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Many basic questions about PROFIBUS have already been answered. Perhaps yours is one? Check below to find out.  If you can't find an answer, go to our Forums and ask the experts there.

QUESTIONS (click the index to find the answer)

What is PI?
How do I terminate the shielding of the cable
What is PROFIBUS-DP?
ident numbers: what are they, where can I get them?
What is PROFIBUS-PA?
Hamming distance (HD): what does it mean?
Why are terminators important?
What is a profile? Which are available?
What are the main advantages of PROFIBUS over other fieldbus types?
Why are Class1 and Class 2 masters different?
What is a failsafe mode? What does a failsafe mode mean?
Why is no signal ground/reference wire used in PROFIBUS cables?
Is PROFIBUS an open or proprietary system?
Is it possible to calculate a cost per device for a PROFIBUS System?
What is a GSD file?
What are the roots of PROFIBUS?
What if the system should fail or a chip in a device fail?
Can new devices be added to a PROFIBUS system without upgrading the system?
Does a PROFIBUS system require skilled personnel? What is the average learning curve?
What after sales support can users of PROFIBUS expect?
What hardware and software is needed to set up a PROFIBUS system?
What connectors, pin out and mandatory signals are used?
Are there any particular applications or sectors of industry that particularly benefit from PROFIBUS?
Cable specifications: What should I use?
 
 
ANSWERS

What is PI?

PI was formerly know as PROFIBUS International. It is the umbrella organization responsible for the PROFIBUS protocol and its promotion and support across the world via a network of Regional PI Associations. When PROFINET, PI's Industrial Ethernet solution, was launched, PROFIBUS International was re-named 'PI' (PROFIBUS and PROFINET International).


How do I terminate the shielding of the cable

It is recommended to connect the shield on both ends low inductively to 'ground' in order to achieve optimal electromagnetic compatibility. In the case of separate potentials (e.g. in a refinery) the shield should be connected only on one end of the cable to 'ground'. Preferably, the connection between shield and protective ground should be made via the metal cases and the screw top of a D-sub connector. If this is not possible the connection can be made via pin 1 of the D-sub connector. It should be noticed that this is not the optimal solution. In such a case it is better to bare the cable shield at an appropriate point and to ground it with a cable as short as possible to the metallic structure of the cabinet. This can be done with a ground bus bar in front of the bus connector.



What is PROFIBUS-DP?

This is the performance optimized version of PROFIBUS, specifically dedicated to time-critical communication between automation systems and distributed peripherals. It is suitable as a replacement for the costly parallel wiring of 24 V and 4(0) to 20 mA measurement signals. PROFIBUS-DP is included into the European Fieldbus Standard EN 50170.


ident numbers: what are they, where do I get them?

Every DP/PA device type has to have an individual ident Number. This number is necessary so that a DP-master is able to identify the types of the connected DP/PA devices without a significant protocol overhead. The master compares the ident Number of each connected device with the ident Number in the configuration database. User data transfer in the operation phase is only possible when the right DP Slave is connected to the correct address. This ensures very high protection against parameterization faults. The vendors must apply to the PPROFIBUS Support Center for an individual ident Number for every DP/PA device type.

There's much more about ident Numbers and how to get them here.


What is PROFIBUS PA?

PROFIBUS-PA is a 'profile' of PROFIBUS designed specifically for use in process automation for connecting control systems with field instruments. PROFIBUS-PA is based on PROFIBUS-DP and, using a linking device called a segment coupler, permits transparent communication between general purpose automation and process automation networks, making PROFIBUS ideal for hybrid applications where factory and process devices intermingle. The PROFIBUS PA profile defines the behavior of the field devices and ensures full interoperability and interchangeability between different manufacturers. PROFIBUS PA operates either with Intrinsically Safe transmission technology (acc. to IEC 61158-2) or standard transmission technology (acc. to RS485). In summary, PROFIBUS PA fulfils the special requirements of all sectors of the process industry as follows:

  • transparent communication between process automation networks and general purpose automation networks is possible.
  • PROFIBUS PA permits powering of the field instruments and data transmission over the same two wires.
  • PROFIBUS PA can be used in potentially explosive atmospheres using Intrinsically Safe transmission technology according to IEC 61158-2.

Hamming distance (HD): what does it mean?

The hamming distance is a measure for how secure a protocol is against misinterpretation of a packet.. HD=4 tells us that at least 4 bits have to be wrong, yet still match the checksum calculations, in order for it to be mistaken as a valid packet.


Why are terminators important?

Termination of the bus prevents signal reflections on the PROFIBUS cable. Wrong or missing termination results in transmission errors when the worst case result is that the communication link is lost. In addition, the PROFIBUS termination provides a defined 'idle' level for the cable.


What is a profile? Which are available?

Profiles are definitions of non-mandatory services and parameters for specific areas of applications. It helps to minimize the implementation efforts to implement PROFIBUS functionality in appropriate field devices.

Profiles are available for a variety of devices and applications. There's a lot more on profiles here.


