English name: transducer/ sensor
A sensor is a physical device or biological organ, which can detect and feel external signals, physical conditions (such as light, heat and humidity) or chemical components (such as smoke), and transmit the detected information to other devices or organs.
[Edit this paragraph] Definition of sensor
The national standard GB7665-87 defines a sensor as "a device or equipment that can sense a specified measured signal and convert it into a usable signal according to certain rules, usually consisting of a sensitive element and a conversion element". Sensor is a kind of detection device that can sense the measured information, and can convert the sensed information into electrical signals or other required forms of information output according to certain rules to meet the requirements of information transmission, processing, storage, display, recording and control. This is the first step to realize automatic detection and automatic control.
[Edit this paragraph] Classification of sensors
Sensors can be classified from different angles: their conversion principle (the basic physical or chemical effect of sensor work); Their uses; Their output signal types, materials and processes for manufacturing them, etc.
According to the working principle of sensors, they can be divided into physical sensors and chemical sensors:
Classification of sensor working principle Physical sensors apply physical effects, such as piezoelectric effect, magnetostrictive phenomenon, ionization, polarization, thermoelectric, photoelectric, magnetoelectric and other effects. Small changes in the measured signal amount will be converted into electrical signals.
Chemical sensors include sensors with chemical adsorption, electrochemical reaction and other phenomena as causal relations, and small changes in the measured signal amount will also be converted into electrical signals.
Some sensors can neither be classified as physical sensors nor as chemical sensors. Most sensors work according to physical principles. Chemical sensors have many technical problems, such as reliability, possibility of mass production, price and so on. After solving these problems, the application of chemical sensors will greatly increase.
The application fields and working principles of common sensors are listed in table 1. 1.
According to the use, sensors can be divided into:
Pressure and force sensors? position detector
Liquid level sensor? Energy consumption sensor
Speed sensor? thermal element
Acceleration sensor? Ray radiation sensor
Vibration sensor? humidity sensor
Magnetic sensor? gas sensor
Vacuum sensor? Biosensors, etc. ?
According to its output signal, the sensor can be divided into:
Analog sensor-converts measured non-electric quantity into analog electric signal. ?
Digital sensor-converts the measured non-electric quantity into digital output signal (including direct and indirect conversion). ?
Pseudo-digital sensor-converts the measured signal into frequency signal or short-period signal for output (including direct or indirect conversion). ?
Switch sensor-When the measured signal reaches a certain threshold, the sensor outputs a set low-level or high-level signal accordingly.
Under the influence of external factors, all substances will make corresponding and characteristic reactions. Among them, those materials that are most sensitive to external effects, that is, materials with functional characteristics, are used to make sensitive elements of sensors. From the perspective of application materials, sensors can be divided into the following categories:
(1) According to the type of materials used?
Metal? Polymer? Ceramics? Mixture?
(2) Divide conductors according to the physical properties of materials? Insulator? Semiconductor? Magnetic material?
(3) According to the crystal structure of the material?
Single crystal? Polycrystalline amorphous material?
The development of sensors closely related to the adoption of new materials can be summarized into the following three directions:?
(1) Explore new phenomena, effects and reactions in known materials, and then apply them in sensor technology. ?
(2) Explore new materials and apply those known phenomena, effects and reactions to improve sensor technology. ?
(3) Explore new phenomena, new effects and new reactions on the basis of studying new materials, and realize them in sensor technology. ?
The progress of modern sensor manufacturing industry depends on the development intensity of new materials and sensitive components used in sensor technology. The basic trend of sensor development is closely related to the application of semiconductors and dielectric materials. Table 1.2 gives some materials that can be used in sensor technology and can convert energy forms. ?
According to its manufacturing process, sensors can be divided into:
Integrated sensor? Thin film sensor? Thick film sensor? Ceramic sensor
Integrated sensors are manufactured by standard technology for producing silicon-based semiconductor integrated circuits. Usually, some circuits used for preliminary processing of measurement signals are also integrated on the same chip. ?
The thin film sensor is formed by a thin film of a corresponding sensitive material deposited on a dielectric substrate (substrate). When a hybrid process is used, a part of the circuit can also be fabricated on the substrate. ?
Thick-film sensor is made by coating the slurry of the corresponding material on a ceramic substrate usually made of Al2O3, and then heat-treating it to form a thick film.
