Omron NX-IA3117, User Manual

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4 Installation and Wiring
NX-series Digital I/O Unit User’s Manual (W521)
4
-4 Wiring
E
x
amp
les
4
4-
4-1 Wiring the Inpu
t Unit
s
(c) Relation between OFF current of the DC Input Unit and sensor leakage current
The DC Input Unit cannot detect sensor output OFF unless the following conditions are satisfied:
I
OFF
≥ I
leak
When I
leak
is greater than I
OFF
, connect a bleeder resistor R.
Use the following equation to calculate the bleeder resistance constant of the resistance input.
R ≤ R
IN
× V
OFF
/ (I
leak
× R
IN
- V
OFF
)
Use the following equation to calculate the bleeder resistance constant of the constant current input.
R ≤ (V
OFF
/ I
OFF
) × V
OFF
/ (I
leak
× (V
OFF
/ I
OFF
) - V
OFF
)
For both the resistance input and constant current input, use the following equation to calculate the
rated power of bleeder resistor.
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
OFF
I
leak
R
IN
V
OFF
Two-wire sensor
DC Input Unit
Communications Coupler Unit or
Additional I/O Power Supply Unit