Chapter1 RoutingSignals with Your NI 2590/2591
NI2590/2591 User Man ual 1-2 ni.com
Theexternal trigger i nput trigger is generated byanother i nstrument or by
softwareand causes the NI 2 590/2591 to advanceto the next entry in the
scanlist. The triggers can be routed to any of the PXI TTL tr iggers or to the
PXIstartrigger.
Refert o Chapter 2, NI 2590/2591 Operation, for more information on
triggers.
RF Switching Precautions
The NI 2590/2591 is a reflective switch, meaning that any channels not
switched to thecommon channel are unterminated, and any signal on an
unterminated channel will be reflected to its source. For most low-power
switching applications this is not a problem. However, operation with an
unterminated output can damage some high-power RF sources. Consult
your RF source documentation for more information about connecting to
unterminated channels.
Caution Alwaysdisconnect all sign alsfro m the front connectors and power downthe
PXI chassis before removing the NI 2590/2591 from the chassis. Observe electrostatic
dischargehandling precautions during and afterr emovalof the module, or when
connecting and disconnecting signals on the front panel.
Warning Donot exceed the channel-to-ground voltage rating. Any connections that
exceedthe maximum voltage for the NI 2590/2591 can result in an electrical shock hazard
and damage to the switch module and any or all of the modules connected to the PXI
backplane.N ational Instrumentsis not l iable for anydamages or injuries resulting from
exceedingmaximum voltage ratings. Refer to Appendix A, Specifications, for information.
Contact Protection
Caution Theco ntacts of the relay are rated for a life of 5 × 106mechanical operations
when operatedw ith no signal or a verysmall signal present. At full rated power—1Aat
24 VDC for the NI 2590 and 0.33 A at 30 VDC for the NI 2591—the life of the switch is
downgradedto 100,000 operation s. If your setup allows,it is always best to turn off the
input signals connected to the switch module during the switching operation to avoid
contactarcing within the switch. Switching large inductive loads can also cause contact
arcing.In such instances, install a flyback diode or varistor across the inductance to protect
the switch.