Introduction to 25 Common Sensor Types
1. Resistive sensor
A resistive sensor is a device that converts these physical quantities to be measured, such as displacement, deformation, force, acceleration, humidity, temperature, etc., into a resistance value. There are mainly resistance strain type, piezoresistive type, thermal resistance, thermal, gas sensitive, humidity sensitive and other resistive sensor devices.
2. Variable frequency power sensor
the variable frequency power sensor performs AC sampling on the input voltage and current signals, and then connects the sampled values with the digital input secondary instrument through transmission systems such as cables and optical fibers. The digital input secondary instrument performs operation on the sampled values of voltage and current to obtain parameters such as voltage effective value, current effective value, fundamental voltage, fundamental current, harmonic voltage, harmonic current, active power, fundamental power, harmonic power, etc.
3. Load cell
the load cell is a force & rarr; electric conversion device that can convert gravity into an electrical signal, and is a key component of an electronic weighing instrument.
Can realize force & rarr; There are many kinds of sensors for electric conversion, common ones are resistive strain type, electromagnetic force type and capacitive type. Electromagnetic force type is mainly used for electronic balance, capacitive type is used for some electronic hanging scales, and the vast majority of weighing products are still used in resistance strain type weighing sensor. The resistance strain weighing sensor has simple structure, high accuracy, wide application, and can be used in relatively poor environments. Therefore, the resistance strain type weighing sensor has been widely used in the weighing instrument.
4. 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, so that the resistance value changes accordingly. There are two main types of resistance strain gauges: metal and semiconductor. Metal strain gauges are divided into metal wire type, foil type and film type. Semiconductor strain gauge has the advantages of high sensitivity (usually dozens of times of wire type and foil type) and small lateral effect.
5. Piezoresistive
A piezoresistive sensor is a device made on a substrate of semiconductor material via a diffused resistor based on the piezoresistive effect of the semiconductor material. The substrate can be directly used as a measuring sensor element, and the diffusion resistor is connected into a bridge form in the substrate. When the substrate is deformed by an external force, each resistance value will change, and the bridge will produce a corresponding unbalanced output. The substrate (or diaphragm) materials used for piezoresistive sensors are mainly silicon wafers and germanium wafers, and silicon piezoresistive sensors made of silicon wafers are becoming more and more important, especially for measuring pressure and speed. The application of solid-state piezoresistive sensors is the most common.
6. Thermal resistance sensor
the thermal resistance temperature measurement is based on the characteristic that the resistance value of the metal conductor increases with the increase of temperature. Most of the thermal resistance is made of pure metal materials, the most widely used is platinum and copper, in addition, has begun to use nickel, manganese and rhodium and other materials to make thermal resistance. The thermal resistance sensor mainly uses the characteristic that the resistance value changes with the temperature to measure the temperature and the parameters related to the temperature. In the temperature detection accuracy requirements are relatively high, this sensor is more suitable. The more extensive thermal resistance materials are platinum, copper, nickel, etc., which have the characteristics of large temperature coefficient of resistance, good linearity, stable performance, wide temperature range, and easy processing. It is used to measure the temperature in the range of -200 ℃ ~ +500 ℃.
7. Laser sensor
sensors for measurement using laser technology. It consists of a laser, a laser detector and a measuring circuit. Laser sensor is a new type of measuring instrument. Its advantage is that it can realize non-contact long-distance measurement, fast speed, high precision, large range, strong anti-light and electrical interference ability, etc.
When the laser sensor works, the laser emitting diode first aims at the target and emits laser pulses. After being reflected by the target, the laser light is scattered in all directions. Some of the scattered light is returned to the sensor receiver, received by the optical system and imaged onto the avalanche photodiode. The avalanche photodiode is an optical sensor with an internal amplification function, so it can detect extremely weak optical signals and convert them into corresponding electrical signals.
The characteristics of high directivity, high monochromaticity and high brightness of laser can be used to realize non-contact long-distance measurement. Laser sensors are often used in the measurement of physical quantities such as length (ZLS-Px), distance (LDM4x), vibration (ZLDS10X), speed (LDM30x), orientation, etc., and can also be used for flaw detection and monitoring of atmospheric pollutants.
8. Hall sensor
hall sensor is a kind of magnetic field sensor based on Hall effect, which is widely used in industrial automation technology, detection technology and information processing. Hall effect is a basic method to study the properties of semiconductor materials. The Hall coefficient measured by the Hall effect experiment can determine the conductivity type, carrier concentration and carrier mobility of the semiconductor material and other important parameters.
