Introduction to Industrial Automation

8.3   Implementation of Industrial Networks

8.3.1   Data Transmission Media

In general, all the physical media for the communication of data transfers for classical public 

communication networks can also be utilized in the case of the industrial networks. The most 

common data transmission media (hardware) are presented next.

Twisted-pair cable. The simplest medium for data transmission in a communication network 

is a twisted-pair cable. It consists of two insulated copper conductors twisted around one another. 

The twisting of wires is made in order to avoid the electromagnetic interactions between two or 

more pairs when they are near. When several wire-pairs go parallel and at long distances, then these 

are grouped in bundles with an external protective casing. The wire pairs at these bundles would 

create an electromagnetic interference between them if they were not twisted. The signal trans-

mission with twisted-pair cables is quite satisfactory (amplification is not needed) for distances 

of a few kilometers. For very large distances between two network nodes, repeaters are required 

in order to communicate. Analog and digital signals can both be transmitted via a twisted-pair 

cable. In this case, the bandwidth depends on the thickness of the wires and the transmission 

distance, while generally some Mbits/sec for distances of a few kilometers can be achieved. In the 

twisted-pair case, the main advantages are the low cost and the ease of installation, while the main 

disadvantages are their sensitivity to noise and the relatively slow speed of transmission.

Coaxial cable. The coaxial cable consists of a stiff copper wire (core) that is surrounded by 

an insulating material. The insulating material is covered by a woven copper braid or a metal-

lic foil that acts both as the second wire in the circuit and as a shield for the inner conductor. 

The external conductor (grid) is covered by a protective plastic cover. There are two types of 

PLC

PLC

PLC

PLC

PLC

PLC

PLC

Logical ring (token)

Active

stations

Passive

stations