How to solve the problem of PLC interface damage

How to solve the problem of PLC interface damage The cause of the PLC interface damage is due to transient overvoltages and static electricity. Now that you understand the causes of the PLC interface damage, it is not difficult to find a solution to the PLC interface damage.

The PLC interface damage solution:

First, consider from inside PLC:

1. The isolated DC/DC is used to isolate the 24V power supply from the 5V power supply. The Mitsubishi, Omron, Schneider PLC, and Siemens PROFIBUS interfaces are all analyzed.

2, choose to use static protection, overheating protection, input failure protection and other protection measures improve the high block RS485 chip, such as: SN65HVD1176D, MAX3468ESA, etc., these chips are generally in the price of more than ten dollars to tens of dollars, while the price of SN75176 is only 1.5 yuan.

3, using a new type of protection device TVS or BL surge absorber with faster response speed and greater transient power, such as P6KE6.8CA clamping voltage of 6.8V, withstand transient power of 500W, BL devices can withstand 4000A Above high current impact.

4, R1 and R2 use positive temperature coefficient self-recovery insurance PTC, such as JK60-010, under normal circumstances the resistance value is 5 ohms, does not affect the normal communication, when subjected to surge, high current flows through the PTC and protection Device TVS (or BL), PTC resistance will suddenly increase, so that the inrush current is rapidly reduced.

Second, consider from outside PLC:

Use isolated PC/PPI cables and try not to use inexpensive non-isolated cables (especially in industrial sites). The PC/PPI cable (6ES7901-3BF00-0XA0) that Siemens produced earlier was not isolated, and it is now changed to an isolated cable!

PLC's RS485 port networking uses isolated bus connectors.

The RS485 ports of third-party devices connected to the PLC, such as inverters and touch screens, are isolated using the RS485 isolator BH-485G, so that there is no “electrical” connection between the RS485 nodes and no circulation of the ground wire, even if A node is damaged and will not be damaged along with other nodes.

The RS485 communication line uses a dedicated shielded cable for the PROFIBUS bus to ensure that the shield is connected to the enclosure of each device and finally to the earth.

For systems with overhead lines, it is best to have dedicated lightning protection facilities on the bus.

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