Programming of industrial networks . 04.12.2010 22:38
Programming of industrial networks .
FINS time cycle strongly depends on the configuration and the number of slaves .
CAN - very inexpensive reliable basis for several common fieldbuses : DeviceNet, CANopen, SDS and others.
Given an order to find a " bulletproof " technology for critical components factory networks , developers DeviceNet, CANopen, SDS and other networks based on CAN eventually chose a turnkey solution in the automotive industry.
The highest degree of reliability.
It is clear that the reliability of communication in the vehicle is literally a matter of life and death. Network failure is simply unacceptable, regardless of its cause. Network CAN survive in the harshest of environments , and the statistical probability of failure is less than one case per century.
Application software layers on top of CAN.
CAN itself is only a low-level messaging protocol arbitration . To convert it into a full-featured network protocol needs an additional software layer .
High-level protocols such as DeviceNet can be regarded as a complex set of " macros " for CAN- messages specifically designed for automation.
SDS network automation and CANopen, also based on CAN.
CAN physical layer standard ISO 11898 specifies a transmission medium with a two-wire differential line impedance of 120 ohms ( terminators ) .
A logical zero is recorded when the signal on line CAN_H higher than line CAN_L.
Logical unit - in the case where signals CAN_H CAN_L and differ by less than 0.5 V.
Using a differential transmission scheme makes it possible for the CAN network in a very difficult external environment .
Logical zero - called dominant bit and logical unit -
recessive. These names reflect the priority logic zero on the bus CAN.
Universal Bus lower and middle levels
Origin : Allen-Bradley, 1994 .
Base: technology CAN (Controller Area Nerwork).
Supporting organization : Open DeviceNet Vendor Association (ODVA).
Typical applications : mainly assembly , welding and transport units . Used for single- cable connection of multi- sensor units , intelligent sensors , pneumatic valves , barcode readers , drives and operator panels . Particularly widespread got the tire in the automotive and semiconductor industries.
Pros : cheap , widespread , high reliability, efficient use of bandwidth , the voltage supply via the network cable .
Disadvantages: limited bandwidth, limited message size , the limited length of the connection.
Flexible , affordable and competitive . DeviceNet fieldbus is a flexible general-purpose , satisfying 80% of the standard requirements for cabling in industrial plants and workshops. Since the supply voltage is applied to automation devices over a network cable , the total number of cables used and the complexity of the wiring is minimal. DeviceNet protocol is supported by hundreds of different devices ( from smart sensors to valves and operator interfaces ) and hundreds of different manufacturers.
Not work harder and smarter. one
the biggest advantages is the DeviceNet
support for multiple types of communication
messaging , which allows the same bus
work " with the mind ." At any time,
to ensure the most efficient and
informative message transfer
network can be used simultaneously
several different methods .
Origin : Government authorities in Germany in collaboration with manufacturers of automation , 1989 .
• Supporting organization : Profibus Trade Organization.
• Applications : Often used in Profibus large assembly units , mechanisms of material handling and process control . This bus allows single cable connection of multi- sensor units , pneumatic valves , complex intelligent devices , smaller subnets (such as AS-I) and operator interfaces .
Pros : Profibus is the most common in the world of networking standard . Version of DP, FMS and PA in general satisfy the requirements of the vast majority of automation systems.
Disadvantages : Relatively high overhead when transferring short messages , no power supply bus , a somewhat higher compared with the value of the other tires .
PROFIBUS-FMS-" Fieldbus Message Specification " .
Protocol Profibus FMS is a format of information exchange between peer devices , which provides the main interaction devices. If necessary, the host device may be any devices connected to the bus. This bus has higher overhead for the transmission of messages in comparison with the Profibus DP
PROFIBUS-DP-" decentralized (distributed ) peripherals ."
The most commonly used messaging format is a Profibus DP network with polling sites (selected master device periodically polls the status of each node ), thus ensuring constant monitoring the status of each device on the network ( one device at a polling cycle can transmit up to 244 bytes of useful information ) . Each message contains an additional 12 bytes , so that the maximum length of the entire message is 256 bytes.
PROFIBUS-PA-" Process Automation " .
Profibus PA protocol is almost identical to last protocol Profibus DP V1 with diagnostic extensions except for the lower levels of voltage and current corresponding to the requirements of internal security (Class I Div . II), adopted in the manufacturing industry . Profibus PA protocol is supported by most major devices , but the use of this protocol requires a decoupling between the transducers and DP PA ( such transmitters are a number of companies ) . PA- powered devices from the mains using the voltages and currents , guaranteeing internal security
PROFIBUS DP-V0 - Main purpose - regular exchange of data input / output .
Slave master can report its status via diagnostic messages .
PROFIBUS DP-V1 - Expanded acyclic exchange. This enables the slave device with the wizard . For example , set ranges and parameters.
This Ethernet -based communication technology , developed as a common communication platform for all automation levels : from the field - to the level of MES ( production management ) . Noncritical the time data is transmitted through the mechanism of Ethernet TCP / IP. For applications with hard real-time requirements is available optimized data exchange mechanism at the object level (Profibus DP). PROFINET technology defines three classes:
PROFINET 1.0 (CBA): communication between management controllers ; PROFINET-SRT: the system of "soft" real-time communication with the controller
I / O devices ;
PROFINET-IRT: hard real-time system primarily designed to control the movement .
Transfer rate 167 Kbit / s, 10 Mbit / s, 100 Mbit / s and 1000 Mbit / s to 100 m
network Layers
MOTION CONTROL
EtherNet (HTTP, FTP, E-mail, Sockets, FINS) EtherNet / IP (IP = Industrial Protocol)
NT Link, Host Link SysmacLink, ControllerLink, EtherNet / IP, FL-net
CompoBus / S ** CAN, DeviceNet, CompoNet Profibus / DP, ProfiNet CompoWay / F, Modbus / RTU, (RS232/422), Mechatrolink-II, EtherCAT.
Modbus / TCP: Characterized by simplicity and accessibility Modbus. However , this standard has inherited all the flaws and Modbus. Technology Modbus / TCP has limited capacity in terms of exchange between devices complex sets of parametric data .
ProfiNet: Profibus on Ethernet technology is designed to combine the existing Profibus protocol with open service OPC / XML. Given the worldwide prevalence of Profibus, can express a favorable outlook for the commercial success of Profibus on Ethernet.
Ethernet / IP: In fact , EtherNet / IP are objects ControlNet / DeviceNet based on TCP / IP and
UDP. In this specification, a very great potential.
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