What are the main advantages of PROFIBUS over other fieldbus types?

This is a subjective issue but - provided that the technical solution is satisfactory for the task - it boils down to cost/benefit comparisons. PROFIBUS provides users with the best possible, future proof bus system that can cope with the broad needs of factory and process automation. Market acceptance and sheer momentum means that PROFIBUS is a de-facto fieldbus standard throughout the world.

Here are some of the facts:

  • PROFIBUS has the largest portfolio of products in the fieldbus world. In 2008 it reached 2400 products and services.
  • It has the largest installed base. At the end of 2008 the total had passed 28 million and by 2012 it is expected to reach 50 million.
  • It is supported by the largest user organization in this industry. PI had over 1400 members at the end of 2008.
  • There are 24 Regional PI Associations worldwide, ensuring local support in all industrialized areas.
  • There are close to 400 vendors of PROFIBUS products and services, hence there is plenty of choice for users.
  • It's supported by manufacturers of both master and slave devices providing a truly open approach and practical vendor independence.
  • Choice drives competition amongst vendors, leading to cost, supply and performance benefits for end users..
  • PROFIBUS technology can be used for several levels within the information flow in a company.
  • Knowledge of one standard can be utilized on several levels.
  • There's wide application potential across factory, process and building automation.
  • It's a stable protocol with many chip options available today.
  • It's suitable for operation in intrinsically safe areas in process control.
  • It is the only fieldbus that can be used in hybrid applications - where process and discrete automation segments co-exist in a plant.
  • Platform independence means PC, PLC and DCS based controllers are available.
  • 244 byte telegram means that large packets of data can be sent without segmentation.
  • > 100km distance is achievable using fiber optics.

Why are Class 1 and Class 2 masters different?

A Class 1 master can communicate actively only with its configured slaves and is able to communicate in a passive way with a Class 2 master. The class 2 master is the 'supervisory' device. It can communicate with Class 1 masters, their slaves and its own slaves for configuration, diagnostic and data/parameter exchange purposes.


What is a failsafe mode? What does a failsafe mode mean?

This mode defines the status of signals in IO modules if a bus or system failure occurs. It is common that all output signals are going to the zero voltage level in a fail safe situation. The status is important in functional safety applications where a profile such as PROFIsafe is used. There's a lot more about functional safety here.


Why is no signal ground/reference wire used in PROFIBUS cables?

To ensure easy handling a signal 'ground' wire is not used by PROFIBUS. However, it is recommended to isolate the interface circuit from the local ground (e.g. using opto couplers) to reduce possible common mode voltages between transceivers.


Is PROFIBUS an open or proprietary system?

PROFIBUS is completely open. It was originally standardized in Germany in 1989 as DIN 19245 and in July 1996 as EN 50 170. The EN 50 170 specification is available through any of the national standards bodies of CENELEC / IEC and the PROFIBUS Specification can be supplied by any of the Regional PROFIBUS Associations. It's now globally standardized under IEC 61158.

Is it possible to calculate a cost per device for a PROFIBUS System?

Not generally but PROFIBUS connectivity should not add significantly to standard field device costs as most devices today are digitally based anyway. It's more instructive to look at wider issues. Having a single cable to connect devices means big savings in design, engineering and installation costs. Furthermore, the availability of data across the plant means even more savings are possible over the lifetime of a device through better operations and improved asset management. Better data flows lead to better plant management too. Overall, any extra cost per device is insignificant compared with the life cycle savings of a fieldbus network.


What is a GSD file?

A GSD file is used to identify the basic operational characteristics of a PROFIBUS device, to aid interoperability and interchangeability. It makes it possible to have manufacturer-independent configuration tools. Typically, a GSD file includes vendor information, baudrates, timing information, the options or features supported and the available I/O signals. A GSD file must be available for every PROFIBUS slave. There's a lot more about GSD files here.


What are the roots of PROFIBUS?

by Armin Steinhoff.

The base of the specification of the PROFIBUS standard was a research project that took place between 1987-1990, supported by the following companies: ABB, Phoenix Contact, AEG, Rheinmetall, Bosch, RMP, Honeywell, Sauter-Cumulus, Kloeckner-Moeller, Schleicher, Landis & Gyr, Siemens.

Five German research institutes also cupported the project: FZI Karlsruhe, LRT, IITB, WZL, LPR

There was also minor sponsorship from the German government.

The result of the project was the first draft of DIN 19245, the PROFIBUS standard, Parts 1 and 2.

Part 3, PROFIBUS-DP, was defined in 1993 by the following working group:

  • Mr. Emmerling, MicroSyst
  • Mr. Dr. Endl, Softing
  • Mr. Schmitz, Pepperl + Fuchs
  • Mr. Schneider, MBB Gelma
  • Mr. Szabo, TMG i-tec
  • Mr. Thiesmeier, Kloeckner-Moeller
  • Mr. Tretter, Siemens
  • Mr. Volz, Bosch
  • Dr. Weber, Siemens

Yes, 10 years is a long time .... hope this helps a little bit to remember!

