Omron DEVICENET#05-2003 - Precautions for Connecting a DC 2-Wire Sensor

42
Specifications Common to All Basic I/O Units Section 4-2
4-2-1 Precautions for Connecting a DC 2-wire Sensor
Check that the following conditions have been satisfied when using a DC 2-
wire sensor with a Transistor Input Unit. Failure to meet these conditions may
result in operating errors.
Transistor Input Unit ON Voltage and Sensor Residual Voltage
V
ON
≤ V
CC
– V
R
V
CC
: I/O supply voltage
(Supply voltage range is 20.4 to 26.4 V, but is calculated at 20.4 V as the
worst-case scenario.)
V
ON
: ON voltage for the Transistor Input Unit
(15 V with a MULTIPLE I/O TERMINAL)
V
R
: Sensor output residual voltage
The above formula can sometimes be satisfied by adjusting the I/O supply
voltage (V
CC
) to 26.4 V.
Transistor Input Unit ON Current and Sensor Control Output (Load
Current)
I
OUT (min.)
≤ I
ON
≤ I
OUT (max.)
I
OUT
: Sensor control output (load current)
I
ON
: ON current of the Transistor Input Unit
I
ON
can be determined as follows:
I
ON
= (V
CC
– V
R
– V
F
) / R
IN
V
F
: The Transistor Input Unit’s internal residual voltage
(1.5 V with a MULTIPLE I/O TERMINAL)
R
IN
: The Transistor Input Unit’s input impedance
(4.4 k
Ω with a MULTIPLE I/O TERMINAL).
When I
ON
is smaller than I
OUT (min.)
, connect a bleeder resistor R. The bleeder
resistor constant can be determined as follows:
R
≤ (V
cc
– V
R
) / (I
OUT (min.)
– I
ON
)
Power W
≥ (V
cc
– V
R
)
2
/ R x 4 [tolerance]
Transistor Input Unit OFF Current and Sensor Leakage Current
I
OFF
≥ I
LEAK
I
OUT
: OFF current of the Transistor Input Unit
(1.0 mA with a MULTIPLE I/O TERMINAL).
I
LEAK
: Sensor leakage current.
If the sensor leakage current is greater than the OFF current of the Transistor
Input Unit, connect a bleeder resistor R. The bleeder resistor constant can be
determined as follows:
R
≤ (I
OFF
x R
IN
+ V
F
) / I
LEAK
– I
OFF
)
Power W
≥ (V
cc
– V
R
)
2
/ R x 4 [tolerance]
2-wire
sensor
Transistor
Input Unit