National Instruments Module NI PXI-8250 - Manual (Page 23)

Chapter 3 Hardware Overview
© National Instruments Corporation 3-7 NI PXI-8250 User Manual
Alert Relay Pins
The NI PXI-8250 has an electromechanical non-latching relay with three
ports: normally open (NO), normally closed (NC), and common (COM).
The top three pins of the front panel connector are connected to a relay as
indicated in Figure 3-5. This relay is useful for a creating a custom external
warning indicator circuit, such as a factory warning light or speaker.
During normal operation without any system status errors, the relay will
have COM connected to NO (and not NC). Once a system status error has
occurred (for instance. if the voltage rail level is out of range), the relay will
flip to connect COM to NC, rather than NO. Refer to Figure 3-6 for other
relay status information.
Notes For a use case where a warning light or speaker should be active (connected) to
show an error, connect from the COM to the NC port.
For a use case where a warning light or speaker should be active (connected) to show
proper, in-spec operation, connect from the COM to the NO port.
The relay alerts an error by connecting COM to NC when the chassis is
powered off or loses power. The relay on the NI PXI-8250 is rated to 30 V
and 1 A switching/carry current. Any connections to the relay on the
NI PXI-8250 must have a wire length less than 20 meters.
Power Output Pins
The lower 5 pins of the 8-pin front panel connector are general purpose
power outputs connected to each voltage rail of the power supply. Refer to
Figure 3-5 for the location of the power output pins. The +5 V, +3.3 V,
+12 V, and –12 V rails are all available from these connector pins along
with a ground connection at the bottom. These pins draw power from the
chassis power supply and are protected from current over-draw with
self-resetting fuses. Table 3-2 lists the maximum power output ratings for
each voltage rail.