National Instruments NI 2590/2591 - Manual (Page 19)

Chapter 2 NI 2590/2591 Operation
© National Instruments Corporation 2-5 NI 2590/2591 User Manual
Relay Operation
NI 2590 Operation
The NI 2590 has four channels, CH0 through CH3, any one of which can
be connected to the single common channel (COM) by closing the
appropriate relays.
You can control the relays individually, or you can use higher-level
commands to energize the correct relays to connect a channel (such as
CH0) to COM. Only one channel can be connected to the common channel
at any time, and it is not possible to connect one channel to another channel
bypassing the common channel.
The NI 2590 relays are single-side stable. When power is removed from the
relay coil, the relay returns to its de-energized state. When all three relays
are de-energized, the default connection is from CH0 to COM, as shown in
Figure 2-1. To connect CH2 to COM, you energize MUX0123; to connect
CH3 to COM, you energize MUX0123 and MUX23. You can specify the
channel to connect to COM and let the NI-Switch driver energize the
appropriate relays for you. Refer to the NI-SWITCH Software User Manual
for further information.
NI 2591 Operation
The NI 2591 is very similar to the NI 2590 in some respects, but different
in others. The NI 2591 has 4 channels, CH0 through CH3, any one of which
can be connected to the single COM by closing the appropriate relays.
The NI 2591 does not allow for control of the individual relays. You must
use the high-level commands to connect the channels, such as CH2 to
COM. Only one channel can be connected to the common channel at any
time, and it is not possible to connect one channel to another channel,
bypassing the common channel. The default (power off) connection of the
NI 2591 is CH3 to COM. Refer to Figure 2-2 to see how the connections in
the NI 2591 are made.