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The sensor principle
Visit: Date:2013-11-29
What are called sensors? Broadly speaking, the sensor is able to perceive the external information and according to certain rules will device available signal convert these information into; simple sensor is a device of external signals are converted to electrical signals. It consists of sensitive components (sensor) and the converter is composed of two parts, some semiconductor sensitive element can be directly output signals, in itself constitute a sensor. Sensitive components variety, the principle of its perception of external information, can be divided into physical, stress, heat, light, electricity, magnetic and other physical effects based on. The chemical class, based on the principle of chemical reaction. The biology class, enzymes, antibodies, and hormone based on molecular recognition function. Usually according to its basic cognitive function can be divided into thermosensitive element, a photosensitive element, gas sensor, force sensor, Ci Min element, humidity sensors, acoustic sensors, radiation sensitive element, color sensors and taste sensors and other ten categories (and there are people who have the sensor can be divided into 46 categories). The commonly used thermal, light, gas sensor, force sensor and the magnetic sensor and its sensing element is introduced as follows.
 
A temperature sensor and thermistor
The temperature sensor is mainly composed of a heat sensitive element. The thermosensitive element varieties more, market sales of the bimetallic strip, copper thermal resistance, thermocouple and platinum thermal resistance, thermal resistance. In a semiconductor thermistor as a temperature sensor detecting element widely, this is because the allowable working conditions in the element, semiconductor thermistor has the characteristics of small size, high sensitivity, high precision, and simple manufacturing process, low price.


The working principle of the 1 semiconductor thermistor
According to the temperature characteristic of thermistor can be divided into two categories, with the rise of temperature resistance increased as the positive temperature coefficient thermistor, contrary to the negative temperature coefficient thermistor.
The working principle of the positive temperature coefficient thermistor
This thermistor with barium titanate (BaTio3) as the basic material, then adding proper amount of rare earth elements, the use of ceramic technology high temperature sintering into seoul. Pure barium titanate is an insulating material, but is doped with rare earth elements such as lanthanum amount (La) and niobium (Nb) and later, a semiconductor material, known semiconducting barium titanate. It is a polycrystalline material, there is grain boundary between grains, for conducting electronic, grain boundary is equivalent to a barrier. When the temperature is low, because of the action of electric field in the semiconducting barium titanate, conducting electrons can easily cross the barrier, so the resistance value is small; when the temperature increases to the Curie point temperature (critical temperature, the components' temperature control points' general barium titanate Curie point is 120 ℃), the electric field within the subject failure, can't help conducting electrons across the barrier, so the performance is dramatically increased resistance value. Because this element has not reached the Curie point of resistance with temperature changes very slowly, with a constant temperature, temperature control and automatic temperature control function, not only fever, redness, no fire, not easy to burn, the voltage AC, DC 3 ~ 440V can, long service life, is very suitable for motor overheating and other electrical device detection.
The principle of negative temperature coefficient thermistor
Negative temperature coefficient thermistor with manganese oxide, cobalt oxide, nickel oxide, copper oxide and aluminum oxide as the main raw material, the manufacturing technology of ceramic and. These metal oxide materials have semiconductor properties, quite similar to germanium, silicon crystal material, the body of carriers (electrons and holes) the number of small, high resistivity; temperature, carrier number increases, the natural resistance to reduce. A lot of negative temperature coefficient thermistor type, used to distinguish between low temperature (-60 ~ 300 ℃), temperature (300 ~ 600 ℃), high temperature (>600 ℃) three, has the advantages of high sensitivity, good stability, fast response, long life, low price advantage, widely applied to fixed-point temperature temperature automatic control circuit the temperature control system, such as refrigerator, air conditioner, greenhouse.
Thermistor is combined with a simple amplifying circuit, can detect a thousand one degree change in temperature, so the electronic meter thermometer, can achieve high precision temperature measurement. The working temperature of general use thermistor is -55 ℃ ~ +315 ℃, special low temperature thermistor temperature below -55 ℃ to -273 ℃.

