Sensors, like human facial features, are important tools for obtaining information. It plays a great role in industrial production, national defense construction and science and technology. However, compared with the rapid development of computers, sensors as “facial features” can not catch up with the development speed of computers as “brain”.
With the development of automation and intelligence of measurement and control system, it is required that the sensor has high accuracy, high reliability, good stability, certain data processing ability, self inspection, self calibration and self compensation. Traditional sensors can not meet such requirements. Some foreign articles call the traditional sensor dumb sensor . In addition, in order to manufacture high-performance sensors, it is also difficult to improve the material process alone. It is necessary to use the combination of computer technology and sensor technology to make up for the lack of performance. Computer technology has made great changes in sensor technology. The combination of microprocessor (or microcomputer) and sensor produces powerful intelligent sensors. It is called intelligent sensor or smart2sensor abroad. In addition, traditional sensors can only measure one parameter. In some cases, it is necessary to measure multiple parameters at the same time. Now scientists in many countries have paid attention to the development of this direction, and have developed some multifunctional sensors.
1. Intelligent sensor
Intelligent sensor is a research hotspot in the international scientific and technological circles, and there is no unified and accurate definition. This article does not discuss the difference between the two terms (In2telligent sensor or smart sensor), which are collectively referred to as smart sensors.
At present, scholars at home and abroad generally believe that intelligent sensor is composed of traditional sensor and microprocessor (or microcomputer). It makes full use of the computing and storage capacity of computer to process the sensor data, and can adjust its internal behavior to optimize the collected data. The functions of the smart sensor are as follows:
(1) Self compensation capability: automatically compensate the nonlinearity, temperature drift, time drift and response time of the sensor through software.
(2) Self calibration function: after the operator inputs zero value or a standard value, the self calibration software can automatically calibrate the sensor online.
(3) Self diagnosis function: after the power is turned on, the sensor can be self checked to check whether all parts of the sensor are normal, and the faulty components can be diagnosed.
(4) Numerical processing function: it can automatically process data according to the internal program of the intelligent sensor, such as statistical processing, eliminating abnormal values, etc.
(5) Two way communication function: a closed loop is formed between the microprocessor and the basic sensor. The microprocessor can not only receive and process the sensor data, but also feed back the information to the sensor to adjust and control the measurement process.
(6) Information storage and memory function.
(7) Digital output function: output digital signal, which can be conveniently connected with computer or interface bus.
At present, the intelligent sensor developed only has part of the above functions. Traditional sensors can only be used as sensitive elements to detect the changes of physical quantities, while intelligent sensors include measurement signal conditioning (such as filtering, amplification, a / D conversion, etc.), data processing and data display. It includes almost all the functions of instruments and meters. It can be seen that the function of intelligent sensor has been extended to the field of instrument.
With the development of science and technology, the function of intelligent sensor will be gradually enhanced. It will use artificial neural network, artificial intelligence and information processing technology (such as sensor information fusion technology, fuzzy theory, etc.) to make the sensor have higher intelligence, analysis, judgment, self-adaptive and self-learning functions, and can complete image recognition, feature detection Multidimensional detection and other complex tasks.
2. Structure of intelligent sensor
Intelligent sensor is mainly composed of sensor, microprocessor (or microcomputer) and related circuits. Its structural block diagram is shown in Figure 1
Figure 1 schematic block diagram of intelligent sensor
The sensor converts the measured physical quantity into the corresponding electrical signal and sends it to the signal conditioning circuit. After filtering, amplification and analog-to-digital conversion, it is sent to the microcomputer. Computer is the core of intelligent sensor. It can not only calculate, store and process the measured data of sensor, but also adjust the sensor through feedback loop. Because the computer gives full play to the functions of various software, it can complete tasks that are difficult to be completed by hardware, so as to greatly reduce the difficulty of sensor manufacturing, improve the performance of sensor and reduce the cost.
The structure of intelligent sensor can be integrated or separated. According to the structure, it can be divided into three forms: integrated, hybrid and modular. Integrated intelligent sensor integrates one or more sensitive devices with microprocessor and signal processing circuit on the same silicon chip, with high integration and small volume. This integrated sensor is still difficult to realize at the current technical level. The sensor, microprocessor and signal processing circuit are made on different chips to form a hybrid smart2sensor. At present, there are many such structures. The primary intelligent sensor can also be composed of many independent modules. For example, if the microcomputer, signal conditioning circuit module, output circuit module, display circuit module and sensor are assembled in the same shell, the group is high and the volume is large, but it is still a practical structural form under the current technical level.
