1. Working principle of intelligent instruments
The sensor picks up the information of the measured parameter and converts it into an electrical signal. After filtering to remove interference, the signal is sent to a multiplexer analog switch. The microcontroller selects each analog switch one by one, sending the signal from each input channel to a programmable gain amplifier. The amplified signal is then converted into a corresponding pulse signal by an A/D converter and sent to the microcontroller. The microcontroller performs corresponding data calculations and processing (such as nonlinear correction) based on the initial value set by the instrument. The calculation results are converted into corresponding data for display and printing. At the same time, the microcontroller compares the calculation results with the set parameters stored in the on-chip FlashROM (flash memory) or E2PROM (electrically erasable memory), and outputs corresponding control signals (such as alarm device triggering, relay contact activation, etc.) according to the calculation results and control requirements. In addition, the intelligent instrument can also form a distributed measurement and control system with a PC. The microcontroller acts as a lower-level machine to collect various measurement signals and data, and transmits the information to the upper-level machine—the PC—through serial communication for global management.
2. Functional characteristics of intelligent instruments
With the continuous development of microelectronics technology, very large-scale integrated circuit chips (i.e., microcontrollers) have emerged, integrating circuits such as CPU, memory, timer/counter, parallel and serial interfaces, watchdog timers, preamplifiers, and even A/D and D/A converters onto a single chip. Using microcontrollers as the core, and combining computer technology with measurement and control technology, the so-called "intelligent measurement and control system," or intelligent instrument, has been formed.
Compared with traditional instruments and meters , intelligent instruments have the following functional characteristics:
①Automated operation. The entire measurement process of the instrument, such as keyboard scanning, range selection, switch start-up and closing, data acquisition, transmission and processing, and display and printing, is controlled by a single-chip microcomputer or microcontroller, realizing full automation of the measurement process.
② It has self-testing functions, including automatic zeroing, automatic fault and status verification, automatic calibration, self-diagnosis, and automatic range switching. The intelligent instrument can automatically detect the location and even the cause of the fault. This self-test can run when the instrument is started up, and also during operation, greatly facilitating instrument maintenance.
③ It has data processing capabilities, which is one of the main advantages of intelligent instruments. Because intelligent instruments use microcontrollers or single-chip microcomputers, many problems that were previously difficult or impossible to solve with hardware logic can now be solved very flexibly with software. For example, traditional digital multimeters can only measure resistance, AC/DC voltage, and current, while intelligent digital multimeters can not only perform these measurements but also have complex data processing functions such as zero-point shifting, averaging, finding extreme values, and statistical analysis of the measurement results. This not only frees users from tedious data processing but also effectively improves the measurement accuracy of the instrument.
④ It has user-friendly human-computer interaction capabilities. The intelligent instrument uses a keyboard instead of the switches found in traditional instruments, allowing operators to perform measurement functions simply by inputting commands through the keyboard. Simultaneously, the intelligent instrument displays the instrument's operating status, working condition, and the processing results of the measurement data, making operation more convenient and intuitive.
⑤ It has programmable operation capability. Most intelligent instruments are equipped with standard communication interfaces such as GPIB, RS232C, and RS485, which can be easily combined with PCs and other instruments to form an automatic measurement system with multiple functions required by the user to complete more complex testing tasks.
3. Overview of the Development of Intelligent Instruments
In the 1980s, microprocessors were used in instruments, and instrument front panels began to evolve towards keyboard-based designs. Measurement systems were often connected via the IEEE-488 bus. Personal instruments, unlike the traditional standalone instrument model, were developed.
In the 1990s, the intelligentization of instruments and meters was prominently reflected in the following aspects: the advancement of microelectronics technology had a more profound impact on the design of instruments and meters; the advent of DSP chips greatly enhanced the digital signal processing capabilities of instruments and meters; the development of microcomputers enabled instruments and meters to have stronger data processing capabilities; the addition of image processing functions was very common; and the VXI bus was widely used.
In recent years, the development of intelligent measurement and control instruments has been particularly rapid. A wide variety of intelligent measurement and control instruments have appeared on the domestic market, such as intelligent throttling flow meters that can automatically perform differential pressure compensation, intelligent multi-segment temperature controllers that can perform programmed temperature control, intelligent regulators that can realize digital PID and various complex control laws, and intelligent chromatographs that can analyze and process various spectra.
Internationally, there is a wide variety of intelligent measuring instruments. For example, the DSTJ-3000 series intelligent transmitter produced by Honeywell in the United States can perform composite measurements of differential pressure and automatically compensate for the temperature and static pressure of the transmitter body, with an accuracy of ±0.1%FS. The 9303 ultra-high level meter from Raca-Dana in the United States uses a microprocessor to eliminate thermal noise generated by current flowing through resistors, achieving a measurement level as low as -77dB. The 5520A super multi-functional calibrator produced by Fluke in the United States uses three microprocessors internally, achieving short-term stability of 1ppm and linearity of 0.5ppm. The digital self-tuning controller produced by Foxboro in the United States uses expert system technology, enabling rapid tuning of the controller based on field parameters, much like an experienced control engineer. This type of controller is particularly suitable for control systems with frequent or nonlinear changes. Because this controller can automatically tune the control parameters, it ensures that the entire system maintains optimal quality throughout the production process.