The 2 thermistor type
I made the thermistor is according to the standard SJ1155-82 to make model, consisting of four parts.
The first part: the LORD says, by the letter 'M' said sensitive element.
The second part: categories, said the positive temperature coefficient thermistor with the letter 'Z', or 'F' letters represent negative temperature coefficient thermistor.
The third part: use or features, with a digit (0-9) representation. General digital '1' represents a general purpose, '2' said regulator uses (negative temperature coefficient thermistor), '3' said microwave measurement purposes (negative temperature coefficient thermistor), '4' said heater (negative temperature coefficient thermistor), '5' '6' temperature measuring purposes, said temperature control uses' 7, 'said degaussing purposes (positive temperature coefficient thermistor),' 8 'represents a linear type (negative temperature coefficient thermistor),' 9 'represents the constant temperature type (positive temperature coefficient thermistor),' 0 'indicates special type (negative temperature coefficient thermistor)
The fourth part: serial number, but also by the digital representation, representative specification, performance.
Usually manufacturers for differences between special needs of this series of products, plus' derived number 'in number, consist of letters, numbers and' - 'number and.
Example: M Z 11

Main parameters of 3 thermistors
A variety of thermistor working conditions must be in the factory parameters within the allowed range. The main parameters of the thermistor has more than ten: nominal resistance values, the use of ambient temperature (maximum working temperature), measurement of power, rated power, rated voltage (maximum working voltage), working current, temperature coefficient, the material constants, time constant. The nominal resistance is the resistance at 25 ℃ zero power value, in fact there is a certain error, should be in within 10%. Operating temperature range of ordinary thermistor is larger, can choose according to need from -55 ℃ to +315 ℃, notably, the highest working temperature differences between different types of thermistor, such as MF11 sheet negative temperature coefficient thermistor is +125 ℃, +70 ℃ and MF53-1 only, should pay attention to students' experiment (generally do not more than 50 ℃).
 
4 experiments with thermistor
The preferred ordinary use of negative temperature coefficient thermistor, because it changes with temperature is generally higher than the positive temperature coefficient thermistor resistance value is easy to observe, continuous decreased significantly. If the selected positive temperature coefficient thermistors, temperature should be in the vicinity of the Curie temperature of the element.
Patients with MF11 negative temperature coefficient thermistor parameters
The MF11 thermistor symbol contour map of main technical parameters of the name parameter value
Nominal resistance (K Ω) 10 ~ 15 flaky appearance symbols
Rated power (W) 0.25
The material constants of B (k) 1980 ~ 3630
Temperature coefficient (10-2/ ℃) - (2.23 ~ 4.09)
Dissipation factor (mW/ ℃) ≥ 5
The time constant (s) ≤ 30
The maximum operating temperature (125 ℃)
Coarse thermistor value should be selected range, moderate and a thermistor measuring small electric current multimeter. If the 10K thermistor, can choose MF10 multimeter, the shift switch to the ohmmeter R × 100, replace the probes are respectively clamped thermistor with alligator clip two pin. When the environment temperature is significantly lower than the body temperature, 10.2k thermistor readings, knead by hand, can see the indication of resistance decreases; the hand, increased resistance, gradually restored. Such a thermistor can be selected (the highest working temperature 100 ℃).

Several practical temperature sensor
A air conditioner: special temperature sensor thermistor sealed in the copper metal.
B temperature sensor

Sensor and photosensitive two optical elements
Light sensor is mainly composed of light elements. At present, the rapid development of photosensitive element, variety, widely used. The market for the sale of a photosensitive resistor, diode, triode, photoelectric photoelectric coupler and optical cell.
1 photosensitive resistors
Photosensitive resistors by semiconductor photoelectric crystal transparent, because the semiconductor photoelectric crystal composition is different, can be divided into visible light photosensitive resistor (cadmium sulfide crystal), infrared light photosensitive resistor (GaAs crystals), and ultraviolet light photosensitive resistor (zinc sulfide crystals). When the wavelength of the light sensitive semiconductor photoelectric surface of the crystal, crystal carrier increased, the conductivity increased (i.e., reduced resistance).
The main parameters of photosensitive resistance:
The light current, light resistance: under a certain applied voltage, when light (100lx) irradiation, current flows through the photosensitive resistor called the light current; voltage and the current ratio of light resistance, usually within a few tens of K Ω K Ω ~.
The dark current, resistance in the dark: under a certain applied voltage, when there is no light (0 LX) irradiation, current flows through the photosensitive resistor called dark current; voltage and the current ratio of resistance in the dark, generally a few hundred thousand more than k Ω K Ω to.
The maximum working voltage: General tens of volts to hundreds of volts.
◆ environment temperature: -25 ℃ to +55 ℃, some models can be -40 ℃ to +70 ℃.
◆ rated power (power): photosensitive resistance light current and voltage product; can be 5mW to 300mW a variety of specifications to choose.
◆ photosensitive resistance of main parameters and response time, sensitivity, spectral response, light, temperature coefficient, I-V characteristics.
Notable is, light (with the strength characteristics of the changes of light), temperature coefficient (temperature dependent properties), volt ampere characteristic is not linear, such as CdS (CDS) resist photoresistance sometimes increased with the increase of temperature, sometimes with increasing temperature and smaller.
The parameters of the cadmium sulphide photoresistor:
Specification MG41-22 MG42-16 MG44-02 MG45-52
The ambient temperature (-40 ℃) to +60 -25 to +55 -40 to +70 -40 to +70
Rated power (mW) 20105200
Light resistance, 100lx (k) ≤ 2 ≤ 50 ≤ 2 ≤ 2
Resistance in the dark, 0lx (M) ≥ 1 ≥ 10 ≥ 0.2 ≥ 1
Response time (MS) ≤ 20 ≤ 20 ≤ 20 ≤ 20
Maximum working voltage (V) 1005020250
 
