Emc Barrier; Grounding System; Baudrate Detection; Profibus Dp Cable Lengths - Procentec ComBricks User Manual

Profibus data hub for repeaters and fiber optics modules

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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.

Fig. 52 - ComBricks as EMC barrier

There are 3 methods to ground the PROFIBUS cable:

Direct grounding

Indirect grouning (through a capacitor)

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".

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.

The length of the PROFIBUS cable connected to the repeater channels should comply with the PROFIBUS DP

cable specifications for RS-485.

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