DCS controller redundancy using ARM processor design
In many areas of automation, the effectiveness of increasingly demanding, and thus the level of fault-tolerant automation system requirements are becoming increasingly high, especially in the cost of equipment downtime very big occasions. In order to meet these stringent requirements, usually in the DCS system using redundant technology, this is the only way to meet the needs of these areas of safety, reliability and effectiveness standards.
In the DCS control system, distributed processing unit is a key part of the system. Processing unit the current distribution of these controller often is based on the construction of 86 series CPU's, this architecture is being widely used. However, due to the distribution of 86 series of the characteristics of processing units, resulting in the current processing unit controller, there are many shortcomings, such as the large heat release. But also in a closed environment, has always been very difficult to solve these problems. With a lot of low-power technology and the emergence of low-power controller, the distribution processing unit of the CPU can have more choices, especially in low-power controllers have very little heat, and the system can be integrated higher degrees.
Whether it is domestic or foreign DCS control systems have little to distinguish between, redundant DCS control technology in these systems have been widely used. DCS control system mainly uses the network redundancy technology, distributed processing module redundancy, IO cards redundancy, power redundancy technology.
1 DCS system model
DCS control system to control technology, computer technology, communications technology and graphics display technology product of the combination of the general architecture shown in figure 1. From Figure 1 DCS control system model block diagram, we can see, DPU refers to the distribution processing unit. DCS control system architecture is divided into 3 layers: the process control layer, control layer and the management. Process control layer which is the basis of DCS control system, the device's main function is to control interface, on-site control unit, the implementation of instrumentation and institutions; monitoring layer mainly by the monitoring computer, senior operator station and interface devices constitute the main responsible for operating the surveillance, system alarm, the trend display and system diagnostics and other functions; the management of the main computer by the management, is responsible for the management of the entire system.
DCS control system set up most of the redundant control and process monitoring layers and layers, so most of the redundant process control technology with the relevant layer. The following combination of the latest ARM-based distributed processing controller unit, the DCS control system technology used in the distribution of redundant processing unit redundancy and network redundancy for discussion.
2 the distribution of ARM based on the structure of processing unit
The distribution of ARM based on the structure of processing unit block diagram Figure 2, the distribution of this and the general processing unit is very similar to the structure. Here the main processing unit to be divided into 6 parts: ARM controller, the upper network module, power management modules, memory modules, low-level network modules and clock modules. ARM controller and memory modules for embedded systems the most basic, the entire DCS control system data processing and control strategies are dealt with here. The upper network module and the management mainly refers to the main communication / redundant network and a realization of the main / redundant distribution of data processing units to carry out the network, this part of the main function is to complete the management of DCS control system to achieve real-time detection and Master / redundant distribution of data redundancy unit. The bottom of the network module is divided into two of the 485 primary and secondary networks, the main module of the ARM controller I / O cards between pieces of data communications. Memory modules can be divided into two parts, part of the operating system used to manage the storage, the other real-time data used to manage storage. Power modules and clock modules, respectively, to achieve power management and clock management.
3 controller redundancy
Distributed Processing Unit in accordance with the redundancy redundancy redundancy can be divided into 1:1 and 1: n both cases. DCS manufacturers in each of the products are different. Both methods have advantages and disadvantages. Here is the redundancy of the redundant set to 1:1.
Distribution processing unit for 1:1 redundancy, that is exactly the same as two of the controller configuration settings into a redundant way. In operation, if there be a breakdown of the distribution processing unit between the two to achieve non-disturbance switch to ensure the normal operation of the system.
The system used by both the distribution of processing units with three network interface, two Ethernet ports which were connected to the A network and the B network, the realization of the work of data communication between sites, the first three I through peer-to-peer data network to connect sub - distribution processing unit between the (peer-to-peer data are now available for selection of optical fiber transmission medium), used to transfer the main, from the distribution processing unit between the backup data; distribution processing unit between the transmission status information from the serial port. Redundant distribution of processing units and network connections see figure 3.
