Programmable Logic Controllers (PLCs) are a new type of general-purpose automation control device that integrates traditional relay control technology, computer technology, and communication technology. They are increasingly widely used due to their advantages such as strong control functions, high reliability, flexible and convenient use, and easy expansion. However, in industrial production sites, the harsh working environment and numerous interference sources, such as voltage fluctuations caused by the starting or stopping of high-power electrical equipment, generating low-frequency interference, and power frequency interference generated by electromagnetic coupling from welding machines, EDM machine tools, and motor brushes, can all affect the normal operation of the PLC. Although PLCs are specifically designed for field use and are designed and manufactured to be adaptable to industrial environments, to ensure the stability and reliability of the entire system, it is still necessary to provide the PLC with good working environmental conditions and take necessary anti-interference measures. Points to note during PLC installation and maintenance: 1. PLC Installation: PLCs are suitable for most industrial sites, but they still have certain requirements regarding the usage environment and ambient temperature. Controlling the PLC's working environment can effectively improve its efficiency and lifespan. When installing a PLC, avoid the following locations: (1) Ambient temperature exceeding 0-50℃; (2) Relative humidity exceeding 85% or condensation (caused by sudden temperature changes or other factors); (3) Direct sunlight; (4) Corrosive and flammable gases, such as hydrogen chloride and hydrogen sulfide; (5) Large amounts of iron filings and dust; (6) Frequent or continuous vibration with a frequency of 10-55Hz and an amplitude of 0.5mm (peak-to-peak); (7) Impacts exceeding 10g (gravitational acceleration). The small programmable controller has mounting holes at each of the four corners of its casing. There are two installation methods: one is screw fixing, with different installation dimensions for different units; the other is fixing with a DIN (German Republican Standard) rail. The DIN rail comes with a pair of mounting plates on each side. First, install the left and right mounting plates on the rail, then install the PLC, and finally tighten the screws. To ensure reliable control system operation, programmable logic controllers (PLCs) are typically installed in a protective enclosure within a control cabinet to prevent dust, oil, and water splashes. To maintain the PLC's temperature within the specified ambient temperature range during operation, the installation should have sufficient ventilation space, with a minimum distance of 30mm between basic and expansion units. If the ambient temperature exceeds 55°C, a fan should be installed for forced ventilation. To avoid electrical interference from other peripheral devices, the PLC should be kept as far away as possible from high-voltage power lines and equipment, with a minimum distance of 200mm between the PLC and high-voltage equipment and power lines. When the PLC is installed vertically, care must be taken to prevent wire ends, metal shavings, etc., from falling into the PLC through the ventilation window, causing short circuits on the printed circuit board, resulting in malfunction or even permanent damage. 2. Power Supply Wiring The PLC is powered by 50Hz, 220V±10% AC. The FX series PLC has a DC 24V output terminal. This terminal provides DC 24V power to input sensors (such as photoelectric switches or proximity switches). If a power failure occurs and the interruption time is less than 10ms, the PLC operation will not be affected. If the power interruption exceeds 10ms or the power drop exceeds the allowable value, the PLC will stop working, and all output points will be disconnected simultaneously. When the power is restored, if the RUN input is connected, the operation will proceed automatically. The PLC itself has sufficient immunity to interference from the power line. If the power interference is particularly severe, a 1:1 isolation transformer can be installed to reduce interference between the equipment and ground. 3. Proper grounding is an important condition for ensuring the reliable operation of the PLC and can avoid the damage caused by accidental voltage surges. The grounding wire should be connected to the grounding terminal of the machine, and the basic unit should be grounded. If an expansion unit is used, its grounding point should be connected to the grounding point of the basic unit. To suppress interference applied to the power supply, input terminals, and output terminals, a dedicated grounding wire should be connected to the programmable controller, and the grounding point should be separate from the grounding point of the power equipment (such as motors). If this requirement cannot be met, it must be grounded together with other equipment, and series grounding with other equipment is prohibited. The grounding point should be as close to the PLC as possible. 4. When using passive contact input devices with DC 24V terminals, the PLC's internal 24V power supply provides 7mA of current per input point through the input device. The 24V terminals on the PLC can also supply current to external sensors (such as proximity switches or photoelectric switches). When the 24V terminal is used as a sensor power supply, the COM terminal is the DC 24V ground terminal. If an expansion unit is used, the 24V terminals of the basic unit and the expansion unit should be connected together. Furthermore, no external power supply should be connected to this terminal. In case of overload, the voltage will automatically drop, and the input at that point will have no effect on the programmable controller. The number of input points for each PLC model is specified. Each unused input point does not consume power, therefore, in this case, the current supply capacity of the 24V power supply terminal can be increased. Unused terminals on FX series PLCs should never be used under any circumstances. 5. Input Wiring: PLCs generally accept switching signals from limit switches, travel switches, etc. Input terminals are the ports for converting signals between the PLC and external sensor loads. Input wiring generally refers to the wiring between external sensors and input ports. The input device can be any passive contact or an open-collector NPN transistor. When the input device is turned on, the input terminal is connected, the input line is closed, and the LED of the input indicator lights up at the same time. The primary circuit and the secondary circuit of the input terminal are isolated by optocoupler. The secondary circuit is equipped with an RC filter to prevent PLC malfunction caused by input contact bounce or electrical noise introduced from the input line. If a diode is connected in series in the input contact circuit, the voltage across the diode should be less than 4V. If a reed switch with an LED is used, the number of diodes connected in series should not exceed two. In addition, the following points should be paid special attention to when wiring the input: (1) The input wiring should generally not exceed 30m. However, if the environmental interference is small and the voltage drop is not large, the input wiring can be longer. (2) The input and output lines should not be on the same cable and should be separated. (3) The width of the pulse signal that the programmable controller can accept should be greater than the scan cycle time. 6 Output wiring (1) The programmable controller has three forms: relay output, thyristor output, and transistor output. (2) Output terminal wiring is divided into independent output and common output. When the output relay or thyristor of the PLC operates, the two output terminals of the same number are connected. Different types and voltage levels of output voltage can be used in different groups. However, the outputs in the same group can only use the same type and voltage level of power supply. (3) Since the output components of the PLC are encapsulated on the printed circuit board and connected to the terminal board, if the load connected to the output component is short-circuited, the printed circuit board will be burned. Therefore, fuses should be used to protect the output components. (4) When using relay output, the size of the inductive load affects the working life of the relay. Therefore, the working life of the relay is required to be long. (5) The output load of the PLC may generate noise interference. Therefore, measures should be taken to control it. In addition, for dangerous loads that can cause harm to users, in addition to considering them in the control program, an external emergency stop circuit should be designed so that when the programmable controller fails, the power supply of the load that causes harm can be cut off. AC output lines and DC output lines should not use the same cable. Output lines should be kept as far away as possible from high-voltage lines and power lines, and parallel operation should be avoided.