Based on Labwindows / CVI Real-time optical network and the SBS Design of Virtual Oscilloscope
With the development of computer hardware and software technology continues to improve, virtual instrument technology has become key technologies in the field of measurement and control. The remote monitoring and control and simulation, the virtual instrument networks, has become a pressing problem. SBS through the use of real-time optical network, virtual instrument technology, ActiveX technology, and DCOM technology to achieve a network-based virtual oscilloscope, so that the remote monitoring and control, data sharing become a reality.
Network Virtual Oscilloscope system Design
Network virtual oscilloscope system generally can be divided into two parts: data collection network, a virtual oscilloscope. Data acquisition network of remote data collection and remote control commands to send. Virtual oscilloscope through the data network will have access to remote data dynamic display, storage. Network virtual oscilloscope system framework of the overall structure shown in Figure 1.
Figure 1 network virtual oscilloscope system architecture
We can see from the diagram, the data collection network consists of remote information data sources, data source control center composed of two parts. Among them, the remote information data source, through the SBS real-time optical network, receiving data from the remote device terminals, and these data according to certain rules integrated into a data stream, sent to the data source control center. Data Source Control Center, in essence, a large server, whose main function is to receive information from the remote data source data, but also these data through real-time optical network or Ethernet to the rest of the data information processing terminal to send, and Data Analysis Center remote control instructions issued by the remote device sent to the terminal. In addition, the data source control center can also be the customer-end data analysis and processing the results, publish to the entire network, enabling the entire network of data and information resources sharing. This is a remote monitoring and control of complex systems is very important, it can be cumbersome and complex systems will generate control instructions to the various customer premises decomposition to complete and realize the parallel control instructions generated, makes the control of complex systems has become fast and reliable. Virtual oscilloscope as a client terminal can directly access from the data source control center data, the completion of the data waveform signal dynamic display, storage tasks.
Data Acquisition Network System Design
For real-time considerations, data collection network to conduct real-time optical network structures. SBS Real-time optical network is developed by the United States has a star-shaped SBS structure of real-time network. It is of light as an information transmission medium, which has a very strong real-time.
SBS radio memory is the only high-performance network of Hub configurations applied to multiple computers in real time to determine the shared memory. Broadcast memory than the ring structure of the Hub structure (such as the VMIC) more stable. A node failure affects only the node does not affect the entire network, while the network with high stability, high bandwidth and very low latency characteristics. Broadcast memory so that all Internet computers (nodes) shared memory (NetRAM), each node has its own NetRAM physical backup, the node through the optical fiber and installation in the center of a Hub port cards connected. Written to the local node, the card data is a broadcast transmitted Hub and simultaneously written to all nodes in memory.
Hub will be merged into a variety of data streams can be broadcast to all nodes transmit ordinary data stream, the broadcast memory to ensure data at the same time, and according to the same memory in order to reach all the nodes. Link transfer rate of up to 43MB / s, write delay is 10 microseconds, in the high priority node delay is smaller, and is predictable. All the nodes through the "Write NetRAM" way, transparent and to determine to be broadcast transmission interruption, message or data block to the other nodes. Through a simple "write NetRAM" from any node to send interrupt, a write interrupt desktop (WIT) control interrupt. NetRAM backup from the node to read data. Hub will separate the data stream from node card into a common data stream, and do simultaneously broadcast to all nodes. A Hub and port through a backplane card slot of the plug 14 to support 28 separate nodes. Every one Hub-port card with FIFOs, to ensure a single node to receive the various data streams together into a common data stream inside and broadcast to all nodes when the maximum transfer rate. Backplane interconnect for the number of nodes is a common link to the card board, to form a network. Integrated error control and error correction features to ensure the highest reliability of the Hub. Data Source Control Center through the real-time data acquisition and remote terminal fiber-optic network for data exchange and information sharing.
