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 to meet the requirements of information transmission, processing, storage, display, recording and control.
The existence and development of sensors, so that the object has the sense of touch, taste and smell, so that the object becomes alive, the sensor is the extension of human features.
The sensor has the characteristics of miniaturization, digitalization, intelligence, multi-function, systematization, networking, etc. It is the primary link to realize automatic detection and automatic control.
The new aluminum nitride sensor can operate at high temperatures up to 900 ° C.
The national standard GB7665-87 defines a sensor as: "A device or device that can feel the specified measured and converted into a usable signal according to a certain law (mathematical function rule), usually consisting of a sensitive element and a conversion element."
The China Internet of Things school-Enterprise Alliance believes that the existence and development of sensors make objects have senses such as touch, taste and smell, and make objects slowly become alive."
"Sensor" is defined as "receiving power from one system, usually in another form, to a device in a second system".
Main classification
By purpose
Pressure and force sensors, position sensors, liquid level sensors, energy consumption sensors, speed sensors, acceleration sensors, radiation sensors, thermal sensors.
In principle
Vibration sensor, humidity sensor, magnetic sensor, gas sensor, vacuum sensor, biological sensor, etc.
Per output
Digital sensor: Converts the measured non-electrical quantity into a digital output signal (including direct and indirect conversion).
Pseudo digital sensor: The output of the measured semaphore into a frequency signal or a short-period signal (including direct or indirect conversion).
Switch sensor: When a measured signal reaches a certain threshold, the sensor outputs a set low or high level signal accordingly.
According to its manufacturing process
Integrated sensors are manufactured using standard process techniques for the production of silicon-based semiconductor integrated circuits. Typically, part of the circuit 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). When the hybrid process is used, part of the circuit can also be manufactured on this substrate.
The thick film sensor is made of 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 by standard ceramic processes or some variant of them (sol, gel, etc.).
After the appropriate preparatory operation is completed, the formed components are sintered at high temperatures. There are many common characteristics between the two processes of thick film and ceramic sensor, and in some respects, the thick film process can be considered as 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 sensor parameters, the use of ceramic and thick film sensors is more reasonable.
By measure
Physical sensors are made using the properties of certain physical properties of the substance being measured to change significantly.
Chemical sensors are made of sensitive elements that can convert chemical quantities such as 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 chemical components in organisms.
In its composition
Basic sensor: It is the most basic single conversion device.
Combined sensor: It is a sensor composed of different individual conversion devices.
Application sensor: It is a sensor composed of a basic sensor or a combined sensor and other mechanisms.
In action form
According to the form of action can be divided into active and passive sensors.
The active sensor has an action type and a reaction type, which can emit a certain detection signal to the tested object, and can detect the change of the detection signal in the tested object, or the signal is formed by the detection signal in the tested object. The mode of detecting the change of the detection 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 examples of action, while photoacoustic effect analysis devices and laser analyzers are examples of reaction.
Passive sensors only receive signals generated by the measured object itself, such as infrared radiation thermometers and infrared camera devices.
Main characteristics
Sensor static
1. Linearity: refers to the degree to which the actual relationship curve between the sensor output and input deviates from the fitted straight line. Defined as the ratio of the maximum deviation between the actual characteristic curve and the fitted line in the full scale range to the full scale output value.
2. Sensitivity: Sensitivity is an important indicator of the static characteristics of the sensor. It is defined as the ratio of the increment of the output quantity to the corresponding increment of the input quantity that causes the increment. The sensitivity is denoted by S.
3. Hysteresis: When the input volume of the sensor changes from small to large (positive stroke) and the input volume changes from large to small (reverse stroke), the phenomenon of non-coincidence of the input and output characteristic curves becomes hysteresis. For the same size of the input signal, the positive and negative stroke output signal of the sensor is not equal, and this difference is called the hysteresis value.
4. Repeatability: Repeatability refers to the degree of inconsistency of the characteristic curve obtained when the input quantity of the sensor is continuously changed in the full range in the same direction.
5. Drift: The drift of the sensor means that the output of the sensor changes with time when the input is unchanged, which is called drift. There are two reasons for the drift: one is the structural parameters of the sensor itself; The second is the surrounding environment (such as temperature, humidity, etc.).
6. Resolution: When the input of the sensor increases slowly from a non-zero value, the output changes observable after exceeding a certain increment, the input increment is called the resolution of the sensor, that is, the minimum input increment.
7. Threshold value: When the input of the sensor increases slowly from zero, the output changes observable after reaching a certain value, which is called the threshold voltage of the sensor.
Sensor dynamics
The so-called dynamic characteristics refer to the characteristics of the output of the sensor when the input changes. In practice, the dynamic characteristics of a sensor are often expressed by its response to some standard input signals. This is because the response of the sensor to the standard input signal is easy to be obtained by experimental methods, and there is a certain relationship between its response to the standard input signal and its response to any input signal, often knowing the former can infer the latter. The most commonly used standard input signals are step signals and sinusoidal signals, so the dynamic characteristics of the sensor are also commonly expressed by step response and frequency response.
linearity
Under normal circumstances, the actual static characteristic output of the sensor is a curve rather than a straight line. In practical work, in order to make the instrument have a uniform scale reading, a fitting line is commonly used to approximate the actual characteristic curve, linearity (nonlinear error) is a performance index of this approximation.
There are many ways to choose the fitting line. For example, the theoretical line connecting zero input and full scale output points is used as the fitting line; Or the theoretical line with the smallest sum of squares deviation from each point on the characteristic curve is taken as the fitting line, which is called the least square fitting line.
Sensitivity
Sensitivity refers to the ratio of the change of output △y to the change of input △x under steady state operation of the sensor.
It is the slope of the output - input characteristic curve. If there is a linear relationship between the output and input of the sensor, then the sensitivity S is a constant. Otherwise, it will change with the amount of input.
The dimension of sensitivity is the ratio of the dimensions of the output and input quantities. For example, a displacement sensor, when the displacement changes by 1mm, the output voltage changes by 200mV, then its sensitivity should be expressed as 200mV/mm.
When the output and input dimensions of the sensor are the same, the sensitivity can be understood as the magnification.
Higher measurement accuracy can be obtained by increasing the sensitivity. However, the higher the sensitivity, the narrower the measurement range, and the worse the stability.
Resolution
Resolution refers to the ability of the sensor to sense the smallest changes being measured. That is, if the amount of input changes slowly from some non-zero value. When the input change value does not exceed a certain value, the output of the sensor will not change, that is, the sensor can not distinguish the change of the input amount. The output changes only when the input volume changes more than the resolution.
Generally, the resolution of each point in the full scale range of the sensor is not the same, so the maximum change value of the input that can make the output step change in the full scale is often used as an indicator to measure the resolution. If the above indicator is expressed as a percentage of the full scale, it is called resolution. The resolution is negatively correlated with the stability of the sensor.