What is a field bus real-time communication technology

Abstract: what is a field bus real-time communication technology information produced by excellent flow meter, flow meter manufacturer to offer you the quotation. Time refers to the uncertainty of industrial control communication network through a transmission network data must be transmitted from source node to the predetermined time night at nodes. In a fieldbus control system, from the field measurement data in the transmitter, need by bus transfer. More flow meter manufacturers choose model price quote you are welcome to inquire, here is what is a field bus real-time communication technology article details. Time refers to the uncertainty of industrial control communication network through a transmission network data must be transmitted from source node to the predetermined time night at nodes. In a fieldbus control system, from the field measurement data in the transmitter, need the bus transfer to the PID control module, and the result will be sent to control valve, due to the sampling time is certain set, it is not affected by other data transmission network, only in this way can ensure the PID control loop with a fixed cycle to complete control of the parameter. For this, there is a requirement for real time control system generally requires network from one node to another node delay time is less than 2 ~ 4 ms. One, the main factors influencing the field bus real-time in any of the following items. (1) field bus data transfer rate, high transmission rate of the system has a high real time capability. Limited in quantity and amount of data transmission, data transmission, good real-time performance. From the station number: from the station number less, less data transmission, good real-time performance. The main data processing speed: the main data processing speed, good real-time performance. Way to control the input and output: single control mode is better than field bus control method of real-time. Communication whether to the gateway, Bridges or routers: after the equipment data transmission of real-time performance. (2) the main application of the size and complexity. They will affect the system response time. 2, can use a variety of solution to the real-time measures: (1) to reduce network traffic throughput, ensure once communication requirements can be realized immediately. I/AS in Foxboro company, for example, control system, using the Ethernet communication allows articulated node number is 1024, Ethernet using CSMA/CD protocol. From the essence, the agreement on solutions to communication conflicts have no certainty of communication features, namely, after a certain node access right to send other nodes can only wait for, needs to be sent and constantly listening network is free, when listening to the network of free time to communicate to compete right to send. Due to the randomness listens for waiting time, therefore, cannot guarantee deterministic communication time. To this end, the system rules permit zui articulated 32 nodes, greatly reduce network traffic throughput, the time delay in under 2 ms, ensure the real-time demand of network communication. Other measures to reduce the traffic including methods of improving the effective traffic. For example, in the TCP/IP packet contains 20 bytes IP packet header and 20 TCP packet header, after a TCP connection is established, the group message header is invalid communication, don't have to repeat in each group to send, therefore, reconfigurable a tabloid head, reduce the communication transmission byte. Normally, using TCP/IP packet header compression, make the cut to 10 bytes in the packet head word. (2) reduce the happen of communication conflict, to guarantee the real time communication. For example, USES the star network topology, which has the function of exchange intelligence type hub. Hung on every node on the network equipment resident in its own segment, and all the segments are connected to the switching hub, the hub provide buffer memory, and have the function of the detection which need to transport the data segment. Although the communication time delay ( Not more than 1 ms) , but for communication conflicts are reduced to low zui, meet the real-time requirements of communication. In addition, the conflict resolution method also can reduce the message delay, for example, the practical of Ethernet CSMA/DCR packet conflict resolution method and improved CSMA/MDCR, CSMA/LDCR. CSMA/DCR using deterministic binary tree addressing method, according to the node address USES the first sequence traversal methods ( PreorderTraversal) Resolve the conflict. CSMA/MDCR using time points information notice sending and send two parts information, information of a node after the success of the notification, can send a few information continuously method of conflict resolution, and addressing CSMA/LDCR dynamic binary tree method, when slack period less than a certain threshold to send information, because these methods are dynamically allocated priority, therefore, can effectively reduce the conflict. (3) using full-duplex communication mode and switched Ethernet. Full-duplex communication mode separate to send and receive, this communication method has the characteristics of high communication efficiency, simple control, can satisfy the requirement of real-time, but communication structure is complex, high cost. Switched Ethernet Ethernet can be divided into several segments, it increasing the throughput and bandwidth for each segment, each segment as a child collision domain by the switch, the switch between different ports can form multiple data channels at the same time, make each node has separate channels connected to the other nodes, so that the sending and receiving data is not affected by conflict, make share bandwidth reserved bandwidth, improve the real-time performance.

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