Omron CJ Series Operation Manual page 150

4 Installation and Wiring
Voltage Drop
Cable Voltage Drop
The voltage drop must be considered so that the power supply voltage at the Slave Unit that is the
farthest from the power supply will still be within the allowable power supply range.
The voltage drop is expressed by the following formula.
Voltage drop (V) = Current (A) × Cable conductor resistance (Ω/m) × Cable length (m) × 2
If the voltage drop is too large and power cannot be supplied to the farthest Slave Unit within the
allowable range, add a Repeater Unit and supply power from the Repeater Unit.
Master
Unit
Power
supply,
24 VDC
• Calculation Example
The allowable power supply voltage range for Slave Units is 14 to 26.4 VDC. If a 24-VDC power sup-
ply is used, the allowable voltage drop is 10 V.
The relationship between the cable and the length that can be extended is expressed by the follow-
ing formula:
10 (V) ≥ {(I
+ I
1
× R
+ ... + {I
n
To provide leeway when selecting the cable, use the following approximation.
10(V) ≥ {(I
+ I
1
R = Cable conductor resistance = 0.025 Ω/m for Flat Cable
The extended length of the cable is thus expressed by the following formula:
L (m) ≤ 200 ÷ (I
4-42
L1 L2
3 m max.
Slave Unit
Slave Unit
current
current
consumption I
consumption I
1
) × R × L × 2} + {(I
+ I + ... + I
2 3 n 1 1
× L × 2}
n n
) × R × L × 2}
+ I + ... + I
2 3 n
+ I + I + ... + I ) ... For Flat Cable
1 2 3 n
CJ-series CompoNet Master Unit Operation Manual for NJ-series CPU Unit (Cat. No. W493)
Ln
L3
Slave Unit Slave Unit
current current
consumption I consumption I
2 3
) × R × L
+ I + ... + I
2 3 n 2 2
Terminating
Resistor
n
× 2} + {(I ) × R × L
+ ... + I
3 n 3 3
× 2}