Hall sensors are divided into linear Hall sensors and switch-type Hall sensors.
(1) The linear Hall sensor is composed of a Hall element, a linear amplifier and an emitter follower, and it outputs analog quantity.
(2) Switching Hall sensor is composed of voltage regulator, Hall element, differential amplifier, Schmidt trigger and output stage, which outputs digital quantity.
9. 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 the evaporator and condenser. The shape of the room temperature sensor and the tube temperature sensor are different, but the temperature characteristics are basically the same. According to the temperature characteristics, there are two types of room temperature tube temperature sensors used by the United States: 1. The constant B value is 4100K 3%, and the reference resistance is 25 ℃, corresponding to the resistance 10KΩ 3%. The corresponding resistance tolerance at 0 ℃ and 55 ℃ is about ± 7%; while below 0 ℃ and above 55 ℃, the resistance tolerance will vary for different suppliers. 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.
(2) Exhaust temperature sensor: The exhaust temperature sensor is used to measure the exhaust temperature at the top of the compressor. The constant B value is 3950K 3%, and the reference resistance is 90 ℃, corresponding to the resistance 5KΩ 3%.
(3) Module temperature sensor: The module temperature sensor is used to measure the temperature of the frequency conversion module (IGBT or IPM). The type of temperature sensing head used is 602F-3500F, and the reference resistance is 25 ℃, corresponding to the resistance of 6KΩ 1%. The corresponding resistance values for several typical temperatures are:-10 ℃ & rarr;(25.897~28.623)KΩ;0 ℃ & rarr;(16.3248~17.7164)KΩ;50 ℃ & rarr;(2.3262~2.5153)KΩ;90 ℃ & rarr;(0.6671~0.7565)KΩ.
There are many types of temperature sensors, and thermal resistors are often used: PT100, PT1000, Cu50, Cu100; Thermocouple: B, E, J, K, S, etc. Temperature sensor is not only a wide variety, but also a variety of combinations, should be based on different places to choose the right product.
Temperature measurement principle: According to the principle that the resistance value and the potential of the thermocouple change regularly with the temperature, we can get the temperature value that needs to be measured.
10. Wireless temperature sensor
the wireless temperature sensor changes the temperature parameter of the control object into an electrical signal, and sends a wireless signal to the receiving terminal to detect, adjust and control the system. It can be directly installed in the junction box of general industrial thermal resistance and thermocouple, and forms an integrated structure with the field sensing element. It is usually used with wireless relay, receiving terminal, communication serial port, electronic computer, etc., which not only saves compensation wires and cables, but also reduces signal transmission distortion and interference, thus obtaining high-precision measurement results. Wireless temperature sensors are widely used in chemical, metallurgy, petroleum, electric power, water treatment, pharmaceutical, food and other automation industries. For example: temperature acquisition on high-voltage cables; Temperature acquisition in harsh environments such as underwater; Temperature acquisition on moving objects; Space transmission sensor data that is not easy to connect; Data acquisition scheme selected simply to reduce wiring cost; Data measurement in workplaces without AC power supply; Data measurement in portable non-fixed places.
11. Smart sensors
A smart sensor is a sensor with an information processing function. Intelligent sensor with microprocessor, with the ability to collect, process and exchange information, is the product of the combination of sensor integration and microprocessor. Compared with general sensors, smart sensors have the following three advantages: high-precision information collection can be achieved through software technology, and the cost is low; it has certain programming automation capabilities; and its functions are diversified. Smart sensor is a relatively independent intelligent unit, its emergence of the original hardware performance requirements have been reduced, and software help can make the performance of the sensor greatly improved.
12. Photosensitive sensor
photosensitive sensor is one of the most common sensors. It has a wide variety, mainly including: photoelectric tube, photomultiplier tube, photoresistor, phototransistor, solar cell, infrared sensor, ultraviolet sensor, optical fiber photoelectric sensor, color sensor, CCD and CMOS image sensor, etc. Its sensitive wavelengths are near visible wavelengths, including infrared wavelengths and ultraviolet wavelengths. The light sensor is not limited to the detection of light, it can also be used as a detection element to form other sensors to detect many non-electric quantities, as long as these non-electric quantities are converted into changes in optical signals. Optical sensor is one of the most output and widely used sensors, which plays a very important role in automatic control and non-electrical measurement technology. The simplest photosensitive sensor [2] is a photoresistor, which generates a current when a photon strikes the junction.
