Omron NX-ID User Manual page 122

4 Installation and Wiring
(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 ≥ I
OFF leak
When I is greater than I
leak
Use the following equation to calculate the bleeder resistance constant of the resistance input.
R ≤ R × V
IN OFF
Use the following equation to calculate the bleeder resistance constant of the constant current input.
R ≤ (V / I
OFF 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
The voltages and currents related to the conditions for NPN type sensors are shown in the figure
below.
Two-wire sensor
4 - 46
, connect a bleeder resistor R.
OFF
/ (I × R - V )
leak IN OFF
) × V / (I × (V / I
OFF leak OFF
CC
R
V V
I I
CC OFF
leak OFF
V
R
) - V )
OFF OFF
2
- V ) / R × 4 [allowable margin]
R
IOV
Communications Coupler Unit or
Additional I/O Power Supply Unit
IOG
IOV
R
IN
IN
DC Input Unit
IOG
NX-series Digital I/O Unit User's Manual (W521)