Six common fault diagnosis of PLC


Detailed 5 positioning technologies of robots

1. The first type of fault (also the most faulty location) is in the relay and contactor.

For example, in the daily maintenance of the PLC control system of the production line, the largest consumption of electrical spare parts is various relays or air switches. In addition to the product itself, the main reason is that the site environment is relatively harsh, the contactor contacts are easy to ignite or oxidize, and then heat and deform until they cannot be used. Therefore, to reduce such failures, high-performance relays should be used as much as possible to improve the use environment of components and reduce the frequency of replacement to reduce its impact on system operation.

2. The second type of faults are frequently found in equipment such as valves or gates.

Because the relative displacement of the key execution parts of this kind of equipment is generally large, or it takes several steps such as electrical conversion to complete the position conversion of the valve or gate, or use the electric actuator to push and pull the valve or gate position conversion, mechanical , Electrical, hydraulic and other links are not in place will cause errors or failures. Long-term use, lack of maintenance, and mechanical and electrical failure are the main reasons for the failure. Therefore, it is necessary to strengthen the inspection of such equipment when the system is running, and deal with the problems in time. Our factory has established a strict inspection system for this type of equipment, and we often check whether the valve is deformed, whether the actuator is flexible and usable, whether the controller is effective, etc., to ensure the effectiveness of the entire control system.

3. The third type of failure point may occur on some components or equipment on switches, extreme positions, safety protection and on-site operations.

The reason may be due to long-term wear, or it may be corrosion and aging due to long-term use. The handling of this type of equipment failure is mainly reflected in regular maintenance to keep the equipment in good condition at all times. For limit switches, especially limit switches on heavy equipment, in addition to regular maintenance, multiple protection measures must be added in the design process.

4. The fourth type of failure point may occur in the sub-equipment in the PLC system.

Such equipment such as junction boxes, wire terminals, bolts and nuts, etc. In addition to the manufacturing process of the equipment itself, the cause of this type of failure is also related to the installation process. For example, some people think that the tighter the wire and screw connection, the better, but it is easy to cause disassembly difficulties during secondary maintenance. It is easy to cause damage to the connector and its nearby components. Long-term sparking, corrosion, etc. are also causes of failure. According to engineering experience, such failures are generally difficult to find and repair. Therefore, the installation and maintenance of the equipment must be carried out in accordance with the installation process required by the installation, without leaving any hidden dangers.

5. The fifth type of failure points are sensors and meters.

Such failures are generally reflected in abnormal signals in the control system. When installing this kind of equipment, the shielding layer of the signal line should be grounded reliably at one end, and should be laid separately from the power cable, especially the output cable of the inverter with high interference. The discovery and treatment of this type of failure are also related to the daily inspection, and the problems should be dealt with in time.

6. The sixth type of fault is mainly the noise (interference) of the power supply, ground wire and signal wire.

The solution or improvement of the problem mainly lies in the experience in engineering design and observation and analysis in daily maintenance.

Although PLC is a control device specially used in the field, many measures have been taken in the design and manufacture to make it more adaptable to the industrial environment, but in order to ensure the stability and reliability of the whole system, it is necessary to make the PLC have good working environment conditions as much as possible, and Take necessary anti-interference measures.

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