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After entering the 21st century, especially after China's accession to the WTO, domestic products are facing great challenges. Various industries, especially traditional industries are in urgent need of the application of electronic technology, automatic control technology for transformation and upgrading. For example, the textile industry, temperature and humidity is an important factor affecting the quality of textiles, but the textile enterprises on the temperature and humidity measurement and control methods are still very rough, very backward, the vast majority of the dry and wet bulb hygrometer is still in use, using manual observation, manual adjustment of valves, fans, the control effect can be imagined. Pharmaceutical industry is also basically so. In the food industry, it is basically based on experience, few people use humidity sensors. It is worth mentioning that, with the development of agriculture to industrialization, many farmers realize the need to get rid of backward traditional farming, breeding methods, the use of modern science and technology to cope with the challenges of imported agricultural products, and enter foreign markets. Around the establishment of more and more new greenhouses, planting anti-seasonal vegetables, flowers; farming on the environment of the measurement and control is also urgent; temperature and cold storage of a large number of construction to the temperature and humidity measurement and control technology provides a broad market. China has introduced the Netherlands, Israel and other countries more advanced large-scale greenhouse more than forty, the degree of automation is higher, the cost is also high. Domestic is gradually digesting and absorbing the relevant technology, generally first engaged in temperature control, lighting, ventilation control; the second step to engage in automatic temperature and humidity control and CO2 measurement and control. In addition, the construction of a large number of national grain reserve project, the temperature and humidity measurement and control technology also put forward requirements.

But at present, in the field of humidity testing most of the performance of moisture-sensitive components can only be used in the usual temperature environment. In the need for special environmental wet applications most of the domestic, including many foreign humidity sensors will be "frowned upon"! For example, in the above mentioned textile printing and dyeing industry, food industry, high temperature materials industry, etc., all need to measure humidity at high temperatures. In general, the printing and dyeing industry in the spindle drying, the temperature can reach 120 degrees Celsius or higher; in the food industry, food baking temperature can reach 80-200 degrees Celsius or so; high-temperature-resistant materials, such as ceramic filter drying can reach 200 degrees Celsius or more. In these cases, ordinary humidity sensors are difficult to measure.

Polymer capacitive humidity sensors are usually insulated substrates such as glass, ceramics, silicon and other materials, screen leakage printing or vacuum coating process to make the electrode, and then impregnated or other means of moisture-sensitive adhesive coated in the electrode made of capacitive elements. Moisture-sensitive components in different relative humidity in the atmosphere, due to the moisture-sensitive film adsorption of water molecules and the capacitance value shows regular changes, which is the basic mechanism of the humidity sensor. Influence of polymer capacitive element temperature characteristics, in addition to the medium as a polymer dielectric constant ε and adsorbed water molecules of the dielectric constant ε by the temperature change, there are also components of the geometric dimensions of the coefficient of thermal expansion by the influence of the change of other factors. According to the viewpoint of Debye's theory, the dielectric constant ε of a liquid is a dimensionless constant related to temperature and frequency. The ε of a water molecule is 78.36 at T = 5°C and 79.63 at T = 20°C. The temperature dependence of ε in organic matter varies from material to material and does not exactly obey a proportional relationship. In some temperature regions ε tends to increase with T, and in some temperature regions ε decreases with increasing T. Most of the literature in the polymer moisture-sensitive capacitive components in the analysis of the moisture-sensitive mechanism that: polymer has a small dielectric constant, such as polyimide in the low humidity when the dielectric constant of 3.0 a 3.8, and water molecules dielectric constant is tens of times the polymer ε. Therefore, the polymer medium in the moisture absorption of the material is different from the temperature, and fully comply with the proportionality relationship. Therefore, the polymer medium in the moisture absorption, due to the presence of water molecules dipole distance, greatly improving the dielectric constant of the water-absorbing heterogeneous layer, which is a multi-phase medium of the composite dielectric constant has the additive nature of the decision. Due to the change of ε, the capacitance C of the moisture-sensitive capacitor element is proportional to the relative humidity. In the design and production process is difficult to group to the moisture-sensitive characteristics of the entire wet range linear. As a capacitor, the thickness d of the polymer dielectric film and the effective area S of the flat capacitor are also temperature dependent. Changes in dielectric geometry caused by temperature changes will affect the C value. The average thermal linear expansion coefficients of polymers can be on the order of . For example, cellulose nitrate has an average thermal coefficient of expansion of 108x10-5/°C. As the temperature rises, the dielectric film thickness d increases, a negative contribution to the C value; but the expansion of the moisture-sensitive film and make the medium of water adsorption increases, that is, a positive contribution to the C value. It can be seen that the temperature characteristics of the moisture-sensitive capacitor is governed by a variety of factors, in different humidity ranges of different temperature drift; in different temperature zones with different temperature coefficients; different moisture-sensitive materials with different temperature characteristics. In short, the temperature coefficient of polymer humidity sensor is not a constant, but a variable. So usually the sensor manufacturer can be in the -10-60 degrees Celsius range is the sensor linearization to reduce the temperature of the moisture-sensitive components of the impact.