Ceramic sensors are produced by standard ceramic technology or some variant technologies (sol-gel, etc.). ).？
After the proper preparation operation is completed, the molded parts are sintered at high temperature. There are many similarities between thick film technology and ceramic sensor technology. In some aspects, thick film technology can be considered as a variant of ceramic technology. ?
Each technology has its own advantages and disadvantages. Due to the low investment in R&D and production and the high stability of sensor parameters, it is more reasonable to use ceramic and thick film sensors.
[Edit this paragraph] Static characteristics of sensor
The static characteristic of sensor refers to the relationship between output and input of sensor for static input signal. Because the input and output have nothing to do with time, the relationship between them, that is, the static characteristics of the sensor can be described by an algebraic equation without time variables, or by a characteristic curve drawn with the input as the abscissa and the corresponding output as the ordinate. The main parameters that characterize the static characteristics of the sensor are linearity, sensitivity, resolution and hysteresis.
[Edit this paragraph] Sensor dynamic characteristics
The so-called dynamic characteristics refer to the characteristics of the output of the sensor when its input changes. In practical work, the dynamic characteristics of the sensor are often expressed by its response to some standard input signals. This is because the response of the sensor to the standard input signal can be easily obtained by experiments, and there is a certain relationship between its response to the standard input signal and its response to any input signal, and the latter can often be inferred by knowing the former. The most commonly used standard input signals are step signal and sine signal, so the dynamic characteristics of the sensor are also commonly expressed by step response and frequency response.
[Edit this paragraph] Linearity of sensor
Usually, the actual static characteristic output of the sensor is a curve rather than a straight line. In practical work, in order to make the instrument have a unified calibration reading, a fitting straight line is often used to approximate the actual characteristic curve, and linearity (nonlinear error) is a performance index of this approximation.
There are many ways to choose a fitting straight line. For example, the theoretical straight line connecting zero input and full-scale output points is used as a fitting straight line; Or the theoretical straight line with the smallest sum of squares of deviations of each point on the characteristic curve is regarded as the fitting straight line, which is called the least square fitting straight line.
[Edit this paragraph] Sensitivity of sensor
Sensitivity refers to the ratio of output change △y to input change △x of the sensor under steady-state working conditions.
It is the slope of the output-input characteristic curve. If there is a linear relationship between the output and the input of the sensor, the sensitivity S is constant. Otherwise it will change with the change of input.
The dimension of sensitivity is the ratio of the dimensions of output and input. For example, when the displacement of the displacement sensor changes 1mm and the output voltage changes by 200mV, its sensitivity should be expressed as 200 mv/mm.
When the output and input of the sensor are the same size, the sensitivity can be understood as the magnification.
Improve the sensitivity and obtain higher measurement accuracy. But the higher the sensitivity, the narrower the measuring range and the worse the stability.
[Edit this paragraph] Resolution of the sensor
Resolution refers to the sensor's ability to feel the smallest measurement change. That is, if the input quantity changes slowly from a non-zero value. When the input change value does not exceed a certain value, the output of the sensor will not change, that is, the sensor cannot distinguish the change of this input. Only when the input changes beyond the resolution will its output change.
Usually, the resolution of each point of the sensor is different in the full-scale range, so the maximum change value of the input quantity that can make the output change step by step in the full-scale range is often used as the index to measure the resolution. If the above indicators are expressed as a percentage of full scale, it is called resolution. The resolution is negatively correlated with the stability of the sensor.
[Edit this paragraph] Resistance sensor
Resistance sensor is a device that converts the measured physical quantities such as displacement, deformation, force, acceleration, humidity and temperature into resistance values. There are mainly resistance strain, piezoresistance, thermal resistance, thermal sensitivity, gas sensitivity, humidity sensitivity and other resistance sensing devices.
[Edit this paragraph] Resistance strain sensor
The resistance strain gauge in the sensor has the strain effect of metal, that is, it produces mechanical deformation under the action of external force, which makes the resistance value change accordingly. There are two kinds of resistance strain gage: metal and semiconductor. Metal strain gauges are divided into wire type, foil type and membrane type. Semiconductor strain gauges have the advantages of high sensitivity (usually dozens of times that of wire and foil) and small lateral effect.
[Edit this paragraph] piezoresistive sensor
Piezoresistive sensor is a device that makes diffusion resistance on semiconductor substrate according to the piezoresistive effect of semiconductor material. Its substrate can be directly used as a measuring sensor, and the diffusion resistor is connected in the substrate in the form of a bridge. When the substrate is deformed by external force, the resistance value will change and the bridge will produce corresponding unbalanced output.
