Development characteristics and prospect analysis of intelligent instrument
Intelligent instrument is a combination of computer technology and testing technology. It has intelligent software with strong processing ability. Instrumentation is no longer a simple hardware entity, but a combination of hardware and software. In recent years, intelligent instruments have begun to develop from more mature data processing to knowledge processing, so that their functions develop to a higher level.
1. The development of intelligent instruments
Since the 1990s, the intelligence of instruments has been highlighted in the following aspects:
(2) Miniaturization. The comprehensive application of micro-electronic technology, micro-mechanical technology, information technology, etc., makes the instrument a small, fully functional intelligent instrument, which can complete the signal acquisition, processing, control signal output, amplification, interface with other instruments and other functions, and has a unique role in automation technology, aerospace, military, biotechnology, medical fields.
(3) Multi-functional. Multifunction itself is a feature of intelligent instrumentation, such as function generators with pulse generators, frequency synthesizers and arbitrary waveform generators, not only in performance (such as accuracy) than dedicated pulse generators and frequency synthesizers, but also in a variety of test functions to provide a better solution.
(4) Intelligence. Modern detection and control systems tend to be more or less intelligent. The further development of intelligent instruments will contain some artificial intelligence, so that detection or control functions can be performed autonomously without human intervention.
(5) Instrument virtualization. In virtual reality system, data analysis and display are completed by PC software, as long as some additional data acquisition hardware is provided, it can be used as a measuring instrument with PC unit. This PC-based measuring instrument is called VirtualInstrument VI(VirtualInstrument VI). In the virtual instrument, using the same hardware system, as long as the application of different software programming, you can get a completely different function of the measuring instrument. “Software is instrument.” As the core of virtual instrument, the software system has universality, popularity, visibility, expansibility and upgradability, which represents the new direction of the development of today’s instrument.
(6) Networking of instrumentation systems. General intelligent instruments have two-way communication function, but this two-way communication function is still far from the real sense of network communication. With the rapid development of network technology, Internet technology enables the instrument and meter to realize the network on the basis of the realization of intelligence, so that the field measurement and control parameters near the network, and has the necessary information processing function.
2. Functional requirements and technical support of networked instruments
2.1 Support remote measurement and control requirements
Networked instruments, such as fieldbus intelligent instruments, are suitable for use in remote measurement and control instruments, which are the results of the deep integration of instrument measurement and control technology, modern computer technology, network communication technology and microelectronics technology. The networked equipment can automatically measure, control, store and display the measurement result and control state of the related physical quantity according to the set program like the ordinary instrument; At the same time, it has important network application characteristics, and authorized instrument users can remotely operate the instrument through the Internet, obtain measurement results, monitor the instrument in real time, set parameters and fault diagnosis, and control its dynamic release of information on the Internet. Like computers, they become independent nodes in the network, which can easily be directly connected with the nearby network communication cable, and “plug and play”, directly send the field test data to the Internet; This information (including processed data, panel images of instruments, etc.) can be viewed in real time by the user through a browser or a compliant application.
2.2 Characteristics of networked instruments
The front-end module of the Internet-based measurement and control system not only completes the signal acquisition and control, but also implements the analysis and transmission of the signal, because it is supported by a powerful microprocessor and an embedded operating system. On this platform, users can easily add and delete various measurement modules and choose different network transmission modes. Secondly, the most significant feature of the Internet-based measurement and control system is that the mode of signal transmission has changed. The transmission of measurement and control signals in Internet-based measurement and control system is built on the public Internet. With the front-end embedded module, the safe and effective transmission of the system’s measurement data becomes possible. Moreover, the expression and output of the measured results have also been greatly improved by the Internet-based measurement and control system. On the one hand, no matter where you are, users can easily browse to various real-time data through the client to understand the current working situation of the equipment; On the other hand, in the control center of the client side, the intelligent software and database system can be called to analyze the measured results, and provide help for the user to issue control instructions or make decisions.
2.3 Methods for Accessing the Internet or Ethernet
The design method of networked instrument is to embed the embedded system into the instrument and make it become the core of measurement and control. In general, there are three ways for embedded instruments to access the Internet or Ethernet to become network instruments:
(1) The 32-bit high-end MCU constitutes an embedded instrument, because there are enough resources to expand and utilize, the entire TCP/IP protocol family can be done in the system, so it can become a direct access to the Internet network instrument, but the development is difficult;
(2) For low-grade 8-bit embedded instruments, a private network (such as RS-232, RS-485, Profibus, etc.) is used to connect a number of embedded instruments to the PC, the PC is used as a gateway, and the PC converts the information on the network into TCP/IP protocol packets and sends them to the Internet to achieve information sharing. However, a PC must be specially equipped for protocol conversion;
(3) By the 8-bit MCU composed of direct access to the Internet embedded networking instrument, the advantage of this solution is that you can use the previous measurement equipment based on the 8-bit MCU, through the additional network chip, directly drive the network interface chip, but the resource (ROM, RAM, CPU) is more, requiring the MCU to have a fast enough speed.
2.4 Interface chips that support networks
The RTL8019AS of RELTEK is used as the network interface chip, which is the ideal chip for Ethernet communication because of its excellent performance and low price.
(1) Main performance
Comply with Ethernet II and IEEE802.3 standards; It is a full-duplex communication interface, sending and receiving can reach the rate of 10Mbps at the same time; Built-in 16K SRAM for receiving and sending buffering, reducing the speed requirements of the main processor; Support 8/16 bit data bus, 8 interrupt request lines and 16 I/O base address selection; It can complete the formation of physical frames, codec, CRC formation and verification, data sending and receiving, etc. It can send and receive data simultaneously on the twisted pair through the switch.