Foreign manufacturers of relatively high-quality products mainly use polyamide resin, the product structure is summarized in borosilicate glass or sapphire substrate on the production of gold electrodes by vacuum evaporation, and then sprayed moisture-sensitive dielectric material (as mentioned above) in the form of flat moisture-sensitive film, and then in the film evaporated on the gold electrodes. The capacitance value of the moisture-sensitive element is proportional to the relative humidity, linearity of about ± 2%. Although, the performance of moisture measurement is still OK but its temperature resistance, corrosion resistance are less than ideal for use in the industrial field, life, temperature resistance and stability, corrosion resistance are to be further improved.

Ceramic moisture sensor is a new type of sensor developed in recent years. Advantage lies in the ability to withstand high temperatures, humidity hysteresis, fast response speed, small size, to facilitate mass production, but due to the porous material, the dust has a great impact on the daily maintenance is frequent, from time to time need to be cleaned by electric heating is easy to affect the quality of the product, susceptible to the impact of humidity, low humidity and high temperature environment, linearity, especially the use of short service life, long-term reliability is poor, is such a humidity-sensitive sensors are urgent to solve the problem.

Currently in the development and research of moisture-sensitive components, resistive humidity sensors should be the most suitable for humidity control in the field of its representative products, lithium chloride humidity sensors with stability, temperature resistance and long service life of a number of important advantages, lithium chloride humidity-sensitive sensors have been more than fifty years of production and research history, there are a variety of product types and production methods, are applied to the application of lithium chloride Wet-sensitive liquid with a variety of advantages, especially the strongest stability.

Lithium chloride hygroscopic devices belong to the electrolyte hygroscopic materials, among the many hygroscopic materials, the first to be noticed and used in the manufacture of hygroscopic devices, lithium chloride electrolyte hygroscopic solution based on the equivalent conductance decreases with the increase in the concentration of the solution. Electrolyte dissolved in water to reduce the principle of water vapor pressure on the surface of the water to realize the moisture-sensitive.

Lithium chloride moisture-sensitive device substrate structure is divided into columnar and comb, lithium chloride polyvinyl alcohol coating as the main ingredient of the moisture-sensitive liquid and the production of gold electrodes are the three components of the lithium chloride moisture-sensitive device. Over the years the product production continues to improve and enhance the product performance continues to improve, lithium chloride moisture-sensitive sensors and its unique long-term stability of other moisture-sensitive materials can not be replaced, but also the most important performance of the humidity sensor. In the product production process, after the preparation of the moisture-sensitive mixture and the strict control of the process is to maintain and play the key to this feature.

