The first model paper of sensor technology paper
Sensor and its overview
abstract
Sensor (English name: transducer/sensor) is a device that directly acts on the measured value and can be converted into the same or other values for output according to certain rules. At present, most of the signals converted by sensors are electrical signals, so in a narrow sense, sensors are devices that convert non-electrical signals input from outside into electrical signals.
Keywords new sensor
1 preface
The sensor is a part of the test system, and its function is similar to that of human sensory organs, and it can also be considered as an extension of human senses. With the help of sensors, people can detect things that people can't or can't directly perceive with their senses. For example, a thermocouple can measure the temperature of a hot object. Ultrasonic sensors can measure the depth of seawater; Infrared remote sensors can be used to detect ground topography, river state and vegetation distribution from high altitude. Therefore, it can be said that the sensor is a powerful tool for people to understand natural things, and it is the interface between measuring instruments and measured objects. Usually, the sensor is at the input end of the test equipment, which is the first link of the test system. Its performance directly affects the whole test system and has a great influence on the test accuracy.
2 Classification of sensors
According to the different measured physical quantities, it can be divided into displacement, force, temperature, flow sensor and so on. According to the different working basis, it can be divided into mechanical sensor, electrical sensor, optical sensor, fluid sensor and so on. According to the characteristics of signal transformation, it can be divided into physical sensor and structural sensor; According to the direct energy relationship between the sensitive element and the measured object, it can be divided into energy conversion sensor and energy control sensor.
3 Introduction of Common Sensors
3. 1 resistance strain sensor
Resistance strain sensor is also called resistance strain gauge, and its sensitive element is resistance strain. The strain gauge is made by sticking a metal wire or foil with a diameter of about 0.025mm on a glass substrate impregnated with insulating materials such as phenol and epoxy resin. Sensitive elements are also called sensitive grids. It has the advantages of small volume, fast dynamic response, high measurement accuracy and simple use. Has been widely used in aviation, machinery, construction and other industries. The working principle of resistance strain gauge is based on the strain effect of metal, that is, the metal conductor is mechanically deformed under the action of external force, and its resistance value changes with the change of mechanical deformation. It can be divided into metal resistance strain gauges and semiconductor strain gauges. Metal strain gauges can be divided into wire type, foil type and film type. Semiconductor strain gauges have the advantages of high sensitivity (usually dozens of times that of wire and foil) and small lateral effect. The main difference between them is that metal resistance strain gauges are caused by conductor deformation, while semiconductor strain gauges are caused by resistivity change.
3.2 Capacitive sensor
Capacitive sensor is a device that converts the measured physical quantity into capacitance change, which is essentially a capacitor with variable parameters. Because the capacitance is inversely proportional to the polar distance and directly proportional to the opposite area and medium, it can be divided into three types: polar distance change type, area change type and medium change type. The advantages of polar distance varactor sensor are that it can be used for dynamic non-contact measurement, which has little influence on the measured system and high sensitivity, and is suitable for measuring small displacement. However, this kind of sensor has nonlinear characteristics, so its application range is limited. The advantage of area change sensor is that the output is linear with the input, but compared with polar distance sensor, the sensitivity is lower, so it is suitable for measuring large straight line or angular displacement. The middle variant is mostly used to measure the height of liquid.
3.3 Induction sensor
Inductive sensor is a device that converts measured physical quantities such as force and displacement into inductance, and its conversion is based on the principle of electromagnetic induction. There are many kinds of inductive sensors, including self-inductance, mutual inductance and eddy current.
Inductive sensor has the following characteristics: simple structure, no moving electrical contacts, so it works reliably and has a long life. The sensitivity and resolution are high, and the displacement change of 0.0 1 micron can be measured. The output signal of the sensor is strong, and the voltage sensitivity can reach hundreds of millivolts per millimeter. Good linearity and repeatability. In a certain displacement range (tens of microns to several millimeters), the nonlinear error of the sensor can reach 0.05% ~ 0. 1%. At the same time, this sensor can realize long-distance transmission, recording, display and control of information, and is widely used in industrial automatic control systems. However, it also has some shortcomings, such as low frequency response, which is not suitable for fast dynamic measurement and control.
3.4 Magnetoelectric Sensor
Magnetoelectric sensor is a kind of sensor that converts the measured physical quantity into induced electromotive force, also known as electromagnetic induction sensor or electric sensor. Its working principle is an N-turn coil. When the magnetic flux passing through it changes, the coil generates induced electromotive force. The change of magnetic flux can be realized in many ways, such as the movement of cutting magnetic lines between the magnet and the coil, the change of magnetic resistance of the magnetic circuit, the change of coil area in a constant magnetic field, etc. Therefore, different types of sensors can be manufactured to measure the speed and torque.
3.5 Piezoelectric sensor
Piezoelectric sensor is a reversible sensor, which works by using the piezoelectric effect of some substances. In the simplest piezoelectric sensor, metal is evaporated on two working surfaces of a piezoelectric wafer to form a metal film, and two electrodes are formed. When the wafer is under pressure, charges of the same amount but opposite polarity are accumulated on the two plates, forming an electric field. Therefore, the piezoelectric sensor can be regarded as both a charge generator and a capacitor.
