What are the common faults of PLC?

When the PLC is powered on, the POWER indicator is on, indicating that the power is normal. If the POWER indicator is not on, the power supply section is faulty. Check whether the power cable is disconnected, the terminals are not properly connected, and so on.

2. When the system is in operation or monitoring status, the PUN light on the host is off, indicating that the basic unit is faulty.

3. When an input contact is connected, the corresponding LED is off, indicating that the input module is faulty. When the output LED is on and the corresponding output contact does not operate, the output block is faulty.

4. When the BATTERY lamp is on, indicating that the lithium battery voltage is not enough, it should promptly replace the battery management.

5. When the ERROR light flashes, the reason may be a degree of syntax error, PLC internal fault, external interference, lithium battery voltage is not enough and so on.

6. When the ERROR light is on, it indicates that the PLC has malfunctioned. Monitor the timer so that the CPU resumes normal operation. This condition may be caused by interference or internal faults.

PLC is composed of semiconductor devices, the aging phenomenon is inevitable after long-term use, it should be regularly checked and maintained PLC. Maintenance time 1-2 times a year generally more appropriate, if the work in harsh environments should be based on the actual increase the frequency of maintenance and maintenance, in peacetime, you can often use a dry cloth for the PLC surface and the wire between the dust pollution Keep working environment clean and hygienic. Maintenance of the main items are the following:

1. Overhaul the power supply. It is possible to detect at the power terminals whether the voltage is within ± 10% of the allowable range.

Working environment Focus on checking temperature, humidity, vibration, dust, interference, etc. are in line with the standard working environment.

3. Input, output power. Can be measured at the corresponding terminal voltage range is red meet the specifications.

4. Check the installation status. Check each module and the module is connected to the wire and the cable between the module is not loose, the external components of the screw is loose. Whether the first year of aging and so on.

5. After checking the battery voltage is in line with standards, such as metal parts are corroded.

In the process of overhauling and maintaining, if any unacceptable situation is found, it should be timely adjusted, repaired and recorded for future reference.

PLC common faults can be divided into several categories, according to classification, can help you analyze the fault occurred parts and causes:

1. External equipment failure. Such failures come from external devices such as various sensors, switches, actuators and loads. This part of the equipment failure will directly affect the system control functions. Such failures are generally caused by the quality and life of the equipment itself.

2 system failure. This is a global failure that affects the operation of the system. System fault can be divided into fixed fault I accidental fault. If the fault occurs, you can restart the system back to normal, give us the same computer system, can be considered a contingency. On the other hand, if the system can not reside normally due to the restart of the system and can not be restored, the system can be considered as a permanent fault. This failure is usually caused by improper system design or long system operation.

Hardware failure. Such failures mainly refers to the failure of the modules in the system, such as CPU, memory, power supply, I / O modules, etc., especially the I / O modules. Such failures than the general

Obviously, and the impact is also accompanied, they are mainly caused by improper use or use of time, aging components within the module.

4 software failure. Such failures are caused by errors contained in the software itself. Mainly software design considerations. In the case of non-implementation will be triggered once the conditions are met. In the practical engineering application, the software error is almost unavoidable due to the complexity and heavy workload of the software, which raises the question of the reliability of the software.

If a PLC control system fails during operation, it can use its own self-diagnostic function to determine the fault as long as the CPU can operate. PLC self-diagnosis has many fault diagnosis, mode function. However, due to different PLC manufacturers, models are different, self-diagnostic function is not consistent, what specific models of PLC products in the end what self-diagnostic capabilities, we need to see the corresponding manual, a PLC system, can provide the following general Self-diagnostic function:

1. Using the system status word and control to determine the fault. We can generally use the programming software to read the system's status word or control word directly on the screen. Depending on the status word, it is possible to see if the hardware and software arrangements are reasonable. I / O address, expansion rack, etc. are in use or are they malfunctioning? You can also analyze an address number based on what you read. Rack, slot, or even some I / O point has failed. With the improvement of CPU performance, the more status words PLC can provide, the more self-diagnosis capability will be.

Use PLC interrupt or stack to determine the fault. Interrupts and stacks are specific areas of data in which PLCs are running and are automatically formed and callable for display by the system's self-diagnostic software. We can also adjust the content to determine the fault.