OPERATION MANUAL CompoBus/S

Supplying Power to the Slaves Section 2-3
38
Master
Power supply
(24 V DC)
L is the length of cable to the last Slave (L 1 + L 2 + ... + L N ).
I 1 + I 2 + ... + I N : Current consumption of each Slave (A)
Note 1. The allowable voltage range for a Sensor Terminal which has a 2-wired
method Proximity Switch connected is 20.4 to 26.4 V DC. If the Special Flat
Cable’s voltage is below 20.4 V DC, use an external power supply for the
Sensor Terminal.
2. When there is no distinction between main and branch lines, substitute the
cable length between the communications power supply and the farthest
end for L in the above formula. If the communications power supply is at
the midway point in the cable path, the cable length on the left-hand side
added with that on the right-hand side will be the maximum length of the
communications cable. If only some Slaves are located far from the Master,
the maximum cable length calculated from the cable length to the last
Slave may be very short. In such cases, calculate the voltage drop at each
branching position and Slave position and design the system with an appropriate
margin so that the voltage applied to each Slave will be high
enough.
Slave Slave Slave Slave
500 mA 500 mA 500 mA 500 mA
500 mA
500 mA
Example
Communications cable: Special Flat Cable
In this example a single power supply can’t provide power to all of the Slaves,
so the Slaves are divided into 2 groups and supplied by 2 power supplies.
Group A
Cable length L A = 50 m
Slave Slave Slave Slave
500 mA
500 mA
Total current consumption I A = 3.55 A
Relay terminal Group B Extension Connector
Power
supply
(24 V DC)
Cable length L B = 45 m
Slave Slave Slave
500 mA
500 mA
500 mA
500 mA
500 mA
Slave Slave Slave
500 mA
Slave
500 mA
Total current consumption I B = 4 A
Slave
500 mA
Terminator
Total current consumption beyond the
Extension Connector I C = 1.5 A
Check that each group meets the current consumption conditions. In this case
the ambient temperature is 30°C.
Group A
Special Flat Cable’s Allowable Current:6 A ≥ 3.55 A (IA )
Cable Length Limit due to Voltage Drop:185/3.55 = 52 m ≥ 50 m (LA )
Group B
Special Flat Cable’s Allowable Current:6 A ≥ 4 A (IB) Extension Connector’s Allowable Current: 4.5 A ≥ 1.5 A (IC) Cable Length Limit due to Voltage Drop:185/4 = 46 m ≥ 45 m (LB)