What types of sensors are there?

(1) resistance type

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.

(2) Frequency conversion power supply

The variable frequency power sensor samples the input voltage and current signals through alternating current, and then connects the sampled values with the digital input secondary instrument through transmission systems such as cables and optical fibers. Digital input secondary instrument calculates the sampled values of voltage and current, and can obtain parameters such as voltage effective value, current effective value, fundamental voltage, fundamental current, harmonic voltage, harmonic current, active power, fundamental power and harmonic power.

(3) Weighing

The weighing sensor is a mechanical-electrical conversion device that converts gravity into electrical signals, and it is a key component of electronic weighing instrument.

There are many kinds of sensors to realize electromechanical conversion, such as resistance strain type, electromagnetic force type and capacitance type. Electromagnetic force type is mainly used in electronic balance, capacitance type is used in some electronic hanging scales, and most weighing instruments use resistance strain type weighing sensors. The invention has the advantages of simple structure, high precision and wide application, and can be used in relatively harsh environment. Therefore, the resistance strain gauge load cell has been widely used in weighing instruments.

(4) Resistance strain type

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.

(5) piezoresistive type

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.

(6) Thermal resistance

Thermal resistance temperature measurement is based on the characteristic that the resistance value of metal conductor increases with the increase of temperature. Thermal resistors are mostly made of pure metal materials. At present, platinum and copper are the most widely used materials. In addition, materials such as nickel, manganese and rhodium have been used to manufacture thermal resistors.

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. The widely used thermal resistance materials are platinum, copper, nickel and so on. They 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℃.

Classification of thermal resistance sensors:

1, NTC thermal resistance sensor:

This sensor is a negative temperature coefficient sensor, that is, the resistance of the sensor decreases with the increase of temperature.

2.PTC thermal resistance sensor:

This sensor is a positive temperature coefficient sensor, that is, the resistance of the sensor increases with the increase of temperature.

(7) Laser

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.

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.

Using the characteristics of high directivity, high monochromaticity and high brightness of laser, non-contact long-distance measurement can be realized. Laser sensors are often used to measure physical quantities such as length (ZLS-Px), distance (LDM4x), vibration (ZLDS 10X), speed (LDM30x) and orientation, and can also be used for flaw detection and monitoring of air pollutants.

(8) Hall

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 Hall effect experiment can be used to judge the conductivity type, carrier concentration, carrier mobility and other important parameters of semiconductor materials.

Hall sensors are divided into linear Hall sensors and switching Hall sensors.

1, linear Hall sensor is composed of Hall element, linear amplifier and emitter follower, and outputs analog quantity.

2. The switch-type Hall sensor is composed of voltage regulator, Hall element, differential amplifier, Schmidt trigger and output stage, which outputs digital quantity.

Hall voltage varies with the change of magnetic field strength. The stronger the magnetic field, the higher the voltage, the weaker the magnetic field and the lower the voltage. Hall voltage is very small, usually only a few millivolts, but it can be amplified by an amplifier in an integrated circuit to output a strong signal. If Hall IC plays a sensing role, it needs to change the magnetic field strength by mechanical means. The method shown in the figure below is to use a rotating impeller as a switch to control the magnetic flux. When the impeller blade is located in the air gap between the magnet and the Hall ic, the magnetic field deviates from the IC and the Hall voltage disappears. In this way, the change of the output voltage of Hall IC can indicate a certain position of the impeller drive shaft. Using this working principle, Hall IC chip can be used as ignition timing sensor. Hall effect sensor is a passive sensor, which can only work with external power supply, which makes it possible to detect low-speed operation.

(9) Temperature

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, Midea uses two kinds of room temperature tube temperature sensors: 1. The value of constant b is 4100k 3%, and the reference resistance is10k ω 3% at 25℃. 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℃. 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, with a constant b of 3950k 3% and a reference resistance of 5k Ω 3% at 90℃.

3. Module temperature sensor: The module temperature sensor is used to measure the temperature of frequency conversion module (IGBT or IPM). The model of the temperature sensor used is 602F-3500F, and the reference resistance is 6kΩ1%at 25℃. 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.

There are many kinds of temperature sensors, including thermal resistance: PT 100, PT 1000, Cu50, Cu100; ; Thermocouple: B, E, J, K, S, etc. There are not only many kinds of temperature sensors, but also various combinations. Choose the right products according to different places.

