sensor

1 Definition

The national standard GB7665-87 defines the sensor as follows: “A device or device that can sense a specified part to be measured and convert it into a usable signal according to a certain law (a mathematical function rule), usually consisting of a sensitive element and a conversion element”.

The China Internet of Things school-enterprise alliance believes that the presence and development of sensors will allow objects to have senses such as touch, taste, and smell, allowing objects to gradually become alive. ”

"Sensors" are defined in the New Wexar dictionary as: "Receive power from one system, usually sending power to devices in the second system in another form."

2 main role

In order to obtain information from the outside world, people must rely on sensory organs.

And relying solely on people’s own sensory organs, their function in the study of natural phenomena and laws and production activities is far from enough. To meet this situation, sensors are needed. Therefore, it can be said that the sensor is an extension of human features, also known as electrical features.

With the arrival of the new technology revolution, the world has begun to enter the information age. In the process of using information, the first thing to solve is to obtain accurate and reliable information, and sensors are the main means and means for acquiring information in the natural and production fields.

In modern industrial production, especially in the automated production process, various sensors are used to monitor and control the various parameters in the production process so that the equipment can be operated in a normal state or an optimal state, and the products can achieve the best quality. Therefore, it can be said that without numerous excellent sensors, modern production loses its foundation.

In the study of basic disciplines, sensors have a more prominent position. The development of modern science and technology has entered many new fields: for example, macroscopic observations of the vast universe of thousands of light years, microcosmic observations of particle worlds as small as fm, and longitudinal observation of the evolution of celestial bodies for hundreds of thousands of years Short response to s. In addition, there have also emerged various kinds of extreme technological researches that have an important role in deepening the understanding of materials, developing new energy, and new materials, such as ultra-high temperature, ultra-low temperature, ultra-high pressure, ultra-high vacuum, super magnetic field, and ultra-weak magnetic field. Obviously, to get a lot of information that human senses cannot directly obtain, there is no suitable sensor. Obstacles to many basic scientific researches are the difficulty in obtaining object information. The emergence of some new mechanisms and high-sensitivity detection sensors will often lead to breakthroughs in this field. The development of some sensors is often a pioneer in the development of some marginal disciplines.

Sensors have already penetrated into an extremely wide range of fields such as industrial production, space development, ocean exploration, environmental protection, resource investigation, medical diagnosis, biological engineering, and even cultural heritage protection. It is no exaggeration to say that from the vastness of space, to the vast oceans, to a variety of complex engineering systems, almost every modern project can not be separated from a variety of sensors.

This shows that the important role of sensor technology in economic development and social progress is very obvious. All countries in the world attach great importance to the development of this field. It is believed that in the near future, sensor technology will take a leap forward and reach a new level commensurate with its important position.

3 main features

The characteristics of the sensors include: miniaturization, digitization, intelligence, multi-functionalization, systematization, and networking. It not only promotes the transformation and replacement of traditional industries, but also creates new industries, thus becoming a new economic growth in the 21st century. point. Miniaturization is based on micro-electro-mechanical system (MEMS) technology. Silicone pressure sensors have been successfully applied to silicon devices.

4 main functions

The function of the sensor is often compared with the human 5 sense organs:

Photosensors - Vision

Acoustic sensor - hearing

Gas Sensor - Olfactory

Chemical Sensors - Taste

Pressure sensitive, temperature sensitive,

Fluid Sensor - Touch

Classification of sensitive components:

Physics, based on physical effects such as force, heat, light, electricity, magnetism, and sound.

Chemicals, based on the principle of chemical reactions.

Biological class, based on molecular recognition functions such as enzymes, antibodies, and hormones.

Usually based on its basic sense of function can be divided into thermal elements, photosensitive elements, gas sensors, force sensors, magnetic sensors, humidity sensors, acoustic sensors, radiation sensitive devices, color sensors and taste sensitive components, etc. Classes (and others have classified sensitive elements into 46 categories).

5 common types of resistance

A resistive sensor is a device that converts physical quantities such as displacement, deformation, force, acceleration, humidity, and temperature into resistance values. Mainly resistance strain type, piezoresistive type, thermal resistance, heat sensitive, gas sensitive, moisture sensitive and other resistive sensors.

Frequency conversion power

The frequency conversion power sensor conducts ac sampling on the input voltage and current signals, and then connects the sampling value with a digital input secondary instrument through a transmission system such as a cable or an optical fiber. The digital input secondary instrument calculates the voltage and current sampling values. Can obtain voltage RMS, current rms, fundamental voltage, fundamental current, harmonic voltage, harmonic current, active power, fundamental power, harmonic power and other parameters.

Weighing

The load cell is a force → electrical conversion device that can convert gravity into an electrical signal and is a key component of the electronic scale.

There are many types of sensors that can achieve force-to-electrical conversion. The common ones are resistance strain type, electromagnetic force type, and capacitance type. Electromagnetic force type is mainly used in electronic balances, and capacitive type is used in some electronic hanging scales. The vast majority of weighing instruments use resistance strain type load cells. The resistance strain type load cell has a simple structure, high accuracy, wide application range, and can be used in a relatively poor environment. Therefore, the resistance strain load cell has been widely used in instruments.

Resistance strain type

The strain gage in the sensor has a strain effect on the metal, that is, it generates a mechanical deformation under the action of an external force, thereby causing a corresponding change in the resistance value. Resistance strain gauges mainly include two kinds of metals and semiconductors. Metal strain gauges are classified into metal wire type, foil type, and film type. Semiconductor strain gauges have the advantages of high sensitivity (usually tens of times that of wire and foil type) and small lateral effects.

Piezoresistive

A piezoresistive sensor is a device made by diffusion resistance of a semiconductor material substrate based on the piezoresistive effect of a semiconductor material. The substrate can be directly used as a measuring sensor element, and the diffusion resistor is formed in the form of a bridge in the substrate. When the substrate is deformed by an external force, the resistance will change and the bridge will produce a corresponding unbalanced output.

