In 100% of the implementations I have seen, and I have seen many, I have only ever seen protective earth used for all needs. I have never seen in any industrial process use separate earth systems to make the so-called clean earth.

At the limit, I have seen fiber optics used and used to interface distant systems that might have had common mode noise problems.

Siemens devices are virtually all opto-isolated, very robust in various electrical realizations.

Thank you for your reply.