The 2 photodiode
Compared with ordinary diode, in addition to the tube core it is a PN junction, has a one-way conductive properties, others are very different. The first tube PN junction in the core of deep and shallow (less than 1 microns), in order to improve the photoelectric conversion ability; second PN junction area of relatively large, the area of the electrode is very small, in order to facilitate the photosensitive surface to collect more light; the third photodiode has a lens made of organic glass sealing, can gather light from the photosensitive surface "window" in appearance; so the sensitivity and response time photodiode is far superior to that of photosensitive resistance.
 
Several photo diode and a symbol common as follows:
2DU has a very, very, before after ring pole three pole. The ring is to reduce dark current photodiode and increase working stability and design, application should be connected to the positive pole. The main parameters of the photoelectric diode has: maximum working voltage (10 ~ 50V), dark current (≤ 0.05 ~ 1 a), the photocurrent (> 6 ~ 80 a), response time, photoelectric sensitivity (tens of ns to several s), junction capacitance and forward drop.
Advantages of photodiode is of good linearity, fast response, wide range of wavelengths of light has the advantages of high sensitivity, low noise; drawback is the output current (or voltage) alone is small, need to add the amplification circuit. Applicable to communication and photoelectric control circuit.
The photodiode detection can be used multimeter R * 1K block, to avoid the optical forward resistance should be 10K Ω to 200 Ω K, reverse ∞, remove the shade right after the deflection angle is larger, the higher the sensitivity.
Photoelectric triode can be regarded as a combination of elements of a photodiode and a triode, with amplification function, so the dark current, photocurrent and photoelectric sensitivity is much higher than the photodiode structure, but the junction capacitance increase, response characteristics. Photoelectric control circuit is widely used in low frequency.
Semiconductor optoelectronic devices and MOS structure, such as a common scanner, camera CCD (charge coupled device) is integrated photodiode array or MOS structure.
 
