What is a sensor? Sensor related knowledge analysis

What is a sensor? What are the classifications of sensors? How does the sensor work? First, the definition of sensor The national standard GB7665-87 defines a sensor as: 'a device or device that can sense the specified measured and convert it into a usable signal according to a certain law, usually composed of sensitive elements and conversion elements'. A sensor is a detection device that can sense the measured information, and can transform the sensed information into electrical signals or other required forms of information output according to certain rules, so as to meet the requirements of information transmission, processing, storage, Display, record and control requirements. 2. Classification of sensors There is currently no unified classification of sensors, but there are three commonly used ones: 1. According to the physical quantity of the sensor, it can be divided into sensors such as displacement, force, speed, temperature, flow, gas composition, etc. 2. Press The working principle of the sensor is classified, which can be divided into resistance, capacitance, inductance, voltage, Hall, photoelectric, grating, thermocouple and other sensors. 3. According to the nature of the sensor output signal, it can be divided into: switch-type sensor whose output is switch quantity ('1' and '0' or 'on' and 'off'); output is analog sensor; output is pulse or The digital sensor of the code. Third, the static characteristics of the sensor The static characteristic of the sensor refers to the static input signal, the output of the sensor and the input of the sensor have a relationship. Because at this time, the input and output are independent of time. , so the relationship between them, that is, the static characteristics of the sensor can be described by an algebraic equation without time variables, or a characteristic curve drawn by taking the input quantity as the abscissa and the corresponding output quantity as the ordinate. The main parameters of the static characteristics of the sensor are: linearity, sensitivity, resolution and hysteresis, etc. Fourth, the dynamic characteristics of the sensor The so-called dynamic characteristics refer to the characteristics of the output of the sensor when the input changes. In actual work, the sensor's The dynamic characteristics 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 obtain experimentally, and its response to the standard input signal and its response to any input signal are between There is a certain relationship, and it is often possible to infer the latter after knowing the former. Commonly used standard input signals include step signal and sinusoidal signal, 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 meter have a uniform scale reading, a fitted straight line is often used to approximately represent the actual characteristic curve, linearity (non-linearity) Linearity error) is a performance index of the degree of approximation. There are many ways to select the fitting straight line. For example, the theoretical straight line connecting the zero input and the full-scale output point is used as the fitting straight line; The theoretical straight line whose sum of squares is small is used as the fitting straight line, and this fitting straight line is called the fitting straight line of the small square method. 6. The sensitivity of the sensor refers to the change of the output quantity of the sensor under steady-state operation △y to the change of the input quantity △ The ratio of x. It is the slope of the output-input characteristic curve. If there is a linear relationship between the output of the sensor and the input, the sensitivity S is a constant. Otherwise, it will vary with the input amount. The dimension of sensitivity is The ratio of the dimensions of output and input. For example, when the displacement of a displacement sensor changes by 1mm, and the output voltage changes to 200mV, its sensitivity should be expressed as 200mV/mm. When the dimensions of the sensor's output and input are the same, the sensitivity It can be understood as the magnification. Higher sensitivity can be obtained by increasing the sensitivity. However, the higher the sensitivity, the narrower the measurement range and the worse the stability. The ability to measure small changes. That is, if the input changes slowly from a certain 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's response to this input The change is indistinguishable. Only when the change of the input quantity exceeds the resolving power, its output will change out. Usually the resolution of each point in the full-scale range of the sensor is not the same, so the large change value in the input quantity that can produce a step change in the output quantity in the full-scale range is often used as an index to measure the resolution. If the above indicators are expressed as a percentage of full scale, it is called resolution. 8. Resistive sensor Resistive sensor is a device that converts physical quantities such as displacement, deformation, force, acceleration, humidity, temperature, etc. into resistance values. There are mainly resistance strain sensor, piezoresistive, thermal resistance, thermal, gas sensor, humidity sensor and other resistive sensor devices.
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