REF615C-D Three processes of PLC troubleshooting

A peripheral circuit component is faulty
This kind of failure often occurs in the failure of the PLC after working for a certain time. In the PLC control loop, if there is a component damage failure, the PLC control system will automatically stop working immediately.
The input circuit is the PLC to accept the switching quantity, analog quantity and other input signals port, the quality of its components, wiring method and whether it is reliable is also an important factor affecting the reliability of the control system. For the switching output, the PLC output has relay output, thyristor output, transistor output in three forms, the specific choice of which form of output should be determined according to the load requirements, improper selection will reduce the reliability of the system when the system can not work normally.
In addition, the PLC output terminal load capacity is limited, if it exceeds the specified maximum value, it must be connected to an external relay or contactor in order to work normally.
The quality of actuator components such as external relays, contactors and solenoid valves is an important factor affecting system reliability. Common faults include coil short circuit, mechanical failure resulting in contact immobility or poor contact. The terminal cable is in poor contact
This kind of failure occurs after the PLC works for a certain time with the increase of the frequency of equipment action. Due to the wiring defects of the control cabinet or the intensification of vibration during use and the mechanical life, the connector or component terminal is easy to loose and cause poor contact.
The method of troubleshooting such faults is to use a multimeter, with the help of the control system schematic diagram or PLC logic ladder diagram for fault diagnosis and maintenance. For some of the more important peripheral terminal wiring, in order to ensure reliable connection, the method of welding cold press sheet or cold press pin is generally used.
Functional failure of PLC caused by interference
The various types of PLCS used in automation systems are control devices specifically designed for industrial production environments. In the design and manufacturing process, multi-level anti-interference and selected components are adopted, so it has a strong ability to adapt to the harsh industrial environment, operating stability and high reliability. Therefore, generally do not need to take any special measures can be used directly in the industrial environment. PLC interference can be divided into internal interference and external interference. In the actual production environment, the external interference is random, independent of the system structure, and the interference source can not be eliminated and can only be limited for specific circumstances.
Internal interference is related to system structure. It is mainly caused by the AC main circuit and analog input signal in the system, and the internal interference can be suppressed to the maximum extent by carefully designing the system circuit or filtering the system software.
The PLC breaks down periodically
PLC periodic crash is characterized by PLC crash or program chaos every several times, or different interruption fault display, and everything is normal after restart. According to practical experience, the most common reason for this phenomenon is due to the long-term ash accumulation of the PLC body. Therefore, the PLC rack slot interface should be regularly purged. When purging, you can first use compressed air or a soft brush to purge the dust on the control board and in each slot, and then wipe the slot and the plug of the control board with 95% alcohol. After cleaning carefully check again, restore the boot can run normally.