Omron CRT1 - 10-2008, Operation Manual

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553
Appendix E
Precautions with Connecting
Two-wire DC Sensors
When using a two-wire sensor with a Slave Unit with DC inputs, check that the following conditions have been
met. Failure to meet these conditions may result in operating errors.
Relation between ON Voltage of Slave Unit with DC Inputs and
Sensor Residual Voltage
V
ON
≤
V
CC
−
V
R
V
CC
: I/O power supply voltage (The allowable power supply voltage range is 20.4 to 26.4 V, so 20.4 V will be
used here to allow for the worst possible conditions.)
V
ON
: ON voltage for a Slave Unit with DC Inputs
V
R
: Sensor's output residual voltage
It is sometimes possible to satisfy the above equation by adjusting the I/O power supply voltage (V
CC
) to
26.4 V.
Relation between ON Current of Slave Unit with DC Inputs 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 Input Slave Unit with DC inputs
I
ON
is calculated as follows:
I
ON
= (V
CC
−
V
R
−
V
F
)/R
IN
V
F
: Internal residual voltage of a Slave Unit with DC Inputs
R
IN
: Input impedance of a Slave Unit with DC Inputs
When I
ON
is smaller than I
OUT
(min), connect a bleeder resistor R.
The bleeder resistor constant can be calculated using the following equation.
R
≤
(V
CC
−
V
R
)/(I
OUT
(min.)
−
I
ON
)
Power W
≥
(V
CC
−
V
R
)
2
/R
×
4 [allowable margin]
Slave Unit
with DC Inputs
2-wire
sensor