to combine or not to combine , this is a problem. In one project , DCS vendor Honeywell requested that the signal earth of DCS system should be seperated from plant electrical earthing system. They said electrical earth maybe disturb instrument signals to DCS. But our electrical engineer suggested that combined earth was better and seperated earth may make system worse. Anyone has experience of control system earthing?
Single-point earthing avoids ground loops (should that be earth loops? I get dizzy thinking about that) The earthing leads should carry no current common to the instruments and the power equipment. In sever cases, instrument amplifiers (or isolation amplifiers) may be helpful.
Jerry
Mine are always earthed to one point, and if several power supplies are used I tie the neutrals together
But my DCS's are cobbled together expansions and bits added to machines rather than something designed from the ground up
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.