Definition and composition of sensors

Definition and composition of sensors

　　The concept of sensor comes from the word "sensor". In order to study natural phenomena, it is far from enough to rely solely on the five senses to obtain external information. Therefore, sensors that can replace or supplement the functions of the five senses were invented. Sensors are also called "transducers" in engineering.

　 According to the national standard (GB7665-87), the definition of a sensor is: "a device or apparatus that can sense the specified measured quantity and convert it into a usable output signal according to a certain rule." The main connotations of the sensor described by this definition include:

　　1) From the perspective of the sensor input: a specified sensor can only sense the specified measured quantity, that is, the sensor has the greatest sensitivity and the best selectivity to the specified physical quantity. For example, a temperature sensor can only be used to measure temperature, and it is not expected to be affected by other physical quantities at the same time.

　　 2) From the output end of the sensor: The output signal of the sensor is a "usable signal". Here, the so-called "usable signal" refers to a signal that is easy to process and transmit. The most common ones are electrical signals and optical signals. It can be expected that the "usable signal" in the future may be other more advanced and practical signal forms.

　　 3) From the perspective of the relationship between input and output: the relationship between them has a "certain law", that is, the input and output of the sensor are not only related, but can also be described by a certain mathematical model, that is, static and dynamic characteristics with certain laws.

　 The basic function of the sensor is to detect signals and convert them. The sensor is always at the forefront of the test system to obtain detection information. Its performance will directly affect the entire test system and play a decisive role in the measurement accuracy. According to its definition, the composition of the sensor is generally composed of three parts: sensitive element, conversion element, and signal conditioning circuit. Sometimes an external auxiliary power supply is required to provide conversion energy, as shown in Figure 4.1.1.

The sensitive element in the figure directly senses the measured quantity (generally non-electrical quantity) and converts it into other physical quantities that are easy to convert into electrical quantities; it is then converted into electrical parameters (voltage, current, resistance, inductance, capacitance, etc.) through the conversion element; finally, the signal conditioning circuit converts this electrical parameter into a form that is easy to further transmit and process.

　　 Of course, not all sensors have sensitive and conversion elements. Some sensors combine the two into one , and some new sensors integrate sensitive elements, conversion elements and signal conditioning circuits into one device.

　　 In the measurement of mechanical quantities (such as force, pressure, displacement, speed, etc.), elastic elements are often used as sensitive elements. This elastic element is also called an elastic sensitive element or a measuring sensitive element, which can transform the measured quantity from one physical state to another required physical state.