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How to prevent air heaters from suppressing peripheral interference?

Time2019-02-27

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  (1) Protection of PLC input and output terminals

  In order to avoid the high impact potential generated by the inductive input or output circuit disconnection, the PLC has a large impact on the PLC, and the drive components of the PLC are mainly composed of the solenoid valve and the AC contactor coil, at the drive component and the PLC output. The use of zero-crossing solid state relay AC-SSR in the middle is an effective solution.

  (2) Error prevention of input and output signals

  In order to reduce the PLC input current and the current on the external load, the parallel shunt resistor is usually adopted at the input and output terminals.

  (3) Leakage current

  When a DC two-wire sensor input signal such as a proximity switch or a photoelectric switch is used, if the leakage current is large, the malfunction caused by this should be considered, so that the PLC input signal cannot be turned off. In this case, a shunt resistor can be connected to the PLC input terminal to reduce the input impedance. When the bidirectional thyristor is used as the output, in order to avoid leakage current and other reasons, the output component can not be turned off, and a shunt resistor can be connected in parallel with the output terminal.

  (4) Surge voltage

  When the controller is a contact output, regardless of whether the controller itself can resist interference, RC absorption is adopted for the AC load, and a freewheeling diode is used for the DC load to absorb the surge voltage generated by the inductive load.

  (5) Inrush current

  When using a transistor or a triac output module to drive an incandescent lamp or other load with a large power supply, it is necessary to parallel the resistor at the output of the PLC or the series connection of the load to limit the current to protect the output module.

  The air heater suppresses the power supply interference. Under normal circumstances, the power supply of the PLC system is separated from the power supply of the power supply system, and a shielded isolation transformer is added between the PLC systems. A twisted pair of 2 m2 or more is used between the secondary side of the isolation transformer and the PLC system. A shield is placed between the two coils on the primary and secondary sides and connected to the ground, so that direct coupling between the coils can be effectively avoided. For eliminating power supply harmonics, you can use a filter before using the isolation regulator.

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