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1. The working principle of intelligent instruments
The sensor picks up the information of the measured parameter and converts it into an electrical signal, and sends the multi-channel analog switch after filtering to remove the interference; the single-channel strobe analog switch sends the signals of each input channel one by one into the program-controlled gain amplifier, and the amplified signal After being converted into the corresponding pulse signal by the A/D converter, it is sent to the single-chip microcomputer; the single-chip computer performs corresponding data calculation and processing according to the initial value set by the instrument (such as nonlinear correction, etc.); the result of the operation is converted into corresponding The data is displayed and printed; at the same time, the MCU compares the operation result with the setting parameters stored in the on-chip FlashROM (flash memory) or E2PROM (Electrically Erasable Memory), and then according to the operation result and control Request, output the corresponding control signal (such as alarm device trigger, relay contacts, etc.). In addition, the intelligent instrument can also form a distributed measurement and control system with the PC. The single-chip microcomputer is used as the lower computer to collect various measurement signals and data, and the information is transmitted to the upper computer-PC through serial communication, which is managed globally by the PC.
2. Features of intelligent instruments
With the continuous development of microelectronics technology, integrated CPU, memory, timer/counter, parallel and serial interface, watchdog, preamplifier and even A/D, D/A converter and other circuits on a single chip Very large scale integrated circuit chips (ie, microcontrollers) have emerged. Taking the single-chip microcomputer as the main body, combining computer technology with measurement control technology, it also constitutes the so-called "intelligent measurement control system", which is a smart instrument.
Compared with traditional instrumentation, smart instruments have the following features:
1 operation automation. The entire measurement process of the instrument, such as keyboard scanning, range selection, switch start and close, data acquisition, transmission and processing, and display printing, are all controlled by a single-chip microcomputer or a microcontroller to achieve full automation of the measurement process.
2 With self-test function, including automatic zero adjustment, automatic fault and status check, automatic calibration, self-diagnosis and automatic range conversion. The smart meter can automatically detect the fault location or even the cause of the fault. This self-test can be run at the start of the instrument and can also be run in the instrument, greatly facilitating the maintenance of the instrument.
3 with data processing capabilities, which is one of the main advantages of smart instruments. Because of the use of single-chip microcomputers or microcontrollers, intelligent instruments make many problems that were originally difficult to solve with hardware logic or can't be solved at present. Now, software can be solved very flexibly. For example, a traditional digital multimeter can only measure resistance, AC and DC voltage, current, etc., and an intelligent digital multimeter can not only perform the above measurements, but also perform measurement such as zero shift, averaging, extremum, and statistics. Analysis and other complex data processing functions not only free users from heavy data processing, but also effectively improve the measurement accuracy of the instrument.
4 has a friendly human-machine dialogue ability. The intelligent instrument uses the keyboard to replace the switch in the traditional instrument, and the operator can realize some measurement function by simply inputting commands through the keyboard. At the same time, the intelligent instrument also tells the operator the operation status, working state and processing result of the measurement data through the display screen, so that the operation of the instrument is more convenient and intuitive.
5 has programmable operation capability. General intelligent instruments are equipped with standard communication interfaces such as GPIB, RS232C, RS485, etc., which can easily form an automatic measurement system with various functions required by the user together with PC and other instruments to complete more complicated test tasks.
3. Overview of the development of intelligent instruments
In the 1980s, microprocessors were used in instruments, and the front panel of the instrument began to move toward the keyboard. Measurement systems were often connected via the IEEE-488 bus.
Personal instruments that differ from traditional stand-alone instrument models have been developed.
In the 1990s, the intelligence of instrumentation was highlighted in the following aspects: the advancement of microelectronics technology has more profoundly affected the design of instrumentation; the advent of DSP chips has greatly enhanced the digital signal processing functions of instrumentation; the development of microcomputers, It makes the instrumentation have stronger data processing capability; the increase of image processing function is very common; VXI bus is widely used.
In recent years, the development of intelligent measurement and control instruments has been particularly rapid. A variety of intelligent measurement and control instruments have appeared on the domestic market. For example, intelligent throttle flow meters that can automatically perform differential pressure compensation, intelligent multi-stage temperature control instruments capable of program temperature control, digital PID and various Intelligent regulators with complex control laws, and intelligent chromatographs that can analyze and process various spectra.
International intelligent measuring instruments are a wide variety. For example, the DSTJ-3000 series of intelligent transmitters produced by HONEYWELL of the United States can perform complex measurement of differential pressure status, which can automatically realize the temperature and static pressure of the transmitter body. Compensation, the accuracy can reach ±0.1% FS; American RACA-DANA company's 9303 ultra-high level meter, using the microprocessor to eliminate the thermal noise generated by the current flowing through the resistor, the measurement level can be as low as -77dB; FLUKE's super multi-function calibrator 5520A uses three microprocessors with short-term stability of 1ppm and linearity of 0.5ppm. The digital self-tuning regulator produced by FOXBORO in the US uses expert system technology. The regulator can be quickly adjusted according to field parameters, like an experienced control engineer. This type of regulator is particularly suitable for control systems where the subject changes frequently or non-linearly. Thanks to this regulator's ability to automatically adjust the tuning parameters, the entire system is always in optimum quality during production.