13. Biosensors
biosensor is an interdisciplinary subject which combines biologically active materials (enzyme, protein, DNA, antibody, antigen, biofilm, etc.) with physical and chemical transducer. It is an advanced detection method and monitoring method essential for the development of biotechnology, and it is also a rapid and micro analysis method at the molecular level. Various biosensors have the following common structure: including one or more related biologically active materials (biofilms) and physical or chemical transducers (sensors) that can convert signals expressed by biological activities into electrical signals. The two are combined together to perform biological signal reprocessing using modern microelectronics and automated instrumentation technology to form various biosensor analysis devices, instruments and systems that can be used.
Classification of biosensors
according to the classification of life substances used in their receptors, they can be divided into: microbial sensors, immunosensors, tissue sensors, cell sensors, enzyme sensors, DNA sensors, and so on.
According to the principle of sensor device detection, it can be divided into: thermal biosensor, field effect tube biosensor, piezoelectric biosensor, optical biosensor, acoustic channel biosensor, enzyme electrode biosensor, mediator biosensor, etc.
According to the type of biological sensitive substance interaction, it can be divided into two types: affinity type and metabolic type.
14. Vision sensor
vision sensors have thousands of pixels that capture light from an entire image. The clarity and delicacy of an image is usually measured in terms of resolution, expressed in terms of the number of pixels. After capturing the image, the vision sensor compares it with a reference image stored in memory to make an analysis. For example, if the vision sensor is set to recognize a machine component with eight bolts correctly inserted, the sensor knows that it should reject a component with only seven bolts, or a component with misaligned bolts. In addition, no matter where the machine part is located in the field of view, the vision sensor can make a determination whether the part is rotating within a 360 degree range.
15. Displacement sensor
displacement sensors, also known as linear sensors, convert displacement into electricity. The displacement sensor is a linear device that belongs to metal induction. The function of the sensor is to convert various measured physical quantities into electricity. It is divided into inductive displacement sensors, capacitive displacement sensors, photoelectric displacement sensors, ultrasonic displacement sensors, and Hall Type displacement sensor. In this conversion process, there are many physical quantities (such as pressure, flow, acceleration, etc.) that often need to be transformed into displacement first, and then the displacement is transformed into electricity. So displacement sensor is a kind of important basic sensor. In the production process, the measurement of displacement is generally divided into two kinds: measuring physical size and mechanical displacement. Mechanical displacement includes linear displacement and angular displacement. According to the form of the measured variable transformation, the displacement sensor can be divided into analog and digital. The analog type can be divided into two types: physical type (such as self-generating type) and structural type. Commonly used displacement sensors are mostly analog structure types, including potentiometer displacement sensors, inductive displacement sensors, self-aligning machines, capacitive displacement sensors, eddy current displacement sensors, Hall displacement sensors, etc. An important advantage of digital displacement sensors is the ease of sending signals directly to a computer system. This kind of sensor develops rapidly and is widely used.
16. Pressure sensor
Pressure sensor is the most commonly used sensor in industrial practice. It is widely used in various industrial automatic control environments, involving water conservancy and hydropower, railway transportation, intelligent building, production automatic control, aerospace, military industry, petrochemical, oil well, electric power, Ships, machine tools, pipelines and many other industries.
17. Ultrasonic distance sensor
the ultrasonic distance measuring sensor adopts the principle of ultrasonic echo distance measurement and accurate time difference measurement technology to detect the distance between the sensor and the target. It adopts a small angle and small blind area ultrasonic sensor, which has the advantages of accurate measurement, no contact, waterproof, anti-corrosion, low cost, etc. It can be applied to liquid level, material level detection, unique liquid level and material level detection methods to ensure foam or large shaking on the liquid level, it is not easy to detect the echo in the case of stable output, application industry: liquid level, material level, material level detection, industrial process control, etc.
