Rockwell-automation 1788-EN2PAR EtherNet/IP and ControlNet to PROFIBUS Manual de usuario descargar pdf (Pagina 20)

20 Rockwell Automation Publication 1788-UM058B-EN-P - September 2014

Chapter 1 Installation

Cable Path

Do not route the PROFIBUS PA cable near any motors or high-voltage/

high-current cables. Motors and high-voltage/high-current cables can generate

noise that decreases communication signal quality on the PA cable, which can

corrupt PA packets and cause field device timeouts.

Cable Lengths

Load and voltage drop determine maximum cable length. Consider these factors

when planning the cable length for your installation:

• The more field devices and junction boxes that are connected, the bigger

the load will be. The bigger the load, the more the signal attenuates, which

can cause the signal to become unreadable.

• The bigger the load and the longer the cable, the bigger the voltage drop

across the cable. The voltage at the end of a long cable can drop below the

allowed PROFIBUS PA level. See Figure 1

for a cable length calculation

example.

Figure 1 - Cable Length Calculation Example

DC resistance per conductor: 24 Ω/km

Total cable resistance: 48 Ω

Total current consumption: (4 x 40 mA) + (16 x 15 mA)

= 320 mA

Total voltage drop: 48 Ω x 320 mA

= 15.36V

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Rockwell-automation 1788-EN2PAR EtherNet/IP and ControlNet to PROFIBUS Manual de usuario Pagina 20