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Appendix B Common Questions
SCXI-1190/1191 User Manual B-2 www.ni.com
One of my modules doesn’t switch properly anymore. What’s wrong?
One of the relays has probably worn out. Relays are mechanical devices
and have a limited switching lifetime. Call National Instruments for
information on replacing your relays.
What is VSWR, and how does it affect my system?
VSWR stands for Voltage Standing Wave Ratio; it is a measure of the
reflection on a transmission line. The percentage of a signal reflected back
to the source is equal to (VSWR-1)/(VSWR+1). This means that a VSWR
of 1 is optimum, with no reflected signal. On higher power applications, a
large VSWR can damage the output stage of the source. High VSWR also
means that a large percentage of the power from the source cannot be
delivered to the load.
What is isolation, and why is it important?
Isolation is a measure of the amount of cross-talk between channels. For
example, if a 1 Vp-p signal is isolated by 40 dB to another channel, then
10 mVp-p will be seen on the adjacent channel (in addition to the signal
already on the channel).