Three gas sensor and gas sensor
Textbooks only requires the thermistor and photosensitive resistance characteristics of a simple experiment. Due to the close correlation of gas and the daily life of human, the detection of gases is to protect and improve the ecological environment indispensable means, gas sensors play an extremely important role. For example, the concentration of carbon monoxide in the living environment of 0.8 ~ 1.15 ml/L, will appear shortness of breath, rapid pulse, even syncope state, up to 1.84ml/L when there is a risk of death within a few minutes, so the carbon monoxide detection must be fast and accurate. Using SnO2 metal oxide semiconductor gas sensing materials, preparation of SnO2 nano particles by ultrafine particle refinement and doping process, and as a catalyst substrate doping, the appropriate sintering process for surface modification, made by thermal sintering CO sensitive element, can CO gas detection range of 0.005% ~ 0.5%. There are a lot of explosive and combustible gas, alcohol gas, automobile exhaust and other toxic gas detection sensor. Commonly used in the main contact combustion type gas sensors, electrochemical gas sensor and semiconductor gas sensor etc.. Contact combustion type gas sensor detecting element is generally platinum wire (also can be coated with platinum, palladium and other rare metal catalyst layer), use of platinum wires connect with current, maintaining 300 ℃ ~ 400 ℃, if contact with combustible gas, the combustible gas will burn in the rare metal catalyst layer therefore, platinum wire temperature rises, the resistance of platinum wire also rose; value changes by measuring the electrical resistance of platinum wire size, known concentration of combustible gas. Electrochemical gas sensor by the liquid (or solid, organic gel electrolyte, etc.) the output could be in the form of direct current oxidation or reduction gas generated, and can also be electromotive force acting on the ion ion electrode. Semiconductor gas sensor with high sensitivity, fast response, good stability, easy to use features, the application is extremely broad; the following highlights the semiconductor gas sensor and a gas sensor.
Semiconductor gas sensor with N type and P type division. Type N in the detection of resistance decreases with the increase of gas concentration; P value increases with the concentration of gas. Like the SnO2 metal oxide semiconductor gas sensitive material, which belongs to the N type semiconductor, at 200 ~ 300 ℃ it absorbed oxygen in the air, forming a negative ion adsorption of oxygen, so that the electron density in the semiconductor is reduced, so that its resistance value increases. When a combustible gas supply electronic (such as CO), the adsorption of oxygen desorption, and the combustible gas in the positive ion adsorption on metal oxide semiconductor surface; oxygen desorption emitted electron, combustible gas line in the positive ion adsorption state to emit electron, increasing the oxide semiconductor conduction band the electron density, the resistance decreases. Combustible gas does not exist, the negative ion adsorption of metal oxide semiconductor will automatically restore oxygen, make the increase of resistance to the initial state. This is the basic principle of semiconductor gas sensor detection of combustible gas.
There are 2 kinds of gas sensor made in china. One is the direct heating, heating wire and a measuring electrode to sintering in metal oxide semiconductor tube core; heating type gas sensor on ceramic substrate, through the pipe heating wire, two measuring electrode tube outside, metal oxides gas sensing materials for measuring electrodes, made by high sintering.
Parameters of gas sensor is mainly a heating voltage, current, voltage measurement circuit, the sensitivity, response time, recovery time, calibration gas (0.1% butane gas) voltage, load resistance etc.. QM-N5 type gas sensor suitable for natural gas, coal gas, hydrogen, alkyl, alkene gases such as gas, gasoline, kerosene, acetylene, ammonia, smoke detection, which belongs to the N type semiconductor device. High sensitivity, good stability, short response and recovery time, the market wide application. The following parameters: QM-N5 gas sensor calibration gas (0.1% butane gas, the best working conditions) voltage is greater than or equal to 2V, the response time ≤ 10S ≤ 30S, recovery time, the best working conditions of 5V, heating voltage measurement circuit voltage of 10V, load resistor RL as 2K, allows the working conditions of electric heating pressure 4.5 ~ 5.5V, measurement circuit voltage 5 ~ 15V, 0.5 ~ 2.2K load resistance. Below is a simple test circuit for gas sensor (sensor), voltage meter pointer changes more, the higher the sensitivity; just add a simple circuit can realize the alarm. Common gas sensor and MQ-31 (dedicated to the detection of CO), QM-J1 alcohol sensor etc..
 
Four Li Min sensor and force sensor
Li Min of the many kinds of sensors, the traditional measurement method is using the deformation and displacement of elastic material to represent. With the development of microelectronic technology, based on the piezoresistive effect of semiconductor materials (i.e., pressure, the one direction and the resistivity changes) and good elasticity, has developed the Li Min sensor has the advantages of small volume, light weight, high sensitivity, widely used in the measurement of mechanical pressure, acceleration, weight.
 
The five magnetic sensor and magnetic sensor
The magnetosensor with Holzer device (based on the Holzer effect), magnetoresistive devices (based on magnetoresistive effect: magnetic field made the semiconductor resistance increases with the magnetic field increases.) , magneto diode and triode. Magnetic sensor based on magneto sensor is widely used in the measurement of electrical, magnetic and mechanical quantities of.
In a certain sense sensor and the sense of people have a corresponding relationship, the perception has been far more than human senses. For example, was observed by using the target's infrared radiation of infrared imaging system (night like instrument), the night can be found 1000 m, 2000 meters found the vehicle; the core components of the imager is infrared sensor. In the 1991 Gulf War, the Iraqi tank configuration of night vision instrument detection distance of only 800 meters, is less than half the coalition, the darkness was badly defeated is inevitable. At present, all the countries in the world to sensor technology as the focus of high-tech development priority. In order to greatly improve the performance of the sensor, the constant use of new structure, new materials and new technology, miniaturization, integration and intelligent direction.

