National Instruments NI 2590/2591 - Manual (Page 10)

Chapter 1 Routing Signals with Your NI 2590/2591
NI 2590/2591 User Manual 1-2 ni.com
The external trigger input trigger is generated by another instrument or by
software and causes the NI 2590/2591 to advance to the next entry in the
scan list. The triggers can be routed to any of the PXI TTL triggers or to the
PXI star trigger.
Refer to 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 the common 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 Always disconnect all signals from the front connectors and power down the
PXI chassis before removing the NI 2590/2591 from the chassis. Observe electrostatic
discharge handling precautions during and after removal of the module, or when
connecting and disconnecting signals on the front panel.
Warning Do not exceed the channel-to-ground voltage rating. Any connections that
exceed the 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. National Instruments is not liable for any damages or injuries resulting from
exceeding maximum voltage ratings. Refer to Appendix A,
Specifications , for information.
Contact Protection
Caution The contacts of the relay are rated for a life of 5
× 10 6 mechanical operations
when operated with no signal or a very small signal present. At full rated power—1 A at
24 VDC for the NI 2590 and 0.33 A at 30 VDC for the NI 2591—the life of the switch is
downgraded to 100,000 operations. 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
contact arcing 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.