350
Application Precautions Section 5-12
5-12 Application Precautions
5-12-1 Two-wire DC Sensor Connections
When connecting a Unit with transistor inputs to a 2-wire DC sensor, check
that the following conditions are satisfied, or otherwise the Unit may malfunc-
tion.
Relationship between ON Voltage of Unit with Transistor Inputs and
Residual Voltage of Sensor
V
ON
≤ V
CC
– V
R
V
CC
: I/O power supply voltage (calculated at 20.4 V in consideration of
the worst condition through the power supply voltage range is be-
tween 20.4 and 26.4 V.)
V
ON
: ON voltage of Unit with transistor inputs (Refer to page 351 for
specifications for each Slave.)
V
R
: Output residual voltage of sensor
The above formula can be satisfied by setting the I/O power supply voltage
(V
CC
) to 26.4 V.
Relationship between ON Current of Unit with Transistor Inputs and
Control Output (Load current) of Sensor
I
OUT
(min) ≤ I
ON
≤ I
OUT
(max)
I
OUT
:Sensor control output (Load current)
I
ON
: ON current of Unit with transistor inputs
I
ON
is obtained from the following formula.
I
ON
= (V
CC
–V
R
–V
F
) / R
IN
V
F
: Residual voltage of Transistor Input (Refer to page 351 for specifi-
cations for each Slave.)
R
IN
:Input impedance of Unit with transistor inputs (Refer to page 351
for specifications for each Slave.)
If I
ON
is smaller than I
OUT
(min), connect the bleeder resistance R obtained
from the following formula.
R
≤ (V
CC
– V
R
) / (I
OUT
(min) – I
ON
)
Power W
≥ (V
CC
– V
R
)
2
/R × 4 (Excess gain)
Relationship between OFF Current of Unit with Transistor Inputs and
Current Leakage of Sensor
I
OFF
≥ I
leak
I
OUT
: OFF current of Unit with transistor inputs (Refer to page 351 for spec-
ifications for each Slave.)
I
leak
: Current leakage of sensor
If I
leak
is smaller than I
OUT
, connect the bleeder resistance R obtained from
the following formula.
R
≤ (I
OFF
× R
IN
+ V
F
) / (I
leak
– I
OFF
)
Power W
≥ (V
CC
– V
R
)
2
/R × 4 (Excess gain)
2-wire
sensor
Unit with
transistor
inputs
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