18.24GHz radar sensor
the 24GHz radar sensor uses high-frequency microwave to measure the speed, distance, direction of movement, and azimuth angle information of an object. It adopts a planar microstrip antenna design and has the characteristics of small size, light weight, high sensitivity, and strong stability. It is widely used in intelligent transportation, Industrial control, security, sports, smart home and other industries. On November 19, 2012, the Ministry of Industry and Information Technology officially issued the "Notice of the Ministry of Industry and Information Technology on Issuing the Use Frequency of Short-distance Vehicle-mounted Radar Equipment in the 24GHz Band" (No. 548 of the Ministry of Industry and Information Technology [2012]), which clearly proposed the 24GHz band Short-distance vehicle-mounted radar equipment is the specification for vehicle-mounted radar equipment.
19. Integrated temperature sensor
the integrated temperature sensor is generally composed of a temperature measuring probe (thermocouple or thermal resistance sensor) and a two-wire solid electronic unit. The temperature measurement probe is directly installed in the junction box in the form of a solid module to form an integrated sensor. Integrated temperature sensors are generally divided into two types: thermal resistance and thermocouple type.
The thermal resistance temperature sensor is composed of reference unit, R/V conversion unit, linear circuit, reverse connection protection, current limiting protection, V/I conversion unit, etc. After the temperature measurement thermal resistance signal is converted and amplified, the nonlinear relationship between temperature and resistance is compensated by a linear circuit, and a 4 ~ 20mA constant current signal which is linear with the measured temperature is output after the V/I conversion circuit.
Thermocouple temperature sensor is generally composed of reference source, cold junction compensation, amplification unit, linearization processing, V/I conversion, broken couple processing, reverse connection protection, current limiting protection and other circuit units. It is the thermal potential generated by the thermocouple by the cold end compensation amplification, and then the cap by the linear circuit to eliminate the thermal potential and temperature of the nonlinear error, and finally amplified into 4 ~ 20mA current output signal. In order to prevent accidents caused by temperature control failure due to broken wires in thermocouple measurements, the sensor is also equipped with a power-off protection circuit. When the thermocouple wire is broken or the connection is not good, the sensor will output the maximum value (28mA) to make the instrument cut off the power supply. The integrated temperature sensor has the advantages of simple structure, saving leads, large output signal, strong anti-interference ability, good linearity, simple display instrument, solid module seismic and moisture-proof, reverse connection protection and current limiting protection, and reliable operation. The output of the integrated temperature sensor is a unified 4 ~ 20mA signal; it can be matched with a microcomputer system or other conventional instruments. It can also be made into explosion-proof or fire-proof measuring instruments as required by users.
20. Liquid level sensor
the liquid level sensor (static pressure level gauge/liquid level transmitter/liquid level sensor/water level sensor) is a pressure sensor that measures the liquid level. The static pressure input type liquid level transmitter (liquid level gauge) is based on the principle that the measured static pressure of the liquid is proportional to the height of the liquid. It uses foreign advanced isolated diffused silicon sensitive elements or ceramic capacitive pressure sensitive sensors to convert the static pressure into electrical signals, which are then converted into standard electrical signals (generally 4 ~ 20mA/1 ~ 5VDC) through temperature compensation and linear correction. It is divided into two categories: one is contact type, including single flange static pressure/double flange differential pressure liquid level transmitter, float type liquid level transmitter, magnetic liquid level transmitter, input type liquid level transmitter, electric internal float liquid level transmitter, electric float liquid level transmitter, capacitive liquid level transmitter, magnetostrictive liquid level transmitter, servo liquid level transmitter, etc. The second category is non-contact, divided into ultrasonic level transmitter, radar level transmitter and so on.
21. Vacuum sensor
the vacuum sensor is produced by advanced silicon micro-machining technology and the absolute pressure transmitter made of integrated silicon piezoresistive sensor as the core component of the sensor. Due to the vacuum reference pressure chamber formed by silicon-silicon direct bonding or silicon-pyroxel glass electrostatic bonding, and a series of stress-free packaging technology and precision temperature compensation technology, it has the outstanding advantages of excellent stability and high precision, it is suitable for the measurement and control of absolute pressure in various situations.