Virtual Oscilloscope Design
We all know, the birth of the virtual instrument technology developed instrumentation set off a revolution. It will soften the hardware and save a lot of the hardware development costs and greatly reduces the equipment's development cycle. Therefore, the area has been monitoring and control persons of all ages. In the virtual oscilloscope design, we use Labwindows / CVI to carry out design and development. Labwindows / CVI by the United States National Instrument, Inc. (United States National Instruments, NI) introduced a virtual instrument design interactive c language development platform. It will provide powerful, flexible C++ language and used for data acquisition and analysis and practical tools for monitoring and control of professional organic combination of the familiar C language developers to create detection systems, automated test environment, data acquisition systems, process monitoring system, virtual instruments provide an ideal software development environment. A virtual oscilloscope and the general is different from the traditional source of data through a virtual oscilloscope A / D sample obtained, the network through a data network virtual oscilloscope to obtain the data, and its own there is no A / D sample waveform distortion problems in order to eliminate A / D sampling frequency on the oscilloscope caused by bottlenecks. According to the characteristics of the network-based virtual oscilloscope, we have designed the network shown in Figure 2, the virtual oscilloscope.
Figure 2 Virtual Oscilloscope
Virtual oscilloscope control program in the network, we use multi-threading technology to ensure the waveform display of the stable and reliable. Multi-threading refers to the data acquisition and waveform display in two different threads were carried out, that is, the thread control procedures carried out in a waveform display, while in another thread in the data collection. In this way, not only to ensure the reliability of data collection, but also ensures a stable waveform display real. Should be pointed out that the data acquisition frequency band fs a direct impact on the oscilloscope. According to Shannon sampling law, the network bandwidth a virtual oscilloscope should be less than fs / 2. Thus, the data acquisition frequency fs will directly affect the size of the oscilloscope band width. In addition, in order to eliminate flicker and jitter waveform displays, we have opened up in the control program, two buffers. Its purpose is to waveform display, the two data buffers alternately displayed, thus eliminating the waveform display in the process of flashing and jitter. Virtual Oscilloscope control process shown in Figure 3.
Figure 3 Virtual Oscilloscope control flow
We can see from Figure 3, the network virtual oscilloscope starts, first of all establish a data network connection, and then to get on the network data is written to an empty buffer, while the data buffer filled with data to the oscilloscope screen, and so Reciprocating, oscilloscope data signals will be continuously displayed. To terminate the waveform display, will have to network a virtual oscilloscope and data network disconnect, and then shut down the network can be a virtual oscilloscope. Of course show that the process, can wave amplitude and phase adjust, has reached the best observation wave effect.
Virtual oscilloscope and data acquisition networks, articulated
How do virtual oscilloscope and data acquisition network is a network mount a key technology for a virtual oscilloscope. Hardware, for hard real-time considerations, we use the SBS as their real-time optical network connection between the body. Of course, the other less demanding for real-time clients may be through the regular Ethernet connections. The software side, in order to be able to get data from the network, we use the ActiveX and DCOM technology. ActiveX is a development-oriented software development can be used in different environments with reusable component technology as a collectively. DCOM technology is a distributed COM technology to use it can be run on the server components, re-used in the same network client. We use DCOM technology, the advantages, by running in the data source control center DCOM server application, access to remote information data sent from the data source and then run a virtual oscilloscope client, by running in its ActiveX on the client application DCOM server process access to remote data, thus, the network virtual oscilloscope data acquisition. Based on the above hardware and software technology, we have achieved a virtual oscilloscope and data acquisition network, the success of hook. In order to achieve a network-based virtual oscilloscope, the network is successfully applied to a virtual oscilloscope UAV ground semi-physical simulation test, the test data-line observations, data playback, storage and analysis provided strong support. Figure 4 shows part of the data during the test curve observations.
Figure 4 Virtual oscilloscope-the-loop simulation test data observations
We will network virtual oscilloscope successfully applied in the remote monitoring and control, semi-physical simulation, etc., which for the need to achieve unattended, fully automated monitoring applications have an important significance. Its emergence can greatly improve the level of industrial automation, reduce personnel consumption, lower costs, for the poor working conditions, working environment to achieve unattended areas of risk, has important application value. Virtual oscilloscope results achieved can be networked virtual instrument for the future to provide an excellent engineering solutions. Of course, the network virtual oscilloscope using SBS optical network to transmit real-time data, a network will cost greatly improved. In the future, we will ensure that the premise of real-time network data transmission, using ordinary Ethernet networking for more in-depth study.
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