External Contact Connection; Long-Distance Wiring - National Instruments RMX-4120 User Manual

Chapter 3 External Control
Figure 3-16. Controlling the Output On and Off States.
H = On
External
contact
L = Off
Output
On
Off

External Contact Connection

Connect your external contact between pins 18 and 19 of the J1 connector. The open-circuit
voltage across pins 18 and 19 is approximately 5 V. The short-circuit current across pins 18 and
19 is approximately 0.5 mA.
Use external contacts that have a contact rating of 0.5 mA or more at 5 VDC. If two or more
units are floating and you are using a single external contact to turn output on and off for all the
units, use a relay or similar device for the external contact signal to isolate the signal transmitted
to each unit.

Long-Distance Wiring

When you are wiring over a great distance, use a small relay and extend the coil side of the relay.
3-18 | ni.com
The OUTPUT key is
disabled. Even if you
press it, output is
not generated.
Figure 3-17. External Contact Connection.
2-core shielded wire or
twisted-pair wire
S
Figure 3-18. Long Distance Wiring.
Relay
Extend this line.
▼ represents that the OUTPUT key has been pressed.
The external contact has
been used to turn output
on, so the OUTPUT key
is enabled.
J1
18
19
Output terminals
S
To use the external contact to
turn output on again,
first turn the output off.
RMX