Owner's manual

Additional Installation Tips
6.6 GalvanicIsolation
USB
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
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.
* *
*
***
**
*
Operator panel Modular controller Printe
r
PCPC
Different ground potential
*
= Internal 0 V (GND) connection
Power CPU COM COM2
RS422 RS232 USB
When a PC is connected to the operator panel, th e 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 operator 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 n umber of units are connected that have a 0 V and a ground connection, an d
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 p anel, 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:
Itisveryimportanttomakesurethatthe24 Vfeedintheexternalinsulationunitisnot
connectedtooneofthecommunica tion outlets. Ifitdoesnothav e100%insulation
againstthe24Vfeed,disturbancesandgroundingcurrentsfromthe0Vonthe24V
sidewilldisruptcommunication.
Usingthistypeofunitsolvesoneproblembutcreatesalargerproblem! Asubstandard
installationmayworknow,butproblemsmayarisewhenotherdevicesareconnected.
BeijerElectronics, MAEN096C
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