The substrate (or diaphragm) used as a piezoresistive sensor is mainly composed of silicon wafers and tantalum wafers. Silicon piezoresistive sensors made of silicon as sensitive materials are receiving more and more attention, especially in measuring pressure. Solid-state piezoresistive sensors with speed and speed are most commonly used.

Thermal resistance

Thermal resistance temperature measurement is based on the characteristic that the resistance value of a metal conductor increases as the temperature increases.

Most of the thermal resistance is made of pure metal materials. Currently, platinum and copper are the most widely used materials. In addition, nickel, manganese, and tantalum have been used to manufacture thermal resistors.

Thermistor sensors measure the temperature and temperature-related parameters by taking advantage of the fact that resistance changes with temperature. This sensor is suitable for applications where the accuracy of temperature detection is relatively high. The wide range of thermal resistance materials are platinum, copper, nickel, etc. They have the characteristics of large temperature coefficient of resistance, good linearity, stable performance, wide operating temperature range, and easy processing. Used to measure temperatures in the range of -200°C to +500°C.

Thermal resistance sensor classification:

1, NTC thermal resistance sensor:

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

2, PTC thermal resistance sensor:

This type of sensor is a positive temperature coefficient sensor, that is, the resistance of the sensor increases as the temperature increases.

laser

Sensors that measure using laser technology.

It consists of a laser, a laser detector and a measuring circuit. The laser sensor is a new type of measuring instrument. Its advantages are that it can realize non-contact long-distance measurement, high speed, high precision, large range, and strong resistance to light and electricity. When the laser sensor is working, the laser emitting diode is aimed at the target emitting laser pulse. The target reflected laser light scattered in all directions. Part of the scattered light is returned to the sensor receiver, which is received by the optical system and imaged onto an avalanche photodiode. An avalanche photodiode is an optical sensor with an internal amplification function, so it can detect extremely weak light signals and convert them into corresponding electrical signals.

The use of lasers with high directionality, high monochromaticity and high brightness enables contactless distance measurements. Laser sensors are commonly used for measuring physical quantities such as length (ZLS-Px), distance (LDM4x), vibration (ZLDS10X), velocity (LDM30x), azimuth, etc., and can also be used for flaw detection and air pollutant monitoring.

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 the basic method for studying the properties of semiconductor materials. The Hall coefficient measured by the Hall effect experiment can determine important parameters such as conductivity type, carrier concentration, and carrier mobility of the semiconductor material.

Hall sensors are classified into linear Hall sensors and switch Hall sensors.

1. The linear Hall sensor consists of a Hall element, a linear amplifier, and an emitter follower, which outputs an analog quantity.

2. The switch Hall sensor consists of a voltage regulator, a Hall element, a differential amplifier, a Schmitt trigger, and an output stage. It outputs a digital quantity.

The Hall voltage changes with the change of the magnetic field strength. The stronger the magnetic field, the higher the voltage, the weaker the magnetic field and the lower the voltage. The Hall voltage is very small, typically only a few millivolts, but it can be amplified by an amplifier in an integrated circuit to produce a strong signal. If Hall ICs are used for sensing, it is necessary to use mechanical methods to change the magnetic field strength. The method shown in the following figure uses a rotating impeller as a switch to control the magnetic flux. When the impeller blade is in the air gap between the magnet and the Hall IC, the magnetic field deviates from the integrated chip and the Hall voltage disappears. In this way, the change of the output voltage of the Hall IC can indicate a certain position of the impeller drive shaft. Using this working principle, the Hall IC chip can be used to act on the ignition timing sensor. Hall effect sensors are passive sensors that require an external power source to operate. This feature makes it possible to detect low operating speeds.

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 wall temperature of the evaporator and the 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 Midea: 1. The constant B value is 4100K±3%, and the reference resistance is 25°C corresponding resistance 10KΩ±3%. The tolerances for the resistors at 0°C and 55°C are approximately ±7%. For resistors below 0°C and 55°C, the tolerance of the resistors will be different. The higher the temperature, the smaller the resistance; the lower the temperature, the greater the resistance. The further away from 25°C, the larger the corresponding resistance tolerance range.

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°C corresponding resistance 5KΩ±3%.

3. Module temperature sensor: The module temperature sensor is used to measure the temperature of the inverter module (IGBT or IPM). The type of the temperature sensor head used is 602F-3500F and the reference resistor is 25°C corresponding resistor 6KΩ±1%. The corresponding resistance of several typical temperatures are: -10°C→(25.897─28.623)KΩ; 0°C→(16.3248─17.7164)KΩ; 50°C→(2.3262─2.5153)KΩ; 90°C→(0.6671─0.7565) KΩ.

There are many kinds of temperature sensors, often used thermal resistance: PT100, PT1000, Cu50, Cu100; thermocouple: B, E, J, K, S and so on. The temperature sensors are not only diverse in variety, but also in a variety of combinations, and suitable products should be selected according to different locations.

Principle of temperature measurement: According to the principle that the resistance of the resistor and the potential of the thermocouple change regularly with temperature, we can obtain the measured temperature value.

Wireless temperature

The wireless temperature sensor converts the temperature parameter of the control object into an electrical signal and sends a wireless signal to the receiving terminal to perform detection, adjustment, and control of the system. It can be directly installed in the junction boxes of general industrial thermal resistance and thermocouples, and it is integrated with the on-site sensing elements. It is usually used together with wireless relay, receiving terminal, communication serial port, electronic computer, etc. This not only saves compensation wires and cables, but also reduces signal transmission distortion and interference, and thus obtains 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 cables; temperature acquisition in harsh environments such as underwater; temperature acquisition on moving objects; transmission of sensor data in spaces that are difficult to pass through; data acquisition schemes that are purely used to reduce wiring costs; no AC power supply Workplace data measurement; Portable non-stationary data measurement.

intelligent

The function of the smart sensor is proposed by simulating human sensory and brain coordination actions, combined with long-term research and practical experience in test technology. Is a relatively independent smart unit, its emergence of the original hardware performance requirements have been reduced, while the help of software can greatly improve the performance of the sensor.