Principle of temperature measurement: According to the principle that the resistance value of resistor and the potential of thermocouple change regularly with different temperatures, we can get the temperature value we need to measure.

(10) wireless temperature

The wireless temperature sensor converts the temperature parameters of the controlled object into electrical signals, and sends wireless signals to the receiving end to detect, adjust and control the system. It can be directly installed in the junction box of general industrial thermal resistors and thermocouples, forming an integrated structure with on-site sensing elements. It is usually used with wireless relay, receiving terminal, communication serial port and electronic computer. It 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, metallurgical, petroleum, electric power, water treatment, pharmaceutical, food and other automation industries. For example: temperature acquisition on high voltage cable; Temperature collection in harsh environment such as underwater; Temperature acquisition on moving objects; Transmit sensor data in a space that is not easy to connect; The data acquisition scheme selected to reduce the wiring cost; Data measurement in workplaces without AC power supply; Portable data measurement in unfixed places.

(1 1) intelligence

The function of intelligent sensor is put forward by simulating the coordinated action of human senses and brain, combined with long-term test technology research and practical experience. It is a relatively independent intelligent unit, and its appearance reduces the harsh requirements for the original hardware performance, but the performance of the sensor can be greatly improved with the help of software.

1, information storage and transmission-With the rapid development of intelligent distributed control system, intelligent units are required to have communication functions, and two-way communication is carried out in digital form by using communication networks, which is also one of the key signs of intelligent sensors. Intelligent sensors can realize various functions by testing data transmission or receiving instructions. Such as gain setting, compensation parameter setting, internal detection parameter setting and test data output.

2. Self-compensation and calculation function-For many years, engineers and technicians engaged in sensor development have been doing a lot of compensation for temperature drift and output nonlinearity of sensors, but they have not fundamentally solved the problem. The self-compensation and calculation functions of intelligent sensors open up a new way for temperature drift and nonlinear compensation of sensors. In this way, the requirement for the machining accuracy of the sensor is relaxed. As long as the repeatability of the sensor is good, more accurate measurement results can be obtained by using the microprocessor to calculate the test signal through software and using the methods of multiple fitting and differential calculation to compensate the drift and nonlinearity.

3. Self-inspection, self-calibration and self-diagnosis functions-ordinary sensors need to be inspected and calibrated regularly to ensure their sufficient accuracy in normal use. These tasks usually need to remove the sensor from the use site and send it to the laboratory or inspection department. The on-line measurement sensor is abnormal and cannot be diagnosed in time. By using intelligent sensors, this situation has been greatly improved. First, the self-diagnosis function performs a self-test when the power supply is turned on, and performs a diagnostic test to determine whether the component is faulty. Secondly, online calibration can be carried out according to the use time, and the microprocessor uses the measured characteristic data stored in EPROM for comparison and proofreading.

4, compound sensitive function-observe the surrounding natural phenomena, common signals such as sound, light, electricity, heat, force, chemistry, etc. Generally speaking, there are two methods to measure sensitive elements: direct measurement and indirect measurement. Intelligent sensors have multiple functions, which can measure various physical quantities and chemical quantities at the same time, and give information that can fully reflect the motion law of substances.

(12) photosensitive

Photosensitive sensor is one of the most common sensors, which has many kinds, mainly including: photocell, photomultiplier tube, photoresistor, phototransistor, solar cell, infrared sensor, ultraviolet sensor, optical fiber photoelectric sensor, color sensor, CCD and CMOS image sensor. Its sensitive wavelength is near the wavelength of visible light, including infrared wavelength and ultraviolet wavelength. Optical sensors are not only limited to detecting light, but also can be used as detection elements to detect many non-electric quantities, as long as these non-electric quantities are converted into changes of optical signals. Optical sensor is one of the most abundant and widely used sensors at present, which plays a very important role in automatic control and non-electric quantity measurement technology. The simplest photosensitive sensor is a photosensitive resistor, which generates current when photons hit the joints.

(13) Biology

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. All kinds of biosensors have the following common structures: including 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 together to reprocess biological signals with modern microelectronics and automation instrument technology to form 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.

