Galvanic Isolation. Beijer Electronics MAEN256B

7.6 Galvanic Isolation

Additional Installation Tips

The operator panel has galvanic isolation against the 24VDC power supply but no galvanic isolation between the communication ports for RS-232, RS-422, RS-485,

CAN and USB. Only the Ethernet connection has galvanic isolation.

PC

*

Operator panel Modular controller

Power CPU COM COM2

* * *

RS422

*

RS232

*

USB

*

Different ground potential

*

= Internal 0 V (GND) connection

Printer

*

PC

*

When a PC is connected to the operator panel, the internal 0 V (GND) of the panel is connected to the protective ground via the PC.

A number of USB devices can have the shield connected together with the protective ground. Here, the 0 V (GND) of the operator panel is connected to the protective ground when, for example, a USB memory stick, keyboard, or similar device is plugged in.

If a number of units are connected that have a 0 V and a ground connection, and these are connected to various grounding points, there is a substantial risk of problems. Grounding currents go through communication cables, the rear plate of the controller, internally in the operator panel, and can cause errors.

Use external units to improve communication and achieve galvanic isolation.

Westermo has good industry-standard insulators that are also insulated from the

24 V DC feed.

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Additional Installation Tips

Note:

It is very important to make sure that the 24 V feed in the external insulation unit is not connected to one of the communication outlets. If it does not have 100% insulation against the 24 V feed, disturbances and grounding currents from the 0 V on the 24 V side disrupt the communication.

Using this type of unit solves one problem but creates a larger problem! A substandard installation may work now, but problems may arise when other devices are connected.

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