Belden expands the line of DataBus cables for FieldBus applications

Leading cable manufacturer Belden has introduced new FieldBus Type A multi-pair and foil/braid cables. These provide installation flexibility for many different environments, particularly where multiple or extended cable runs are required.

FieldBus is an all digital, serial and two way communications protocol designed to standardise the interconnection of field devices at a communications rate of 31.25kB/s.

The benefit to the end user is the freedom to implement tightly integrated digital control based on unified system architecture and a high speed backbone (HSE) for plant operations. This, in turn, removes the constraints on device and sub-system interoperability.

How FieldBus works

By using a system of linking devices, the field devices are made accessible to communication networks (running at 1 or 2.5 Mc/s). The secret is a simple twisted pair of wires which carry the signals between the field devices and the networks. The advantage to the end user is that the amount of l/O and control equipment is reduced (because of distribution of control into the field devices).

In addition, fewer Intrinsically Safe (IS) barriers, cabinets, cables and connectors need to be used. This results in a more reliable and more cost effective industrial control system because the pair of wires can support multiple functions within a single device – such as diagnostics, control and auto error correction.

Special cabling features of FieldBus

Clearly, the number of devices possible on a FieldBus link will vary depending on different factors. Commonly, these will include the power consumption of each device, the use of repeaters, signal attenuation, the type of cable used and the distance.

The table below provides suggested transmission distances (calbe lenghts) for each type of cable.

Fieldbus Type	Communication Rate	Transmission Distance Ft./m
A	31.25 Kb/s	6,232/1900
B	31.25 Kb/s	3,936/1200
High Speed	1.0 MHz	2,460/750
	2.5 MHz	1,640/500

Because of the superior features of Belden DataBus cables, distance limitation can be exceeded without any enhancements to the system or any sacrifice in its performance.

Features can be summarised as:-

• Compliant with FieldBus specifications

• Excellent electrical characteristics

• Low capacitance for long runs

• Versions available in 22,18,16 and 14 AWG standard tinned copper conduction

• Versions available with Belfoil® and Belfoil® Plus Braid shields

• Multi-pair cables available from 2 to 24 pairs

• PLTC-ER versions available

• Easily identifiable orange jacket

• Blue jacket available for Instrinsically Safe (IS) applications

• Suitable for use in Class 1, Division 2 applications

• RoHS compliant and CE approved

FieldBus also enjoys the features which are common to all Belden industrial cables. Ratings include Multi-pair Type 8 22 AWG PLTC-rating and Multi-pair 18 AWG TC-rating – both individually and/or overall shielded - as well as 600v TC rating. Visual recognition means various jacket colours as well as alternate black/white colour-coded pairs. In addition, cables can have aluminium or steel interlocked armour and CPE or LSOH jackets.

FieldBus uses Ethernet for HSE control backbone 100 Mb/s transmissions.

To help end users selecting Category 5e or Category 6 cables, Belden has published the DataTuff Industrial Ethernet Cable Selection Guide. A new Technical Bulletin about FieldBus cables is also available or visit www.belden.com