What are called sensors? Broadly speaking, the sensor is able to perceive the external information and according to certain rules will device available signal convert these information into; simple sensor is a device of external signals are converted to electrical signals. It consists of sensitive components (sensor) and the converter is composed of two parts, some semiconductor sensitive element can be directly output signals, in itself constitute a sensor. Sensitive components variety, the principle of its perception of external information, can be divided into physical, stress, heat, light, electricity, magnetic and other physical effects based on. The chemical class, based on the principle of chemical reaction. The biology class, enzymes, antibodies, and hormone based on molecular recognition function. Usually according to its basic cognitive function can be divided into thermosensitive element, a photosensitive element, gas sensor, force sensor, Ci Min element, humidity sensors, acoustic sensors, radiation sensitive element, color sensors and taste sensors and other ten categories (and there are people who have the sensor can be divided into 46 categories). The commonly used thermal, light, gas sensor, force sensor and the magnetic sensor and its sensing element is introduced as follows.
 
A temperature sensor and thermistor
The temperature sensor is mainly composed of a heat sensitive element. The thermosensitive element varieties more, market sales of the bimetallic strip, copper thermal resistance, thermocouple and platinum thermal resistance, thermal resistance. In a semiconductor thermistor as a temperature sensor detecting element widely, this is because the allowable working conditions in the element, semiconductor thermistor has the characteristics of small size, high sensitivity, high precision, and simple manufacturing process, low price.

The working principle of the 1 semiconductor thermistor
According to the temperature characteristic of thermistor can be divided into two categories, with the rise of temperature resistance increased as the positive temperature coefficient thermistor, contrary to the negative temperature coefficient thermistor.
The working principle of the positive temperature coefficient thermistor
This thermistor with barium titanate (BaTio3) as the basic material, then adding proper amount of rare earth elements, the use of ceramic technology high temperature sintering into seoul. Pure barium titanate is an insulating material, but is doped with rare earth elements such as lanthanum amount (La) and niobium (Nb) and later, a semiconductor material, known semiconducting barium titanate. It is a polycrystalline material, there is grain boundary between grains, for conducting electronic, grain boundary is equivalent to a barrier. When the temperature is low, because of the action of electric field in the semiconducting barium titanate, conducting electrons can easily cross the barrier, so the resistance value is small; when the temperature increases to the Curie point temperature (critical temperature, the components' temperature control points' general barium titanate Curie point is 120 ℃), the electric field within the subject failure, can't help conducting electrons across the barrier, so the performance is dramatically increased resistance value. Because this element has not reached the Curie point of resistance with temperature changes very slowly, with a constant temperature, temperature control and automatic temperature control function, not only fever, redness, no fire, not easy to burn, the voltage AC, DC 3 ~ 440V can, long service life, is very suitable for motor overheating and other electrical device detection.
The principle of negative temperature coefficient thermistor
Negative temperature coefficient thermistor with manganese oxide, cobalt oxide, nickel oxide, copper oxide and aluminum oxide as the main raw material, the manufacturing technology of ceramic and. These metal oxide materials have semiconductor properties, quite similar to germanium, silicon crystal material, the body of carriers (electrons and holes) the number of small, high resistivity; temperature, carrier number increases, the natural resistance to reduce. A lot of negative temperature coefficient thermistor type, used to distinguish between low temperature (-60 ~ 300 ℃), temperature (300 ~ 600 ℃), high temperature (>600 ℃) three, has the advantages of high sensitivity, good stability, fast response, long life, low price advantage, widely applied to fixed-point temperature temperature automatic control circuit the temperature control system, such as refrigerator, air conditioner, greenhouse.
Thermistor is combined with a simple amplifying circuit, can detect a thousand one degree change in temperature, so the electronic meter thermometer, can achieve high precision temperature measurement. The working temperature of general use thermistor is -55 ℃ ~ +315 ℃, special low temperature thermistor temperature below -55 ℃ to -273 ℃.