Substrates (or diaphragms) used as piezoresistive sensors are mainly silicon wafers and germanium wafers. Silicon piezoresistive sensor with silicon wafer as sensitive material has attracted more and more attention, especially the solid-state piezoresistive sensor used to measure pressure and speed is the most widely used.
[Edit this paragraph] Thermal resistance sensor
Thermal resistance sensor mainly uses the characteristics of resistance value changing with temperature to measure temperature and temperature-related parameters. This sensor is suitable for occasions with high temperature detection accuracy. At present, platinum, copper, nickel and other thermal resistance materials widely used have the characteristics of large temperature coefficient of resistance, good linearity, stable performance, wide temperature range and easy processing. Used to measure the temperature in the range of -200℃ ~+500℃.
[Edit this paragraph] Temperature sensor
1, room temperature tube temperature sensor:
The room temperature sensor is used to measure the indoor and outdoor ambient temperature, and the tube temperature sensor is used to measure the tube wall temperature of evaporator and condenser. The room temperature sensor and the tube temperature sensor have different shapes, but the temperature characteristics are basically the same. According to the temperature characteristics, there are two kinds of room temperature tube temperature sensors currently used in Midea: 1, constant B value 4100k 3%, reference resistance 25℃, and corresponding resistance10k Ω 3%. The higher the temperature, the smaller the resistance; The lower the temperature, the greater the resistance. The farther away from 25℃, the greater the tolerance range of the corresponding resistance; The corresponding resistance tolerance is about 7% at 0℃ and 55℃. However, the resistance tolerance of different suppliers will be different below 0℃ and above 55℃. Attached is a table showing the relationship between the temperature and the resistance of "NKI" sensor (nominal value in the middle, minimum value and maximum value in the left and right respectively):-10 ℃→ (57.1821-62.2756-67.5438+07). -5 ℃→( 48. 1378—46.5725—50.2355)kω； 0 ℃→( 32.88 12—35.2024—37.6537)kω； 5 ℃→( 25.3095—26.8778—28.5 176)kω； 10 ℃→( 19.6624—20.7 184—2 1.8 1 14)kω； 15 ℃→( 15.4099— 16. 155— 16.8383)kω； 20 ℃→( 12. 1779— 12.643 1— 13. 1 144)kω； 30 ℃→( 7.67922—7.97078—8.26595)kω； 35 ℃→( 6. 12564—6.4002 1—6.68 106)kω； 40 ℃→( 4.92 17 1—5. 175 19—5.43683)kω； 45 ℃→( 3.98 164—4.2 1263—4.4530 1)kω； 50 ℃→( 3.24228—3.45097—3.66978)kω； 55 ℃→( 2.65676—2.8442 1—3.042 14)kω； 60 ℃→ (2.18999—2.35774—2.53605) kω. Except for some old products, this type of sensor is used in the room temperature tube temperature sensor used in Midea air conditioner electronic control. The value of constant b is 3470k 1%, the reference resistance is 25℃, and the corresponding resistance is 5kΩ1%. Similarly, the higher the temperature, the smaller the resistance; The lower the temperature, the greater the resistance. The farther away from 25℃, the greater the tolerance range of the corresponding resistance. Attached is the corresponding table of temperature and resistance of "Hokuriku" sensor (nominal value in the middle, minimum value and maximum value in the left and right respectively):-10 ℃→ (22.1498-22.7438+055-23.2829) kω; 0 ℃→( 13.9408— 14.2293— 14.5224)kω； 10 ℃→( 9.0344—9. 18 10—9.3290)kω； 20 ℃→( 6.0 125—6.0850—6. 1579)kω； 30 ℃→( 4.0833—4. 1323—4. 18 15)kω； 40 ℃→( 2.8246—2.8688—2.9 134)kω； 50 ℃→( 1.994 1—2.032 1—2.0706)kω； 60 ℃→ (1.4343—1.4666—1.4994) kω. This kind of sensor is only used in some old products, such as RF7.5WB, T-KFR 120C, KFC23GWY, etc.
