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National Instruments Corporation
11
NI 6520/6521 User Guide
The output lines on the NI 6520/6521 consist of electromechanical
non-latching relays. For information about connecting to these signals for
Form C and Form A relays, refer to the
Relay Signal Connection Example
section.
The input lines on the NI 6520/6521 consist of input photocouplers, which
react to a voltage differential rather than only to a voltage increase. For an
input channel, if the voltage difference between two input lines is greater
than logic threshold, the reading on the digital line will be logic high. Refer
to the
Input Signal Connection Example
section for more information on
input connection.
For information on safely connecting to the NI 6521, refer to the
37-Pin
High-Voltage Accessory Safety Kit Installation Guide
shipped with your
device, and also available on
ni.com/manuals
.
Pin Assignments
Figure 5 shows the pin assignments for the 37-pin connector on the
NI 6520/6521 device.
The naming convention for each input pin is P0.
X
, where
X
is the line
number and a
+
or
–
indicates whether the terminal is positive or negative.
The naming convention for each output pin is P1.
X
NO, P1.
X
COM, and
P1.
X
NC for Form C, where
X
is the output channel number, and P1.
X
NO
and P1.
X
COM for Form A, where
X
is the output channel number.
Note
For input ports, you can connect signals to the two pins of each line, regardless of
which one has the higher voltage. Output lines are electromechanical relays and act as
bi-directional switches.