Filter 18.432M

The correct connection is a prerequisite for the plc to work properly. The wrong or bad connection not only affects the reliability and stability of the PLC work, but also may cause malfunction or even damage to the mechanical equipment and PLC hardware, causing fire and other safety accidents, which must be taken seriously.
1. Basic requirements for connection Due to the differences in PLC specifications and PLC module specifications and models, PLC connections may differ, but in general, PLC connections should follow the following common principles:
All connections of 1PLC must be correct, especially for the power supply voltage, the type of control voltage, voltage, polarity, etc., must be carefully checked to ensure correct.
2PLC connections must be secure, reliable, and in compliance with specifications.
3 The insulation level and wire diameter of the connecting wires must match the voltage and current of the load; the color of the wires must conform to the standard.
4PLC connection work must be carried out by personnel with appropriate professional qualifications in case of power failure.
5 PLC module, connection cable insertion and extraction should be carried out according to the specified methods and procedures in the case of PLC power failure.
6 Before touching the PLC, the static electricity on the human body should be released by touching the grounded metal parts.
2. The arrangement of the connecting lines is reasonable to arrange the PLC connecting lines, which can reduce and eliminate the interference in the line and improve the reliability. The connection lines, cables, etc. of the PLC are preferably classified according to the voltage level and the type of the signal.
Figure 7-5.1 shows the recommended more reasonable PLC cable laying method, which can be used by designers.

The cable laying in Figure 7-5.1 adopts the “layered laying” method, and the isolation measures shown in Figure 7-5.2 are used inside the “trailing trough”; outside the “trailing trough”, it is sealed by the metal shielding shell. This can effectively prevent electromagnetic interference.

Of course, in actual use, considering the cost and other factors, it may be difficult to completely follow the requirements of the PLC manufacturer. Even so, it is advisable to separate the power cable, the control cable and the signal cable separately, and to arrange the "slots" as much as possible in the electrical cabinet.
3. Power line layout
The PLC has relatively low requirements on the input power supply, and it is usually easier to meet the requirements. However, when there is interference in the power supply line or the power grid fluctuates drastically, in order to ensure the normal operation of the PLC, the isolation transformer and surge absorber should be considered in the power input circuit. Or take a stabilizing measure.
In terms of the external power connection of the PLC, the following points should be considered:
1PLC's input power, I/O power supply and other power supplies of the equipment should be separately routed in principle. Each power supply circuit should have an independent protection circuit.
2 When using an isolation transformer, the connection between the isolation transformer and the PLC power supply is as short as possible to reduce interference in the line.
3PLC's power cable should have enough wire diameter to reduce the voltage drop of the line.
The 4DC loop and the AC loop should be routed as far as possible.
5 When the input/output connection cannot be laid separately from the power line, the input/output should be shielded as much as possible, and the shield should be grounded on the PLC side; the input signal and output signal are not declared in the same cable, and should be used separately. Connection cable.
6 When the input power supply may have large interference, take necessary anti-interference measures (see below).
7 In principle, the PLC I/O connection line should not exceed 20m. When it is greater than this length, necessary measures should be taken to prevent interference and increase of line voltage drop.
The cable of the 8 expansion unit is a part that is easily disturbed, and the distance between the cable and the power line should be 30 to 50 mm.
4. Interference and prevention In order to prevent the influence of interference in the line on the reliability of the PLC system, corresponding measures can be taken according to the following different situations.
1 power interference. The power supply interference mainly comes from lightning strikes in external lines, start/stop of high-power loads inside the equipment, and on/off of contactors, and the like.
The countermeasure against power supply interference is to install an isolation transformer and a surge absorber on the incoming line of the PLC power supply to absorb the interference voltage of the line: at the same time, the connection between the PLC and the equipment is protected by a well-grounded metal hose.
2 high frequency interference. High frequency interference mainly comes from high frequency devices in control systems or other equipment. The measure to prevent high-frequency interference is to install a high-frequency filter on the power supply line and splicing the power line.
3 grounding interference. Grounding interference is mainly caused by incorrect ground or poor grounding. The equipment used for PLC control should have a well-grounded ground wire, and the grounding control should be used for the equipment's standby control part. The common ground wire cannot be used.
4 Inductive load on and off interference. The method of solving the interference caused by the inductive load on and off is to install an overvoltage absorber at both ends of the inductive load. For AC inductive loads, RC suppressors and varistors can be used; for DC inductive loads, diodes, varistors, RC suppressors, etc. can be installed.
5 electromagnetic interference. For electromagnetic interference caused by the on/off of the high-power load and the arc caused by the switch, magnetic shielding should be performed by means of installing a metal shield on the switch.