The 2 thermistor type
I made the thermistor is according to the standard SJ1155-82 to make model, consisting of four parts.
The first part: the LORD says, by the letter 'M' said sensitive element.
The second part: categories, said the positive temperature coefficient thermistor with the letter 'Z', or 'F' letters represent negative temperature coefficient thermistor.
The third part: use or features, with a digit (0-9) representation. General digital '1' represents a general purpose, '2' said regulator uses (negative temperature coefficient thermistor), '3' said microwave measurement purposes (negative temperature coefficient thermistor), '4' said heater (negative temperature coefficient thermistor), '5' '6' temperature measuring purposes, said temperature control uses' 7, 'said degaussing purposes (positive temperature coefficient thermistor),' 8 'represents a linear type (negative temperature coefficient thermistor),' 9 'represents the constant temperature type (positive temperature coefficient thermistor),' 0 'indicates special type (negative temperature coefficient thermistor)
The fourth part: serial number, but also by the digital representation, representative specification, performance.
Usually manufacturers for differences between special needs of this series of products, plus' derived number 'in number, consist of letters, numbers and' - 'number and.
Example: M Z 11

Main parameters of 3 thermistors
A variety of thermistor working conditions must be in the factory parameters within the allowed range. The main parameters of the thermistor has more than ten: nominal resistance values, the use of ambient temperature (maximum working temperature), measurement of power, rated power, rated voltage (maximum working voltage), working current, temperature coefficient, the material constants, time constant. The nominal resistance is the resistance at 25 ℃ zero power value, in fact there is a certain error, should be in within 10%. Operating temperature range of ordinary thermistor is larger, can choose according to need from -55 ℃ to +315 ℃, notably, the highest working temperature differences between different types of thermistor, such as MF11 sheet negative temperature coefficient thermistor is +125 ℃, +70 ℃ and MF53-1 only, should pay attention to students' experiment (generally do not more than 50 ℃).
 
4 experiments with thermistor
The preferred ordinary use of negative temperature coefficient thermistor, because it changes with temperature is generally higher than the positive temperature coefficient thermistor resistance value is easy to observe, continuous decreased significantly. If the selected positive temperature coefficient thermistors, temperature should be in the vicinity of the Curie temperature of the element.
Patients with MF11 negative temperature coefficient thermistor parameters
The MF11 thermistor symbol contour map of main technical parameters of the name parameter value
Nominal resistance (K Ω) 10 ~ 15 flaky appearance symbols
Rated power (W) 0.25
The material constants of B (k) 1980 ~ 3630
Temperature coefficient (10-2/ ℃) - (2.23 ~ 4.09)
Dissipation factor (mW/ ℃) ≥ 5
The time constant (s) ≤ 30
The maximum operating temperature (125 ℃)
Coarse thermistor value should be selected range, moderate and a thermistor measuring small electric current multimeter. If the 10K thermistor, can choose MF10 multimeter, the shift switch to the ohmmeter R × 100, replace the probes are respectively clamped thermistor with alligator clip two pin. When the environment temperature is significantly lower than the body temperature, 10.2k thermistor readings, knead by hand, can see the indication of resistance decreases; the hand, increased resistance, gradually restored. Such a thermistor can be selected (the highest working temperature 100 ℃).

Several practical temperature sensor
A air conditioner: special temperature sensor thermistor sealed in the copper metal.
B temperature sensor

Sensor and photosensitive two optical elements
Light sensor is mainly composed of light elements. At present, the rapid development of photosensitive element, variety, widely used. The market for the sale of a photosensitive resistor, diode, triode, photoelectric photoelectric coupler and optical cell.
1 photosensitive resistors
Photosensitive resistors by semiconductor photoelectric crystal transparent, because the semiconductor photoelectric crystal composition is different, can be divided into visible light photosensitive resistor (cadmium sulfide crystal), infrared light photosensitive resistor (GaAs crystals), and ultraviolet light photosensitive resistor (zinc sulfide crystals). When the wavelength of the light sensitive semiconductor photoelectric surface of the crystal, crystal carrier increased, the conductivity increased (i.e., reduced resistance).
The main parameters of photosensitive resistance:
The light current, light resistance: under a certain applied voltage, when light (100lx) irradiation, current flows through the photosensitive resistor called the light current; voltage and the current ratio of light resistance, usually within a few tens of K Ω K Ω ~.
The dark current, resistance in the dark: under a certain applied voltage, when there is no light (0 LX) irradiation, current flows through the photosensitive resistor called dark current; voltage and the current ratio of resistance in the dark, generally a few hundred thousand more than k Ω K Ω to.
The maximum working voltage: General tens of volts to hundreds of volts.
◆ environment temperature: -25 ℃ to +55 ℃, some models can be -40 ℃ to +70 ℃.
◆ rated power (power): photosensitive resistance light current and voltage product; can be 5mW to 300mW a variety of specifications to choose.
◆ photosensitive resistance of main parameters and response time, sensitivity, spectral response, light, temperature coefficient, I-V characteristics.
Notable is, light (with the strength characteristics of the changes of light), temperature coefficient (temperature dependent properties), volt ampere characteristic is not linear, such as CdS (CDS) resist photoresistance sometimes increased with the increase of temperature, sometimes with increasing temperature and smaller.
The parameters of the cadmium sulphide photoresistor:
Specification MG41-22 MG42-16 MG44-02 MG45-52
The ambient temperature (-40 ℃) to +60 -25 to +55 -40 to +70 -40 to +70
Rated power (mW) 20105200
Light resistance, 100lx (k) ≤ 2 ≤ 50 ≤ 2 ≤ 2
Resistance in the dark, 0lx (M) ≥ 1 ≥ 10 ≥ 0.2 ≥ 1
Response time (MS) ≤ 20 ≤ 20 ≤ 20 ≤ 20
Maximum working voltage (V) 1005020250
 
