• The fault 1: Programmable controller (PLC) programs lost, or PLC CPU directly damaged. Due to the moisture content of dust, the electrical conductivity becomes stronger, which is attached to the two poles of a battery, and is in the state of semi-short circuit leakage. In this way, when the battery leakage is below a certain voltage, the program stored in the PLC will be lost, causing the device to fail to operate.
• The fault 2: Dc power module short circuit causes abnormal control voltage, resulting in the failure to provide system control power, the equipment cannot work.
• The fault 3: Frequency converter trip, dc governor damaged.
• The fault 4: Contact of contactor short circuit, three-phase power short circuit fire, terminal short circuit fire. The machine breaker trips and cannot be energized to start the machine.

Case analysis is as follows: In February 2011, Dongfang TOPRA printing machine used in a factory in Zhejiang province, they feedback that the machine cannot run, after inspection is the PLC program is missing. The reason is that during the Chinese New Year holiday, when snow dissolved after snow, the weather became warm and humid, and the PLC battery cover was not well covered, and it was covered with dust, resulting in a short circuit, causing the PLC battery power leakage. The machine did not start charging for a week, so the program was lost. In addition, Dongfang TOPRA-MD1224 printing slot machine used by a factory in Guangdong province reported in April 2011 that the machine was shut down automatically after about 10 minutes of operation in use, and they analyze that it was the frequency changer tripping. After asking the customer again that the fault code of the converter was that the internal temperature of the converter was too high. Similarly, the reason is that in April, there was frequent rain, dust attached to the converter caused a short circuit, which caused the relay output circuit of the converter's own cooling fan to be abnormal or protected, and the cooling fan failed to work properly when the converter was running. After the dust of frequency converter is cleaned by air gun, the machine is started again. The heat dissipation fan of frequency converter is working normally. The frequency converter is no longer tripping and everything is back to normal. Both of the above faults are caused by wet weather and dust, so it is very important to maintain the equipment regularly during the wet season. We Should Turn a sudden stop fault into a planned stop for repair, discover hidden fault in time, accomplish prevent trouble in advance. It is especially important to prevent short circuit accidents caused by dampness.

• Method 1: to clear the dust on the attached to the electrical equipment regularly, because especially in carton factory, the size dust all has, the dust is all-pervasive, especially the small dust, easy to absorb moisture, easy to adhere to electrical components, which famous as electrical components "invisible killer". It is recommended that the average every two days to clean machine with air gun, such as PLC, frequency converter, etc.
• Method 2: tighten the contactor terminal screw to prevent short circuit caused by poor contact
• Method 3: the dust cover of electrical components must be well covered, such as the battery cover of PLC and the cover of the converter, etc, check whether the cabinet exhaust fan is intact, and replace it in time if it is broken. The door of electric appliance cabinet should be closed and the sealing gasket should be checked to see if it is in good condition. Reduce as much dust as possible into the electrical cabinet. At the same time, drying agent can be placed in the cabinet to reduce air humidity, and often replace the drying agent.
• Method 4: keep the machine at least 40-60 minutes of starting up and preheating operation every day, and let the machine preheat to generate temperature drying electronic components. Another purpose of this is to charge the PLC CPU battery, which is especially important for the machine with longer time.
• Method 5: install the dehumidifier in the workshop. Reduce humidity and prevent condensation on electrical components.
• Method 6: pay attention to rust prevention. Smear some oil on parts of machinery that are prone to rust to prevent rust.

Actually, as long as we do the above points carefully, the failure rate will gradually reduce. At the same time, it indirectly reduces the cost, improves the utilization efficiency of mechanical equipment, and thus improves the efficiency of every enterprise using equipment