Maintenance and fault diagnosis of programmable controllers

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Maintenance and fault diagnosis of programmable controllers [Copy link]

In order to ensure the normal operation of the system , regular inspection and maintenance of the PLC system is essential, and you must also be familiar with general fault diagnosis and troubleshooting methods.

1. Inspection and maintenance

1. Regular inspection

PLC is an industrial control device . Although many measures have been taken to ensure its reliability, the working environment still has a great impact on PLC . Therefore, PLC should be checked regularly every six months . If the working conditions of PLC do not meet the standards specified in Table 1 , some emergency measures should be taken to make PLC work in the specified standard environment.

　

Table 1 Periodic inspection list

Inspection items	Check content	standard
AC Power 1. Voltage 2. Stability	1. Measure whether the voltage applied to the PLC is the rated value 2. Whether the voltage power supply changes frequently and sharply	1. The power supply voltage must be within the operating voltage range 2. Power supply voltage fluctuation must be within the allowable range
Environmental conditions temperature humidity vibration dust	Are the temperature and humidity within the corresponding range? (When the PLC is installed on the dashboard, the temperature of the dashboard can be considered as the ambient temperature of the PLC )	0~ 55 ℃ Relative humidity below 85% Amplitude less than 0.5mm (10~55Hz) No large amounts of dust, salt and iron filings
Installation conditions	Are the basic unit and expansion unit installed firmly? Are the connecting cables of the basic unit and the expansion unit fully plugged in? Are the wiring screws loose? Is the external wiring damaged?	The mounting screws must be tightened The connecting cable cannot be loose The connecting screws cannot be loosened External wiring should not have any abnormal appearance
Service life	1. Is the lithium battery voltage reduced? 2. Relay output contacts	1. Work for about 5 years 2. Lifespan 3 million times ( 35V and above)

2. Daily maintenance

In addition to lithium batteries and relay output contacts, PLC has basically no other vulnerable components. Since the random access memory ( RAM ) storing user programs , counters and auxiliary relays with retention functions are all protected by lithium batteries, the life of lithium batteries is about 5 years. When the voltage of the lithium battery gradually decreases to a certain level, the battery voltage drop indicator on the PLC basic unit lights up. Remind the user that the program supported by the lithium battery can be retained for about a week, and the battery must be replaced. This is the main content of daily maintenance.

Steps to replace lithium battery:

① Before disassembly, the PLC should be powered on for more than 15 seconds (this can charge the capacitor used as the backup power supply for the memory. After the lithium battery is disconnected, the capacitor can provide short-term power to the PLC to protect the information in the RAM from being lost);

②Disconnect the AC power supply of PLC

③Open the battery cover of the base unit

④Remove the old battery and install a new one

⑤ Put on the battery cover

The time for battery replacement should be as short as possible, generally not more than 3 minutes . If the time is too long, the programs in RAM will disappear.