Omron C200HW-SRM21-V1 - 08-2007 - Page 58

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Supplying Power to the Slaves Section 2-3
3. Allowable Current for CJ-series Communications Connector
The allowable current for the communications connector of the CJ-series
Master Unit is 4 A. The total current consumption of Slaves must be no
more than 4 A when the CJ-series Master Unit communications connector
is connected to the communications power supply. (The same applies
when there is no distinction between main and branch lines.)
I
1
+I
2
+ ... +I
N
≤ 4 A
(I
1
, I
2
, w..., I
N
represents the current consumption of each Slave being sup-
plied with communications power supply.)
4. Cable Length Limit Due to Voltage Drop
The voltage drop can be calculated from the cable’s length, the cable’s re-
sistance, and the Slave’s current consumption. (The cable’s length is mul-
tiplied by 2 because there are two wires carrying current, + and –.)
Voltage drop (V) = Current (A)
× (Cable’s length × 2 × Cable’s resistance)
(
Ω)
The allowable voltage range for the Slaves is 14 to 26.4 V DC, so the max-
imum voltage drop is 10 V DC when using a 24-V DC power supply.
The equation yielding the voltage drop for the following system is shown
below. This is an approximate equation allowing some margin for error.
10
≥ (I
1
+ I
2
+ ... + I
N
) × L × 2 × R
10: Max. voltage drop (V)
R: Resistance of the Special Flat Cable (
Ω/m)
4-conductor VCTF cable: 0.025
Special Flat Cable: 0.027
L
1
+ L
2
+ ... + L
N
: Length of cable between the Slaves
The maximum cable length (L) can be calculated from this equation as fol-
lows:
L
≤ 10 / { (I
1
+ I
2
+ ... + I
N
) × 2 × R}
↓
L ≤ 200 / (I
1
+ I
2
+ ... + I
N
) ... 4-conductor VCTF cable
185 / (I
1
+ I
2
+ ... + I
N
) ... Special Flat Cable
Slave
Current: I
1
Slave
Current: I
2
Slave
Current: I
N
Termi-
nator
Power supply
(24 V DC)
Master
Current consumption of Slaves being supplied
with communications power supply.
Master
Power supply
(24 V DC)
Slave
Current: I
2
Te r m i -
nator
Slave
Current: I
1
Slave
Current: I
N
L
1
L
2
L
N