Intelligent Instrumentation System Architecture and Features

Intelligent instrument is a combination of computer technology and testing technology. The instrument has intelligent software with powerful processing capabilities. Instrumentation is no longer a simple hardware entity, but a combination of hardware and software. In recent years, smart devices have begun to develop from more sophisticated data processing to knowledge processing, and their functions have been developed to a higher level.

1 Development of Intelligent Instruments Since the 1990s, the intelligentization of instrumentation has been highlighted in the following aspects:

(2) Miniaturization. The integrated application of microelectronics, micro-mechanics, and information technology makes the instrument a small, full-featured intelligent instrument capable of performing signal acquisition, processing, control signal output, amplification, and interface with other instruments, etc. The automation technology, aerospace, military, biotechnology, and medical fields have a unique role.

(3) Multifunction. Multifunction itself is a feature of smart instrumentation. For example, a function generator with functions such as pulse generator, frequency synthesizer, and arbitrary waveform generator not only has higher performance (eg, accuracy) than dedicated pulse generators and frequency synthesizers. , but also provides better solutions for various test functions.

(4) Intelligent. Modern detection and control systems tend to be more or less intelligent. The further development of smart instruments will contain certain artificial intelligence so that the detection or control functions can be performed autonomously without human intervention.

(5) Instrument Virtualization. In the virtual reality system, the data analysis and display are accomplished with PC software, and as long as additional data acquisition hardware is provided, the measurement instrument can be composed with a PC. This PC-based measurement instrument is called Virtual Instrument VI. In the virtual instrument, using the same hardware system, as long as the application of different software programming, you can get completely different measuring instruments. "Software is the instrument." The software system at the heart of the virtual instrument is versatile, popular, visual, extensible, and scalable. It represents a new direction for the development of today's instruments.

(6) Networking of instrumentation systems. General smart instruments and meters have two-way communication functions, but this two-way communication function is still far from the real network communication. Accompanied by the rapid development of network technology, Internet technology enables instruments and meters to be networked at the same time on the basis of intelligence, so that the on-site measurement and control parameters are approached on the nearest network and have the necessary information processing functions.

2 Functional requirements and technical support for networked instruments 2.1 Support for remote monitoring and control requirements Networked instruments, such as field bus smart meters, are instruments suitable for use in remote monitoring and control, instrument measurement and control technologies, modern computer technologies, network communications technologies and microelectronics. The result of deep integration of technology. The networked equipment can automatically measure, control, store, and display measurement results and control status of related physical quantities according to a set program as an ordinary instrument. At the same time, it has important network application features. Authorized instrument users can remotely through the Internet. Perform functional operations on the instrument, obtain measurement results, and monitor the instrument in real time, set parameters and fault diagnosis, and control its dynamic information release on the Internet. Like computers, they become independent nodes in the network. It is easy to connect directly to the nearest network communication cable, and “plug-and-play” directly sends on-site test data to the Internet; users can use the browser or comply with The standard application can view this information in real time (including processed data, instrumentation panel images, etc.).

2.2 The characteristics of networked instruments The front-end module in the Internet-based measurement and control system not only completes signal acquisition and control, but also takes into consideration the implementation of signal analysis and transmission, because it is supported by a powerful microprocessor and an embedded operating system. . On this platform, users can easily add, delete, and select different types of measurement function modules. Second, the most prominent feature of the Internet-based measurement and control system is the change in the way the signal is transmitted. Internet-based measurement and control systems transmit measurement and control signals on the public Internet. With front-end embedded modules, safe and effective transmission of measured data from the system becomes possible. Furthermore, the Internet-based measurement and control system has also greatly improved the expression and output of measured results. On the one hand, regardless of where the user is, the user can conveniently browse various real-time data through the client and understand that the device is now The working conditions; On the other hand, in the client's control center, the owned intelligent software and database system can be invoked to analyze the measured results and to provide the user with control instructions or make decisions.

