What is Profibus : Working & Its Applications

The international networking standard like ProfiBus is extensively accepted and normally used in large assembly, material handling & process control machines. This control network simply supports multi-input wiring with single-cable sensor blocks, smaller sub-networks like AS-i, complex intelligent devices, operator interfaces, and pneumatic valves. The main purpose of PROFIBUS is to provide the interaction between the controllers or the control system and the field sensors. This network uses the OSI model to ensure that devices from various vendors can interact together effectively & easily.

Profibus was first promoted by the German department of education and research. After that used by Siemens in the year 1989 in collaboration with different automation equipment manufacturers. At present, above 11.5 millions PROFIBUS based devices are used in process automation systems.

So this article discusses an overview of Profibus, architecture working & its applications.

What is Profibus/Profibus Definition?

The term “Profibus” stands for “Process Field Bus” and it is the most widely used industrial control network worldwide for industrial process control, motion control, automation, and safety networks. This network is supported by above 1400 equipment vendors worldwide. In the OSI model, this control network provides services at different layers like layer1, layer2 & layer7.

The two most frequently used Profibus versions are Profibus-DP & Profibus-PA.

The devices used by Profibus are masters & slaves. The main function of Master devices is to control the bus once they have the right to access the bus, so they may transmit messages without any remote request known as active stations.

Slave devices are normally peripheral devices like sensors, transmitters & actuators which may allow received messages at the master’s request, send messages to that master which is known as passive stations.

Profibus Working Principle

PROFIBUS uses a master-slave communication in between the component of the control network. In a master-slave communication, the master includes a unidirectional control on all its slave devices as well as processes. So the controller is always the master whereas the IO devices will be always slaves.

Profibus Types

The Profibus is available in three compatible versions Profibus-DP, Profibus-PA & Profibus-FMS.

Profibus-DP

PROFIBUS DP is one of the most frequently used variants of Profibus so-called the standard PROFIBUS. The main benefits of this variant are; plug & play, data transfer can be done very fastly & most frequently used in production environments globally.

This variant is particularly designed for high-speed data communication in between automation control systems & distributed I/O at the level of the device. The central controllers Like PCs or PLCs interact with their distributed field devices through a high-speed serial link. So, most of this data communication through the distributed devices can be carried out cyclically.

In addition to executing cyclic functions, acyclic communication functions are obtainable especially for intelligent field devices by allowing configuration, diagnostics, and handling alarm. Profibus DP supports up to 126 nodes over a bus, permits several masters which are available on the network only if all slaves are connected with a single master. PROFIBUS DP includes three different versions DP-V0, DP-V1& DP-V2.

DPV0 version is mainly used in simple & remote equipment. The features of the DPV0 version mainly include; cyclic data that can be exchanged between masters & slaves, Diagnostics and GSD, or general station description.

DPV1 version is mainly used whenever an exchange of asynchronous data is required. The main features of the DPV1 version include; acyclic data exchange can be done between master & slave, alarm management, combination with FDT & EDDL, and functional blocks.

DPV2 version is mainly used to execute different functions with high performance like exchange of data in broadcast and synchronous communication. The features of this DPV2 version mainly include; time mode of cyclic is deterministic, data exchange can be done by using the slave to slave communication, upload & download redundancy, HART protocol implementation over DP, etc.

Profibus-PA

Profibus PA is mainly designed for an automation process. So it allows different sensors as well as actuators connected on a single common bus line even in intrinsically secure regions. It allows power & data communication on the bus through two-wire technology based on the (international standard (IEC) 1158-2.

PROFIBUS PA improves & replaces conventional systems within process automation like 4-20 mA and HART. As compared to PROFIBUS DP, the power supply & data in Profibus PA are transmitted on similar two wires. In addition, both the PROFIBUS DP & PA are the same in terms of use and protocol.

Profibus-FMS

The Profibus FMS or PROFIBUS field bus message specification is a general-purpose solution, especially for communication tasks at the cell level. This was mainly designed to interact between PLCs & PCs by transmitting complex data between them.

This was not suitable for low-complex messages otherwise communication on a more complicated and wider network. Powerful FMS services provide huge flexibility and also be used for complex & wide communication tasks. At present, PROFIBUS FMS is still used by more operators.

Profibus Specifications

The specifications of Profibus DP & Profibus PA include the following.

