8.1.2.1
Calculating the voltage drop
1. Determine the current consumption of a module.
Current PS [A]
Current PL [A]
Power consumption
è
Technical data of the module
Power consumption PS/PL of the sensors/actuators
Current consumption of the following module at
connection [XD2]
Sum of current consumption
Tab. 8 Determination of the current consumption at connection [XD1]
2. Determine line resistance
è
Tab. 9 Determining the line resistance.
Cable length [m]
1)
0.3
0.5
1.0
2.0
5.0
7.5
10.0
15.0
Line resistance [
Ω
]
0.04
0.06
0.09
0.16
0.37
0.55
0.72
1.07
1) The specified values are valid for permissible cables with a core cross-section of 0.5 mm² from the Festo catalogue.
Tab. 9 Determining the line resistance
The specification of the line resistance comprises the forward and return line including the for-
ward resistance of the modules.
3. Calculate voltage drop (starting with the last module).
Formula: voltage drop = line resistance × current
Line resist-
ance [
Ω
]
Current PS
[A]
Voltage
drop PS [V]
Current PL
[A]
Voltage
drop PL [V]
Last module (n)
–
–
–
Cable between
Modules n and n
–
1
Cable between
Module n
–
1 and n
–
2
…
Supply line to the inter-
face
Total
Tab. 10 Calculating the voltage drop
Installation
18
Festo — CPX-AP — 2019-06