The 2 photodiode
Compared with ordinary diode, in addition to the tube core it is a PN junction, has a one-way conductive properties, others are very different. The first tube PN junction in the core of deep and shallow (less than 1 microns), in order to improve the photoelectric conversion ability; second PN junction area of relatively large, the area of the electrode is very small, in order to facilitate the photosensitive surface to collect more light; the third photodiode has a lens made of organic glass sealing, can gather light from the photosensitive surface "window" in appearance; so the sensitivity and response time photodiode is far superior to that of photosensitive resistance.
 
Several photo diode and a symbol common as follows:
2DU has a very, very, before after ring pole three pole. The ring is to reduce dark current photodiode and increase working stability and design, application should be connected to the positive pole. The main parameters of the photoelectric diode has: maximum working voltage (10 ~ 50V), dark current (≤ 0.05 ~ 1 a), the photocurrent (> 6 ~ 80 a), response time, photoelectric sensitivity (tens of ns to several s), junction capacitance and forward drop.
Advantages of photodiode is of good linearity, fast response, wide range of wavelengths of light has the advantages of high sensitivity, low noise; drawback is the output current (or voltage) alone is small, need to add the amplification circuit. Applicable to communication and photoelectric control circuit.
The photodiode detection can be used multimeter R * 1K block, to avoid the optical forward resistance should be 10K Ω to 200 Ω K, reverse ∞, remove the shade right after the deflection angle is larger, the higher the sensitivity.
Photoelectric triode can be regarded as a combination of elements of a photodiode and a triode, with amplification function, so the dark current, photocurrent and photoelectric sensitivity is much higher than the photodiode structure, but the junction capacitance increase, response characteristics. Photoelectric control circuit is widely used in low frequency.
Semiconductor optoelectronic devices and MOS structure, such as a common scanner, camera CCD (charge coupled device) is integrated photodiode array or MOS structure.
 