In the domestic nine pure health science and technology rely on the National Institute of Metrology, the Chinese Academy of Sciences Institute of Automation, the Institute of Chemical Technology and other large research institutions engaged in the development of temperature and humidity sensor products, production. Selection of lithium chloride moisture-sensitive materials as the main direction, the production of lithium chloride moisture-sensitive sensors and related transmitters, automation instrumentation and other products, drawing on the successful experience of this technology at home and abroad at the same time, and strive to overcome the weaknesses of the traditional products, to achieve substantial progress. The products use Al2O3 and SiO2 ceramic substrate as the substrate, the substrate area is greatly reduced, using a special process, moisture resistance and adhesion are greatly improved. The use of sintering process, sintered on the substrate set piece of 5 9 industrial pure gold made of comb electrode, lithium chloride moisture-sensitive mixture of new products using additives and intrinsic ingredients mixed with a special aging and coating process, the service life of the moisture-sensitive substrate and the long-term stability is greatly improved, in particular, temperature resistance to -40 ° C -120 ° C, to the combination of a number of pieces of moisture-sensitive components of the unique process, is the sensor sensing the wet range of 1%RH-98%RH, with 15%RH range below the measurement performance, drift curve and moisture-sensitive curve have achieved a better level of linearization, so that the humidity compensation can be conveniently implemented and easier to ensure the accuracy of the measurement of humidity in a wide temperature range. Closed system using circulation cooling device, the first on the measured gas sampling, and then cooling detection and ensure that the absolute humidity is constant, so that the probe temperature range to 600 ℃ or so, greatly enhancing the function of high temperature humidity measurement. Successfully solved the "high temperature humidity measurement" this humidity measurement field problems. Now, the split high-temperature type temperature and humidity sensor JCJ200W, which directly measures humidity in the environment within 150 degrees Celsius without any device, has been successfully used in wood drying, high and low temperature test chambers and other systems. At the same time, JCJ200Y products can withstand temperatures up to 600 degrees, has also been successfully applied in the printing and dyeing industry spindle automatic drying system, food automatic baking system, special ceramic materials, automatic drying system, the export of large-scale drying machinery, etc., and showed good results for the domestic automation control field to fill the gaps in the measurement of temperature and humidity for the process of China's industrialization has laid a certain foundation.

Sensor paper:

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Hall element is a Hall effect-based magnetic sensors, has developed into a variety of magnetic sensor product family, and has been widely used. This article briefly introduces its working principle, product characteristics and its typical applications.

Hall devices have many advantages, their structure is solid, small size, light weight, long life, easy to install, low power consumption, high frequency (up to 1MHZ), vibration, not afraid of dust, oil, water vapor and salt spray pollution or corrosion.

Hall linear device of high precision, good linearity; Hall switch device without contact, no wear, clear output waveform, no jitter, no jump back, position repeatability (up to μm level). Taking a variety of compensation and protection measures Hall device operating temperature range, up to -55 ℃ ~ 150 ℃.

In accordance with the function of Hall devices can be divided into: Hall linear devices and Hall switching devices. The former outputs analog and the latter outputs digital.

According to the nature of the object to be detected, their applications can be divided into: direct applications and indirect applications. The former is a direct detection of the magnetic field or magnetic properties of the object to be detected itself, the latter is the detection of the object to be inspected on the artificial setting of the magnetic field, the magnetic field to be detected as a carrier of information, through which many non-electric, non-magnetic physical quantities, such as force, torque, pressure, stress, position, displacement, speed, acceleration, angle, angular speed, number of revolutions, rotational speed, as well as changes in the operating state of the time to change into the electrical quantities to detect and control. Electricity to detect and control.

Operating principle of Hall device

Under the action of the magnetic field, the metal plate with current generates a transverse potential difference as shown in Figure 1:

This voltage is proportional to the magnetic field and the control current:

VH=K╳??IC?

Wherein, VH is the Hall voltage, H is the magnetic field, IC is the control current, and K is the Hall coefficient. The coefficients of K are the Hall coefficients.

The Hall effect is more significant in semiconductors than in metals, so generally Hall devices are made of semiconductors.

With Hall devices, non-contact current measurement can be carried out, as we all know, when the current through a long straight wire, in the wire around the magnetic field, the size of the magnetic field and the current flowing through the wire is proportional to the size of the magnetic field can be aggregated through the soft magnetic material, and then detected by the Hall device, due to the magnetic field and the output of the Hall device has a good linear relationship, and therefore can be utilized to Hall devices. Measured signal size, a direct response to the size of the current, that is: I ∞ B ∞ VH

Which I for the current through the wire, B for the wire through the current produced by the magnetic field, VH for the Hall device in the magnetic field B Hall voltage, elected to be used in the appropriate ratio coefficients, it can be expressed as an equation. Hall sensor is made according to this principle of operation.

Two Hall sensor applications

1 Hall proximity sensors and proximity switches

In the Hall device behind the bias of a piece of permanent magnet, and they and the corresponding processing circuitry mounted in a shell, made into a probe, the Hall device's input leads and the processing circuitry of the output lead with a cable to connect up, constituting a proximity sensor as shown in Figure 1. Their functional boxes are shown in Fig. 19.(a) is a Hall linear proximity sensor and (b) is a Hall proximity switch.