(14) Vision

Vision sensor refers to the ability to capture thousands of pixels of light from the whole image. The clarity and fineness of an image are usually measured by resolution and expressed by pixels.

The vision sensor has thousands of pixels and can capture the light in the whole image. The clarity and fineness of an image are usually measured by resolution and expressed by pixels.

After capturing an image, the vision sensor compares it with a reference image stored in a memory for analysis. For example, if the vision sensor is set to distinguish machine parts with eight bolts inserted correctly, the sensor knows that parts with only seven bolts or parts with misaligned bolts should be rejected. In addition, no matter where the machine part is located in the field of vision, no matter whether the part rotates within 360 degrees, the vision sensor can make a judgment.

The low cost and ease of use of vision sensors have attracted machine designers and process engineers to integrate them into various applications, which used to rely on manpower, multiple photoelectric sensors or no detection at all. Industrial applications of vision sensors include inspection, metrology, measurement, positioning, defect detection and classification. The following are just some application examples:

In the automobile assembly plant, check whether the rubber beads painted on the door frame by the robot are continuous and the width is correct;

In the bottling plant, check whether the bottle cap is sealed properly, whether the filling amount is correct, and whether any foreign matter falls into the bottle before sealing;

On the packaging production line, ensure that the correct packaging label is affixed at the correct position;

In the drug packaging production line, check whether the blister packaging of aspirin tablets is damaged or missing;

In metal stamping company, the inspection speed of stamping parts is more than 150 pieces per minute, which is faster than manual inspection 13 times.

(15) displacement

Displacement sensor, also known as linear sensor, converts displacement into electricity. Displacement sensor is a linear device, which belongs to metal induction. The function of the sensor is to convert various measured physical quantities into electricity. It can be divided into inductive displacement sensor, capacitive displacement sensor, photoelectric displacement sensor, ultrasonic displacement sensor and Hall displacement sensor.

In this conversion process, many physical quantities (such as pressure, flow, acceleration, etc. ) It is often necessary to convert displacement into electricity first. Therefore, the displacement sensor is an important basic sensor. In the production process, displacement measurement is generally divided into physical dimension measurement and mechanical displacement measurement. Mechanical displacement includes linear displacement and angular displacement. According to the different transformation forms of measured variables, displacement sensors can be divided into analog and digital. Analog type can be divided into physical type (such as self-generating type) and structural type. The most commonly used displacement sensors are analog structures, including potentiometer displacement sensor, inductive displacement sensor, synchro, capacitive displacement sensor, eddy current displacement sensor, Hall displacement sensor and so on. An important advantage of digital displacement sensor is that it is convenient to send signals directly to computer system. This kind of sensor develops rapidly and is widely used.

(16) Pressure

Pressure sensor is the most commonly used sensor in industrial practice, which is widely used in various industrial automatic control environments, involving water conservancy and hydropower, railway transportation, intelligent buildings, automatic production control, aerospace, military industry, petrochemical industry, oil wells, electric power, ships, machine tools, pipelines and many other industries.

(17) ultrasonic ranging

Ultrasonic distance sensor adopts the principle of ultrasonic echo ranging, uses accurate time difference measurement technology to detect the distance between sensor and target, and adopts ultrasonic sensor with small angle and small blind area, which has the advantages of accurate measurement, non-contact, waterproof, anti-corrosion and low cost. , and can be applied to liquid level and material level detection. The unique liquid level and material level detection method can ensure stable output even if there is foam or large shaking on the liquid level, and it is not easy to detect echo, so it is applied to industry.

(18) 24 Gigabit Gereda

24GHz radar sensor uses high-frequency microwave to measure the speed, distance, direction and azimuth information of objects, and adopts planar microstrip antenna design, which has the characteristics of small size, light weight, high sensitivity and strong stability, and is widely used in intelligent transportation, industrial control, security, sports, smart home and other industries. On 20 1 10.09, the Ministry of Industry and Information Technology officially issued the Notice of the Ministry of Industry and Information Technology on Releasing the Use Frequency of Short-range Vehicle-mounted Radar Equipment in 24GHz Band (No.[2065438+02] 548 of the Ministry of Industry and Information Technology), in which the specification of short-range vehicle-mounted radar equipment in 24GHz band was clearly put forward.

