ProfiBus Overview & Application Summary

Profibus: The World’s Most Popular Fieldbus

Origin: German Government in cooperation with automation manufacturers, 1989

Implemented on ASIC chips produced by multiple vendors. Based on RS485 and the European EN50170 Electrical specification.

Formats: Profibus DP (Master/Slave), Profibus FMS (Multi-master/Peer to Peer), and Profibus PA (intrinsically safe).

Connectors: 9-Pin D-Shell connector (impedance terminated) or 12mm quick-disconnect.

Maximum Number of Nodes: 127

Distance: 100M to 24 KM (with repeaters and fiber optic transmission)

Baudrate: 9600 to 12M Bit/sec

Message size: up to 244 bytes of data per node per message

Messaging formats: Polling, Peer-to-Peer

Supporting Trade Organization: Profibus Trade Organization, www.profibus.com

Typical Applications: Commonly found in Process Control and large assembly, and material handling machines. Single-cable wiring of multi-input sensor blocks, pneumatic valves, complex intelligent devices, smaller sub-networks (such as ASI), and operator interfaces. 

Advantages: Profibus is the most widely accepted international networking standard. Nearly universal in Europe and also popular in North America, South America, and parts of Africa and Asia. Profibus can handle large amounts of data at high speed and serve the needs of large installations. The DP, FMS and PA versions collectively address the majority of automation applications.

Disadvantages: High overhead to message ratio for small amounts of data; no power on the bus; slightly higher cost than some other buses.
 

Profibus is the world's most widely installed open Fieldbus. Its substantial speed, distance and data handling capabilities make it ideal for many process control and data intensive applications. Profibus DP, which is the most commonly messaging format for I/O, is a polling network, meaning that its assigned master periodically requests the status of each node. This ensures that each device on the network (which can send up to 244 bytes of data per scan) is updated consistently and reliably. Each message contains 12 bytes of overhead for a maximum message length of 256 bytes.

Multi-Master

Multiple masters are possible with Profibus DP, in which case each slave device is assigned to one master. This means that multiple masters can read inputs from the device but only one master can write outputs to that device.

Peer to Peer

Profibus FMS is a peer to peer messaging format, which allows masters to communicate with one another. Just as in Profibus DP, up to 126 nodes are available and all can be masters if desired. FMS messages consume more overhead than DP messages.

"COMBI mode" is when FMS and DP are used simultaneously in the same network, and Synergetic's DP/FMS masters support this. This is most commonly used in situations where a PLC is being used in conjunction with a PC, and the primary master communicates with the secondary master via FMS. DP messages are sent via the same network to I/O devices.

Intrinsically Safe

The Profibus PA protocol is the same as the latest Profibus DP with V1 diagnostic extensions, except that voltage and current levels are reduced to meet the requirements of intrinsic safety (Class I div. II) for the process industry. Synergetic master cards support Profibus PA, but barriers which convert between DP and PA are necessary (available from a number of companies). PA devices are normally powered by the network at intrinsically safe voltage and current levels.

Troubleshooting Tips

Profibus (especially DP) is straightforward from a user's point of view, as the messaging format is fairly simple. However, the following notes will be helpful in identifying common problems:

-Perhaps Profibus' best-known feature is it's high 12 Mbaud data rate (it can also be operated at speeds as low as 9600 baud). If you plan on using Profibus at high speeds you may need a scope or analyzer to check and fine tune impedance terminations and dropline lengths. Such problems are magnified at the higher speeds. Users who initially intend to run their network at maximum speed often find that a lower speed setting performs just as well and is easier to get working.

-The most common problem our customers encounter in configuring a Profibus network is selecting the wrong GSD (device description) file for a particular node. Because GSD files reside in a separate disk and are not embedded in the product itself, files are sometimes paired with the wrong devices.

Check out our Handheld Profibus Network Analyzer to add quick troubleshooting capability to your Profibus toolkit!

The Profibus Book

Synergetic sells a book, "The Rapid Way to Profibus DP" published by the Profibus Trade Organization. It offers an overview of Profibus and a considerable amount of useful installation information.

Synergetic’s offering

PC Adapter Cards: We have PC/ISA, PC104, PCI, PCMCIA, CompactPCI* and VME* Masters and Slaves for Profibus. They use the same configuration tools, hardware and software interface as all of our other Fieldbus interfaces (DeviceNet, AS-I, Interbus, etc…).

*Call for availability

Embedded Master and Slave Modules: Our COMMUNICATOR modules are credit-card sized boards that you can design into your controller, PLC, operator interface, drive, barcode reader, signal processor or other device that you wish to convert to Fieldbus. The same dual port memory, software drivers and configuration tool as our PC card is used regardless of the bus.

COMMMUNICATOR modules require a custom user hardware design with the COM module mounted as a daughter board and the Fieldbus connector on your hardware board. All other Fieldbus components are on the COM module. After designed, all other COM modules can be plugged into the same socket.

Turn-Key Slave Modules: The ANYBUS-S DeviceNet module allows you to design instant ControlNet, Profibus, Interbus, and other Fieldbus connectivity into your product in a matter of weeks. Now you don’t have to be a Fieldbus expert to manufacture a Fieldbus-compatible product!

A custom hardware design is required, and all Fieldbus components, including connectors, are on the Anybus board. After designed in, all Anybus cards in the same family can be interchanged as different Fieldbuses require.
 

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