Redundant distribution of the working principle of processing units: two distributed processing unit hardware configuration is identical, with the same internal operating system, the same configuration software, the same configuration information. Only at the same time a distribution processing unit through the dual-card machine to accept the process of information exchange and processing, and finally have a control structure to control the process equipment, the distribution processing unit processing units known as the main distribution. At the same time, the distribution of redundancy and there is no idle processing units, which work in each cycle through the optical fiber between two-plane distribution of the main processing unit accepted the outcome of the process of information and computing for real-time copy, the distribution of such redundancy is always the main processing unit Distribution of synchronous processing unit. Redundant processing unit at the same time testing the distribution of copies of the information is complete, whether or not permitted within the fault tolerance. Once the information is incomplete or error, then the distribution of the main processing unit is not working correctly. In this case, the redundant processing units through the distribution of the main distribution of optical bypass processing unit, while the distribution of switch-based processing unit to continue its work. Choose the shortest switching time of the computing cycles (tens of ms or less), in order to achieve non-disturbance switch. The main processing unit until the normal distribution, the distribution processing unit redundancy automatically returned to the main control over the distribution of processing units, to redundant backup status.
Figure 3 shows the distribution processing unit double circuit working principle of arbitration will be distributed to the respective processing units to add their own diagnosis of the arbitration circuit, and read the results of the arbitration to determine the state of their own Lord of Des. Through programming, to determine the priority of the state, as the dual-distribution processing unit are in line with the results of arbitration of their state of primary and secondary, so as long as the changes in the outcome of the arbitration, the two-distribution processing unit to switch automatically.
4 network redundancy
DCS control system in at least two networks, one is between layer management and control of communication networks, the other is the process control layer and the underlying I / O cards 485 between layer networks. The main role of the upper network management is to achieve real-time control layer, and the lower controller tasks, such as configuration settings. Network was designed to lower I / O cards collected pieces of data to process control layer, and then the control layer to control data transmission to the I / O cards. This two networks in DCS control system is self-evident importance.
For the upper network module redundancy, today's industrial automation field link redundancy support a wide range of industrial Ethernet switch features, and they resolved the network by the node failure problem of paralysis. In order to enhance the overall reliability of data communication and fault tolerance, the DCS control system is also expanding the use of premium network ring structure. However, due to inherent ring network node failure is caused by the shortcomings of the whole network fails, the data communication link redundancy technology came into being. 2-layer network in order to ensure the smooth progress of the work of two networks are set up using the 1:1 redundancy. Detection of the distribution of processing units to the main network fails, a waiver from the main port network communications, network redundancy at the same time opening the port, the data transferred to the redundant network to send and receive. Redundant at this time to enter the data communications network, and the main network to be patched in time. Loop network technology to achieve the redundancy of the transmission medium, in the basis of TurboRing further enhance the reliability of the system. But the loop network management and switching are complex, the system uses a simple method.
For each of the network a node, may be in one of the following five kinds of situations:
(1) online networking is running, the system at least two nodes in the operation; (2) single-line operation, the system is running only the local node; (3) off-line stand-alone operation, the nodes of the network adapter exists and is normal, but there is no Internet; (4) off-line stand-alone operation, the nodes of the network card, but failure; (5) off-line stand-alone operation, the node network adapter does not exist.
At present, the network controller provides a command, diagnostic, configuration and status registers, through the reading and writing these registers, they can distinguish between the above-mentioned five kinds of situations. When the system is running, there may be a variety of factors, in order to reflect the network line to run the state of each node, each node can set up a network status table to record each of the nodes on the network card running. When a node on one or two changes in the status of the network card, the other nodes as possible should be able to know within a short period of time. To this end, each node needs two network cards regularly broadcasting a test packet, indicating the existence of the node of the network card. The other nodes receive the packets, modify the network state table corresponding to this node on the state of the network card. However, in running the course, if a node of a network card offline, it can neither receive nor send. Before that, it has in other nodes of the network status registration form, all the other nodes will be that the card exists and is normal, obviously does not reflect the true state of the network card running. In order to accurately reflect the state of the network card, each node of the two test card from time to time broadcast package, we will state the network node table in the state of all the card counting 1, until the maximum LIMIT. When a node received the test package, the node count state corresponding clearance card to 0. In this way, to ensure that the maximum number of states is less than LIMIT and timing cycle can be broadcast online in real time to monitor the operation of the network, which accurately reflect the status of nodes. In between the two networks also have the routing function can be added between the transmission equipment of the network, when two network failure at the same time, inter-network transmission equipment can also automatically search for viable path to form a loop to maintain the normal system communications.
Test kits for radio, as long as the nodes of the network card on-line operation, that is, from the appropriate link to send test packets to send after the network status table, you can choose the normal operation of a small number of nodes, the load lighter links, for data packets sent. workflow dual-network shown in Figure 4.
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