(XIX) integration temperature

An integrated temperature sensor usually consists of a temperature probe (thermocouple or thermal resistance sensor) and a two-wire solid-state electronic unit. The temperature measuring 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 thermal resistance and thermocouple.

Thermal resistance temperature sensor consists of reference unit, R/V conversion unit, linear circuit, reverse connection protection, current limiting protection and V/I conversion unit. After the thermal resistance signal of temperature measurement is converted and amplified, the nonlinear relationship between temperature and resistance is compensated by linear circuit, and a constant current signal of 4 ~ 20 mA with linear relationship with the measured temperature is output by V/I conversion circuit.

Thermocouple temperature sensor is generally composed of reference source, cold end compensation, amplification unit, linearization processing, V/I conversion, decoupling processing, reverse connection protection, current limiting protection and other circuit units. The thermoelectric potential generated by thermocouple is amplified by cold end compensation, and then the nonlinear error between thermoelectric potential and temperature is eliminated by linear circuit, and finally amplified and converted into 4 ~ 20 mA current output signal. In order to prevent accidents caused by temperature control failure due to thermocouple disconnection, there is also a power-off protection circuit in the sensor. When the thermocouple is damaged or poorly connected, the sensor will output the maximum value (28mA) to cut off the power supply of the instrument. The integrated temperature sensor has the advantages of simple structure, saving lead wires, 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 used in conjunction with microcomputer systems or other conventional instruments. Can also be made into explosion-proof or fire-proof measuring instruments according to user requirements.

(20) liquid level

1, float level sensor

The floating ball type liquid level sensor consists of a magnetic floating ball, a measuring conduit, a signal unit, an electronic unit, a junction box and an installation piece.

The specific gravity of magnetic floating ball is generally less than 0.5, and it can float above the liquid level and move up and down along the measuring conduit. A measuring element is installed in the catheter, which can convert the measured liquid level signal into a resistance signal proportional to the liquid level change under the action of an external magnetic field, and convert the electronic unit into a 4 ~ 20mA or other standard signal for output. The sensor is a modular circuit, which has the advantages of acid resistance, moisture resistance, impact resistance and corrosion resistance. The circuit includes constant current feedback circuit and internal protection circuit, which can make the maximum output current not exceed 28mA, thus reliably protecting the power supply and preventing the secondary instrument from being damaged.

2. Floating liquid level sensor

Float-type liquid level sensor is designed according to Archimedes buoyancy principle by changing magnetic floating ball into buoy. Buoy-type liquid level sensor uses tiny metal film strain sensing technology to measure liquid level, boundary or density. When working, you can press the button on the spot to carry out routine setting operation.

3. Static pressure or liquid level sensor

The sensor works based on the measurement principle of hydrostatic pressure. Generally, a silicon pressure sensor is selected to convert the measured pressure into an electrical signal, which is amplified by an amplifier circuit and compensated by a compensation circuit, and finally output in a current mode of 4 ~ 20ma or 0 ~ 10ma.

(2 1) vacuum degree

Vacuum sensor is produced by advanced silicon micromachining technology, and it is an absolute pressure transmitter with integrated silicon piezoresistive sensor as its core component. The vacuum reference pressure chamber formed by silicon-silicon direct bonding or silicon-Pax glass electrostatic bonding, as well as a series of stress-free packaging technologies and precise temperature compensation technologies, have outstanding advantages of good stability and high precision, and are suitable for absolute pressure measurement and control in various occasions.

Adopt low-range chip vacuum absolute pressure packaging, and the product has high overload capacity. The chip adopts silicone oil filled vacuum isolation and stainless steel film transition pressure, which has excellent medium compatibility, is suitable for measuring the vacuum pressure of most gas-liquid media, and has no corrosion to 3 16L stainless steel. The influence of vacuum degree is suitable for low vacuum measurement and control in various industrial environments.

(22) Capacitance level

Capacitive liquid level sensor is suitable for industrial enterprises to measure and control the production process, which is mainly used for long-distance continuous measurement and indication of the liquid level of conductive and non-conductive media or powder solid.