1, information storage and transmission - with the rapid development of smart distributed control system (SmartDistributedSystem), the smart unit requires a communication function, the use of communication networks for digital two-way communication, which is one of the key indicators of smart sensors. Smart sensors implement various functions by testing data transmission or receiving instructions. Such as gain setting, compensation parameter setting, internal inspection parameter setting, test data output, etc.

2. Self-compensation and calculation functions—Engineers and technicians engaged in sensor development for many years have been doing a lot of compensation work for sensor temperature drift and output nonlinearity, but they have not solved the problem fundamentally. The self-compensation and calculation functions of smart sensors open up a new path for sensor temperature drift and nonlinear compensation. In this way, to relax the sensor processing precision, as long as the repeatability of the sensor can be ensured, the signal of the test signal is calculated by the microprocessor through software, and the drift and the nonlinearity are compensated by the multiple fitting and the difference calculation method, so that the Get more accurate measurement pressure sensors.

3, self-test, self-school, self-diagnosis function - ordinary sensors need regular inspection and calibration, to ensure that it is sufficient accuracy in normal use, these tasks generally require the sensor to be disassembled from the use of the site to the laboratory or inspection department get on. If the online measurement sensor is abnormal, it cannot be diagnosed in time. The situation with smart sensors is greatly improved. First, the self-diagnosis function performs self-test when the power is turned on, and diagnostic tests are performed to determine whether the components are faulty. Secondly, it can be calibrated on-line according to the time of use. The microprocessor uses the metering characteristic data stored in the EPROM for comparison and proofreading.

4, compound sensitive function - observe the surrounding natural phenomena, common signals sound, light, electricity, heat, force, chemistry and so on. Sensing element measurements generally take two forms: direct and indirect measurements. The smart sensor has a complex function that can simultaneously measure a variety of physical and chemical quantities, giving information that can fully reflect the law of motion of the material.

Photosensitive

Photosensitive sensor is one of the most common sensors. It has a wide range of types, including photocells, photomultipliers, photoresistors, phototransistors, solar cells, infrared sensors, ultraviolet sensors, fiber optic sensors, color sensors, and CCDs. CMOS image sensors, etc. Its sensitive wavelength is near the visible light wavelength, including infrared wavelength and ultraviolet wavelength. The optical sensor is not limited to the detection of light. It can also be used as a detection element to form other sensors and detect many non-electrical quantities. It is only necessary to convert these non-electrical quantities into changes in the optical signal. Optical sensor is one of the most widely used and most widely used sensors at present. It plays a very important role in automatic control and non-electricity measurement. The simplest photosensitive sensor is a photoresistor, which generates current when the photons strike the junction.

biological

Biosensor concept

Biosensors are an interdisciplinary subject that combines biologically active materials (enzymes, proteins, DNA, antibodies, antigens, biofilms, etc.) and physico-chemical transducers. It is an advanced detection method that is essential for the development of biotechnology. And monitoring methods are also fast and micro-analytical methods for the molecular level of matter. Various types of biosensors have the following common structures: one or more related bioactive materials (biofilms) and physical or chemical transducers (sensors) capable of converting signals expressed by bioactivity into electrical signals. Together, the reprocessing of biological signals using modern microelectronics and automated instrumentation technologies constitutes a variety of biosensor analysis devices, instruments, and systems that can be used.

The principle of biosensors

The substance to be tested enters the biologically active material through diffusion and undergoes a biological reaction through molecular recognition. The resulting information is then converted into a quantifiable and processable electrical signal by a corresponding physical or chemical transducer, and then amplified by the secondary instrument. And output, you can know the analyte concentration.

Classification of biosensors

According to the classification of living substances used in its receptors, it can be divided into: microbial sensors, immunosensors, tissue sensors, cell sensors, enzyme sensors, DNA sensors, and the like.

Classification according to the principle of sensor device detection, can be divided into: thermal biosensor, FET biosensor, piezoelectric biosensor, optical biosensor, acoustic channel biosensor, enzyme electrode biosensor, mediator biosensor and so on.

According to the type of interaction of biologically sensitive substances, they can be divided into two types: affinity type and metabolic type.

Vision

working principle:

The visual sensor refers to the ability to capture thousands of pixels from a whole image, and the resolution of the image is usually measured in terms of the number of pixels.

Vision sensors have thousands of pixels that capture light from an entire image. The clarity and sophistication of an image is usually measured in terms of resolution, expressed in number of pixels.

After the image is captured, the vision sensor compares it with a reference image stored in memory for analysis. For example, if the vision sensor is set to identify a machine part with eight bolts correctly inserted, the sensor knows that only seven bolts should be rejected, or that the bolts are misaligned. In addition, the visual sensor can make a decision regardless of the position of the machine component in the field of view, whether or not the component rotates within 360 degrees.

Application area:

The low cost and ease of use of vision sensors has attracted machine designers and process engineers to integrate them into a variety of applications that have relied on labor, multiple photo sensors, or have not been tested at all. Industrial applications of vision sensors include inspection, metrology, measurement, orientation, helium detection, and delivery. The following are just a few examples of applications:

At the automobile assembly plant, check whether the plastic beads applied to the door frame by the robot are continuous and have the correct width.

At the bottling plant, verify that the cap is properly sealed, that the fill level is correct, and that no foreign objects have fallen into the bottle prior to capping;

In the packaging line, ensure that the correct packaging label is affixed to the correct location;

In the pharmaceutical packaging line, whether there are broken or missing tablets in the blister pack of aspirin tablets;

In the metal stamping company, stamped parts are inspected at a speed of more than 150 sheets per minute, which is 13 times faster than manual inspection.

Displacement

Displacement sensor, also known as a linear sensor, converts displacement into a sensor of electrical quantity. Displacement sensor is a kind of linear device that belongs to metal induction. The function of sensor is to convert various measured physical quantities into electricity. It is divided into inductive displacement sensor, capacitive displacement sensor, photoelectric displacement sensor, ultrasonic displacement sensor, Hall. Displacement sensor.