22. Capacitive level sensor
capacitive level sensor is suitable for industrial enterprises to measure and control the production process in the production process, mainly used for long-distance continuous measurement and indication of the liquid level or powder solid level of conductive and non-conductive media. The capacitive liquid level sensor is composed of a capacitive sensor and an electronic module circuit. It uses a two-wire 4 ~ 20mA constant current output as the base type. After conversion, it can be output in a three-wire or four-wire manner. The output signal is formed as 1~5V, 0~5V, 0 ~ 10mA and other standard signals. The capacitive sensor consists of an insulated electrode and a cylindrical metal container containing the measuring medium. When the level rises, the dielectric constant of the non-conductive material is significantly less than the dielectric constant of air, so the capacitance changes with the height of the material. The module circuit of the sensor consists of reference source, pulse width modulation, conversion, constant current amplification, feedback and current limiting units. The advantages of using the pulse width modulation principle for measurement are low frequency, radio frequency interference to the surrounding elements, good stability, good linearity, and no obvious temperature drift.
23. Antimony electrode acidity sensor
antimony electrode acidity sensor is an industrial on-line analytical instrument integrating PH detection, automatic cleaning and electrical signal conversion. It is a PH value measurement system composed of antimony electrode and reference electrode. In the acid solution to be tested, the antimony trioxide layer will be generated on the surface of the antimony electrode, so that a potential difference will be formed between the metal antimony surface and the antimony trioxide. The magnitude of this potential difference depends on the concentration of the three antimony oxides, which corresponds to the moderation of hydrogen ions in the acid solution being measured. If the moderation of antimony, antimony trioxide and aqueous solution is regarded as 1, the electrode potential can be calculated by the Nester formula. The solid module circuit in the antimony electrode acidity sensor is composed of two parts. For the safety of the field function, the power supply part adopts AC 24V to supply power for the secondary instrument. In addition to providing driving power for the cleaning motor, this power supply should also be converted into the corresponding DC voltage through the current conversion unit for the use of the transmission circuit. The second part is the measurement sensor circuit, which is from the sensor of the reference signal and PH acidity signal after amplification to the slope adjustment and positioning adjustment circuit, so that the signal resistance is reduced and adjustable. The amplified PH signal and the temperature compensated signal are superimposed and then added into the conversion circuit, and finally the 4 ~ 20mA constant current signal corresponding to the PH value is output to the secondary instrument to complete the display and control of the PH value.
24. Acid, alkali and salt sensor
acid, base, salt concentration sensors determine concentration by measuring solution conductance values. It can continuously detect the concentration of acid, alkali and salt in aqueous solution in the industrial process. It is mainly composed of conductivity cell, electronic module, display meter and shell. The electronic module circuit is composed of excitation power supply, conductivity cell, conductivity amplifier, phase-sensitive rectifier, demodulator, temperature compensation, overload protection and current conversion units. This sensor is mainly used in boiler water treatment, chemical solution preparation and environmental protection and other industrial production processes. The working principle of the acid, alkali, and salt concentration sensor is: within a certain range, the concentration of the acid-base solution is proportional to its conductivity. Therefore, as long as the size of the conductivity of the solution is measured, the concentration of acid and base can be known. When the measured solution flows into the dedicated conductivity cell, it can be equivalent to a pure resistance if the electrode polarization and distributed capacitance are ignored. When a constant voltage alternating current flows through, its output current is linearly related to the conductivity, and the conductivity is proportional to the concentration of acid and alkali in the solution. Therefore, as long as the solution current is measured, the concentration of acid, alkali and salt can be calculated.
25. Conductivity sensor
conductivity sensors are sensors that are used to measure the conductivity of various solutions such as ultrapure water, pure water, drinking water, sewage, etc. or the concentration of overall ions in water samples in the laboratory, industrial production and detection fields. It is a process meter (integrated sensor) that indirectly measures the ion concentration by measuring the conductivity value of the solution, and can continuously detect the conductivity of the aqueous solution in the industrial process online. Because the electrolyte solution is the same as a good conductor of electricity as a metal conductor, there must be resistance when the current flows through the electrolyte solution, and it conforms to Ohm's law. However, the resistance temperature characteristic of the liquid is opposite to that of the metal conductor and has a negative temperature characteristic. In order to distinguish it from the metal conductor, the conductivity of the electrolyte solution is expressed by conductance (the reciprocal of resistance) or conductivity (the reciprocal of resistivity). When two electrodes insulated from each other form a conductivity cell, if the solution to be measured is placed in the middle of it and a constant voltage alternating current is passed, a current loop is formed. If the voltage and electrode size are fixed, there is a certain functional relationship between the loop current and the conductivity. In this way, the conductivity of the solution to be measured can be measured by measuring the current flowing in the solution to be measured. The structure and circuit of the conductivity sensor is the same as that of the acid, alkali and salt concentration sensor.