4. The development trend of intelligent instruments
4.1 Miniaturization
Micro-intelligent instruments refer to the comprehensive application of microelectronics technology, micro-mechanical technology and information technology in the production of instruments, thus making the instrument a small-sized, fully functional intelligent instrument. It can complete signal acquisition, linearization processing, digital signal processing, control signal output, amplification, interface with other instruments, and interaction with people. With the continuous development of micro-electro-mechanical technology, micro-intelligent instruments continue to mature and their prices continue to decrease, so their application fields will continue to expand. It not only has the functions of traditional instruments, but also plays a unique role in automation technology, aerospace, military, biotechnology, and medical fields. For example, at present, it is necessary to measure several different parameters of a patient at the same time, and to control certain parameters. Usually, several tubes are inserted into the patient's body, which increases the chance of infection of the patient. The micro-intelligent instrument can simultaneously measure multiple parameters. And small size, can be implanted in the human body, so that these problems are solved.
4.2 multi-functional
Multifunction itself is a feature of smart instrumentation. For example, in order to design a digital system that is faster and more complex, the instrument manufacturer manufactures a function generator with functions such as a pulse generator, a frequency synthesizer, and an arbitrary waveform generator. This versatile, integrated product offers higher performance (such as accuracy) than dedicated pulse generators and frequency synthesizers, and provides a better solution for a variety of test functions.
4.3 Artificial intelligence
Artificial intelligence is a new field of computer application. It uses computers to simulate human intelligence and is used in robotics, medical diagnosis, expert systems, and proof of reasoning. The further development of intelligent instruments will contain a certain amount of artificial intelligence, that is, to replace part of the mental work of human beings, thus in vision (graphics and color interpretation), auditory (speech recognition and language comprehension), thinking (reasoning, judgment, learning and association) Other aspects have certain capabilities.
In this way, the smart instrument can autonomously perform detection or control functions without human intervention. Obviously, the application of artificial intelligence in modern instrumentation allows us to solve not only a type of problem that is difficult to solve by traditional methods, but also to solve problems that cannot be solved by traditional methods.
4.4 Integrate ISP and EMIT technologies to realize Internet access (networking) of instrumentation systems
With the rapid development of network technology, Internet technology is gradually infiltrating into the field of industrial control and intelligent instrumentation system design, realizing the communication capability of intelligent instrumentation system based on Internet and remotely upgrading and resetting the designed intelligent instrumentation system. And system maintenance.
In-System Programming (ISP) is the latest technology to modify, configure or reorganize software. It is the first proposed by LATTICE Semiconductor to enable us to perform every step of the product design and manufacturing process, even after the product is sold to the end user, with the logic and functionality of its device, board or the entire electronic system. The latest technology for configuration or reorganization capabilities. ISP technology eliminates some of the limitations and connection deficiencies of traditional technologies and facilitates board design, manufacturing, and programming. The ISP hardware is flexible and easy to modify by software, making it easy to design and develop. Since ISP devices can be processed on a printed circuit board (PCB) like any other device, programming ISP devices does not require specialized programmers and more complex processes, as long as they are performed by PC, embedded system processor or even INTERNET remote network. Programming.
EMIT embedded micro Internet interconnection technology is proposed by emWare company to establish ETI (eXtendtheInternet) to expand the Internet alliance. It is a technology that connects embedded devices such as single-chip microcomputers to the Internet. With this technology, 8-bit and 16-bit single-chip microcomputer systems can be connected to the Internet to realize remote Internet data collection, intelligent control, uploading/downloading of data files and other functions.
Currently, ConnectOne, EmWare, TASKING, and P&S in China provide Internet-based Device-Networking software, firmware, and hardware products.
4.5 Virtual instrument is a new stage in the development of intelligent instruments
The main functions of the measuring instrument are composed of data acquisition, data analysis and data display. In virtual reality systems, data analysis and display is done entirely with PC software. Therefore, as long as additional data acquisition hardware is provided, a measuring instrument can be formed with the PC. This PC-based measuring instrument is called a virtual instrument. In a virtual instrument, using the same hardware system, as long as different software programming is applied, a completely different measuring instrument can be obtained. It can be seen that the software system is the core of the virtual instrument, "software is the instrument."
Traditional intelligent instruments mainly use some kind of computer technology in instrument technology, while virtual instruments emphasize the absorption of instrument technology in general computer technology. The software system, which is the core of the virtual instrument, has universality, popularity, visibility, scalability and upgradeability, which can bring great benefits to users. Therefore, it has the application prospect and market unmatched by traditional intelligent instruments. .
5. Conclusion
Intelligent instruments are a combination of emerging technologies such as computer science, electronics, digital signal processing, artificial intelligence, and VLSI, and traditional instrumentation technologies. With the development of related technologies such as ASICs and personal instruments, smart instruments will be more widely used. The single-chip computer technology, which is the core component of intelligent instruments, is the driving force for the development of smart instruments in the direction of miniaturization, multi-functionality and more flexibility. It is expected that intelligent instruments of various functions will be widely used in various fields of society in the near future.
The emergence of intelligent instruments has greatly expanded the range of applications of traditional instruments. With its small size, strong function and low power consumption, intelligent instruments have been widely used in household appliances, scientific research units and industrial enterprises.