In this conversion process there are many physical quantities (such as pressure, flow, acceleration, etc.) often need to be transformed into displacement, and then convert the displacement into electricity. Therefore, the displacement sensor is an important basic sensor. In the production process, the displacement measurement is generally divided into measuring the physical size and the mechanical displacement. Mechanical displacements include line and angular displacements. According to the different forms of measured variables, displacement sensors can be divided into analog and digital two. Simulation can be divided into physical (such as self-generating) and structural two. Commonly used displacement sensors are mostly analog ones, including potentiometer-type displacement sensors, inductive displacement sensors, self-segment anglers, capacitive displacement sensors, eddy current displacement sensors, and Hall-type displacement sensors. An important advantage of a digital displacement sensor is that it facilitates the direct feeding of signals into computer systems. This sensor has developed rapidly and has become more widely used.

pressure

Pressure sensor cited is the most commonly used sensor in industrial practice. It is widely used in various industrial automation environments, involving water conservancy and hydropower, railway transportation, intelligent buildings, production automation, aerospace, military, petrochemical, oil wells, electricity, ships, Machine tools, pipelines and many other industries.

Ultrasonic distance measurement

The ultrasonic distance measuring sensor adopts the principle of ultrasonic echo distance measurement. It uses precise time difference measurement technology to detect the distance between the sensor and the target. It adopts a small angle, small blind ultrasonic sensor with accurate measurement, no contact, waterproof and anti-corrosion. The advantages of low cost, such as liquid level, level detection, unique liquid level, material level detection method, can ensure that there is foam or large shaking on the liquid surface, and there is a stable output when the echo is not easily detected. Application industry: level, level, material level detection, industrial process control, etc.

24GHz radar

24GHz radar sensor uses high-frequency microwaves to measure the speed, distance, and movement of objects

RFbeam 24GHz Radar Sensor

The direction and azimuth angle information adopts the planar microstrip antenna design, featuring small size, light weight, high sensitivity, and strong stability. It is widely used in intelligent transportation, industrial control, security, sports, and smart home industries. On November 19, 2012, the Ministry of Industry and Information Technology formally released the "Ministry of Industry and Information Technology Released a Notice Concerning the Release of Vehicle-mounted Radar Equipment Usage Frequencies at Short Range from the 24GHz Frequency Band" (Ministry of Industry and Information Technology No. No. [2012] No. 548), which explicitly stated that the 24 GHz band is short-range. Car radar equipment as a vehicle radar equipment specification.

Integrated temperature

Integrated temperature sensors generally consist of a temperature probe (thermocouple or RTD sensor) and two-wire solid state electronics. The solid-state module is used to mount the temperature probe directly in the junction box to form an integrated sensor. Integrated temperature sensors are generally classified into two types: thermal resistance and thermocouple type.

Thermal resistance temperature sensor is composed of reference unit, R/V conversion unit, linear circuit, reverse connection protection, current limit protection, V/I conversion unit and so on. After the temperature-resistor resistance signal is converted and amplified, the linear circuit compensates the nonlinear relationship between the temperature and the resistance. After the V/I conversion circuit, a constant current signal of 4-20 mA which is in a linear relationship with the measured temperature is output.

Thermocouple temperature sensor is generally composed of a reference source, cold junction compensation, amplification unit, linearization, V / I conversion, burnout processing, reverse connection protection, current limiting protection and other circuit units. It is the thermal potential generated by the thermocouple through the cold-end compensation after amplification, and then cap 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 galvanic disconnection in thermocouple measurement, a power failure protection circuit is also provided in the sensor. When the thermocouple breaks or fails to connect, the sensor will output the maximum value (28mA) to make the meter cut off the power. The integrated temperature sensor has the advantages of simple structure, saving lead wire, large output signal, strong anti-interference ability, good linearity, simple display instrument, solid module moisture resistance, reverse connection protection and current limit protection, and reliable work. The output of the integrated temperature sensor is a unified 4-20mA signal; it can be used with a microcomputer system or other conventional instruments. Can also be made of explosion-proof or fire-proof measuring instruments.

Liquid level

1、Floating ball level sensor

The float level sensor is composed of a magnetic float, a measurement catheter, a signal unit, an electronic unit, a junction box, and a mounting member.

Generally, the specific gravity of the magnetic float is less than 0.5, and it can float on the liquid surface and move up and down along the measuring tube. The catheter is equipped with a measuring element, which can convert the measured liquid level signal into a resistance signal proportional to the change of liquid level under the action of external magnetic flux, and converts the electronic unit into 4-20 mA or other standard signal output. The sensor is a module circuit, which has the advantages of acid resistance, moisture resistance, shockproof, anti-corrosion, etc. The circuit contains a constant current feedback circuit and an internal protection circuit, so that the maximum output current does not exceed 28mA, so it can reliably protect the power supply and make the secondary instrument Not damaged.

2, floating type liquid level sensor

The buoyancy level sensor is to change the magnetic float to buoy, which is designed according to the Archimedes buoyancy principle. Float type liquid level sensors use tiny metal film strain sensing technology to measure liquid level, boundary level, or density. It can use the on-site buttons to perform routine setup operations while working.

3, static pressure or liquid level sensor

The sensor works with the principle of hydrostatic pressure measurement. It generally selects the silicon pressure pressure sensor to convert the measured pressure into an electric signal, and then compensates by the amplifying circuit and the compensating circuit, and finally outputs the current by 4-20 mA or 0-10 mA.

Vacuum degree

Vacuum level sensor, manufactured using advanced silicon micromachining technology, is an absolute pressure transmitter made of a silicon pressure resistive element as the core element of the sensor due to the use of silicon-silicon direct bonding or silicon-pyrox glass static electricity The vacuum reference pressure chamber formed by bonding, and a series of non-stressed encapsulation technologies and precision temperature compensation technologies have excellent advantages of excellent stability and high precision, and are suitable for measurement and control of absolute pressure in various situations.

Features and uses

Low-capacity chip vacuum vacuum package, the product has a high overload capacity. The chip is vacuum-filled with silicone oil, and the stainless steel film transfers pressure with excellent media compatibility. It is suitable for vacuum pressure measurement of most gas-liquid media that are not corroded by 316L stainless steel. The degree of vacuum is used to infect low vacuum measurement and control in various industrial environments.