Capacitive liquid level sensor consists of capacitive sensor and electronic module circuit. Based on double-wire 4 ~ 20 mA constant current output. After conversion, it can be output in three or four wires, and the output signals form standard signals such as 1 ~ 5V, 0 ~ 5V, 0 ~ 100 mA. Capacitance sensor consists of insulated electrode and cylindrical metal container filled with measuring medium. When the material level rises, because the dielectric constant of non-conductive materials is obviously lower than that of air, the capacitance changes with the material height. The module circuit of the sensor consists of reference source, pulse width modulation, conversion, constant current amplification, feedback and current limiting. The advantages of using the principle of pulse width modulation are low frequency, radio frequency interference to surrounding components, good stability, good linearity and no obvious temperature drift.

(XXIII) Acidity of antimony electrode

Antimony electrode acidity sensor is an industrial on-line analytical instrument integrating PH detection, automatic cleaning and electrical signal conversion. It is a PH measuring system composed of antimony electrode and reference electrode. In the acid solution to be tested, an antimony trioxide oxide layer will be formed on the surface of antimony electrode, which will form a potential difference between the metal antimony surface and antimony trioxide. The potential difference depends on the concentration of antimony trioxide, which corresponds to the moderation of hydrogen ions in the acid solution to be measured. If a proper amount of antimony, antimony trioxide and aqueous solution are all regarded as 1, the electrode potential can be calculated by Nernst formula.

The solid module circuit in the antimony electrode acidity sensor consists of two parts. For the safety of field operation, the power supply part uses AC 24V to supply power to the secondary instrument. This power supply not only provides driving power for the cleaning motor, but also converts it into corresponding DC voltage for the transmission circuit through the current conversion unit. The second part is the measuring sensor circuit, which amplifies the reference signal and pH signal from the sensor and sends them to the slope adjustment and positioning adjustment circuit to reduce and adjust the internal resistance of the signal. The amplified PH signal is superimposed with the temperature compensation signal and then sent to the conversion circuit. Finally, the 4 ~ 20mA constant current signal corresponding to the PH value is output to the secondary instrument to display and control the PH value.

(24) Acids, bases and salts

The concentration sensor of acid, alkali and salt determines the concentration by measuring the conductivity of the solution. It can continuously detect the concentration of acid, alkali and salt in aqueous solution in industrial process on line. This sensor is mainly used in industrial production processes such as boiler feed water treatment, chemical solution preparation and environmental protection.

The working principle of acid-base salt concentration sensor is: within a certain range, the concentration of acid-base solution is directly proportional to its conductivity. Therefore, the acid-base concentration can only be known by measuring the conductivity of the solution. When the measured solution flows into a special conductivity cell, it can be equivalent to a pure resistance if the electrode polarization and distributed capacitance are ignored. When constant voltage alternating current flows, its output current has a linear relationship with conductivity, and the conductivity is directly proportional to the concentration of acid and alkali in the solution. So as long as the solution current is measured, the concentrations of acid, alkali and salt can be calculated.

The pH sensor is mainly composed of conductivity cell, electronic module, display instrument and shell. The electronic module circuit consists of excitation power supply, conductance cell, conductance amplifier, phase-sensitive rectifier, demodulator, temperature compensation, overload protection and current conversion.

(25) Conductivity

It is a process instrument (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 electrolyte solution is a good conductor of electricity like metal conductor, there must be resistance when current flows through electrolyte solution, which conforms to ohm's law. However, the temperature resistance of liquid is opposite to that of metal conductor, and it has negative temperature characteristics. In order to distinguish it from metal conductor, the conductivity of electrolyte solution is expressed by conductance (reciprocal of resistance) or conductivity (reciprocal of resistivity). When two mutually insulated electrodes form a conductivity cell, if the solution to be measured is placed in the middle and constant voltage alternating current is applied, a current loop is formed. If the voltage and electrode size are fixed, there is a certain functional relationship between loop current and conductivity. In this way, by measuring the current flowing in the solution to be measured, the conductivity of the solution to be measured can be measured. The structure and circuit of conductivity sensor are the same as those of acid, alkali and salt concentration sensor.

Transducer/sensor (English name: transducer/sensor) is a 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.

Main features:

The characteristics of sensors include miniaturization, digitalization, intelligence, multifunction, systematization and networking. It not only promotes the transformation and upgrading of traditional industries, but also may establish new industries, thus becoming a new economic growth point in 2 1 century. Miniaturization is based on MEMS technology, and has been successfully applied to silicon devices to make silicon pressure sensors.