Figure 1 Hall proximity sensor outline

a) Hall linear proximity sensor

(b) Hall proximity switch

Figure 2 Hall proximity sensor's function box

Hall linear proximity sensor is mainly used for ferrous metal's self-control counting, ferrous metal's thickness detecting, distance detecting, gears' counting teeth, speed detecting, speed measurement and speed regulation, notch sensing, tension detection, sliver uniformity detection, electromagnetic quantity detection, angle detection and so on.

Hall proximity switches are mainly used in a variety of automatic control devices, to complete the required position control, processing size control, automatic counting, a variety of counting, a variety of automatic convergence of the process, level control, speed detection, etc. 3.2.7 Hall wing switch

Hall wing switch is the use of blocking the way of working of a product, its shape is shown in Figure 20, the internal structure and principle of operation is shown in Figure 20, the internal structure and working principle of the Hall wing switch. The internal structure and working principle is shown in Figure 21.

Figure 3 Hall wing switch shape

2 Hall gear sensor

As shown in Figure 4, a new generation of Hall gear speed sensor, widely used in a new generation of automotive intelligent engine, as the ignition timing with the speed sensor, used in the ABS (automotive anti-lock braking system) as a speed sensor, etc.

The Hall gear sensor is used in a new generation of automotive intelligent engine, as a speed sensor, as a speed sensor, etc.

The Hall gear sensor is used in a new generation of automotive intelligent engine.

In ABS, the speed sensor is a very important component. the working principle of ABS is schematically shown in Figure 23. In the figure, 1 is the speed gear sensor; 2 is the pressure regulator; 3 is the controller. In the braking process, the controller 3 constantly receive from the speed gear sensor 1 and wheel speed corresponding pulse signal and processing, get the vehicle slip rate and deceleration signals, according to its control logic timely and accurately to the brake pressure regulator 2 commands, regulator timely and accurately respond to the braking air chamber to perform inflate, hold or bleed command, adjust the brake pressure of the brakes in order to prevent the wheels from holding dead, to achieve anti-skid, to achieve the anti-skid, to release the pressure regulator, and to prevent the wheel from slipping, to prevent the wheel from slipping, to prevent the wheel from slipping, to prevent the wheel from slipping. Holding dead, to achieve anti-skidding, tailgating, improve braking safety and drivability in the braking process. In this system, the Hall sensor, as a wheel speed sensor, is a real-time speed collector during braking and is one of the key components in ABS.

In the new generation of intelligent engines in automobiles, Hall gear sensors are used to detect the crankshaft position and the speed of the piston movement in the cylinder to provide more accurate ignition timing, which is difficult to be replaced by other speed sensors, and it has many new advantages as follows.

(1) high phase accuracy, can meet the requirements of 0.4 ° crankshaft angle, do not need to use phase compensation.

(2) It can meet the requirement of flameout detection for 0.05° crankshaft angle.

(3) The output is a rectangular waveform, and the amplitude is independent of the vehicle speed. Costs are reduced when further sensor signal adjustments are made in the electronic control unit.

With a gear sensor, in addition to detecting RPM, angles, angular speeds, flow rates, flow velocities, directions of rotation, and so on, can be measured.

Figure 4 Internal structure of Hall speed sensor

1. wheel speed sensor 2. pressure regulator 3. electronic controller

2. Fig. 4 Schematic diagram of the operating principle of the ABS air brake system

3 Rotary sensors

Set up the magnets according to the various methods shown in Fig. 5, and combining them with the Hall switching circuit can constitute a variety of rotary sensors. When the Hall circuit is energized, the magnet outputs a voltage pulse every time it passes through the Hall circuit.

(a) Radial Magnetic Pole (b) Axial Magnetic Pole (c) Blocking Type

Figure 5 Rotary Sensor Magnet Setup

Thus, physical quantities such as number of revolutions, rotational speeds, angles, and angular speeds of a rotating object can be detected. By fixing an impeller and a magnet on a rotating shaft and using a fluid (gas, liquid) to push the impeller to rotate, a flow rate and flow rate sensor can be formed. In the wheel spindle mounted on the magnet, near the position of the magnet on the Hall switch circuit, can be made into a speedometer, odometer, etc., these applications are shown in Figure 25, for example.

Figure 6 of the shell is equipped with a magnet with the impeller, the magnet is equipped with Hall switching circuit next to the measured fluid from one end of the pipeline into the impeller to drive the impeller is connected to the magnet rotating through the Hall device, the circuit output pulse voltage, the number of pulses, you can get the flow rate of the fluid. If you know the inner diameter of the pipe, the flow rate and pipe diameter can be obtained from the flow rate. The Hall circuit is powered and output by cable 35.