Capacitive level

Capacitive level sensor is suitable for industrial enterprises to measure and control the production process during the production process. It is mainly used as a continuous measurement and indication for remote distances of liquid level or powdered solid material level in 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 constant current output of 4 to 20 mA as a basic type. After conversion, it can be output in a three-wire or four-wire mode, and the output signal is formed as 1 to 5 V. 0 ~ 5V, 0 ~ 10mA and other standard signals. The capacitive sensor consists of an insulated electrode and a cylindrical metal vessel equipped with a measuring medium. When the material level rises, the dielectric constant of the non-conductive material is significantly smaller than the dielectric constant of air, so the capacitance changes with the height of the material. The module circuit of the sensor is composed of reference source, pulse width modulation, conversion, constant current amplification, feedback and current limiting units. The advantage of using the pulse width modulation principle to measure is that it has a low frequency, interference with ambient radio frequency, good stability, good linearity, and no significant temperature drift.

Electrode acidity

The 锑 electrode acidity sensor is an industrial on-line analysis instrument that integrates PH detection, automatic cleaning, and electrical signal conversion. It is a PH value measurement system consisting of a helium electrode and a reference electrode. In the measured acidic solution, a germanium trioxide oxide layer is formed on the surface of the germanium electrode, so that a potential difference is formed between the germanium surface and the germanium oxide. The magnitude of this potential difference depends on the concentration of trioxotide, which corresponds to the appropriate level of hydrogen ions in the acidic solution being tested. If the appropriateness of yttrium, yttria and aqueous solution is taken as 1, the electrode potential can be calculated using the Nernst formula.

The solid module circuit in the pH sensor consists of two major components. For the sake of safety in the field, the power supply uses AC 24V to power the secondary instrument. In addition to supplying power to the cleaning motor, this power supply should also be converted into a corresponding DC voltage by the current conversion unit for use by the transmission circuit. The second part is the measurement sensor circuit, which sends the reference signal from the sensor and PH acidity signal to the slope adjustment and positioning adjustment circuit after amplification, so that the signal internal resistance can be reduced and can be adjusted. The amplified PH signal and the temperature compensated signal are superposed and then converted into the conversion circuit. Finally, the 4-20 mA constant current signal corresponding to the PH value is output to the secondary meter to complete the display and control the PH value.

Acid, alkali, salt

The acid, alkali, and salt concentration sensors determine the concentration by measuring the conductance of the solution. It can continuously monitor the concentration of acid, alkali and salt in aqueous solution in the industrial process. 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 sensors is that within a certain range, the concentration of the acid-base solution is proportional to the size of its electrical conductivity. Therefore, as long as the measurement of the conductivity of the solution changes, the concentration of acid and alkali can be known. When the measured solution flows into a dedicated conductivity cell, if the electrode polarization and distributed capacitance are ignored, it can be equivalent to a pure resistance. When there is a constant voltage alternating current flowing, the output current is linear with 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.

The acid, alkali, and salt concentration sensors mainly consist of a conductivity cell, an electronic module, a display head, and a housing. The electronic module circuit is composed of excitation power supply, conductivity cell, conductance amplifier, phase sensitive rectifier, demodulator, temperature compensation, overload protection and current conversion.

Conductance

It is a process meter (integrated sensor) that measures the ion concentration indirectly by measuring the conductance value of a solution, and can continuously detect the conductivity of an aqueous solution in an industrial process on-line.

Because the electrolyte solution is the same good electrical conductor as the metal conductor, there must be an electrical resistance when the current flows through the electrolyte solution, and it is in accordance with Ohm's law. However, the resistance temperature characteristics of liquids are contrary to those of metal conductors and have negative temperature characteristics. In order to distinguish from the metal conductor, the conductivity of the electrolyte solution is represented by conductance (reciprocal of resistance) or conductivity (reciprocal of resistivity). When two electrodes that are insulated from each other form a conductivity cell, a current loop is formed if the solution to be measured is placed in between, and a constant voltage alternating current is passed through. If the voltage size and the electrode size are fixed, the loop current and the conductivity have a certain function. In this way, measuring the current flowing in the solution to be measured, the conductivity of the solution to be measured can be measured. The conductivity sensor has the same structure and circuit as the acid, alkali, and salt concentration sensors.

6 major classification by purpose

Pressure sensitive and force sensitive sensors, position sensors, level sensors, energy sensors, speed sensors, acceleration sensors, ray radiation sensors, thermal sensors.

By principle

Vibration sensor, humidity sensor, magnetic sensor, gas sensor, vacuum sensor, biosensor, etc.

Press output signal

Analog sensors: Convert the non-electrical quantities that are measured into analog electrical signals.

Digital Sensors: Convert the measured non-electrical quantities into digital output signals (including direct and indirect conversions).

膺 digital sensor: The amount of signal to be measured is converted to the output of a frequency signal or short-cycle signal (including direct or indirect conversion).

Switch sensor: When a measured signal reaches a certain threshold, the sensor outputs a set low or high signal accordingly.

According to its manufacturing process

Integrated sensors are manufactured using standard process technologies for producing silicon-based semiconductor integrated circuits.

Parts of the circuits that are used to initially process the measured signal are also typically 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 using a hybrid process, some circuits can also be fabricated on this substrate.

The thick film sensor is made by coating a ceramic substrate with a slurry of a corresponding material. The substrate is usually made of Al2O3 and then heat-treated to form a thick film.

Ceramic sensors are produced using a standard ceramic process or some variant process (sol, gel, etc.).

After an appropriate preliminary operation is completed, the formed element is sintered at a high temperature. There are many common characteristics between the two processes of thick film and ceramic sensor. In some aspects, it can be considered that the thick film process is a variation of the ceramic process.

Each process technology has its own advantages and disadvantages. Due to the low capital investment required for research, development and production, as well as the high stability of sensor parameters, it is reasonable to use ceramic and thick-film sensors.

By measurement

Physical sensors are made using properties where the physical properties of the material being measured change significantly.