2.3 Method of accessing the Internet or Ethernet The design method of network instrumentation is to embed the embedded system into the instrument and make it the core of measurement and control. In general, there are three ways that an embedded instrument can be connected to the Internet or Ethernet to become a network instrument:

(1) The 32-bit high-end MCU constitutes the embedded device. Because there are enough resources to expand and use, the entire TCP/IP protocol suite can be used in the system. Therefore, it can be a network device directly connected to the Internet, but it is difficult to develop.

(2) For low-end 8-bit embedded devices, use a dedicated network (such as RS-232, RS-485, Profibus, etc.) to connect a number of embedded devices to the PC, use the PC as a gateway, and the PC to the network. The information on the conversion to TCP / IP protocol packets sent to the Internet to achieve information sharing, but must be specifically assigned to a PC for protocol conversion;

(3) The embedded networked instrument directly connected to the Internet is composed of 8-bit single-chip microcomputer. The advantage of this solution is that it can use the previous 8-bit single chip-based measurement equipment to directly drive the network interface chip through an external network chip, but it takes up resources. (ROM, RAM, CPU) is more, require the one-chip computer to have enough fast running speed.

2.4 Supporting Network Interfaces The chip network interface chip uses RELTEK's RTL8019AS. Because of its excellent performance and low price, it is an ideal chip for Ethernet communication.

(1) The main performance complies with Ethernet II and IEEE802.3 standards; for full-duplex communication interface, the transceiver can achieve 10Mbps at the same time; Built-in 16K SRAM is used to send and receive buffers to reduce the speed requirements for the main processor; support 8/ 16-bit data bus, 8 interrupt request lines and 16 I/O base address selections; can complete the formation of physical frames, codec, CRC formation and verification, data transmission and reception, etc., can be passed through the switch on the twisted pair Send and receive data at the same time.

(2) Internal structure RTL8019AS can be divided into remote DMA interface, local DMA interface, MAC (media access control) logic, data encoding and decoding logic and other ports. Remote DMA interface refers to the one-chip computer reads and writes the internal RTL8019AS RAM bus, that is, the interface part of the ISA bus. Single-chip transceiver data only need to remote DMA operation. The local DMA interface is the connection channel between the RTL8019AS and the network cable, which completes the data exchange between the controller and the network cable.

(3) Internal RAM address space allocation The RTL8019AS has two internal RAM areas. A 16K-byte address is 0x4000~0x7fff; a 32-byte address is 0x0000~0x001f. The RAM is stored page by page, one page per 256 bytes. Generally, the first 12 pages of RAM (ie 0x4000~0x4bff) memory area are used as the sending buffer, and the last 52 pages (ie 0x4c00~0x7fff) are used as the receiving buffer. The 0th page address is 0x0000~0x001f, used to store Ethernet physical address.

(4) I/O address assignment The RTL8019AS has a 32-bit input/output address with an address offset of 00H~1FH. Among them, 00H~0FH total 16 addresses are register addresses. The registers are divided into four pages: PAGE0, PAGE1, PAGE2, PAGE3. The pages to be accessed are determined by the PS1 and PS0 bits in the CR (Command Register Command Register) of the RTL8019AS. Remote DMA addresses, including 10H~17H, can be used as remote DMA ports. Just use one of them. The reset port includes 8 addresses of 18H~1FH, and the function is the same. It is used to reset the RTL8019AS.

3 Networked Instrumentation Architecture and Implementation 3.1 Abstract Model Networked instrumentation is an organic combination of electrical and electronic, computer hardware and software, and networking, communications, and other multi-faceted technologies. The structure is relatively complex, and many use the architecture to represent its overall framework and system. Features. The networked instrumentation architecture includes basic network system hardware, application software, and various protocols. Figure 1 is a simple model of a networked instrument architecture. The model divides the networked instrument into logical layers, which can more essentially reflect the principle of information acquisition, storage, transmission, and analysis processing of networked instruments. The first is hardware. Layer, mainly refers to the remote sensor signal acquisition unit, including the microprocessor system, signal acquisition system, hardware protocol conversion and data stream transmission control system. The realization of the function of the hardware layer benefits from the technological progress of the embedded system and the development of the large-scale integrated circuit technology in recent years. The hardware protocol conversion and data flow transmission control rely on FPGA/CPLD.

