Ⅰ. The impact of sensors on the environment
Ⅱ. Selection of the number of sensors and range
Ⅲ. Classification of sensors
Ⅳ. The principle and application of sensor
Ⅴ. Sensor precision and accuracy
Ⅰ. The impact of sensors on the environment
1. Inflammable and explosive not only cause complete damage to the sensor, but also pose a great threat to other equipment and personal safety. Therefore, sensors working in flammable and explosive environments put forward higher requirements for explosion-proof performance: in flammable and explosive environments, explosion-proof sensors must be selected. The sealed outer cover of this sensor must not only consider its airtightness, but also The explosion-proof strength, as well as the waterproof, moisture-proof, and explosion-proof properties of the cable outlets should be considered.
2. The high-temperature environment causes problems such as melting of the coating material, opening of the solder joints, and structural changes in the internal stress of the elastomer to the sensor. For sensors working in high temperature environments, high temperature resistant sensors are often used; in addition, devices such as heat insulation, water cooling or air cooling must be added.
3. In a highly corrosive environment, such as humidity and acidity, which may cause damage to the elastic body or short circuit of the sensor, the outer surface should be sprayed with plastic or a stainless steel cover, and the sensor with good corrosion resistance and good airtightness should be selected.
4. Dust and moisture will cause a short circuit to the sensor. Under this environmental condition, a sensor with high airtightness should be selected. Different sensors have different sealing methods, and there are great differences in their airtightness.
Common seals include sealant filling or coating; rubber pad mechanical fastening seal; welding (argon arc welding, plasma beam welding) and vacuum nitrogen filling seal. From the perspective of sealing effect, the welding seal is the best, and the filling and coating sealant is the worst. For sensors that work in a clean and dry environment indoors, you can choose a sensor that is glued and sealed. For some sensors that work in a humid and dusty environment, you should choose a diaphragm shrink seal or a diaphragm welded seal. Vacuum nitrogen sensor.
5. The influence of the electromagnetic field on the output disorder signal of the sensor. In this case, the shielding of the sensor should be strictly checked to see if it has good anti-electromagnetic ability.
Ⅱ. Selection of the number of sensors and range
The choice of the number of sensors is based on the use of the electronic scale and the number of points that the scale body needs to support. Generally speaking, if the scale body has several support points, several sensors should be selected, but for some special scale bodies such as electronic hook scales, only one sensor can be used, and some electromechanical combination scales should determine the selection of sensors according to the actual situation. number.
The selection of the measuring range of the sensor can be determined based on the comprehensive evaluation of the maximum weighing value of the scale, the number of selected sensors, the self-weight of the scale body, the possible maximum eccentric load and dynamic load and other factors. In general, the closer the sensor's range is to the load assigned to each sensor, the more accurate it will be. However, in actual use, since the load on the sensor includes loads such as the self-weight of the scale body, tare weight, eccentric load, and vibration and shock in addition to the object to be weighed, many factors must be considered when selecting the sensor range to ensure Sensor safety and longevity.
The calculation formula of the measuring range of the sensor is determined through a large number of experiments after fully considering various factors affecting the scale body.
The formula is as follows:
C=K-0K-1K-2K-3 (Wmax+W)/N
C—the rated range of a single sensor; W—the weight of the scale body; N—the number of support points used by the scale body; Wmax—the maximum net weight of the object being weighed; K-0—the insurance factor, generally between 1.2 and 1.3 K-1—impact coefficient; K-2—center of gravity offset coefficient of the scale body; K-3—wind pressure coefficient.
Generally, the sensor should work within 30% to 70% of its range, but for some weighing instruments that have a large impact force during use, such as dynamic track scales, dynamic truck scales, steel scales, etc., when selecting sensors, it is generally necessary to expand Its range makes the sensor work within 20% to 30% of its range, and increases the weighing reserve of the sensor to ensure the safety and life of the sensor.
The accuracy level of the sensor includes the technical indicators such as the nonlinearity, creep, creep recovery, hysteresis, repeatability, and sensitivity of the sensor. The choice of sensor level must meet the following two conditions:
1. Meet the accuracy requirements of the entire electronic scale. An electronic scale is mainly composed of three parts: scale body, sensor and instrument. When selecting the accuracy of the sensor, the accuracy of the sensor should be slightly higher than the theoretical calculation value, because the theory is often limited by objective conditions. The strength of the body is poor, the performance of the instrument is not very good, the working environment of the scale is relatively bad and other factors directly affect the accuracy requirements of the scale.
