The sensor (English name: transducer/sensor) is a detection device that can feel the measured information, and can transform the felt information into an electrical signal or other required form of information output according to a certain law, so as to meet the requirements of information transmission, processing, storage, display, recording and control. The sensor has the characteristics of miniaturization, digitization, intelligence, multi-functionalization, systematization, networking, etc., and it is the primary link to realize automatic detection and automatic control.
Main classifications:
By use
Pressure and Force Sensitive Sensors, Position Sensors, Liquid Level Sensors, Energy Consumption Sensors, Speed Sensors, Accelerometer Sensors, Radiation Sensors, Thermal Sensors.
According to the principle
Vibration sensors, moisture sensors, magnetic sensors, gas sensors, vacuum sensors, biosensors, etc.
Press the output signal
Analog Sensor: Converts the measured non-electrical quantity into an analog electrical signal.
Digital sensor: Converts measured non-electrical quantities into digital output signals (both direct and indirect).
Digital sensor: The output (including direct or indirect conversion) that converts the measured signal into a frequency signal or a short-period signal.
Switching sensors: When a measured signal reaches a certain threshold, the sensor outputs a set low or high signal accordingly.
Manufactured according to it
Process integrated sensors are manufactured using standard process techniques for the production of silicon-based semiconductor integrated circuits. Often, part of the circuitry used for the initial processing of the signal under test is also integrated on the same chip.
Thin-film sensors are formed by depositing a thin film of the corresponding sensitive material on a dielectric substrate (substrate). In the case of a hybrid process, part of the circuit can also be fabricated on this substrate.
Thick film sensors are made by using a slurry of the corresponding material, coated on a ceramic substrate, which is usually made of Al2O3, and then heat treated to form the thick film.
Ceramic sensors are produced using standard ceramic processes or some variation of them (sols, gels, etc.). After the appropriate preparatory operation, the formed components are sintered at high temperatures. There are many common characteristics between the two processes, thick film and ceramic sensors, and in some ways, the thick film process can be considered a variant 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 the sensor parameters, ceramic and thick-film sensors make sense.
By Measurement Purpose
Physical sensors are made by taking advantage of the property that some of the physical properties of the substance being measured have changed significantly.
Chemical sensors are made of sensitive components that convert chemical quantities such as the composition and concentration of chemical substances into electrical quantities.
Biosensors are sensors that use the characteristics of various organisms or biological substances to detect and identify the chemical components of living organisms.
According to its composition
Basic Sensor: This is the most basic single transducer.
Combined sensor: A sensor that is composed of a combination of different individual transducers.
Application-oriented sensor: A sensor that is composed of a basic sensor or a combined sensor combined with other mechanisms.
By the form of action
According to the form of action, it can be divided into active and passive sensors.
The active sensor has a role type and a reaction type, this kind of sensor can send a certain detection signal to the measured object, can detect the change of the detection signal in the measured object, or form a signal by the detection signal in the measured object. The mode of detecting the change of the signal is called the action type, and the mode of detecting the response and forming the signal is called the reaction type. Radar and radio frequency range detectors are action-type examples, while photoacoustic effect analysis devices and laser analyzers are reaction-type examples.
Passive sensors only receive signals generated by the measured object itself, such as infrared radiation thermometers, infrared camera devices, etc.
Selection principle
In order to carry out a specific measurement work, it is necessary to first consider the principle of the sensor, which needs to be determined after analyzing many factors. Because, even if the same physical quantity is measured, there are a variety of principles of sensors to choose from, which principle of the sensor is more suitable, it is necessary to consider the following specific issues according to the characteristics of the measurement and the use conditions of the sensor: the size of the measuring range, the volume of the sensor at the measured position, the measurement method is contact or non-contact, the method of signal extraction, wired or non-contact measurement, the source of the sensor, domestic or imported, whether the price can be afforded, or self-developed. After considering the above questions, it is possible to determine which type of sensor to use, and then consider the specific performance indicators of the sensor.
Selection of sensitivity
In general, within the linear range of the sensor, the higher the sensitivity of the sensor, the better. This is because only when the sensitivity is high, the value of the output signal corresponding to the change to be measured is relatively large, which is conducive to signal processing. However, it should be noted that the sensitivity of the sensor is high, and the external noise that is not related to the measurement is also easy to mix, and will also be amplified by the amplification system, affecting the measurement accuracy. Therefore, it is required that the sensor itself should have a high signal-to-noise ratio to minimize the interference signal introduced from the outside world. The sensitivity of the sensor is directional. When the measured is a one-vector quantity and its directionality is required to be high, the sensor with low sensitivity in other directions should be selected, and if the measurement is a multi-dimensional vector, the smaller the cross-sensitivity of the sensor, the better.
Frequency response characteristics
The frequency response characteristics of the sensor determine the frequency range to be measured and must be undistorted within the permissible frequency range. In fact, there is always a certain delay in the response of the sensor, and the shorter the delay time, the better. The higher the frequency response of the sensor, the wider the frequency range of the signal that can be measured. In dynamic measurements, the response characteristics should be based on the characteristics of the signal (steady-state, transient, random, etc.) to avoid excessive errors.
Linear range
The linear range of a sensor is the range in which the output is proportional to the input. Theoretically, the sensitivity remains constant within this range. The wider the linear range of the sensor, the greater the measuring range and the measurement accuracy. When selecting a sensor, when the type of sensor is determined, the first thing to see is whether its range meets the requirements. But in reality, no sensor can guarantee absolute linearity, and its linearity is also relative. When the required measurement accuracy is relatively low, within a certain range, the sensor with small nonlinear error can be approximately regarded as linear, which will bring great convenience to the measurement.
stability
The ability of a sensor to maintain its performance unchanged over a period of time is known as stability. In addition to the structure of the sensor itself, the factors that affect the long-term stability of the sensor are mainly the environment in which the sensor is used. Therefore, in order for the sensor to have good stability, the sensor must have strong environmental adaptability. Before selecting a sensor, it is necessary to investigate the environment in which it will be used, and select the appropriate sensor according to the specific environment in which it will be used, or take appropriate measures to reduce the impact of the environment. There are quantitative indicators for the stability of the sensor, and after the expiration of the service life, it should be recalibrated before use to determine if the performance of the sensor has changed. In some occasions where the sensor is required to be used for a long time and cannot be easily replaced or calibrated, the stability of the selected sensor is more stringent and can withstand the test for a long time.
precision
Accuracy is an important performance index of the sensor, and it is an important link related to the measurement accuracy of the whole measurement system. The higher the accuracy of the sensor, the more expensive it is, so the accuracy of the sensor only needs to meet the accuracy requirements of the entire measurement system, and it is not necessary to choose too high. This makes it possible to choose from a wide range of sensors for the same measurement purpose, which are relatively inexpensive and simple sensor Atlas compressor accessories. If the measurement purpose is qualitative analysis, the sensor with high repeatability can be selected, and the absolute accuracy is not high; if it is for quantitative analysis, the accurate measurement value must be obtained, and the accuracy level can meet the requirements of the sensor. For some special use occasions, if the suitable sensor cannot be selected, the sensor needs to be designed and manufactured by itself. The performance of the self-made sensor should meet the requirements of use.