careful in confirming that the right type of a replacement is in the process of being installed.
Each I/O system has different capabilities, whereas some of them permit switching out modules while the control of power is still on, others will require using to power off.
So, if replacing a module creates no issue but the failure recurs in quite a short time, the user should verify the inductive loads.
The inductive loads might be producing voltage and current values higher than the rated, in this case the external suppression may be employed.
If ever the fuse of the module blows again after replacement, the issue could be on the module’s output current limit, or that the output device is shorted.