hi Kai

Thanks for your precision response.

I accept that we must be careful about ground in galvanic systems,Can you give some link about this topic ?(for more study)

I saw many DAQ cards from large companies that use galvanic isolation in their product.What you think about their design? If we solve earthing problem ,then there is no danger and system is better than when we do not have galvanic isolation.

Last question:
If I want to isolate my cards (galvanic),then is it necessary isolation between analog input section(amplifier and ADC) and microcontroller section and
RS485 bus??(between three parts)

Or is it enough to isolate between analog section + micro and rs485 bus??

Thanks