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PROFIBUS architecture

The PROFIBUS standard has three established methods of transmission technology: RS 485, fiberglass and MBP (only with PROFIBUS PA). There are other transmission technologies available, but these are not fixed in the standard (such as wireless and power-rail). RS 485 is present in every network because masters are required to be equipped with this technology. It is therefore essential that PROFIBUS engineers can apply the RS 485 architecture guidelines.

The following features of PROFIBUS architecture makes this installation unique: 

Guidelines

The standard PROFIBUS cable is a two-wire twisted pair in which every device is fed separately. This cable satisfies certain specifications to maintain the transmission speed of PROFIBUS over a relatively long distance. Designing and installing an RS 485 segment requires that one keeps architectural guidelines in consideration. With high transmission speeds, overlooking these guidelines can result in problems with the data communication.

There are five critical elements that should always be in order:

  1. The cable length (dependent on the selected baud rate).
  2. Branch lines (dependent on the selected baud rate).
  3. Termination.
  4. A maximum of 32 devices per segment (including network components).
  5. Grounding and shielding.

Expertise is necessary to ensure that an installation satisfies the requirements. The PROCENTEC training courses are a reliable starting point to bridge the frequently made architectural mistakes. PROCENTEC training courses are, also beneficial for experienced users to discuss their personal situation with experts and receive advice.

Cable length and branch lines

The user can select a baud rate that lies between 9,6 Kbps and 12 Mbps. The maximum allowed cable length per segment is linked to the chosen baud rate. With low transmission speeds one can apply more cable than to high transmission speeds (for example: 1.5 Mbps = 200 meter cable per segment). Branch lines are also dependent on the transmission speed. The higher the transmission speed, the less the main cable needs to be intercepted. For example, with 1.5 Mpbs the sum of branches is a maximum of 6.6 meters per segment. At 3.6 and 12 Mbps a branch is no longer allowed.

Termination

With RS 485, the cable is terminated with supplied termination that have a prescribed value (390/220/390). The termination is usually integrated in plugs or equipment that is active with switches.

Number of devices

The maximum number of connected devices is 32 per segment, because the electrical circuits of a transmitter can only deliver a limited amount of power and send information at high speeds. This includes repeaters, fiber optics connectors and other network components.

Grounding and shielding 

The shielding needs to provide protection against electrostatic injection and earth currents. This remains a difficult concept even after years of PROFIBUS usage. There are many theories regarding correct grounding in industrial environments. Every day, the experts at PROCENTEC are working to define an appropriate grounding system for users.

Reliable network components

The architectural guidelines mentioned above have to be strictly complied with. PROCENTEC delivers network components to make PROFIBUS architecture as easy as possible to implement for the user.

Do you want to learn more about what PROFIBUS and PROCENTEC have to offer for your facility? Get in touch with Service and Support. We are happy to help.

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