Relation between Input Current at Trigger Input Terminals and Sensor
Control Output (Load Current)
The trigger inputs of the High-speed Analog Input Units can detect sensor output ON only when the
following conditions are satisfied:
I
OUT
(min) ≤ I
in
≤ I
OUT
(max)
I
OUT
(min): Minimum value of load current
I
OUT
(max): Maximum value of load current
Use the following equation to calculate the input current:
I
in
= I
ON
Note At the trigger input terminals of the High-speed Analog Input Units, the input current does not increase
linearly for the input voltage. If you gradually raise the input voltage and once the input current reaches
I
ON
, the input current does not increase any further, and remains roughly constant even when the input
voltage is raised.
When I
in
is smaller than I
OUT
(min), connect a bleeder resistor R. The bleeder resistor constant can
be calculated as follows: Select an appropriate bleeder resistor R so that both equations can be
satisfied.
R ≤ (V
CC
- V
R
)/(I
OUT
(min.) - I
ON
)
Rated power W of bleeder resistor ≥ (V
CC
- V
R
)
2
/R × 4 [allowable margin]
The voltages and currents related to the conditions for NPN type sensors are shown in the figure
below.
IN
*
IOG
IOV
IOG
*
IOV
*
V
R
V
CC
R
I
in
I
OUT
Two-wire sensor
Unit that can supply I/O power
to the NX bus
High-speed Analog Input Unit
The voltages and currents related to the conditions for PNP type sensors are shown in the figure
below.
4 Installation and Wiring
4 - 28
NX-series Analog I/O Units User’s Manual for High-speed Analog Input Units (W592)