Chemical sensors are made using sensitive elements that convert the chemical composition and concentration into electrical quantities.

Biosensors are sensors that use various biological or biological properties to detect and identify chemical constituents in living organisms.

According to its composition

Basic sensor: It is the most basic single transducer.

Combination sensor: A sensor that consists of a combination of different individual transducers.

Application sensor: A sensor that is a combination of a basic sensor or a combination sensor and other mechanisms.

According to the form of action

按作用形式可分为主动型和被动型传感器。

主动型传感器又有作用型和反作用型，此种传感器对被测对象能发出一定探测信号，能检测探测信号在被测对象中所产生的变化，或者由探测信号在被测对象中产生某种效应而形成信号。检测探测信号变化方式的称为作用型，检测产生响应而形成信号方式的称为反作用型。雷达与无线电频率范围探测器是作用型实例，而光声效应分析装置与激光分析器是反作用型实例。

被动型传感器只是接收被测对象本身产生的信号，如红外辐射温度计、红外摄像装置等。

7主要特性传感器静态

传感器的静态特性是指对静态的输入信号，传感器的输出量与输入量之间所具有相互关系。因为这时输入量和输出量都和时间无关，所以它们之间的关系，即传感器的静态特性可用一个不含时间变量的代数方程，或以输入量作横坐标，把与其对应的输出量作纵坐标而画出的特性曲线来描述。表征传感器静态特性的主要参数有：线性度、灵敏度、迟滞、重复性、漂移等。

1、线性度：指传感器输出量与输入量之间的实际关系曲线偏离拟合直线的程度。定义为在全量程范围内实际特性曲线与拟合直线之间的最大偏差值与满量程输出值之比。

2、灵敏度：灵敏度是传感器静态特性的一个重要指标。其定义为输出量的增量与引起该增量的相应输入量增量之比。用S表示灵敏度。

3、迟滞：传感器在输入量由小到大（正行程）及输入量由大到小（反行程）变化期间其输入输出特性曲线不重合的现象成为迟滞。对于同一大小的输入信号，传感器的正反行程输出信号大小不相等，这个差值称为迟滞差值。

4、重复性：重复性是指传感器在输入量按同一方向作全量程连续多次变化时，所得特性曲线不一致的程度。

5、漂移：传感器的漂移是指在输入量不变的情况下，传感器输出量随着时间变化，此现象称为漂移。产生漂移的原因有两个方面：一是传感器自身结构参数；二是周围环境（如温度、湿度等）。

6、分辨力：当传感器的输入从非零值缓慢增加时，在超过某一增量后输出发生可观测的变化，这个输入增量称传感器的分辨力，即最小输入增量。

7、阈值：当传感器的输入从零值开始缓慢增加时，在达到某一值后输出发生可观测的变化，这个输入值称传感器的阈值电压。

传感器动态

所谓动态特性，是指传感器在输入变化时，它的输出的特性。在实际工作中，传感器的动态特性常用它对某些标准输入信号的响应来表示。这是因为传感器对标准输入信号的响应容易用实验方法求得，并且它对标准输入信号的响应与它对任意输入信号的响应之间存在一定的关系，往往知道了前者就能推定后者。最常用的标准输入信号有阶跃信号和正弦信号两种，所以传感器的动态特性也常用阶跃响应和频率响应来表示。

线性度

通常情况下，传感器的实际静态特性输出是条曲线而非直线。在实际工作中，为使仪表具有均匀刻度的读数，常用一条拟合直线近似地代表实际的特性曲线、线性度（非线性误差）就是这个近似程度的一个性能指标。

拟合直线的选取有多种方法。如将零输入和满量程输出点相连的理论直线作为拟合直线；或将与特性曲线上各点偏差的平方和为最小的理论直线作为拟合直线，此拟合直线称为最小二乘法拟合直线。

Sensitivity

灵敏度是指传感器在稳态工作情况下输出量变化△y对输入量变化△x的比值。

它是输出一输入特性曲线的斜率。如果传感器的输出和输入之间显线性关系，则灵敏度S是一个常数。否则，它将随输入量的变化而变化。

灵敏度的量纲是输出、输入量的量纲之比。例如，某位移传感器，在位移变化1mm时，输出电压变化为200mV，则其灵敏度应表示为200mV/mm。

当传感器的输出、输入量的量纲相同时，灵敏度可理解为放大倍数。

提高灵敏度，可得到较高的测量精度。但灵敏度愈高，测量范围愈窄，稳定性也往往愈差。

分辨率

分辨率是指传感器可感受到的被测量的最小变化的能力。也就是说，如果输入量从某一非零值缓慢地变化。当输入变化值未超过某一数值时，传感器的输出不会发生变化，即传感器对此输入量的变化是分辨不出来的。只有当输入量的变化超过分辨率时，其输出才会发生变化。

通常传感器在满量程范围内各点的分辨率并不相同，因此常用满量程中能使输出量产生阶跃变化的输入量中的最大变化值作为衡量分辨率的指标。上述指标若用满量程的百分比表示，则称为分辨率。分辨率与传感器的稳定性有负相相关性。

8选型原则

To carry out a specific measurement work, we must first consider the principle of the use of sensors, which need to analyze many factors before you can determine. Because, even if it is to measure the same physical quantity, there are many kinds of principle sensors available for selection. Which kind of principle sensor is more appropriate, we need to consider the following specific problems according to the characteristics of the measured and the use conditions of the sensor: the size of the range; The measured position of the sensor volume requirements; measurement method for contact or non-contact; signal extraction method, wired or non-contact measurement; sensor source, domestic or imported, the price can withstand, or self-developed.

After considering the above issues, it is possible to determine which type of sensor to use, and then consider the specific performance indicators of the sensor.

The choice of sensitivity

Generally, in the linear range of the sensor, it is desirable that the sensitivity of the sensor is as high as possible. Because only the sensitivity is high, the value of the output signal corresponding to the measured change is relatively large, which is advantageous for signal processing. However, it should be noted that the sensitivity of the sensor is high, and external noise that is not related to the measurement is easily mixed in, and it is also amplified by the amplification system, which affects the measurement accuracy.因此，要求传感器本身应具有较高的信噪比，尽量减少从外界引入的干扰信号。

The sensitivity of the sensor is directional. When it is measured as a single vector and its directionality is higher, sensors with small sensitivity in other directions should be selected; if the measured is a multidimensional vector, the cross sensitivity of the sensor is required to be as small as possible.