4 new sensors
4. 1 biosensor
Biosensor is an interdisciplinary subject that organically combines bioactive substances (enzyme, protein, DNA, antibody, antigen, biofilm, etc.). ) and physical and chemical sensors. It is an indispensable advanced detection means and monitoring means for the development of biotechnology, and it is also a rapid and trace analysis method at the molecular level of substances. Various biosensors have the same structure as follows: they include one or several related bioactive materials (biomembrane) and physical or chemical transducers (sensors) that can convert signals expressed by biological activities into electrical signals. They are combined to reprocess biological signals with modern microelectronics and automatic instrument technology, forming various available biosensor analysis devices, instruments and systems. The principle of biosensor: the substance to be detected diffuses into the bioactive material, and after molecular recognition, a biological reaction occurs. The generated information is converted into a quantifiable and treatable electrical signal by the corresponding physical or chemical transducer, and then amplified and output by the secondary instrument, so that the concentration of the substance to be detected can be known.
4.2 Laser sensor
Laser sensor: a sensor that uses laser technology to measure. It consists of a laser, a laser detector and a measuring circuit. Laser sensor is a new type of measuring instrument, which has the advantages of non-contact long-distance measurement, high speed, high precision, large measuring range and strong anti-photoelectric interference ability. Principle of laser sensor: When the laser sensor works, the laser emitting diode is aimed at the target to emit laser pulses. The laser is reflected by the target and scattered in all directions. Part of the scattered light returns to the sensor receiver and is imaged on the avalanche photodiode after being received by the optical system. Avalanche photodiode is an optical sensor with internal amplification function, so it can detect extremely weak optical signals and convert them into corresponding electrical signals.
5 concluding remarks
With the rapid development of science and technology, people's ability to understand the world is constantly improving. Sensors play an important role in obtaining nature and production. At present, sensor technology plays an important role in promoting economic development and social progress. I believe that in the future, there will be a leap in sensor technology.
Brief introduction of the author
Yang (199 1-), female, from Handan City, Hebei Province. Now he is an undergraduate of Zhengzhou University. His main research interests are mechanical engineering and automation.
Author unit
School of Mechanical Engineering, Zhengzhou University, Zhengzhou City, Henan Province 45000 1
The second model of sensor technology paper
temperature sensor
Abstract: Temperature sensor is the earliest developed and most widely used sensor. According to the survey, as early as 1990, the market share of temperature sensors greatly exceeded that of other sensors. From the beginning of17th century, when Galileo invented the thermometer, people began to measure the temperature. The sensor that really converts temperature into electric signal was invented by German physicist Sebe in 182 1, which is the thermocouple sensor we use now. Subsequently, platinum resistance temperature sensor, semiconductor thermocouple temperature sensor, PN junction temperature sensor and integrated temperature sensor came out one after another. This also makes the temperature sensor more widely used in our production and life. This paper mainly introduces the classification, working principle and application of temperature sensor.
Keywords: temperature sensor; Temperature; degree Celsius
China Library ClassificationNo.: TP2 12 Document ID: A DocumentNo.:1674-7712 (2014) 02-0000-01.
The temperature sensor converts the temperature into a usable output signal by using the law that various physical properties of a substance change with temperature. Temperature sensor is the core part of temperature measuring instrument, and there are many kinds. According to the measurement method, modern temperature sensors can be divided into contact and non-contact types. Their shapes are very small, which makes them widely used in various fields of production practice and provides countless conveniences and functions for our lives.
First, the relevant knowledge of temperature
Temperature is a physical quantity used to characterize the degree of heat and cold of an object. The level of temperature should be quantified by numbers, and the temperature scale is the numerical representation of temperature. The commonly used temperature scales are centigrade scale and thermodynamic temperature scales.
In the centigrade scale, the temperature of boiling water is set to 100℃, the temperature of ice-water mixture is set to 0℃, and equal parts of 100 are made between 100℃, and each part is 1 0℃. The thermodynamic temperature scale was put forward by William and Tom. Based on the second law of thermodynamics, the thermodynamic temperature scale was established, in which the temperature is only related to heat and has nothing to do with matter. Because it is summarized in Kelvin, it is also called Kelvin temperature scale.
Second, the classification of temperature sensors
According to different measurement methods, temperature sensors can be divided into contact and non-contact types. Contact temperature sensor means that the sensor is in direct contact with the measured object, thus measuring the temperature. This is also the basic form of temperature measurement. Among them, the contact temperature sensor is divided into thermocouple temperature sensor, thermal resistance temperature sensor, semiconductor thermistor temperature sensor and so on.
The non-contact temperature sensor measures the infrared ray emitted by the thermal radiation of the object, thus measuring the temperature of the object, which can be used for telemetry.
Third, the working principle of temperature sensor
(1) Thermocouple temperature sensor. Thermocouple temperature sensor is the most widely used temperature sensor with simple structure, which is only welded by two conductors or semiconductors of different materials.