• The physical layer used in Profibus DP is RS485.
• Shielded twisted pair cabling is used for signals.
• Cable length mainly depends on the Baud rate.
• The number of devices is 32 for each segment and up to 126 including four repeaters.
• Bus power is 24 VDC supply.
• Transmission rate from 9.6k to 12M bits per second.
• The size of data transfer mainly depends on the type of device like the input is up to 246 bytes and output is up to 246 bytes.
• The device identification can be done based on the particular ID number for every device.
• The physical layer of Profibus PA is IEC61158-2.
• The topology used is a trunk with branching.
• The length of the cable is 1900meters.
• The number of devices used is 32.
• Bus power is up to 0/5A for every segment.
• The rate of transmission is 31.25 kbits/sec.

Profibus Architecture

PROFIBUS is an open field and vendor-independent standard bus used in different fields of applications like process automation & manufacturing. These are ensured through international standards like EN 50254 & EN 50170.

PROFIBUS simply allows communication between different manufacturers’ devices without any adjustment of a special interface. It can be simply used for both time-critical, high-speed & difficult communication-based tasks. PROFIBUS gives communication protocols like FMS & DP based on the request, the transmission technologies like RS-485, IEC 1158-2 otherwise fiber optics are accessible.

The architecture of PROFIBUS protocol architecture is the Open System Interconnection
(OSI) reference model. In this type of architecture, each transmission layer exactly handles defined tasks. So the physical layer or Layer 1 simply defines the characteristics of physical transmission.

The data link layer or Layer 2 simply describes the bus access protocol and the application layer or Layer 7 simply describes the application functions. The architecture of Profibus is shown above.

Application Profiles

Application Profiles of PROFIBUS mainly describe the communications protocol through the transmission technology being utilized and they also describe the field devices’ behavior throughout communication using PROFIBUS. So, the most significant Application Profile of PROFIBUS is presently the PROFIBUS PA because this defines the function blocks & parameters of process automation devices like measuring valves, positioners & transducers.

Application Layer or Layer7

In the OSI model, the application layer simply provides the services of the application for the users. So these services will make an efficient as well as open data transfer achievable in between the layer 2 & application programs. The application layer includes two protocols DP & FMS.

DP

DP is a very efficient communications protocol that uses layer1, layer2, and the user interface. So, this streamlined architecture will ensure a very efficient & fast transmission of data.

The DDLM or Direct Data Link Mapper simply provides the user interface to layer 2. The functions of application obtainable to the operator and the device & the system behavior of the various types of DP device are specified within the user interface.

FSM

The universal communications protocol in FMS importance is to connect layers 1, 2 & 7. Layer 7 or application layer mainly includes FMS (Fieldbus Message Specification) & the LLI (Lower Layer Interface). So, FMS simply describes a huge number of communication services intended for the master to master & master to slave communication. The lower layer interface defines the depiction of the FMS services over the layer2 data transmission protocol.

FSM is a common communication profile that offers several complicated application functions used for communication in between intelligent devices. But further PROFIBUS technical development & the utilization of TCP/IP at the level of the cell, FMS will play a less significant role in the future.

Physical Layer or Layer1

The field bus system application is mostly determined through the transmission technology available and also the normal demands made over bus systems like large distances, maximum transmission speed, high transmission reliability, automation process and also extra requirements should be satisfied like operation within dangerous areas, the transmission of data & energy on a normal cable.

Once it is not achievable to satisfy all necessities through a single transmission technology, then presently three transmission methods are obtainable for PROFIBUS:

• RS-485 transmission is used in manufacturing automation for universal applications.
• IEC 1158-2 transmission is used in process automation.
• Optical fibers are used to improve interference immunity & also the distance of a large network.

Data Link Layer or Layer2

The Layer 2 or data link layer simply defines the bus access technique description with the security of data. By using PROFIBUS, this is the master-slave technique within combination through the token method.

Generally, the data link layer is accountable for moving messages or frames from one node to another. In this layer, a unit of communication is a frame. This layer uses the packets from the network layer, to sum up, them into frames If the size of the frame turns into very large, then the packet can be separated into small frames. So data link layer at the receiver end receives signals & gathers them into messages or frames.

The following diagram will show the main relationship of the data link layer toward the network & physical layers. The main responsibilities of this layer are discussed below.

Framing

The data link layer simply separates the stream of bits obtained from the network layer into controllable frames.

Physical Addressing

If frames or messages are transmitted to various systems on the network, then this layer inserts a header toward the frame to describe the sender & receiver of the frame or message.

Flow Control

At which point, the absorbed data speed through the receiver is low as compared to the data generated within the sender, then the data link layer imposes a mechanism for flow control to avoid the receiver from being overwhelming.

Error Control

The data link layer inserts consistency toward the physical layer by including mechanisms to notice & retransmit lost frames. It also utilizes a mechanism to identify duplicate messages or frames. So, error control is usually attained throughout a trailer including to the frame end.
Access control

Once the minimum of two or above devices is linked to a similar link, then protocols of this layer are required to decide which device has the power to control the link in a given time.