Figure 6 Hall Flow Meter

As seen in Figure 7, the speed of the vehicle can be obtained from the digital display after a simple signal conversion.

Using a locking Hall circuit, not only can the speed be detected, but also the direction of rotation can be identified, as shown in Figure 27.

Curve 1 corresponds to structure (a), curve 2 corresponds to structure (b), and curve 3 corresponds to structure (c).

Figure 7 Block diagram of Hall speedometer

Figure 8 Direction and speed determination using Hall switch locker

4 Application in large current detection

There are many ultra-large current-using devices in metallurgy, chemical industry, superconductor applications, and high-energy physics (e.g., controlled nuclear fusion) test devices. The current sensor made of multi-Hall probes to measure and control large currents can meet the requirements of measurement accuracy without introducing insertion losses, and also eliminates the need for expensive test equipment such as those required in the Rogo Kansky coil method. FIG. 9 illustrates a Hall current sensor device for use in a DIII-D tokamak. With this Hall current sensor, currents up to 300 kA can be detected.

Fig. 9 (a) shows a G-10 mounting structure with a current sink in the center, (b) a cable-type multi-Hall probe, and (c) a Hall voltage amplification circuit.

(a) G?10 mounting structure (b) cable-type multi-Hall probe (c) Hall voltage amplification circuit

Figure 9 Multi-Hall probe high-current transducer

Figure 10 Hall clamp-on digital ammeter line schematic

Figure 11 Hall power meter schematic

(a) Hall control circuit

(b) Hall magnetic field circuit

Figure 12 Hall multiplier in Hall three-phase power transmitter

Figure 13 Hall power meter functional block diagram

Figure 14 Functional block diagram of Hall isolation amplifier

5 Hall displacement transducer

If the operating current of the Hall element is made to remain constant while it is moved through a uniformly graded magnetic field, it outputs the Hall voltage VH value is determined only by its displacement Z in that magnetic field. Fig. 15 shows the output characteristic curves of three magnetic systems generating a gradient magnetic field and their displacement sensors composed with Hall devices, which can be fixed to the system under test to form a Hall microdisplacement sensor. As can be seen from the curve, structure (b) has a good linear relationship between VH and Z at Z<2mm, and the resolution can be up to 1μm, and structure (C) has a high sensitivity, but the working distance is small.

Figure 15 Static characteristics of several magnetic systems generating gradient magnetic fields and several Hall displacement sensors

There are many advantages of measuring displacement with Hall elements: small inertia, fast frequency response, reliable operation and long life.

Based on micro-displacement detection, it can constitute pressure, stress, strain, mechanical vibration, acceleration, weight, weighing and other Hall sensors.

6 Hall pressure sensor

Hall pressure sensor consists of elastic element, magnetic system and Hall element and other parts, as shown in Figure 16. In FIG. 16, (a) the elastic element is a diaphragm box, (b) is a spring sheet, and (c) is a bellows. The magnetic system is preferably made of a composite system capable of forming a uniform gradient magnetic field, such as (a) and (b) in FIG. 29, or a single magnet, such as (c). The addition of pressure causes a relative displacement between the magnetic system and the Hall element, changing the magnetic field acting on the Hall element and thus changing its output voltage VH. The value of the measured pressure p can be obtained from the pre-calibrated p~f(VH) curve.

Figure 16 Composition principle of several Hall pressure sensors

7 Hall acceleration sensor

Figure 17 shows the structural principle and static characteristic curve of Hall acceleration sensor. In the box on the O point fixed homogeneous spring plate S, the middle of the plate S U installed an inertia block M, the end of the plate S b fixed to measure the displacement of the Hall element H, H on the lower part of the mounting of a pair of permanent magnets, which are installed with the same polarity relative. The cassettes are fixed to the object to be measured, and when they are accelerated vertically upward together with the object to be measured, the inertia block causes the Hall element H to produce a displacement relative to the cassette under the action of the inertial force, producing a change in the Hall voltage VH. The acceleration can be obtained from the curve of VH versus acceleration.

Figure 17 Hall acceleration sensor structure and its static characteristics

Three Summary

Currently Hall sensors have been developed from discrete components to integrated circuits, is becoming more and more people's attention, the application is increasingly widespread.