What is Profibus?
Profibus (Bus Field Process) is the bus standard communication field in automation technology. Profibus stands for Process field bus.
Profibus is an open digital communication system with a wide range of applications, especially in the fields of process automation and factory, transport and energy distribution. PROFIBUS is suitable for both fast and critical applications and complex communication tasks.
First, the complex communication protocol Profibus FMS (Field Message Message bus), which is designed to demand communication tasks, is determined. Subsequently, in 1993, the specifications were simple and thus far faster the Profibus DP protocol (Peripherals Decentralization) was completed.
Profibus FMS is used for (non-deterministic) data communication between Profibus Masters. Profibus DP is a protocol created for (deterministic) communication between Profibus masters and their remote I / O.
Profibus DP and Profibus PA:
There are two variations of Profibus currently in use, the most commonly used Profibus DP, and the lower used, certain applications, Profibus PA:
Profibus DP (Decentralization Peripherals ) is used to operate sensors and actuators through centralized controllers in the production (manufacturing) of automation applications. Many standard diagnostic options, in particular, focus here.
Profibus PA is used to monitor measurement equipment through process control systems in process automation applications. This variant is designed for use in explosions / hazardous areas (Ex-zones 0 and 1).
The Physical Layer (i.e. cable) complies with IEC 61158-2, which allows power to be sent via a bus to the field instrument while limiting the current so that the explosion conditions are not created, even if damage occurs. total) (Process Automation) is used to monitor measurement equipment through process control systems in process automation applications.
This variant is designed for use in explosions / hazardous areas (Ex-zones 0 and 1). The Physical Layer (i.e. cable) complies with IEC 61158-2, which allows power to be sent via a bus to the field instrument, while limiting the current so that the explosion conditions are not created, even if damage occurs.
The number of devices attached to PA segments is limited by this feature. PA has a data transmission rate of 31.25 kbit / s. However, PA uses the same protocol as DP, and can be connected to a DP network using a coupler device. Much faster DP acts as a backbone network for transmitting process signals to the controller. This means that DP and PA can work closely together, especially in hybrid applications where process and network automation plants operate side by side. In more than 30 million Profibus nodes installed at the end of 2009. 5 million are in industrial processes.
Different working Layers of Profibus:
To take advantage of these functions, various levels of DP protocol services are defined:
- DP-V0 for cyclic exchange of data and diagnosis
- DP-V1 for acyclic and cyclic data exchange and alarm handling
- DP-V2 for isochronous mode and broadcast data exchange (slave to slave communication).
The FDL security layer ( Field bus Data Link ) works with a hybrid access method that combines token passing with the master-slave method. In a Profibus DP network, controllers or process control systems are rulers and sensors and actuators are slaves.
Various types of datas are used. They can be distinguished from them starting to limit (SD):
- No data: SD1 = 0x10
- Variable Length Data: SD2 = 0x68
- Token : SD4 = 0xDC
- Brief acknowledgement : SC = 0xE5
SD: Starting Limit
LE: Length of data unit protocols (including DA, SA, FC, DSAP, SSAP)
LER: Repetition of data unit protocols (Hamming distance = 4)
FC: Code Function
DA: Destination Address
SA: Source Address
DSAP: Purpose of Access Point Services
SSAP: Access Point Services source
Three different methods are specified for the transmission bit layer:
With electricity transmission in accordance with EIA-485, twisted pair cables with a 150 ohm impedance are used in the bus topology. Bit rates from 9.6 kbit / s to 12 Mbit / s can be used. The cable length between two repeaters is limited to 100-1.200 m, depending on the bit rate used. This transmission method is mainly used with Profibus DP.
With optical transmission through optical fibers, stars, buses and topological rings used. The distance between repeater can be up to 15 km. Topology rings can also be carried out excessively.
With MBP (Manchester Bus Powered) the transmission, data and electric field technology of the bus is fed through the same cable. Power can be reduced in such a way that it is possible to use it in a dangerous explosion environment. The bus topology can be up to 1,900 m long and allow branching to field devices (max. 60 branches). The bit rate here is still 31.25 kbit / s. This technology is specifically established to be used in the automation process for Profibus PA.