Note added 2009: Yes, a long time indeed!


What if my PROFIBUS system should fail, or a chip fail in a device?

PROFIBUS has been designed to allow configurations where redundant cabling is possible to take account of wire breaks. Also, node failures can be configured to be ignored, or to trigger a 'stop' in the master. In this case unaffected nodes can continue operation. When a failure is identified the master immediately resends the telegram and it's possible to configure the number of times this is attempted. Information relating to the failure is generally available on a node, a module within a node and on a channel specific basis. Certification testing of devices through an authorized test laboratory ensures that potential failures conform to what is expected of them. Media redundancy can be achieved through dual master systems.


Can new devices be added to a PROFIBUS system without upgrading the system?

PROFIBUS guarantees backwards compatibility. So, if new functions are offered in a device it will still be possible to use this device on the same wire with older devices, allowing progression of the system without forcing users to upgrade unless they specifically wish to enhance their functionality.


Does a PROFIBUS system require skilled personnel? What is the average learning curve?

PROFIBUS has been designed to be simple. Assuming a knowledge of PLCs and field device technology it has been our experience that the information needed to set up a network can be imparted in as little as half a day. There are many training courses available from vendor members and PI Training labs. PI itself runs a series of practical workshops from integration to device implementation. Check our events pages to find a training course suitable for your needs.


What after sales support can users of PROFIBUS expect?

There are currently more than 1400 companies worldwide who have committed to PI, some 150 of which companies manufacture PROFIBUS products and support them via their thousands of agents, distributors and subsidiaries worldwide. Many of these companies are vendors of both (a) master and (b) slave technology. Our network of Regional PROFIBUS Associations also provide support in a number of countries where they can offer advice on product sourcing, implementation and application by 'phone, fax and email. Many of these associations run training courses and seminars. PROFIBUS is of course a core part of most vendors product offering and you would expect many of their support staff to be able to deal with PROFIBUS technical issues.


What hardware and software is needed to set up a PROFIBUS system?

In addition to a PLC and the devices to be controlled

  • a cable - Shielded Twisted Pair with terminating resistors or Fibre Optic with Optical Link Modules
  • a GSD file for each device. (A simple ASCII text file containing device data like identification info, what transmission speeds are supported, data format, time required to respond etc.)
  • a software configuration tool. This configures the active stations and tells them what devices are present on the bus and how much data it needs to exchange with them etc. is required.

What connectors, pinout and mandatory signals are used?

The PROFIBUS Standard does not specify an alternative to the 9 pin D-SUB connectors, but it is often necessary to have alternatives available.

The test specification for DP Slaves defines:

  • Alternative connectors may be used. No special connector is defined. But if the device with these alternative connectors should be certified, it must have all the mandatory signals of the PROFIBUS D-SUB connector available.
  • Furthermore, you should take into consideration for high speed usage, that some additional components should be used in combination with the D-SUB connector, or any other one.
  • These components (R, L, C) are specified into the Implementation Guideline for PROFIBUS-DP, and are explained in detail including sample circuit diagrams in the new PROFIBUS-DP book (The Rapid Way to PROFIBUS-DP). This book may be ordered from your local PROFIBUS organization.

Are there any particular applications or sectors of industry that particularly benefit from PROFIBUS?

PROFIBUS has already found many applications in factory, process and building automation, for example from Automotive manufacture at General Motors across Europe, to Breweries like Bitburger and Guinness to building management like the Russian Kremlin building. PROFIBUS is also being used in applications that were never envisaged from its conception, because it has been constructed in a way that allows for many new device types to be added. However, the two key areas of industry that can most benefit from its adoption are :

  • Factory Automation, where signal wiring costs are cut significantly and many devices can be installed directly on the bus, thus removing the need for many input and output signals.
  • Process Automation, where cabling costs are significantly reduced; devices can be placed directly in the hazardous areas; many analogue I/O cards can be eliminated by transferring all data on one twisted pair cable. This also reduces the need for I/S barriers.

Cable specifications: What should I use?

The PROFIBUS standard defines two variations of the bus cable. However it is recommended to use cable Type A in all new installations.

Type A is recommended for high transmission speeds and permits a doubling of the network distance in comparison to Type B.

Type A Technical specification:

  • Impedance: 35 up to 165 Ohm at frequencies from 3 to 20 Mhz.
  • Cable capacity: < 30 pF per meter.
  • Core diameter: > 0,34 mm², corresponds to AWG 22.
  • Cable type: twisted pair cable. 1x2 or 2x2 or 1x4 lines.
  • Resistance: < 110 Ohm per km.
  • Signal attenuation: max. 9 dB over total length of line section.
  • Shielding: CU shielding braid or shielding braid and shielding foil.
  • Max. Bus length: 200 m at 1500 kbit/s, up to 1,2 km at 93,75 kbit/s. Extendable by repeaters.