Another logical layer is the embedded operating system kernel. The main function of this layer is to provide a platform for control signal acquisition and data stream transmission. The main resources of the front-end module unit of the platform include a processor, a memory, a signal acquisition unit and information; the main function is to reasonably allocate and control the processor, control the signal acquisition unit so as to make it work normally, and ensure the effective transmission of the data stream. The logic layer is mainly composed of a link layer, a network layer, a transport layer, and an interface. According to different applications, the specific implementation of this layer may be different, and can be simplified in a certain program.

3.2 Peripheral Hardware Design There are two hardware designs for Internet or Ethernet communications.

(1) Use a dedicated CPU as the controller and use C programming to implement TCP/IP communication. The advantage is that the dedicated CPU has a strong processing capability, which facilitates the implementation of other functions of the test instrument. The disadvantages are slightly higher costs and slightly more complicated hardware.

(2) CPUs using the 51 series microcontroller as the controller do not use an embedded operating system and use C51 programming directly to implement the data link layer protocol and the TCP/IP protocol. The advantage is that the hardware is relatively simple and the price is low. The disadvantage is that the software is heavy and difficult. The basic structure of a networked instrument composed of a single-chip microcomputer and an RTL8019 Ethernet interface chip as a network instrument interface is shown in FIG. 2 .

3.3 Protocols and Design The system performs initialization operations, mainly configuring the network interface chip. After the configuration is complete, the system waits until the client has data sent. The data is received through the network interface chip, which can perform packet filtering on the physical frames on the network. When an Ethernet station's information frame is sent to a shared signal channel or medium, all Ethernet interfaces connected to the channel read in the frame and view the first 48-bit address field of the frame, which contains the destination address . Each interface compares the destination address of the frame with its own 48-bit address. If the address is the same as the destination address of the frame, the Ethernet site will continue to read in the entire frame and send it to the upper network software that the computer is running. The upper layer network software reads in the type field of the frame, judges whether this information frame is an ARP packet or an IP packet, and then passes it to a different protocol stack for processing. When other network interfaces find that the destination address is different from their address, they will stop reading the frame.

When sending data, the data to be sent is encapsulated in a frame format, sent to the sending buffer in RTL8019AS through a remote DMA channel, and then a transmission command is issued to complete the sending of the frame. You need to set the Ethernet destination address, Ethernet source address, and protocol type, and then set the data segment according to the set protocol type. After starting the remote DMA, data is written to the RTL8019AS RAM, and then the local DMA is started and the data is sent to the Internet. The RTL8019AS cannot store data packets into the FIFO through the DMA channel at one time. It must wait for the previous data packet transmission to complete before forming a new data packet. In order to improve the transmission efficiency, it is designed to divide the 12-page transmit buffer into two 6-page transmit buffers, one for data packet transmission and the other for data packet construction.

4 Conclusion With the advancement and continuous development of computer technology and network technology, the 21st century instrument concept will be an open system concept. Based on PCs and workstations, the establishment of a network to form a practical measurement and control system to increase production efficiency and share information resources has become the direction of modern instrumentation development. The concept of networked instruments is a breakthrough in the concept of traditional measuring instruments. In a sense, computers and modern instruments have been mutually inclusive, and the computer network is a universal instrument network. If more and more different types of smart devices are connected to the network as nodes of the network like computers and workstations in the measurement and control system, they will not only be able to share more resources, but also make full use of the devices of the more mature Internet network. , Reduce the cost of building systems, but also improve the function of measurement and control systems, and expand the scope of their applications. "The network is the instrument" concept, an accurate overview of the instrument's network development trends.