Omron DRT1 Series - Page 369

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Appendix D
Precautions when Connecting Two-wire DC
Sensors
When using a two-wire sensor with a 12-V DC or 24-V DC input device, check that the following conditions
have been met. Failure to meet these conditions may result in operating errors.
Relation between Slave with Transistor Inputs and Sensor Residual Voltage
V
ON
≤ V
CC
– V
R
V
CC
: I/O power supply voltage (The allowable power supply range is 20.4 to 26.4 V, and thus
20.4 V will be used to allow for the worst possible conditions.)
V
ON
: ON voltage for a Slave with Transistor Inputs
V
R
: Sensor’s output residual voltage
ON Current for Slave with Transistor Inputs and Sensor Control Output (Load Current)
I
OUT
(min) ≤ I
ON
≤ I
OUT
(max.)
I
OUT
: Sensor control output (load current)
I
ON
:Slave ON current
I
ON
= (V
CC
– V
R
– V
F
)/R
IN
V
F
: Internal residual voltage of Slave
R
IN
: Input impedance of Slave
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
≥ (V
CC
– V
R
)
2
/R × 4 [allowable margin]
Relation between OFF Current of Slave with Transistor Inputs and Sensor Leakage Current
I
OFF
≥ I
leak
I
OFF
: OFF current of Slave
I
leak
: Leakage current of Slave
Connect a breeder resistor if I
leak
is greater than I
OFF
. Use the following equation to calculate the
breeder resistance constant.
R
≤ (I
OFF
x R
IN
+ V
F
)/(I
leak
– V
OFF
)
Power W
≥ (V
CC
– V
R
)
2
/R × 4 [allowable margin]
R
V CC
V R
R IN
2-wire
sensor
Slave with
Transistor
Input