Chapter 4
Signal Connections
4-12
ni.com
Figure 4-8.
Encoder Input Circuit Connected to a Sourcing Output Device
with a +24 V Power Supply
Connections for Input Voltages Higher Than 5 V
When connecting to devices with output voltages higher than 5 V, an
external resistor (R
EXT
) must be included.
Note
Use a resistor tolerance of 5% or better for R
EXT
.
Caution
Failure to include the resistor with the specified resistance will permanently
damage the encoder input circuit.
The required external resistor value is calculated using the following
equation:
R
EXT
= [100(
∆
V
) – 480]
Ω
where
∆
V
= V
+
– V
–
PCI-7390
Output
V+
V–
High Speed Optocoupler
V
cc
R
LIMIT
R
EXT
Encoder–
Input
Input
Encoder with
Sourcing Output
Isolated Ground
Isolated Ground
+24 V
2 k
Ω
