Intrinsically safe barrier with zener diodes

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Any info how to make zener barrier between uC and sensors that operates in ex zone?
Is it same to use TH and SMD diodes?
 

You'll want to refer to recent technical standards for intrinsic safety. I remember, that at least in previous standards, surface mounted Z-diodes haven't been recognized as reliable connected.
 

Do you have any documentation about zener barriers? Do I have ti use special zener diodes and what about power ratings, is it 0,5W enough?
 

Zener diode power rating refers to the maximum power that can be supplied by the circuit in case of fault, considering only current limiting resistors and possibly fuses. The diodes must be loaded with 2/3 of rated power maximum, many standards require double or triple redundancy (number of parallel diodes).

Intrinsic safety also depends on reliable grounding or safe insulation.
 
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