2. Exhaust temperature sensor:
The exhaust temperature sensor is used to measure the exhaust temperature at the top of the compressor. The value of constant b is 3950k 3%, and the reference resistance is 90℃, corresponding to a resistance of 5k Ω 3%. Attached is the corresponding table of temperature and resistance of "Japan Zhipu" sensor (nominal value in the middle, minimum value and maximum value in the left and right respectively):-30 ℃→ (823.3-997.1-1206) kω; -20 ℃→( 456.9—542.7—644.2)kω； - 10 ℃→( 263.7—307.7—358.8)kω； 0 ℃→( 157.6— 180.9—207.5)kω； 10 ℃→( 97.09— 109.8— 124.0)kω； 20 ℃→( 6 1.6 1—68.66—76.45)kω； 25 ℃→( 49.59—54.89—60.70)kω； 30 ℃→( 40. 17—44. 17—48.53)kω； 40 ℃→( 26.84—29. 15—3 1.63)kω； 50 ℃→( 18.35— 19.69—2 1. 12)kω； 60 ℃→( 12.80— 13.59— 14.42)kω； 70 ℃→( 9. 107—9.589— 10.05)kω； 80 ℃→( 6.592—6.859—7. 130)kω； 100 ℃→( 3.560—3.702—3.846)kω； 1 10 ℃→( 2.652—2.78 1—2.9 13)kω； 120 ℃→( 2.003—2. 1 17—2.235)kω； 130 ℃→( 1.532— 1.632— 1.736)Kω.
3. Module temperature sensor: The module temperature sensor is used to measure the temperature of frequency conversion module (IGBT or IPM). At present, the model of the temperature sensor used is 602F-3500F, and the reference resistance at 25℃ is 6kΩ1%. The resistance values corresponding to several typical temperatures are-10 ℃→ (25.897—28.623) kω; 0 ℃→( 16.3248— 17.7 164)kω； 50 ℃→( 2.3262—2.5 153)kω； 90 ℃→( 0.667 1—0.7565)Kω.
[Edit this paragraph] Humidity sensor
Polymer capacitive humidity sensors are usually made on insulating substrates made of glass, ceramics, silicon and other materials by screen printing or vacuum coating, and then humidity-sensitive glue is coated on electrodes by dipping or other methods to make capacitive elements. In the atmospheric environment with different relative humidity, the capacitance of the humidity sensor changes regularly because the humidity sensitive film absorbs water molecules, which is the basic mechanism of the humidity sensor. The temperature characteristics of polymer capacitor elements are affected by temperature, not only the dielectric constant ε of polymer as medium and the dielectric constant ε of adsorbed water molecules, but also the geometric size of the elements is affected by the thermal expansion coefficient. According to Debye's theory, the dielectric constant ε of liquid is a dimensionless constant related to temperature and frequency. The ε of water molecule is 78.36 at t = 5℃ and 79.63 at t = 20℃. The relationship between organic matter ε and temperature varies from material to material, and does not completely follow the proportional relationship. In some temperature regions, ε increases with the increase of T, while in some temperature regions, ε decreases with the increase of T.. In the analysis of humidity-sensitive mechanism of polymer humidity-sensitive capacitive elements, most documents think that the dielectric constant of polymer is small, for example, the dielectric constant of polyimide is 3.0-3.8 at low humidity. While that dielectric constant of wat molecules is ten of times that of polymer ε. Therefore, the dielectric constant of the water-absorbing heterogeneous layer after moisture absorption is greatly improved due to the dipole distance of water molecules, which is determined by the additivity of the composite dielectric constant of multiphase media. Due to the change of ε, the capacitance c of humidity-sensitive capacitive element is proportional to the relative humidity. It is difficult to establish the full humidity range linearity of humidity sensing characteristics in the design and manufacturing process. As a capacitor, the thickness d of polymer dielectric film and the effective area s of flat capacitor are also related to temperature. The change of medium geometry caused by temperature change will affect C value. The average thermal expansion coefficient of polymers can reach orders of magnitude. For example, the average thermal expansion coefficient of nitrocellulose is 108x 10-5/℃. With the increase of temperature, the thickness d of dielectric film increases, which has a negative contribution to c; However, the expansion of the humidity-sensitive film increases the adsorption of water by the medium, which is a positive contribution to C. It can be seen that the temperature characteristics of the humidity-sensitive capacitor are dominated by many factors, and the temperature drift is different in different humidity ranges. It has different temperature coefficients in different temperature regions; Different humidity-sensitive materials have different temperature characteristics. In a word, the temperature coefficient of polymer humidity sensor is not a constant, but a variable. Therefore, in general, the sensor manufacturer can linearize the sensor in the range of-10-60 degrees Celsius to reduce the influence of temperature on the humidity sensor.
