1. Introduction to PROFIBUS
PROFIBUS is an international, open fieldbus standard that does not depend on equipment manufacturers. PROFIBUS transmission speed can be selected within the range of 9.6Kbps~12Mbps, and when the bus system starts, all devices connected to the bus should be set to the same speed. It is widely used in manufacturing automation, process industry automation and automation in other fields such as buildings, transportation and electric power.
ROFIBUS is a fieldbus technology for factory automation workshop-level monitoring and field device layer data communication and control. The distributed digital control and field communication network that can realize the monitoring from the field equipment level to the workshop level provides a feasible solution for realizing the comprehensive automation of the factory and the intelligence of the field equipment.
PROFIBUS is the abbreviation of Process Field Bus, which officially became the international standard of Field Bus in 1989. At present, it occupies a dominant position in various automation fields, and the number of device nodes in the world has exceeded 20 million. It consists of three compatible parts, namely PROFIBUS-DP (Decentralized Periphery). PROFIBUS-PA (Process Automation). PROFIBUS-FMS (Fieldbus Message Specification). Among them, PROFIBUS-DP is used at the field level. It is a high-speed and low-cost communication used for communication between equipment-level control systems and distributed I/O. The bus cycle is generally less than 10ms, using the first and second layers of the protocol and user Interface to ensure fast and effective data transmission; PROFIBUS-PA is suitable for process automation, allowing sensors and actuators to be connected to a common bus, which can be applied to intrinsic control fields; PROFIBUS-FMS is used for workshop level Monitoring network, which is a real-time multi-master network with token structure, is used to complete the communication between the controller and intelligent field devices and the information exchange between the controllers. Mainly use the master-slave method, usually periodically exchange data with the transmission
2. Characteristics of PROFIBUS-DP
The physical layer transmission of PROFIBUS-DP communication actually adopts the principle of RS-485, so its characteristics are similar to RS-485:
l The baud rate is from 9.6Kbps to 12Mbps.
l Shielded twisted-pair cables.
l There are 32 stations in each segment, and a maximum of 127 stations are allowed.
l The distance depends on the baud rate, 12Mbps≤100m; 1.5Mbps≤400m; 187.5Kbps≤1000m.
l The distance can be extended to 10 kilometers with a repeater.
l 9-pin D-type connector,
As shown below:
3. GSD file related
Generally speaking: GSD file (electronic device database file) is the driver file of PROFIBUS-DP products, and it is a standard communication interface established by different manufacturers for mutual integration and use. Generally, when the manufacturer of the slave station module is different from that of the master station PLC, it is necessary to install the GSD file of the slave station module during the configuration of the master station.
In order to integrate PROFIBUS products produced by different manufacturers, the equipment manufacturer must provide GSD files to describe the functional parameters of the products. The PROFIBUS configuration tool can integrate its devices in the same bus system according to the GSD file provided by the manufacturer.
In the GSD file, the characteristics of each PROFIBUS-DP device are described. The GSD file contains specific parameters of all devices, such as the supported baud rate; the supported information length; the amount of input and output data; the meaning of diagnostic information; Equipment valid selection etc.
Note: PROFIBUS-DP communication does not require parameter setting in general software (some instruments need to select PROFIBUS as the communication mode), as long as the instrument is correctly connected to the PROFIBUS bus, and the GSD file of the weighing controllers is loaded on the master station. .