Beijer-electronics EPC TA70 AM EN Manual de usuario descargar pdf (Pagina 29)

Additional Installation Tips

7.6 GalvanicIsolation

USB

RS232RS422/485

+24 V DC

0 V

Filter

DC/DC

galvanic isolation

VCC

0 V (GND)

DC/AC

CFL

Ethernet

Internal electronic

1.5 m

5356

The Panel PC 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 con nection has galvanic isolation.

* *

***

Panel PC Modular controller Printe

PCPC

Not same ground potential

* = Internal 0 V (GND) connection

Power CPU COM COM2

RS422 RS232 USB

5357

When a PC is connected to the panel, the panel’s internal 0 V (G

ND) will be

connected to the p rotective ground via the PC.

A number of USB devices can have t he shield connected together with the

protective ground. Here, the panel’s 0 V (GND) is conn ec ted to the protective

ground when, for example, a USB memory stick, keyboard or simil ar device is

plugged in.

If a number of units are connected that have a 0 V a

nd a ground connection, and

these are connected to various grounding poin

ts, there is a substantial risk of

problems. Grounding currents go through com

munication cables, the rear plate

of the controller, and i nternally in th

e Panel PC, 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:

Itisveryimportanttomakesurethatthe24Vfeedintheexternalinsulationunitisnot

connectedtooneofthecommunicationoutlets. Ifitdoe snothave100%insula tion

againstthe24Vfeed,disturbancesandgroundingcurrentsfromthe0Vonthe24V

sidewilldisruptcommunication.

Usingthistypeofunitsolvesoneproblembutcr eat esalargerproblem ! Asubstandard

installationmayworknow,butproblemsmayarisewhenotherdevicesareconnected.

BeijerElectronics, MAEN042

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Beijer-electronics EPC TA70 AM EN Manual de usuario Pagina 29

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