Hello
I want to design a data aquisition card with 8 channel input (for example 8 of 4-20mA)and a RS485 bus with MODBUS protocol as output.
I want to isolate the input /power/output of card.

Which method is better for isolation(or ,is
the first method enough? )

First: I set isolation between the Input/RS485 output and Input/POWER supply.microcontroller and ADC is at input side.

Really this is two way isolation (galvanic)

Second:I set isolation between the input/microcontroller and input/power supply and
power supply/micro and micro/RS485.

the isolation is between input/micro/power/rs485

This is three way isolation.


The cost of second method is higher but it is more reliable because micro and eeprom section is isolated from input power ans rs485 and input!


But I see some vendors that build their cards with first method.
I do not know what to do ,please help me.
Regards