High-quality products mainly use polyamide resin. The product structure is summarized as follows: vacuum evaporation of gold-plated electrodes on borosilicate glass or sapphire substrate, then spraying a planar humidity-sensitive film in the form of humidity-sensitive dielectric material (as mentioned above), and then evaporation of gold-plated electrodes on the film. The capacitance of the humidity sensor is proportional to the relative humidity, and the linearity is about 2%. Although the humidity measurement performance is ok, the temperature resistance and corrosion resistance are not ideal. In the industrial field, the service life, temperature resistance, stability and corrosion resistance need to be further improved.
Ceramic humidity sensor is a new type of sensor developed vigorously in recent years. The advantages are high temperature resistance, humidity lag, fast response speed, small volume and convenience for mass production. However, due to the porous material, which has a great influence on dust and frequent daily maintenance, it often needs to be cleaned by electric heating, which easily affects the product quality and humidity. The poor linearity in low humidity and high temperature environment, especially the short service life and poor long-term reliability, is an urgent problem for this kind of humidity sensor.
At present, in the development and research of humidity sensor, resistance humidity sensor should be the most suitable for humidity control. Its representative product, lithium chloride humidity sensor, has many important advantages such as stability, temperature resistance and long service life. Lithium chloride humidity sensor has more than 50 years of production and research history, and there are many product types and manufacturing methods, all of which apply the advantages of lithium chloride humidity sensitive liquid, especially the strongest stability.
Lithium chloride humidity sensitive device belongs to electrolyte humidity sensitive material. Among many humidity-sensitive materials, lithium chloride electrolyte humidity-sensitive liquid first attracted people's attention and was used to manufacture humidity-sensitive devices. The equivalent conductance of lithium chloride electrolyte humidity-sensitive liquid decreases with the increase of solution concentration. Electrolyte is dissolved in water to reduce the water vapor pressure on the water surface.
The substrate structure of lithium chloride humidity sensor is divided into columnar and dressing-like, and the humidity-sensitive liquid and gold electrode with lithium chloride polyvinyl alcohol coating as the main components are the three components of lithium chloride humidity sensor. Over the years, product manufacturing has been continuously improved and product performance has been continuously improved. The unique long-term stability of lithium chloride humidity sensor is irreplaceable by other humidity sensitive materials, and it is also the most important performance of humidity sensor. In the process of product production, the preparation of humidity-sensitive mixture and strict control of process are the keys to maintain and exert this characteristic.
The concept of 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 (biofilm) and physical or chemical transducers (sensors), which can convert signals expressed by biological activities into electrical signals. They are combined together to reprocess biological signals with modern microelectronics and automation instrument technology, thus forming various available biosensor analysis devices, instruments and systems.
The principle of biosensor
The substance to be detected enters the bioactive material through diffusion and undergoes molecular recognition and biological reaction. The generated information is converted into a quantifiable and processable electrical signal by the corresponding physical or chemical sensor, and then amplified and output by the secondary instrument, so that the concentration of the substance to be measured can be known.
Classification of biosensors
According to the classification of living substances used by its receptors, it can be divided into microbial sensors, immune sensors, tissue sensors, cell sensors, enzyme sensors, DNA sensors and so on.
According to the detection principle of sensor devices, it can be divided into: thermosensitive biosensor, field effect tube biosensor, piezoelectric biosensor, optical biosensor, acoustic channel biosensor, enzyme electrode biosensor, mediator biosensor and so on.
According to the types of interactions between biologically sensitive substances, they can be divided into affinity type and metabolic type.
UVA- 12 10 is a near-ultraviolet photoelectric sensor, which has no response in the visible range, and the output current has a linear relationship with the ultraviolet index. Suitable for mobile phones, PDA, MP4 and other portable mobile products to measure the ultraviolet index, and remind people (especially ladies) of the intensity of ultraviolet rays at any time and pay attention to sun protection. It is also suitable for ultraviolet band detectors and ultraviolet index detectors.
uv sensor/transducer
■ Electrical characteristics
Adopting gallium nitride-based materials;
PIN photodiode;
Photovoltaic working mode;
No response to visible light;
Low dark current;
The output current has a linear relationship with the ultraviolet index.
Comply with EU RoHS directive, lead-free and cadmium-free.
■ Typical application
Measurement of ultraviolet index: mobile phones, digital cameras, MP4, PDA, GPS and other portable mobile products;
Used for ultraviolet detectors: full ultraviolet band detector, single UV-A band detector, ultraviolet index detector, ultraviolet germicidal lamp irradiation detector.
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