National Instruments SCXI-1161 - Manual (Page 26)

© National Instruments Corporation 3-1 SCXI-1161 User Manual
Chapter
3
Signal Connections
This section describes the signal connections to the SCXI-1161 board
via the SCXI-1161 screw terminals and rear signal connector, and
includes specifications and connection instructions for the SCXI-1161
connector signals.
Screw Terminal Connections
The SCXI-1161 has 24 screw terminals for easy signal connection to the
inputs. Each input consists of a common (COM) position, a normally
closed (NC) position, and a normally open (NO) position. At power up
and at reset, the SCXI-1161 COM positions on all the channels connect
to the NC positions.
All contacts have a working common-mode voltage of 250 VAC or
VDC. The contact-to-contact breakdown voltage is 750 V
rms
. The
contact-to-coil breakdown voltage is 1,500 V
rms
. Please refer to the
module specifications listed in Appendix A, Specifications, for further
details before connecting the signals to the relay contacts.
Contact Protection for Inductive Load Connections
When inductive loads are connected to the relays, a large
counter-electromotive force can occur at relay switching time because
of the energy stored in the inductive load. These flyback voltages can
severely damage the relay contacts and greatly shorten the life of the
relay.
It is best to limit these flyback voltages at your inductive load by
installing, across your inductive load, a flyback diode for DC loads
(see Figure 3-1) or an MOV for AC loads. Refer to Appendix B,
Contact Protection, for further details.