2. Meet the requirements of instrument input. The weighing display instrument displays the weighing result after the output signal of the sensor is amplified and A/D converted.
Therefore, the output signal of the sensor must be greater than or equal to the input signal required by the instrument, that is, the output sensitivity of the sensor is replaced by the matching formula of the sensor and the instrument, and the calculation result must be greater than or equal to the input sensitivity required by the instrument.
Ⅲ. Classification of sensors
1. Inductive sensor: Inductive sensor is a device that uses changes in coil self-inductance or mutual inductance to achieve measurement. Inductive sensors can be used to measure physical quantities such as displacement, vibration, pressure, flow, weight, torque, and strain. Its advantages: simple and reliable structure, high output power, strong anti-interference ability, low requirements for working environment, high resolution and good stability. The principle of inductance is based on Faraday's law of electromagnetic induction, that is, when a conductor (or metal) moves in a changing magnetic field, an induced current will be generated in the conductor, thereby generating an induced electromagnetic field.
2. Pyroelectric sensor: It is a sensor that works on the principle of pyroelectric effect and is used to measure temperature. The thermoelectric effect refers to the generation of a voltage difference between the contact points of two dissimilar materials when a temperature difference exists, thereby generating an electric current. This effect is used in pyroelectric sensors, where temperature can be determined by measuring the resulting voltage or current.
3. Ultrasonic sensor: It is a device that uses ultrasonic waves (high-frequency sound waves) to measure the distance of objects, detect the presence of objects, and perform distance measurement. These sensors calculate the distance between an object and the sensor by emitting ultrasonic pulses and receiving their reflected signals. Ultrasonic sensors usually have the advantages of non-contact measurement, high precision, and wide application fields. The sensor emits a pulse of ultrasound that travels through the air at the speed of sound. The frequency of this pulse is usually between 20kHz and 200kHz. When an ultrasonic pulse encounters an object and intersects its surface, some of the acoustic energy is reflected by the object back to the sensor. The sensor receives reflected acoustic signals that have a delay proportional to the distance of the object.
4. Isotope sensor: It is a sensor used to detect and measure the presence and activity of radioactive isotopes (radionuclide) in the environment. Radioisotopes are nuclides with unstable nuclei that release radiation through radioactive decay. These sensors are commonly used in nuclear radiation monitoring, nuclear energy industry, medical radiation therapy, nuclear waste management and other fields. The working principle of isotope sensors involves measuring the radiation released by the decay of radioactive isotopes, such as alpha rays, beta rays, gamma rays, etc. This radiation interacts with sensitive elements in the sensor, such as radiation-sensitive detectors, to generate a measurement signal.
5. Resistive sensor: It is a kind of sensor. Its basic principle is to convert the change of the measured physical quantity into the change of the resistance value, and then display the change of the measured quantity through the corresponding measurement circuit. The force measurement, pressure measurement, weighing, displacement measurement, acceleration measurement, torque measurement, temperature measurement and other test systems composed of resistive sensors and corresponding measurement circuits have become one of the indispensable means for production process detection and production automation. . Potentiometer is a common electromechanical component.
According to its different structure, potentiometer can be divided into wire wound type, film type, photoelectric type, etc.; according to different characteristics, it can be divided into linear potentiometer and nonlinear potentiometer. The potentiometer sensor has a series of advantages, such as simple structure, small size, light weight, high precision, large output signal, stable performance and easy realization of arbitrary functions. Its disadvantage is that it requires a large input energy, and it is easy to wear between the brush and the resistance element.
6. Piezoelectric sensor: It is a kind of sensor based on the piezoelectric effect, which is used to detect and measure physical quantities such as pressure, force, acceleration, and vibration. The piezoelectric effect refers to the unbalanced charge distribution that certain crystalline materials produce when subjected to pressure or force, resulting in a potential difference. This effect can be used to convert mechanical energy into electrical signals. Piezoelectric sensors use piezoelectric materials as sensing elements, and the most common piezoelectric materials are quartz crystals and ceramic materials such as PZT (lead barium zirconate titanate), etc.
When external pressure, force, or vibration acts on a piezoelectric material, the lattice structure within the material is slightly deformed, resulting in an imbalanced distribution of positive and negative charges. Deformation of the piezoelectric material results in an uneven charge distribution, causing charges to be generated on the surface of the material. Due to the uneven charge distribution, a potential difference, a voltage signal, is generated between the two surfaces of the piezoelectric material.
