National Instruments NI 6520 User Manual

Also see for NI 6520: User guide Manual

Contents

National Instruments NI 6520 User Manual Manual pdf 15 page image

© National Instruments Corporation 15 NI 6520/6521 User GuideMechanical RelaysRelay FormsTable 4 describes the relay forms available on the NI 6520/6521.Non-Latching RelaysThe relays on the NI 6520/6521 are non-latching. A non-latching relay hasan initial position of normally closed (NC). This position is maintained bythe force of a spring or permanent magnet while no current flows. Thenormally open (NO) contact is closed by the force of a magnetic field whilecurrent flows through the coil. When the current stops, the relay revertsback to its initial NC position.Non-latching armature relays are useful in control applications when theswitch must return to a known state if power is lost.Figure 8. Non-Latching Relay StatesRelay Power RatingsCaution The maximum switching current is limited by the maximum switching power, themaximum voltage, and must not exceed 60 W, 60 VA.(NI PCI-6520 Only) The maximum power rating for the NI PCI-6520 relays is60 W or 60 VA, with a maximum current of 2 A for all channels from 0 to55 °C, external PC ambient.Table 4. NI 6520/6521 Relay FormsForm Symbol DescriptionForm A Single-pole single-throw (SPST) relays with a default state ofnormally open.Form C Single-pole double-throw (SPDT) relays that break theconnection with one throw before making contact with the other(break-before-make).NCNONC PositionNCNOCOMNO PositionNCNOCOM