1, in the relay, contactor on the point of failure
This is the most frequent point of failure. Such as the production line plc control system in the daily maintenance, the largest consumption of electrical spare parts for all types of relays or air switch. The main reason in addition to the product itself, is the site environment is relatively poor, contactor contacts easy to fire or oxidation, and then heat deformation until it can not be used. Therefore, to reduce such failures should try to use high-performance relays, improve the use of components environment, reduce the frequency of replacement, in order to reduce its impact on system operation.

2, in the valve, the gate on the point of failure
Because the key implementation of such equipment, the relative displacement is generally large, or to go through electrical conversion and other steps to complete the valve or gate position conversion, or the use of electric actuators push the valve or gate position conversion, mechanical , Electrical, hydraulic and other aspects of a little bit in place will produce errors or failures. Long-term use of the lack of maintenance, machinery, electrical failure is the main cause of failure, so the system is running to strengthen the inspection of such equipment, found the problem in a timely manner. I plant on the establishment of such equipment strict inspection system, often check whether the deformation of the valve, the implementation of flexible institutions are available, the controller is valid, etc., a good guarantee of the effectiveness of the entire control system.

3, in the switch, limit and other components on the fault point
The reason may be due to long-term wear, it may be long-term without rust aging. For such equipment failure is mainly reflected in the regular maintenance, so that equipment at all times in good condition. For limit switches, especially heavy-duty equipment on the limit switch in addition to regular maintenance, but also in the design process to add multiple protection measures.



4, in the system neutron device on the point of failure
Such equipment such as junction boxes, wire terminals, bolts and nuts. The reason for this type of failure in addition to the equipment itself, the production process and the installation process is also related to, if some people think that the wire and screw connection is the pressure of the more tight, but in the second maintenance can easily lead to demolition difficult, Likely to cause damage to the connector and its nearby parts. Long-term ignition, corrosion, etc. is also the cause of failure. According to engineering experience, such failures are generally difficult to find and repair. So the installation and maintenance of equipment must be installed in accordance with the requirements of the installation process, leaving the equipment hidden.


5, in the sensor and instrument on the point of failure
This type of failure in the control system is generally reflected in the signal is not normal. This type of equipment installation of the signal line shield should be single-ended grounding, and as far as possible with the power cable separately laying, especially the high interference of the inverter output cable. The discovery and handling of such failures is also related to the daily inspection, found that the problem should be dealt with in a timely manner.

6, in the power, ground and signal lines on the interference source of the fault point
The solution or improvement of the problem lies mainly in the design experience and the observation and analysis in routine maintenance. Although the PLC is a special control device used in the field, in the design and manufacture has taken a lot of measures to make it more adaptable to the industrial environment, but in order to ensure the stability and reliability of the entire system, or should try to make PLC a good working environment conditions, and Take the necessary anti-jamming measures.

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