11066 Searchpoint Optima Plus v2.indd - Merkantile

MAN0551.P65 Issue 06 - 03/042108M05014. ELECTRICAL CONNECTIONSrecommended that surge suppression devices beinstalled close to the unit. Suitable, certified surgesuppression devices include MTL’s TP-48-I-NDI andPepperl & Fuchs’ FN-LB-1. Two of these devices aresufficient to provide protection of the +24V, 0V, 4-20mAand RS485 (A) connections to a unit.h. In general, correctly engineered star earthingarrangements minimise earth current crosstalk andnoise, improving the reliability and performance ofinstrumentation.i. Low noise instrument (clean) earth should only beconnected to safety earth (usually dirty) at a singlepoint on a site / installation. This connection should bemade in such a manner that it does not introduce noiseonto the instrument earth.j. The entire length of the field cabling connected to a unitshould be screened / shielded. This screen / shieldshould be connected to a low noise instrument (clean)earth at a single end. (The screen / shield can beconnected to the unit’s earth in the junction box,provided that this is isolated from all other earths /grounds.)k. For installations where the field cable conductors runthrough conduit or armour connected to safety (dirty)earth, the conduit or armour should not be consideredas a sufficient screen / shield. A separate cable screen/ shield, connected to a low noise instrument earthshould be employed.l. The screens / shields of field cabling should not beconnected in a manner that creates earth loops or thatwill result in the screens / shields carrying largecurrents from heavy plant or equipment.33