Part 2

Plug-In Assembly Configuration 48'1-CAUTIONEXTERNAL RELAY CONTACT PROTECTIONMAY BE REQUIRED FOR INDUCTIVE LOADSSEE TEXT FOR GUIDELINES.LEAD-IN WIRE12 GAGE MAXT OHIGHVOLTAGEACTUATORCARDACTUATORTERMINAL CARD(COVER REMOVE01- : GROUNDING STRAPTO CUSTOMEREARTH GROUNDFigure 138. Option 115 -Connecting loads to the AssemblyContact Protection FundamentalsWhenever relay contacts open or close, electrical breakdown can occur between thecontacts which can cause high frequency radiation, voltage and current surges andphysical contact damage. Two types of breakdown are important in switching contacts:glow discharge and metal-vapor or arc discharge.Glow discharge occurs when the gas between the contacts is ionized. The voltagerequired to start a glow discharge between contacts depends on the gas, the gaspressure and the space between the contacts. After a glow discharge has beenstarted, a slightly smaller voltage (about 300V in air) will keep the gas ionized. Thisvoltage is approximately constant, regardless of the separation of the contacts.An arc discharge starts whenever an energized contact is opened or closed. Theminimum arcing voltage (Va) and arcing current (la) necessary to start an arcdischarge depend on the type of relay contact material. Typical values range fromVa = 9V, la = 400mA for gold alloy up to Va = 17.5V, la = 700 mA for platinumcontacts. For the high voltage actuator, la = 400 mA.0After an arc discharge has been started, the arc must be broken as quickly as possibleto minimize damage to the contacts. If it is not broken quickly, some materialtransfers from one contact to the other.Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com