2. Multifunctional sensor
The multifunctional sensor can convert more than two different physical quantities. For example, special ceramics are used to integrate temperature and humidity sensitive elements into a temperature and humidity sensor; The sensitive elements for detecting sodium and potassium ions are integrated on a substrate to make a sensor for measuring ion components in blood; The multi-functional sensors for detecting H2S, C8H18, NH3 and c20h2o are made on the same substrate by thick film manufacturing process; A strain gauge and temperature sensitive element are made on the same silicon wafer to make a multifunctional sensor for measuring pressure and temperature at the same time. The sensor can also realize temperature compensation. In addition, Japanese scholars have also developed other multifunctional sensors, such as sensors for measuring temperature, humidity and wind speed, and for measuring object surface finish and temperature. Some multifunctional sensors are hybrid. Several sensors are made and assembled respectively. The multifunctional sensor is combined with microprocessor and signal processing circuit to form a multifunctional intelligent sensor.
4. Application of intelligent sensor and multifunctional sensor
Smart sensors were first used in the aerospace field. Spacecraft need to measure a large number of parameters, including speed, acceleration, attitude, orientation and other parameters reflecting the orbit, and temperature, humidity, air pressure, air composition and other parameters reflecting the living environment of astronauts. Therefore, a large number of sensors are needed. If these large amounts of raw data are directly sent to the computer, it will undoubtedly increase the burden of the host computer and affect the processing speed. In order to improve efficiency and reliability, the distributed processing method is adopted, that is, these data are preprocessed by their respective processing systems, and then transmitted to the host for centralized processing. This is the smart sensor developed when NASA developed the spacecraft. Due to the strong function, high integration and small volume of intelligent sensors and multi-functional sensors, the number of sensors and the weight of connecting cables can be greatly reduced, which is just needed by missiles, satellites, spacecraft and other aircraft, so they play a very important role in the field of aerospace.
In industrial production, with the development of production process automation, more and more data are collected, and a large number of sensors and computers need to be used. In particular, intelligent sensors are needed.
Intelligent sensors and multifunctional sensors have broad application prospects in robots. Such as visual sensor, tactile sensor, force sensor, proximity sensor, etc. In particular, intelligent robots need to identify, judge and make decisions according to the collected information. Intelligent sensors, such as human facial features, can make the robot have sensing function. Now some countries are researching and developing tactile sensors that can recognize the shape of objects and olfactory sensors that can distinguish different gases.
With the development of intelligent sensors and multifunctional sensors, they will be more widely used in industry, science and technology, national defense and other departments.
5. Current situation and development
At present, all countries in the world are developing all kinds of intelligent sensors and multifunctional sensors. The most successful one is the dstj – 3000 intelligent differential pressure sensor developed by Honeywell company of the United States. On the same semiconductor substrate, three sensitive elements of differential pressure, static pressure and temperature are configured and diffused by ion implantation. The whole sensor also includes converter, multiplexer, pulse modulation, microprocessor and digital output interface. In addition, the characteristic data of the sensor is installed in the prom to realize nonlinear compensation. Par scientific developed 1000 series digital quartz intelligent sensor. Hitachi Research Institute in Japan has developed olfactory sensors that can recognize four kinds of gases. Intelligent sensor is a comprehensive intensive technology combining measurement technology, semiconductor technology, computing technology, information processing technology, microelectronics and material science. At present, scientists from various countries are developing and researching in the following technical ways:
(1) The basic sensor is developed by using new materials. Basic sensor is the basis of intelligent sensor. Its fabrication and performance have a great impact on the whole intelligent sensor. Silicon removal materials have excellent physical properties and can be easily made into various integrated sensors. In addition, functional ceramics, quartz and memory alloy are high-quality materials for making sensors.
(2) Using new processing technology. In recent years, micromachining technology is becoming more and more mature. It can be used to process high-performance microstructure sensors, ASIC manufacturing technology, and intelligent sensors.
(3) New measurement principles and methods are adopted. The resonant sensor outputs digital quantity, which can be directly connected with microcomputer and interface bus without a / D converter. In addition, optical fiber sensors, chemical sensors and biosensors provide new information sources for intelligent sensors.