频率响应特性

传感器的频率响应特性决定了被测量的频率范围，必须在允许频率范围内保持不失真。实际上传感器的响应总有—定延迟，希望延迟时间越短越好。

传感器的频率响应越高，可测的信号频率范围就越宽。

在动态测量中，应根据信号的特点（稳态、瞬态、随机等）响应特性，以免产生过大的误差。

Linear range

The linear range of the sensor refers to the range of the output proportional to the input. In theory, in this range, the sensitivity remains constant. The wider the linear range of the sensor, the larger the range, and can guarantee a certain measurement accuracy. When selecting a sensor, when the type of the sensor is determined, it first depends on whether or not the range satisfies the requirement.

But in fact, any sensor cannot guarantee absolute linearity, and its linearity is also relative. When the required measurement accuracy is relatively low, within a certain range, the sensor with smaller nonlinear error can be approximated as linear, which will bring great convenience to the measurement.

稳定性

传感器使用一段时间后，其性能保持不变的能力称为稳定性。影响传感器长期稳定性的因素除传感器本身结构外，主要是传感器的使用环境。因此，要使传感器具有良好的稳定性，传感器必须要有较强的环境适应能力。

在选择传感器之前，应对其使用环境进行调查，并根据具体的使用环境选择合适的传感器，或采取适当的措施，减小环境的影响。

传感器的稳定性有定量指标，在超过使用期后，在使用前应重新进行标定，以确定传感器的性能是否发生变化。

在某些要求传感器能长期使用而又不能轻易更换或标定的场合，所选用的传感器稳定性要求更严格，要能够经受住长时间的考验。

精度

精度是传感器的一个重要的性能指标，它是关系到整个测量系统测量精度的一个重要环节。传感器的精度越高，其价格越昂贵，因此，传感器的精度只要满足整个测量系统的精度要求就可以，不必选得过高。这样就可以在满足同一测量目的的诸多传感器中选择比较便宜和简单的传感器阿特拉斯空压机配件。

如果测量目的是定性分析的，选用重复精度高的传感器即可，不宜选用绝对量值精度高的；如果是为了定量分析，必须获得精确的测量值，就需选用精度等级能满足要求的传感器。

对某些特殊使用场合，无法选到合适的传感器，则需自行设计制造传感器。自制传感器的性能应满足使用要求。

9常用术语

1、传感器

能感受规定的被测量并按照一定的规律转换成可用输出信号的器件或装置。通常有敏感元件和转换元件组成。

1）敏感元件是指传感器中能直接（或响应）被测量的部分。

2）转换元件指传感器中能较敏感元件感受（或响应）的被测量转换成是与传输和（或）测量的电信号部分。

3）当输出为规定的标准信号时，则称为变送器。

2、测量范围

在允许误差限内被测量值的范围。

3、量程

测量范围上限值和下限值的代数差。

4、精确度

被测量的测量结果与真值间的一致程度。

5、重复性

在所有下述条件下，对同一被测的量进行多次连续测量所得结果之间的符合程度：

相同测量方法

相同观测者

相同测量仪器

相同地点

相同使用条件

在短时期内的重复。

6、分辨力

传感器在规定测量范围内可能检测出的被测量的最小变化量。

7、阈值

能使传感器输出端产生可测变化量的被测量的最小变化量。

8、零位

使输出的绝对值为最小的状态，例如平衡状态。

9、激励

为使传感器正常工作而施加的外部能量（电压或电流）。

10、最大激励

在市内条件下，能够施加到传感器上的激励电压或电流的最大值。

11、输入阻抗

在输出端短路时，传感器输入端测得的阻抗。

12、输出

有传感器产生的与外加被测量成函数关系的电量。

13、输出阻抗

在输入端短路时，传感器输出端测得的阻抗。

14、零点输出

在室内条件下，所加被测量为零时传感器的输出。

15、滞后

在规定的范围内，当被测量值增加和减少时，输出中出现的最大差值。

16、迟后

输出信号变化相对于输入信号变化的时间延迟。

17、漂移

在一定的时间间隔内，传感器输出中有与被测量无关的不需要的变化量。

18、零点漂移

在规定的时间间隔及室内条件下零点输出时的变化。

19、灵敏度

传感器输出量的增量与相应的输入量增量之比。

20、灵敏度漂移

由于灵敏度的变化而引起的校准曲线斜率的变化。

21、热灵敏度漂移

由于灵敏度的变化而引起的灵敏度漂移。

22、热零点漂移

由于周围温度变化而引起的零点漂移。

23、线性度

校准曲线与某一规定直线一致的程度。

24、非线性度

校准曲线与某一规定直线偏离的程度。

25、长期稳定性

传感器在规定的时间内仍能保持不超过允许误差的能力。

26、固有频率

在无阻力时，传感器的自由（不加外力）振荡频率。

27、响应

输出时被测量变化的特性。

28、补偿温度范围

使传感器保持量程和规定极限内的零平衡所补偿的温度范围。

29、蠕变

当被测量机器多有环境条件保持恒定时，在规定时间内输出量的变化。

30、绝缘电阻

如无其他规定，指在室温条件下施加规定的直流电压时，从传感器规定绝缘部分之间测得的电阻值。

10环境影响

环境给传感器造成的影响主要有以下几个方面：

（1）高温环境对传感器造成涂覆材料熔化、焊点开化、弹性体内应力发生结构变化等问题。对于高温环境下工作的传感器常采用耐高温传感器；另外，必须加有隔热、水冷或气冷等装置。

