ComBricks User Manual v6.4.0 | January 18| © PROCENTEC
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7.3
EMC barrier
The galvanic isolation and bit recovery circuit in the repeater modules, make the ComBricks perfect to act as an
EMC barrier for sensitive areas.
7.4
Grounding system
There are 3 methods to ground the PROFIBUS cable:
1
Direct grounding
2
Indirect grouning (through a capacitor)
3
Combination of direct and indirect
In most cases it is recommended always to use Direct Grounding with the power supply and the shielding of
the PROFIBUS cables. If you do not want to ground all or some cables to the common ground, the cable
shielding should be connected to pin ‘I’. A capacitor with a parallel high value resistor will separate the 2
potentials (see Fig. 51).
If the Direct Grounding is connected with the Indirect Grounding by mistake
, the Direct Grounding “wins”.
7.5
Baudrate detection
It takes less than 10 seconds for a module to detect the baudrate (in practice it will be around 3 seconds). The
detection mechanism is started when telegrams enter the module from the field side (not the backplane). If the
baudrate has been detected, the 'ER' LED will be OFF.
When the baudrate has been detected, the module has to "see" a valid telegram within 50 seconds, otherwise
the module unlocks the baudrate and the 'ER' LED will be ON.
7.6
PROFIBUS DP cable lengths
The length of the PROFIBUS cable connected to the repeater channels should comply with the PROFIBUS DP
cable specifications for RS-485.
Fig. 52 - ComBricks as EMC barrier
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