Preparation before wiring
Be familiar with the electrical schematic:
Before wiring, you must have a deep understanding of the electrical schematic of the PLC control cabinet. Clarify the connection relationship between various components (such as PLC modules, sensors, actuators, relays, etc.), including the type of input and output signals (digital or analog), address allocation and other information. For example, for a PLC control cabinet of an automated production line, you need to know which sensor signal is connected to which input point of the PLC, and how the output point of the PLC controls the actuators such as motors and cylinders.
Check components and tools:
Check whether the models and specifications of all electrical components in the PLC control cabinet are consistent with the design requirements. Check whether the components are damaged, such as whether the pins of the PLC module are bent, whether the coil of the relay is short-circuited, etc. At the same time, prepare suitable tools, such as screwdrivers, wire strippers, wire crimping pliers, etc., and ensure that the quality of the tools is good and can meet the needs of wiring work.
Plan the wiring path:
Plan a reasonable wiring path according to the internal structure of the control cabinet and the layout of components. Generally, the principle of separate wiring of strong and weak electricity should be followed to reduce electromagnetic interference. For example, separate the PLC power supply line from the input and output signal lines, use shielded wires for analog signal lines, and lay them separately, away from strong power lines and interference sources. At the same time, the wiring should be as neat and beautiful as possible to facilitate subsequent inspection and maintenance.
Tips in the wiring process
Clear marking:
Mark both ends of each wire, and the marking content should be consistent with the wire number in the electrical schematic. You can use wire number tubes, labels, etc. to mark. For example, for the sensor signal line connected to the PLC input point I0.0, both the sensor end and the PLC end should be marked as “I0.0”, so that the corresponding line can be found quickly and accurately during subsequent debugging and maintenance.
Connect the wire correctly:
Be careful not to damage the core wire of the wire when stripping the wire, and the stripping length should be moderate. Generally, stripping is performed according to the requirements of the terminal. When connecting the wire to the terminal, ensure that the wire is in good contact with the terminal. For multi-strand wires, use wire crimping pliers to crimp to avoid looseness. For example, when connecting the input and output terminals of the PLC module, the wires should be correctly inserted or tightened according to the wiring method of the terminals (such as plug-in type, screw-tightening type, etc.).
Grounding treatment:
Good grounding is the key to ensuring the safe and stable operation of the PLC control cabinet. The metal shell of the PLC control cabinet should be reliably grounded, and the grounding resistance should meet the requirements (generally not more than 4Ω). At the same time, the shielding layer of the shielded wire should also be properly grounded, such as grounding at one end or both ends (depending on the specific situation) to reduce the impact of external electromagnetic interference on the signal.
Follow the wiring specifications:
Different types of wires should be wired according to the specified colors. For example, AC power lines generally use red, black and other colors, DC power lines use red (positive), blue (negative) and other colors, and signal transmission lines can use yellow, green and other colors. The bending radius of the wire must meet the requirements to avoid excessive bending and damage to the wire. In addition, try to avoid wire crossing when wiring. If crossing cannot be avoided, vertical crossing should be used and insulation should be done well.
Inspection work after wiring
Appearance inspection:
Check whether the wiring is neat, whether all the wires are fixed, and whether there is no looseness or hanging. Check whether the markings are clear and accurate, and whether the line number is consistent with the electrical schematic. At the same time, check whether the grounding is good and whether the grounding wire is firmly connected.
Conduction test:
Use tools such as multimeters to test the circuit for continuity, check whether each line is connected correctly, and whether there is a break or short circuit. For digital input and output lines, you can check whether the input and output status of the PLC is correct by shorting or disconnecting the input signal; for analog lines, check whether the signal transmission is normal, such as measuring whether the voltage and current signals meet expectations.
Insulation test:
Perform insulation resistance test to check whether the insulation resistance between different lines (such as strong current lines and weak current lines, lines of different voltage levels, etc.) and between the line and the cabinet meets the requirements. Generally, the insulation resistance should not be less than the specified value (such as 1MΩ) to ensure electrical safety.