FDL or Fieldbus Data Link

The PROFIBUS uses a uniform medium access protocol which is implemented through the data link layer or layer2 of the OSI model. So, this also comprises data security, telegrams, and transmission protocols handling. The layer2 within PROFIBUS is known as FDL or Fieldbus Data Link.

The FDL or Field bus Data Link simply works through a hybrid access technique that unites token passing through a master-slave technique. The process control systems or the controllers within a PROFIBUS DP network are the masters whereas the actuators & sensors are the slaves.

Profibus Dp Vs Pa

The difference between Profibus Dp and Profibus Pa includes the following.

Profibus Dp	Profibus Pa
PROFIBUS Decentralised Peripherals is used to activate sensors & actuators through a centralized controller within industrial automation-based applications.	Profibus process automation is used to enhance & replace conventional systems within process automation.
It uses RS-485, although the physical layer is not the same, the protocols are similar.	It uses MBP (Manchester Encoded Bus Powered) physical layer.
It is identified as a bus network with high performance and it is capable of transmitting 1000s of I/O point data in below a few milliseconds.	The Profibus-PA can be used as an alternative for HART & 4 to 20mA signal transmission within the process industries.

Profinet Vs Profibus Vs Ethernet Vs Modbus

The difference between Profinet and Profibus include the following.

Profinet	Profibus
Profine or process field net is a communication protocol based on an Ethernet.	Profibus or process field bus is used for Fieldbus communication within automation technology.
It includes two main categories like Profinet IO & Profinet CBA.	It includes three categories like Profibus DP, FMS & PA.
It operates at 100 megabits/sec.	It operates at 9600 bits/sec to 12 megabits/sec speed.
The cable length for Profinet is up to 100 meters.	The cable length of Profibus is up to 1000 meters.
The physical layer used in Profinet is Ethernet.	The physical layer used in Profinet is RS485.
The type of communication used in this is master/slave.	The technology used in this is provider or consumer.
Files used by an inprofinet are to determine hardware are GSD files.	Files used by a Profibus are to determine hardware are GSD files.
The files in Profinet use XML files.	The files in Profibus use ASCII files.

Advantages

The benefits of Profibus include the following.

• Profibus is easy to use and flexible.
• It is based on modularity & standards.
• The only communication protocol allows completely integrated solutions for continuous-discrete & security-based processes to run on a similar bus.
• It allows hybrid automation and eliminates the use of separate systems.
• Maintenance is better.
• Allows quick & very flexible production.
• It uses less hardware & wiring.
• The operator can sense the condition constantly and respond properly.

Disadvantages

The disadvantages of Profibus include the following.

• Its high utilization within the transmission of the short message.
• The lack of power on the bus.
• Expensive as compared to other buses.
• The data bandwidth limit of Profibus DP is low like 244 bytes for each node.
• Installation cost is high by including distance extenders & cable.
• Profibus PA has a slow data rate like 31.25kbit/s.
• The flow of current throughout the bus lines is slow but it is intrinsically secure & perfect to utilize in explosion-hazardous locations.

Applications

The applications of Profibus include the following.

• It provides communication between the field sensors & the controllers or control system.
• The PROFIBUS solutions are employed in industrial automation, industries process, manufacturing, etc.
• It is used for both complex communication tasks & high-speed time-critical applications.

Why Profibus is used?

Profibus is a protocol used in automation technology for field bus communication. This network simply connects controllers & automation systems through different devices like sensors, encoders & actuators. By using these networks, data exchange can be done with a single bus cable.

Are Profinet and Ethernet the Same?

PROFINET & Ethernet both are not the same because Profinet is an application based on Ethernet.

Is Profibus Still Used?

Profibus is not frequently used but it is migrating gradually to current technologies like Profinet. But in the Italian market, it is implemented as an essential protocol in industrial communication

Is Profinet Cable Twisted Pair?

Profinet cable is an industrial Ethernet cable and these cables are sometimes known as industrial two-pair Cat5 or Cat5.

What is the Speed of Profibus?

Profibus network speed ranges from 9600 bits/sec to 12 megabits/sec.

Thus, this is all about an overview of an industrial protocol namely Profibus which is mainly used for cross-device communication as well as automation Profibus cables are used for industrial field bus fast-connect-type systems, mainly developed for process applications. They provide an outstanding electrical transmission performance for their own DP (Decentralized Peripherals) & PA (Process Automation) applications. Here is a question for you, what is Profinet?