Thermocouple temperature sensor is made according to the principle of thermoelectric effect: two different metals A and B form a closed loop, and the two contact temperatures are t 1 and t2 respectively, which will generate an electromotive force in the loop.
Thermocouple is also welded by two conductors or semiconductors A and B of different materials, and the welding end is called working end or hot end. The end connected to the wire is called the free end or cold end, and the conductors A and B are called hot electrodes, collectively referred to as thermocouples. When measuring, the working end is in contact with the measured object. The measuring instrument is a potentiometer, which is used to measure the thermoelectromotive force of thermocouple. Connecting wires are compensation wires and copper wires.
What we observe from the table is thermoelectromotive force, and to know the temperature of the object, we need to look at the graduation table of thermocouple.
In order to ensure the accuracy of temperature measurement results, there are also strict requirements in the selection of hot electrode materials: high physical and chemical stability; Low temperature coefficient of resistance; High conductivity; Thermoelectromotive force is large; Thermoelectromotive force should have a linear or simple functional relationship with temperature; Good reproducibility; Easy to process, etc. According to the commonly used hot electrode materials, thermocouple temperature sensors can be divided into standardized thermocouples and non-standardized thermocouples. Platinum-rhodium-platinum thermocouple is a commonly used standardized thermocouple with high melting point, which can be used to measure high temperature with small error, but it is expensive and generally suitable for more precise temperature measurement. Iron-constantan is a commonly used non-standard thermocouple, the upper limit of temperature measurement is 600 degrees Celsius, which is easy to rust, but the temperature has a good linear relationship with thermoelectromotive force and has high sensitivity.
(2) Resistance temperature sensor. Although the thermocouple temperature sensor is simple in structure and accurate in measurement, it is only suitable for measuring high temperature above 500 degrees Celsius. In order to measure the medium and low temperature objects at -200℃ to 500℃, it is necessary to use the resistance temperature sensor.
Resistance temperature sensor measures temperature by using the characteristic that the resistance value of conductor or semiconductor changes with temperature. The resistance of most metals will increase by 0.4% to 0.6% when the temperature rises 1 Celsius. The resistance temperature sensor converts the change of temperature into the change of resistance value, and then converts it into a voltage signal through the measuring bridge and sends it to the display instrument.
(3) Semiconductor thermistor. Semiconductor thermistor is characterized by high sensitivity, small size and fast response. It is made by using the characteristic that the resistance value of semiconductor changes significantly with temperature. There are three types: (1)NTC thermistor, which is mainly sintered by oxides of metals such as manganese, cobalt, nickel and iron, and has a negative temperature coefficient. (2)CTR thermistor, which uses oxides of V, Ge, W, P and other elements to form a sintered body in a weak reducing atmosphere, also has a negative temperature coefficient. (3)PTC thermistor is a semiconductor ceramic element sintered with barium titanate doped with rare earth elements, which has a positive temperature coefficient. Because PTC thermistor has a positive temperature coefficient, it is also made into a temperature control switch.
(4) Non-contact temperature sensor. The temperature measuring element of non-contact temperature sensor is not in contact with the measured object. At present, the most commonly used principle is radiation heat transfer. The main characteristics of this temperature measurement method are: it can be used to measure small moving targets and objects with small heat capacity or rapid change, and it can also be used to measure the temperature distribution of temperature field, but it is greatly affected by environmental temperature.
Four, the application example of temperature sensor
(a) Application of temperature sensors in automobiles. The function of temperature sensor is to measure the temperature of intake air, cooling water and fuel oil. And the measurement results are converted into electrical signals and sent to ECU. For all electronic control systems of gasoline engines, intake air temperature and cooling water temperature are two essential temperature parameters for ECU control, while other temperature parameters are different due to the types of electronic control systems and control needs. The air temperature sensor is usually installed in the air flow meter or the air inlet between the air cleaner and the throttle body or in the air flow meter, and the water temperature sensor is installed in an appropriate position on the engine cooling water passage, cylinder head or engine block. There are many types of sensors that can be used to measure temperature, such as winding resistance, diffusion resistance, semiconductor transistor, metal core, thermocouple and semiconductor thermistor. At present, thermistor temperature sensor is widely used in the measurement of intake air temperature and cooling water temperature.
(2) Use the temperature sensor to adjust the temperature of the bathroom. The temperature sensor can also adjust the temperature of the bathroom, especially when taking a bath, so it is necessary to automatically adjust the temperature of the bathroom. Through the temperature and humidity sensor and gas sensor, we can control the environment of the bathroom well and let us have a comfortable life. At present, most hotels and some public places have realized automatic adjustment, while the toilets in ordinary families are still manually operated and have not realized automatic adjustment. This is mainly because ordinary customers don't know that automation can be realized by using sensors. With the further understanding of people in the future, the toilets in ordinary families can also be automatically adjusted.
References:
Qi zhou. Design of integrated temperature sensor [D]. xidian university, 2007.