National Instruments SCXI-1161 User Manual

Also see for DAQ SCXI-1161: Getting started Getting started guide Getting started guide Instructions for safe use

National Instruments SCXI-1161 User Manual Manual pdf 38 page image

Chapter 4 Theory of Operation©National Instruments Corporation4-5SCXI-1161 User ManualRelay ChannelsThe SCXI-1161 has eight independent one form C (single-poledouble-throw) relays. Each relay has three connections at the frontscrew terminals–the common (COM), the normally closed (NC), andthe normally open (NO) positions. Each relay has pads for arcsuppressors to protect the relays from inductive loads. Refer to theContact Protection for Inductive Load Connections section ofChapter 3, Signal Connections, for further details on contact protection.All eight relays are single-side stable relays. When you energize therelay coil, the COM connects to the NO position. The Data Registercontrols the relays as follows. The four LSBs of the least significantbyte of the Data Register control the coils of relays 0 through 3. Thefour LSBs of the most significant byte of the Data Register control thecoils of relays 4 through 7. When you do not energize the coils, theCOM connects to the NC position.After a write to the Data Register, the data is latched and the selectedrelay coils are continuously driven.Each relay can be set (the relay COM position connected to the NOposition) or reset (the relay COM position connected to the NCposition) without affecting the other relays, or all relays can changestates at the same time. However, each time a relay changes its state, theData Register is rewritten to. Refer to the SCXI-1161 Register-LevelProgrammers Manual for further details.The relays are break-before-make, but only if you do not exceed thespecified relay operation speed. In addition, each relay is fully isolatedfrom the other relays and from earth ground, with a workingcommon-mode voltage of 250 V rms .Note: It is important to notice that this module has no access to the analogbackplane; this protects the backplane from faults when high voltages areavailable on the relay contacts.