Beijer-electronics EXTER T150-st EN Manuel d'utilisateur télécharger pdf (Page 22)

Additional Installation Tips

22 Beijer Electronics, MAEN967

6.6 Galvanic Isolation

The operator panel has galvanic isolation against the 24 V DC feed but no galvanic

isolation between the communication ports for RS232, RS422/485 and USB. Only

the Ethernet connection has galvanic isolation.

When a PC is connected to the panel, the panel’s internal 0 V (GND) will be

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 panel’s 0 V (GND) 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, and 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.

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 will disrupt 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.

5356

Internal electronic

Filter

DC/DC

galvanic isolation

1.5 m

VCC

0 V (GND)

Ethernet

DC/AC

CFL

0 V

+24 V DC

RS422/485 RS232 USB USB

* *

***

5357

Operator panel

Modular controller

RS422 RS232 USB

CPU COM COM2Power

Not same ground potential

Printer

* = Internal 0 V (GND) connection

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Beijer-electronics EXTER T150-st EN Manuel d'utilisateur Page 22

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