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5 Installation and Wiring
NX-series NX1P2 CPU Unit Hardware User’s Manual (W578)
5-4 Wiring
5
5-4-9 Wiring the Built-in I/O
Precautions When Connecting a Two-wire DC Sensor
When a two-wire sensor is used with a DC input, check that the following conditions are met. Failure
to meet these conditions may result in operating errors.
(a) Relation between ON voltage of the DC input and sensor residual voltage
V
ON
V
CC
- V
R
(b) Relation between input current to the DC input and sensor control output (load current)
I
OUT
(min) I
ON
I
OUT
(max)
I
ON
= (V
CC
- V
R
- 1.5 [internal residual voltage of DC input]) / R
IN
When I
ON
is smaller than I
OUT
(min), connect a bleeder resistor R. The bleeder resistor constant can
be calculated as follows:
R (V
CC
- V
R
) / (I
OUT
(min) - I
ON
)
Power W of bleeder resistor (V
CC
- V
R
)
2
/ R × 4 [allowable margin]
V
CC
: Input voltage of DC input
V
R
: Sensor's output residual voltage
I
ON
: Input current of DC input
I
OUT
: Sensor control output (load current)
R
IN
: Input resistor of DC input
(c) Relation between OFF current of the DC input and sensor leakage current
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.
R R
IN
× V
OFF
/ (I
leak
× R
IN
- V
OFF
)
Power W of bleeder resistor (V
CC
- V
R
)
2
/ R × 4 [allowable margin]
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