(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 MCU RTL8019AS internal RAM to read and write the bus, that is, the interface part of the ISA bus. Single chip microcomputer to send and receive data only need to remote DMA operation. The local DMA interface is the connection channel between the RTL8019AS and the network cable, and completes the data exchange between the controller and the network cable.
(3) Internal RAM address space allocation
The RTL8019AS has two RAM areas inside. A 16K byte with the address 0x4000~0x7fff; A block of 32 bytes, the address is 0x0000 to 0x001f. RAM is stored on a page basis, with each 256 bytes being one page. Generally, the first 12 pages of RAM (i.e. 0x4000~0x4bff) are used as the send buffer; The last 52 pages (i.e. 0x4c00~0x7fff) store serves as the receive buffer. The addresses on page 0 are 0x0000 to 0x001f and are used to store Ethernet physical addresses.
(4)I/O address allocation
The RTL8019AS has 32-bit input and output addresses with address offsets ranging from 00H to 1FH. There are 16 addresses from 00H to 0FH, which are register addresses. The register is divided into four pages: PAGE0, PAGE1, PAGE2 and PAGE3. The PS1 and PS0 bits in CR(CommandRegister command register) of RTL8019AS determine the page to be accessed. Remote DMA address includes 10H~17H, can be used as a remote DMA port, as long as one of them can be used. The reset port contains eight addresses ranging from 18 h to 1FH, and has the same function. It is used for resetting the RTL8019AS.
3. Architecture and implementation of networked instruments
3.1 Abstract Model
Networked instrument is an organic combination of electrical and electronic, computer hardware and software, network, communication and many other technologies, the structure is more complex, and most of the system structure is used to express its overall framework and system characteristics. The architecture of networked instrument includes basic network system hardware, application software and various protocols. Figure 1 is a simple model of networked instrument architecture, which divides networked instrument into several logical layers, which can more essentially reflect the principle characteristics of networked instrument information collection, storage, transmission and analysis and processing
The first is the hardware layer, which 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 hardware layer function benefits from the technical progress of embedded system and the development of large-scale integrated circuit technology in recent years. Hardware protocol conversion and data stream transmission control rely on FPGA/CPLD.
Another logical layer is embedded operating system kernel, the main function of this layer is to provide a control signal acquisition and data flow transmission platform. The main resources of the front-end module unit of the platform include processor, memory, signal acquisition unit and information. The main function is to rationally allocate and control the processor, control the signal acquisition unit to make it work normally, and ensure the effective transmission of data flow. The logical layer consists of link layer, network layer, transport layer and 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 scheme
There are two hardware designs for Internet or Ethernet communication.
(1) With a dedicated CPU as a controller, the use of C language programming to achieve TCP/IP communication. The advantage is that the processing power of the dedicated CPU is strong, and it is easy to realize other functions of the test instrument. The disadvantage is that the cost is slightly higher and the hardware is slightly complex.
(2) Using 51 series single chip microcomputer as the CPU of the controller, without using the embedded operating system, directly using C51 programming, to achieve the data link layer protocol and TCP/IP protocol. The advantage is that the hardware is relatively simple and the price is low. The disadvantage is that the software workload is large and difficult. The basic structure of the networked instrument, which is based on single chip microcomputer and uses RTL8019 Ethernet interface chip as network instrument interface, is shown in Figure 2.
3.3 Protocol and design
The initial operation of the system is mainly to configure the network interface chip. After the configuration is complete, the system is in a waiting state until data is sent from the customer. The reception of data is realized through the network interface chip, which can filter the physical frames on the network. When a frame of information from an Ethernet site is sent to a shared signal channel or medium, all Ethernet interfaces connected to the channel read 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 continues to read in the entire frame and sends it to the upper-layer network software that the computer is running. The upper-layer network software reads the type field of the frame, determines whether the 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 frame format and sent to the sending buffer in RTL8019AS through remote DMA channel, and then the transmission command is issued to complete the sending of frames. You need to set the Ethernet destination address, Ethernet source address, and protocol type, and then set the data segment based on the protocol type. After that, the remote DMA is started, the data is written to the RAM of the RTL8019AS, and then the local DMA is started to send the data to the network. The RTL8019AS cannot store packets into the FIFO once through the DMA channel, so it must wait for the previous packet to complete before forming a new packet. In order to improve transmission efficiency, the 12-page send buffer is divided into two 6-page send buffers, one for packet sending and the other for packet construction, which are used alternately.
4. Closing remarks
With the development of computer technology and network technology, the concept of instrument in the 21st century will be an open system concept. Based on PC and workstation, it has become the development direction of modern instrumentation to form a practical measurement and control system by building a network to improve production efficiency and share information resources. The concept of networked instrument is a breakthrough to the concept of traditional measuring instrument. In a sense, computers and modern instruments have been mutually inclusive, and the computer network is the universal instrument network. If more different types of intelligent devices in the measurement and control system also become nodes of the network like computers and workstations, they make full use of the equipment of the Internet network that has been relatively mature at present, it will not only realize the sharing of more resources, reduce the cost of building the system, but also improve the function of the measurement and control system, and expand its scope of application. The concept of “the network is the instrument” accurately Outlines the development trend of the instrument network.