4. Development Trends of Intelligent Instruments
4.1 Miniaturization
Miniature intelligent instruments refer to instruments that integrate microelectronics, micromechanics, and information technology in their production, resulting in small, fully functional intelligent instruments. They can perform functions such as signal acquisition, linearization, digital signal processing, signal output control, amplification, interfacing with other instruments, and human interaction. With the continuous development of microelectromechanical technology, miniature intelligent instruments are becoming increasingly sophisticated and affordable, thus expanding their application areas. They not only possess the functions of traditional instruments but also play unique roles in automation, aerospace, military, biotechnology, and medical fields. For example, currently, simultaneously measuring several different parameters of a patient and controlling certain parameters typically requires inserting several tubes into the patient's body, increasing the risk of infection. Miniature intelligent instruments, capable of simultaneously measuring multiple parameters and being small enough to be implanted in the human body, solve these problems.
4.2 Multifunctional
Multifunctionality is a characteristic of intelligent instruments. For example, to design fast and complex digital systems, instrument manufacturers produce function generators that integrate pulse generators, frequency synthesizers, and arbitrary waveform generators. These multifunctional integrated products not only offer higher performance (such as accuracy) than dedicated pulse generators and frequency synthesizers, but also provide better solutions for various testing functions.
4.3 Artificial Intelligence
Artificial intelligence (AI) is a new field of computer applications that uses computers to simulate human intelligence for applications in robotics, medical diagnosis, expert systems, reasoning and proof, and other areas. Further development of intelligent instruments will incorporate a degree of AI, meaning they will replace some of the mental labor of humans, thus possessing certain abilities in areas such as vision (graphic and color recognition), hearing (speech recognition and language comprehension), and thinking (reasoning, judgment, learning, and association). In this way, intelligent instruments can autonomously complete detection or control functions without human intervention. Clearly, the application of AI in modern instrumentation allows us not only to solve problems that are difficult to solve using traditional methods, but also promises to solve problems that are fundamentally unsolvable using traditional methods.
4.4 Integrate ISP and EMIT technologies to achieve Internet access (networking) for instrumentation systems.
With the rapid development of network technology, Internet technology is gradually penetrating the fields of industrial control and intelligent instrumentation system design, enabling intelligent instrumentation systems to communicate via the Internet and to remotely upgrade, reset, and maintain designed intelligent instrumentation systems.
In-System Programming (ISP) technology is a cutting-edge technology for modifying, configuring, or reconfiguring software. First proposed by Latte Semiconductor, it enables users to configure or reconfigure the logic and functionality of devices, circuit boards, or entire electronic systems at any stage of product design and manufacturing, and even after the product is sold to the end user. ISP technology eliminates some limitations and connectivity drawbacks of traditional technologies, facilitating on-board design, manufacturing, and programming. ISP hardware is flexible and easy to modify, simplifying design and development. Because ISP devices can be processed on printed circuit boards (PCBs) like any other device, programming ISP devices does not require specialized programmers or complex processes; programming can be performed via a PC, embedded system processor, or even remotely via the Internet.
EMIT (Embedded Micro-Internet Technology) was proposed by emWare when it founded the ETI (eXtend the Internet) alliance. It is a technology that connects embedded devices such as microcontrollers to the Internet. Using this technology, 8-bit and 16-bit microcontroller systems can be connected to the Internet to achieve functions such as remote data acquisition, intelligent control, and uploading/downloading data files via the Internet.
Currently, companies such as ConnectOne, emWare, and TASKING in the United States, and P&S in China, all provide Internet-based Device Networking software, firmware, and hardware products.
4.5 Virtual instruments represent a new stage in the development of intelligent instruments.
The main functions of measuring instruments consist of three parts: data acquisition, data analysis, and data display. In virtual reality systems, data analysis and display are entirely performed using PC software. Therefore, by providing additional data acquisition hardware, a measuring instrument can be formed by combining it with a PC. This type of PC-based measuring instrument is called a virtual instrument. In a virtual instrument, using the same hardware system, different software programming can produce measuring instruments with completely different functions. It is evident that the software system is the core of a virtual instrument; "software is the instrument."
Traditional intelligent instruments primarily utilize certain computer technologies within instrument technology, while virtual instruments emphasize incorporating instrument technology into general-purpose computer technology. The software system at the core of virtual instruments possesses versatility, accessibility, visualization, scalability, and upgradeability, bringing significant benefits to users. Therefore, it boasts application prospects and a market that traditional intelligent instruments cannot match.
5. Conclusion
Intelligent instruments combine emerging technologies such as computer science, electronics, digital signal processing, artificial intelligence, and VLSI with traditional instrumentation technologies. With the development of application-specific integrated circuits (ASICs), personal instruments, and related technologies, intelligent instruments will find even wider applications. Single-chip computer technology, as the core component of intelligent instruments, is the driving force behind their miniaturization, multi-functionality, and increased flexibility. It is foreseeable that intelligent instruments with various functions will be widely used in all sectors of society in the near future.