（2）粉尘、潮湿对传感器造成短路的影响。在此环境条件下应选用密闭性很高的传感器。不同的传感器其密封的方式是不同的，其密闭性存在着很大差异。

常见的密封有密封胶充填或涂覆；橡胶垫机械紧固密封；焊接（氩弧焊、等离子束焊）和抽真空充氮密封。

从密封效果来看，焊接密封为最佳，充填涂覆密封胶为最差。对于室内干净、干燥环境下工作的传感器，可选择涂胶密封的传感器，而对于一些在潮湿、粉尘性较高的环境下工作的传感器，应选择膜片热套密封或膜片焊接密封、抽真空充氮的传感器。

（3）在腐蚀性较高的环境下，如潮湿、酸性对传感器造成弹性体受损或产生短路等影响，应选择外表面进行过喷塑或不锈钢外罩，抗腐蚀性能好且密闭性好的传感器。

（4）电磁场对传感器输出紊乱信号的影响。在此情况下，应对传感器的屏蔽性进行严格检查，看其是否具有良好的抗电磁能力。

（5）易燃、易爆不仅对传感器造成彻底性的损害，而且还给其它设备和人身安全造成很大的威胁。因此，在易燃、易爆环境下工作的传感器对防爆性能提出了更高的要求：在易燃、易爆环境下必须选用防爆传感器，这种传感器的密封外罩不仅要考虑其密闭性，还要考虑到防爆强度，以及电缆线引出头的防水、防潮、防爆性等。

11选择使用

对传感器数量和量程的选择：

传感器数量的选择是根据电子衡器的用途、秤体需要支撑的点数（支撑点数应根据使秤体几何重心和实际重心重合的原则而确定）而定。一般来说，秤体有几个支撑点就选用几只传感器，但是对于一些特殊的秤体如电子吊钩秤就只能采用一个传感器，一些机电结合秤就应根据实际情况来确定选用传感器的个数。

传感器量程的选择可依据秤的最大称量值、选用传感器的个数、秤体的自重、可能产生的最大偏载及动载等因素综合评价来确定。一般来说，传感器的量程越接近分配到每个传感器的载荷，其称量的准确度就越高。但在实际使用时，由于加在传感器上的载荷除被称物体外，还存在秤体自重、皮重、偏载及振动冲击等载荷，因此选用传感器量程时，要考虑诸多方面的因素，保证传感器的安全和寿命。

传感器量程的计算公式是在充分考虑到影响秤体的各个因素后，经过大量的实验而确定的。

公式如下：

C=K-0K-1K-2K-3（Wmax+W）/N

C—单个传感器的额定量程

W—秤体自重

Wmax—被称物体净重的最大值

N—秤体所采用支撑点的数量

K-0—保险系数，一般取值在1.2～1.3之间

K-1—冲击系数

K-2—秤体的重心偏移系数

K-3—风压系数

根据经验，一般应使传感器工作在其30%～70%量程内，但对于一些在使用过程中存在较大冲击力的衡器，如动态轨道衡、动态汽车衡、钢材秤等，在选用传感器时，一般要扩大其量程，使传感器工作在其量程的20%～30%之内，使传感器的称量储备量增大，以保证传感器的使用安全和寿命。

要考虑各种类型传感器的适用范围：

传感器的准确度等级包括传感器的非线形、蠕变、蠕变恢复、滞后、重复性、灵敏度等技术指标。在选用传感器的时候，不要单纯追求高等级的传感器，而既要考虑满足电子秤的准确度要求，又要考虑其成本。

对传感器等级的选择必须满足下列两个条件：

1、满足仪表输入的要求。称重显示仪表是对传感器的输出信号经过放大、A/D转换等处理之后显示称量结果的。因此，传感器的输出信号必须大于或等于仪表要求的输入信号大小，即将传感器的输出灵敏度代人传感器和仪表的匹配公式，计算结果须大于或等于仪表要求的输入灵敏度。

2、满足整台电子秤准确度的要求。一台电子秤主要是由秤体、传感器、仪表三部分组成，在对传感器准确度选择的时候，应使传感器的准确度略高于理论计算值，因为理论往往受到客观条件的限制，如秤体的强度差一点，仪表的性能不是很好、秤的工作环境比较恶劣等因素都直接影响到秤的准确度要求，因此要从各方面提高要求，又要考虑经济效益，确保达到目的。

12国家标准

与传感器相关的现行国家标准

GB/T 14479-1993 传感器图用图形符号

GB/T 15478-1995 压力传感器性能试验方法

GB/T 15768-1995 电容式湿敏元件与湿度传感器总规范

GB/T 15865-1995 摄像机（PAL/SECAM/NTSC）测量方法第1部分:非广播单传感器摄像机

GB/T 13823.17-1996 振动与冲击传感器的校准方法声灵敏度测试

GB/T 18459-2001 传感器主要静态性能指标计算方法

GB/T 18806-2002 电阻应变式压力传感器总规范

GB/T 18858.2-2002 低压开关设备和控制设备控制器-设备接口（CDI） 第2部分:执行器传感器接口（AS-i）

GB/T 18901.1-2002 光纤传感器第1部分:总规范

GB/T 19801-2005 无损检测声发射检测声发射传感器的二级校准

GB/T 7665-2005 传感器通用术语

GB/T 7666-2005 传感器命名法及代号

GB/T 11349.1-2006 振动与冲击机械导纳的试验确定第1部分：基本定义与传感器

GB/T 20521-2006 半导体器件第14-1部分: 半导体传感器-总则和分类

GB/T 14048.15-2006 低压开关设备和控制设备第5-6部分：控制电路电器和开关元件-接近传感器和开关放大器的DC接口（NAMUR）

GB/T 20522-2006 半导体器件第14-3部分: 半导体传感器-压力传感器

GB/T 20485.11-2006 振动与冲击传感器校准方法第11部分：激光干涉法振动绝对校准

GB/T 20339-2006 农业拖拉机和机械固定在拖拉机上的传感器联接装置技术规范

GB/T 20485.21-2007 振动与冲击传感器校准方法第21部分：振动比较法校准

GB/T 20485.13-2007 振动与冲击传感器校准方法第13部分: 激光干涉法冲击绝对校准

GB/T 13606-2007 土工试验仪器岩土工程仪器振弦式传感

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