7. Capacitive sensor: It is a kind of sensor based on the principle of capacitance, which is used to detect and measure physical quantities such as the position, proximity, touch, liquid level, and humidity of objects. These sensors use changes in capacitance to sense the properties of a target object. Capacitance is the ability to store electrical charge, usually determined by the distance and material between two conductors. Capacitance is the charge storage capacity between two conductors, usually expressed as the voltage difference per unit charge.
The capacitance value is inversely proportional to the distance between two conductors and directly proportional to the dielectric constant of the medium. When a target object approaches a capacitive sensor, it changes the electric field distribution of the capacitor. This can lead to a change in capacitance value as the presence of the target object changes the distance or permittivity between conductors. Capacitive sensors measure changes in capacitance, usually by measuring voltage or current across the sensor. The change in capacitance value can be used to infer the properties of the target object, such as location, shape, proximity, etc.
8. Temperature sensor: A temperature sensor is a type of sensor used to measure ambient temperature. Its function is to convert temperature changes into electrical signals for processing and display in electronic devices.
Common temperature sensor types:
Semiconductor temperature sensors: These sensors are based on the electrical properties of semiconductor materials changing with temperature. The most common type is a negative temperature coefficient (NTC) thermistor, whose resistance decreases as temperature increases. The other is a positive temperature coefficient (PTC) thermistor, which increases in resistance as temperature increases.
Thermocouples: Thermocouples measure temperature using the potential difference between two different metallic materials at different temperatures. The working principle of thermocouples is based on the thermoelectric effect, that is, the conductivity of different metals changes due to temperature changes, resulting in a small potential difference. Thermocouples are suitable for high temperature environments and rough applications.
Infrared Temperature Sensors: Also known as thermal imaging cameras or infrared thermometers, the temperature of an object is inferred by measuring the infrared radiation emitted by the object. This sensor is suitable for remote temperature measurement, such as measuring the temperature in a furnace or for remote measurement.
RTD, Resistance Temperature Detector): Thermistor is a sensor that works based on the principle that the resistance value changes with temperature. The most common type is PT100, which has a resistance of 100 ohms at 0°C and varies linearly with temperature. The PT1000 is a similar sensor with a resistance of 1000 ohms at 0°C. The high accuracy of the thermistor is especially suitable for precise temperature measurement.
9. Gas sensor: It is a type of sensor used to detect and measure the concentration of different gases in the environment. These sensors can sense various gases such as hazardous gases, combustible gases, volatile organic compounds (VOCs), air quality index (AQI), etc.
10. Pressure sensor: It is a sensor used to measure pressure. It can measure the pressure of liquid or gas, and convert the pressure change into an electrical signal, which can be processed and displayed in electronic equipment. Pressure sensors typically contain a sensing element that responds to external pressure applied to it. Sensing elements can be materials such as curved films, metal diaphragms, and silicon micromachining. When external pressure is applied to the sensing element, the element deforms or strains slightly. These strains cause changes in the electrical properties (eg, resistance, capacitance) of the sensing element. Changes in strain on the sensing element are converted into electrical signals, usually amplified, filtered and converted by circuitry. Ultimately, this electrical signal can be expressed as a voltage or current signal proportional to the externally applied pressure.
11. Flow sensor: It is a sensor used to measure the flow rate of liquid or gas, and the flow rate is determined by monitoring the rate at which the fluid passes through the sensor.
Common Flow Sensor Types:
Thermal Flow Sensors: Thermal flow sensors measure flow rate based on the heat transfer properties of a fluid. The sensor heats the heating element to a certain temperature and then measures the time it takes for the fluid to cool the heating element to calculate the flow rate.
Turbine Flow Sensors: Turbine flow sensors measure flow rate through a turbine rotating in a fluid. The rotational speed of the turbine is directly proportional to the flow rate, and the sensor converts the number of revolutions into an electrical signal to measure the flow.
Ultrasonic Flow Sensors: Ultrasonic flow sensors use ultrasonic waves to measure the flow rate of a fluid. They calculate flow velocity by sending an ultrasonic signal through the fluid and then measuring the time it takes for the signal to travel.
12. Illuminance sensor: It is a sensor used to measure light intensity (illuminance), which is widely used in lighting control, environmental monitoring, photography, automatic adjustment equipment and other fields. A light sensor typically consists of a light-sensitive element that responds to changes in the intensity of incoming light. The most common light-sensitive elements are light-dependent resistors (LDRs) and photodiodes (photodiodes).