Three gas sensor and gas sensor
Textbooks only requires the thermistor and photosensitive resistance characteristics of a simple experiment. Due to the close correlation of gas and the daily life of human, the detection of gases is to protect and improve the ecological environment indispensable means, gas sensors play an extremely important role. For example, the concentration of carbon monoxide in the living environment of 0.8 ~ 1.15 ml/L, will appear shortness of breath, rapid pulse, even syncope state, up to 1.84ml/L when there is a risk of death within a few minutes, so the carbon monoxide detection must be fast and accurate. Using SnO2 metal oxide semiconductor gas sensing materials, preparation of SnO2 nano particles by ultrafine particle refinement and doping process, and as a catalyst substrate doping, the appropriate sintering process for surface modification, made by thermal sintering CO sensitive element, can CO gas detection range of 0.005% ~ 0.5%. There are a lot of explosive and combustible gas, alcohol gas, automobile exhaust and other toxic gas detection sensor. Commonly used in the main contact combustion type gas sensors, electrochemical gas sensor and semiconductor gas sensor etc.. Contact combustion type gas sensor detecting element is generally platinum wire (also can be coated with platinum, palladium and other rare metal catalyst layer), use of platinum wires connect with current, maintaining 300 ℃ ~ 400 ℃, if contact with combustible gas, the combustible gas will burn in the rare metal catalyst layer therefore, platinum wire temperature rises, the resistance of platinum wire also rose; value changes by measuring the electrical resistance of platinum wire size, known concentration of combustible gas. Electrochemical gas sensor by the liquid (or solid, organic gel electrolyte, etc.) the output could be in the form of direct current oxidation or reduction gas generated, and can also be electromotive force acting on the ion ion electrode. Semiconductor gas sensor with high sensitivity, fast response, good stability, easy to use features, the application is extremely broad; the following highlights the semiconductor gas sensor and a gas sensor.
Semiconductor gas sensor with N type and P type division. Type N in the detection of resistance decreases with the increase of gas concentration; P value increases with the concentration of gas. Like the SnO2 metal oxide semiconductor gas sensitive material, which belongs to the N type semiconductor, at 200 ~ 300 ℃ it absorbed oxygen in the air, forming a negative ion adsorption of oxygen, so that the electron density in the semiconductor is reduced, so that its resistance value increases. When a combustible gas supply electronic (such as CO), the adsorption of oxygen desorption, and the combustible gas in the positive ion adsorption on metal oxide semiconductor surface; oxygen desorption emitted electron, combustible gas line in the positive ion adsorption state to emit electron, increasing the oxide semiconductor conduction band the electron density, the resistance decreases. Combustible gas does not exist, the negative ion adsorption of metal oxide semiconductor will automatically restore oxygen, make the increase of resistance to the initial state. This is the basic principle of semiconductor gas sensor detection of combustible gas.
There are 2 kinds of gas sensor made in china. One is the direct heating, heating wire and a measuring electrode to sintering in metal oxide semiconductor tube core; heating type gas sensor on ceramic substrate, through the pipe heating wire, two measuring electrode tube outside, metal oxides gas sensing materials for measuring electrodes, made by high sintering.
Parameters of gas sensor is mainly a heating voltage, current, voltage measurement circuit, the sensitivity, response time, recovery time, calibration gas (0.1% butane gas) voltage, load resistance etc.. QM-N5 type gas sensor suitable for natural gas, coal gas, hydrogen, alkyl, alkene gases such as gas, gasoline, kerosene, acetylene, ammonia, smoke detection, which belongs to the N type semiconductor device. High sensitivity, good stability, short response and recovery time, the market wide application. The following parameters: QM-N5 gas sensor calibration gas (0.1% butane gas, the best working conditions) voltage is greater than or equal to 2V, the response time ≤ 10S ≤ 30S, recovery time, the best working conditions of 5V, heating voltage measurement circuit voltage of 10V, load resistor RL as 2K, allows the working conditions of electric heating pressure 4.5 ~ 5.5V, measurement circuit voltage 5 ~ 15V, 0.5 ~ 2.2K load resistance. Below is a simple test circuit for gas sensor (sensor), voltage meter pointer changes more, the higher the sensitivity; just add a simple circuit can realize the alarm. Common gas sensor and MQ-31 (dedicated to the detection of CO), QM-J1 alcohol sensor etc..
 
Four Li Min sensor and force sensor
Li Min of the many kinds of sensors, the traditional measurement method is using the deformation and displacement of elastic material to represent. With the development of microelectronic technology, based on the piezoresistive effect of semiconductor materials (i.e., pressure, the one direction and the resistivity changes) and good elasticity, has developed the Li Min sensor has the advantages of small volume, light weight, high sensitivity, widely used in the measurement of mechanical pressure, acceleration, weight.
 
The five magnetic sensor and magnetic sensor
The magnetosensor with Holzer device (based on the Holzer effect), magnetoresistive devices (based on magnetoresistive effect: magnetic field made the semiconductor resistance increases with the magnetic field increases.) , magneto diode and triode. Magnetic sensor based on magneto sensor is widely used in the measurement of electrical, magnetic and mechanical quantities of.
In a certain sense sensor and the sense of people have a corresponding relationship, the perception has been far more than human senses. For example, was observed by using the target's infrared radiation of infrared imaging system (night like instrument), the night can be found 1000 m, 2000 meters found the vehicle; the core components of the imager is infrared sensor. In the 1991 Gulf War, the Iraqi tank configuration of night vision instrument detection distance of only 800 meters, is less than half the coalition, the darkness was badly defeated is inevitable. At present, all the countries in the world to sensor technology as the focus of high-tech development priority. In order to greatly improve the performance of the sensor, the constant use of new structure, new materials and new technology, miniaturization, integration and intelligent direction.


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