3-14
|
ni.com
Chapter 3
External Control
External Resistance (Rext) Connection
For Rext, use a resistor that is rated at approximately 10 k
Ω
, 1/2 W or greater, that has a low
temperature coefficient, and that will change little over time. Examples of such resistors are
metal film or wire wound resistors.
To reduce the noise on the output, connect a 2-core shielded wire or a twisted-pair wire, and keep
the wire as short as possible. If the wiring between the RMX programmable power supply and
the external contact is long, it becomes easy for noise to influence the operation of the RMX
programmable power supply. Even if you use cables that are designed to suppress noise, the
RMX programmable power supply may not operate properly.
Figure 3-13.
CV Rext Connection.
If you use a shielded cable, connect the shield to the negative output terminal. Use pins 20, 22,
and 23 of the J1 connector.
Controlling the Output Current
This section explains how to control the output current using an external voltage (Vext) or an
external variable resistor of approximately 10 k
Ω
(Rext).
Caution
Risk of electric shock. If neither output terminal is tied to chassis ground,
the reinforced or double insulation of Vext or Rext and the connected cable must be
greater than or equal than or equal to the isolation voltage of the RMX programmable
power supply. Refer to Appendix A,
, for the isolation voltage of your
model.
If one of the output terminals is connected to chassis ground, the insulation of Vext or
Rext and the connected cable must have a reinforced or double insulation with a
capacity greater than or equal to the maximum output voltage relative to the chassis.
When using shielded cables for the connection, for uncovered sections of the shielded
cables, use insulation tubes to secure reinforced or double insulation with a capacity
greater than or equal to the isolation voltage of the RMX programmable power supply.
2-core shielded wire or
twisted-pair wire
Wiper
Output terminals
J1
20
22
2
3
RMX
R
ext
V
ext
