Power wiring part:
Power input: Generally speaking, three-phase AC (L1, L2, L3) is connected to the control cabinet as the main power supply. These three phase lines provide the main source of electrical energy, providing power for the PLC system and the connected external devices. For example, in an industrial production site, the factory’s three-phase power supply line will be connected to the power input of the PLC control cabinet.
Neutral (N) connection: The neutral line is the path for the current to return in the circuit, and together with the phase line, it forms a complete AC circuit. It provides a loop for some equipment or circuits that require 220V voltage, such as small transformers and indicator lights in some control circuits.
Main circuit breaker and fuse: The main circuit breaker is the main power switch of the entire control cabinet. When an overload, short circuit or other fault occurs in the circuit, the main circuit breaker will automatically trip and cut off the power supply to protect the safety of equipment and personnel. The fuse is an overcurrent protection device. When the current exceeds the rated current of the fuse, the fuse in the fuse will melt, disconnect the circuit, and prevent excessive current from damaging the equipment.
Input module wiring:
Connection of input signal sources such as sensors: Input modules are used to receive signals from external sensors, buttons, switches and other devices. For example, the temperature sensor converts the detected temperature signal into an electrical signal, and then connects it to the input module of the PLC control cabinet through a signal line. Each input signal needs to be connected to the corresponding input terminal, and the correctness and stability of the connection must be ensured.
Matching of signal type: Select the appropriate input module and wiring method according to the type of input signal (such as digital signal or analog signal). Digital input signals usually have only two states (high level or low level, on or off), and can be directly connected to the corresponding terminals of the digital input module. Analog input signals (such as continuously changing signals such as voltage and current) need to be connected to analog input modules and correctly set and wired according to the range and accuracy requirements of the signal.
Shielding and grounding of input signals: In order to reduce the impact of external electromagnetic interference on the input signal, the input signal line usually needs to use a shielded cable. One end of the shielding layer should be grounded to ensure a good shielding effect. The grounding method can be to connect the shielding layer to the grounding terminal of the control cabinet, or to a dedicated grounding system according to specific system requirements.
Output module wiring:
Control device connection: The output module is used to output the signal processed by the PLC to external devices, such as relays, contactors, solenoid valves, indicator lights, etc. For example, when the PLC determines that a motor needs to be started according to the program, it will send a control signal to the contactor through the output module to close the contactor and turn on the power of the motor. The connection of the output signal should be correctly wired according to the type of output device and the control requirements to ensure the accuracy of signal transmission and control.
Choice of output type: There are many types of output modules, such as relay output, transistor output, thyristor output, etc. Relay output is suitable for controlling high-power equipment, but the response speed is relatively slow; transistor output has a fast response speed and is suitable for controlling high-speed and high-precision equipment, but the output power is small; thyristor output is suitable for controlling AC loads. When selecting an output module, it is necessary to select it according to the actual control requirements and load characteristics.
Protection of output signals: In order to prevent the failure or abnormality of the output device from affecting the PLC system, it is usually necessary to add protection devices such as fuses and overload protectors to the output circuit. These protection devices can cut off the output circuit in time to protect the PLC system and output devices when the output current is too large or the load is short-circuited.
Communication interface wiring:
Serial communication: If the PLC control cabinet needs to communicate with other devices via serial ports, such as data exchange with the host computer, touch screen, other PLCs, etc., it is necessary to connect the serial communication line. The serial communication line generally includes the transmit line (TXD), the receive line (RXD) and the ground line (GND). These lines need to be connected to the corresponding serial port interface respectively, and the correct communication parameters (such as baud rate, data bit, stop bit, etc.) need to be set.
Ethernet communication: Ethernet communication is usually used for occasions where high-speed and large-capacity data communication is required. Ethernet communication requires connecting the network cable to connect the Ethernet interface of the PLC control cabinet to other devices in the network. When performing Ethernet communication, network parameters such as IP address, subnet mask, gateway, etc. need to be set to ensure normal communication between devices.
Grounding part:
Safety grounding: Safety grounding is to connect the grounding end of the power cord and the cabinet to the earth. Its main purpose is to prevent the equipment from leaking or causing electric shock to personnel when the cabinet is energized. If the equipment has a leakage fault, the current can be led into the ground through the safety grounding wire to protect the safety of personnel.
System grounding: System grounding is to make the PLC system and the controlled devices at the same potential to ensure the accuracy and stability of signal transmission. Generally, it is necessary to connect the system ground of the PLC device and the negative end of the switching power supply in the control cabinet together, and then connect to a dedicated grounding system or the earth.
Signal and shield grounding: Signal grounding is to provide a common reference potential for the signal to ensure the accuracy and reliability of the signal. Shield grounding is to reduce the impact of external electromagnetic interference on the signal. The shielding layer needs to be grounded at one or both ends. When actually wiring, be careful to avoid multi-point grounding to avoid forming a ground loop and affecting signal transmission.
