Omron 3G8F7-CRM21 User Manual page 227

Wiring for Power Supply
Voltage Drop
Cable Voltage Drop
Voltage drop (V) = Current flow (A) ×Cable conductor resistance (Ω/m) ×Cable length
(m) ×2
If the voltage drop is too large and the power supplied to the farthest Slave
Unit exceeds the allowable range, a Repeater Unit must be added and the
power must be supplied from the Repeater Unit.
L1
Master
Board
3 m max.
24-VDC
Slave Unit
Power
current
Supply
consumption I
•
Calculation Example
The allowable power supply voltage range for Slave Units is 14.0 to 26.4 VDC.
If a 24-VDC power supply is used, the allowable voltage drop is 10 V.
The following formula expresses the relation between the available cables and
the permissible cable extension length:
10 (V) >= {(I + I
1
+ {(I +...+ I ) × R
3 n
Use the following approximation formula if you want to add some margin in the
cable selection.
10 (V) >= {(I + I
1
Where R is the cable conductor resistance, 0.025 Ω/m, for a Flat Cable.
When a Flat Cable is used, the extendable length is:
L (m) <= 200 / (I1 + I2 + I3 + ... + In)
L (m) <= 200 ÷ (I
L2 L3
Slave Unit Slave Unit
current
consumption I consumption I
1 2
) × R × L × 2} + {(I
+ I +...+ I
2 3 n 1 1
× L × 2} +... + {I × R
3 3 n
) × R × L × 2}
+ I + ... + I
2 3 n
+ I + I + ... + I )
1 2 3 n
Section E-5
Ln
Slave Unit
current current
consumption I
3 n
) × R
+ I +...+ I
2 3 n
× L × 2}
n n
Terminating
Resistor
× L × 2}
2 2
207