13. Hall effect sensor: It is a sensor that works on the principle of Hall effect and is used to measure the strength of magnetic field, detect the direction of magnetic field and monitor the position of objects. The Hall effect means that in a conductive material, when the current passes through the material, it is subjected to the Lorentz force perpendicular to the direction of the current and magnetic field, resulting in a lateral displacement of the charge in the material. Hall effect sensors typically contain a Hall element, which is a thin sheet or crystal that detects changes in an external magnetic field. The current passing through the Hall element is usually called Hall current. This current creates an electric field within the element. When an external magnetic field is applied to the element, the electrons in the current flow experience a Lorentz force that deflects the electrons, causing charge to accumulate on one side of the element and decrease on the other.
14. Analog sensor: It is a type of sensor that converts physical quantities or environmental parameters into analog electrical signals. The output signal generated by these sensors is analog, usually a voltage or current, whose magnitude is proportional to the physical quantity or parameter being sensed. The output signal of the analog sensor changes continuously, and its precision and accuracy depend on the design and manufacturing quality of the sensor.
15. Digital sensor: It is a type of sensor that converts physical quantities or environmental parameters into digital signals. Unlike analog sensors, the output signals of digital sensors are discrete digital values that can be directly interacted with, processed and analyzed by digital electronic systems. Its advantage is that it makes accurate measurement and representation easier, less susceptible to electromagnetic interference, can directly interact, process and analyze with digital electronic systems, and reduces the complexity of data processing.
16. Vibration sensor: It is a sensor used to detect the vibration, shock or mechanical movement of an object. These sensors measure information such as the vibration frequency, amplitude and acceleration of an object and convert it into an electrical signal for monitoring, analysis and control. Vibration sensors can be used in structural health monitoring, medical equipment, industrial machinery, and automotive.
17. Optical sensor: It is a type of sensor that works on the principle of optics and is used to detect information such as light, color, distance, and shape. They measure properties of light to generate electrical signals, which are then used in applications such as data acquisition, control, analysis, and more.
18. Motion sensor: It is a type of sensor used to detect the motion, position, direction and other information of objects. These sensors can monitor parameters such as acceleration, angular velocity, and angle of an object, and convert this information into electrical signals for applications such as motion analysis, control, and navigation.
19. Touch sensor: A touch sensor is a type of sensor used to detect the contact or approach of an object, which can sense the contact, pressure or position of the human body, object or other physical quantities.
20. Magnetic sensor: It is a type of sensor used to detect magnetic fields, which can sense the strength and direction of the magnetic field around objects. These sensors convert magnetic field information into electrical signals for applications such as magnetic field measurement, navigation, position detection, and more.
21. Current sensor: It is a type of sensor used to measure current, which can detect the current intensity passing through the conductor. These sensors convert current information into a voltage or electrical signal.
Ⅳ. The principle and application of sensor
1. Principle
The principle of the sensor is based on physical and electrical principles. The function of the sensor is to convert the physical quantity into an electrical signal, and this conversion process is completed by the sensing element inside the sensor. A sensing element is an element that can change its electrical properties according to changes in external physical quantities.
2. Application
Smart Home: Sensors can be used to control home devices such as smart lights, temperature, doors, windows, etc. to improve home safety and comfort.
Smart Transportation: Sensors can be used to monitor parameters such as position, speed, direction of vehicles to optimize traffic flow and improve road safety.
Industrial automation: Sensors can be used to monitor parameters such as temperature, humidity, pressure, and flow of production lines to achieve automated control and improve production efficiency.
Agriculture: Sensors can be used to monitor parameters such as soil moisture, temperature, and light to improve the yield and quality of crops.
Ⅴ. Sensor precision and accuracy
Accuracy: Accuracy is the deviation or error between the sensor measurement and the actual measurement. Accuracy is usually expressed as a percentage or a specific number, reflecting the difference between the measured value of the sensor and the true value. For example, a temperature sensor with an accuracy of ±1% may have an error of up to ±1% in the measurement process. The higher the accuracy, the closer the sensor's measurement is to the true value.
Accuracy: Accuracy refers to the repeatability and consistency between the measurement results obtained by the sensor in multiple measurements. Accuracy describes how consistent a sensor is when it makes multiple measurements under the same conditions. A sensor has high accuracy if its measurements vary little over multiple measurements.
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