ABB LMS100 Series Operating Instructions Manual

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ABB LMS100 Series Operating Instructions Manual Manual pdf 9 page image

OI/LMS100-EN Rev. A | LMS100 Magnetic Level Gauge Switch 95.3 Typical ApplicationsSome ABB switch products (LMS100, MS50, MS10) are basedon magnetically operated reed switches. Since reed switcheshave the inherent characteristic of very closely spaced switchcontacts, it is extremely important to protect these contactsfrom high voltage transients caused by inductive loads. Whenan inductive load is de-energized., the collapsing magnetic fieldinduces a high voltage of opposite polarity into itself and thus theswitch . Two basic methods exist to clamp this voltage and thusprotect the switch contacts.5.4 Typical D.C. ApplicationsFor D.C. applications, a diode is placed in parallel with the induc-tive load (note the polarity of the diode and power supply). A1N4001 general purpose diode is normally sufficient to clamp theinduced voltage of the inductive load to as safe level. NOTE: Notevaluated for use in hazardous locations5.5 Typical A.C. ApplicationsFor A.C. applications, a Metal Oxide Varistor (MOV transientsurge suppressor) is placed either in parallel with the switch orthe inductive load. The MOV changes from a high impedance toa very low impedance when the voltage across the MOV exceedsits rated voltage (the MOV rating must correspond with the powersupply voltage). For 120 VAC control systems a typical MOwould be the GE (General electric Co.) part number V130LA10A.In either case shown, the result is the limiting of the switch volt-age to approximately 130 volts. NOTE: Not evaluated for use inhazardous locationsD.C. Contact ProtectionA.C. Contact ProtectionDC POWER SUPPLYINDUCTIVELOAD DIODEWHITE(COMMON)BLACK OR RED(NO) (NC)+ -AC POWER SUPPLYINDUCTIVELOAD MOVWHITE(COMMON)BLACK OR RED(NO) (NC)+ -DC POWER SUPPLYINDUCTIVELOAD DIODEWHITE(COMMON)BLACK OR RED(NO) (NC)+ -AC POWER SUPPLYINDUCTIVELOAD MOVWHITE(COMMON)BLACK OR RED(NO) (NC)+ -