Sensors generally consist of a sensing element, a conversion element, a signal conditioning circuit, and auxiliary circuits. However, not all sensors must include both a sensing element and a conversion element. If the sensing element directly outputs an electrical quantity, it also functions as a conversion element. Sensing element (pre-converter): This refers to the part of the sensor that directly senses or responds to the measured quantity (non-electrical quantity) and outputs another quantity (non-electrical quantity) that has a definite relationship with it. Conversion element: This refers to the part of the sensor that converts the measured quantity sensed or responded to by the sensing element into a usable output signal (usually an electrical signal) suitable for transmission or measurement. Signal conditioning circuit: This is the circuit that converts the electrical signal output by the conversion element into a useful electrical signal that is easy to display, record, process, and control. Auxiliary circuit: This usually refers to the power supply, i.e., the AC or DC power supply system.
Common types of sensors include: temperature sensors, pressure sensors, touch sensors, image sensors, motion sensors, smoke or gas sensors, flame sensors, leak sensors, tilt sensors, and energy consumption sensors.
Based on the type of measurement: Physical quantities: pressure sensors, vibration sensors, displacement sensors, vacuum sensors; visible light sensors, infrared light sensors, ultraviolet light sensors; temperature sensors; magnetic sensors; Chemical quantities: gas sensors, humidity sensors, ion sensors. Biosensors: enzyme sensors, immune sensors, DNA sensors, microbial sensors.
Based on output signal, sensors can be categorized as follows: analog sensors convert the measured non-electrical quantity into an analog electrical signal. Digital sensors convert the measured non-electrical quantity into a digital output signal (including direct and indirect conversion).
According to the measurement principle, they can be divided into: physical type: piezoresistive, piezoelectric, photoelectric, pyroelectric, etc.; chemical type: semiconductor surface control, catalytic combustion, electrochemical current type, electrochemical potential type, hybrid potential type; and biological type: field-effect transistor biosensors, piezoelectric biosensors, optical biosensors, enzyme electrode biosensors, mediator biosensors, etc.
A thermistor is a sensing element that converts temperature into an electronic signal. Its working mechanism includes the pyroelectric effect, thermoelectric effect, and semiconductor junction effect. The latter, based on the thermistor's thermal sensitivity, accounts for 55% of thermistor elements. This type of sensor is used when high measurement accuracy is required. Commonly used heat-resistant materials include platinum, copper, and nickel. These materials have a large temperature coefficient of resistance, good linearity, stable performance, wide application range, and are easy to manufacture. They are suitable for temperature measurements from -200 to +500 degrees Celsius.
Photosensitive sensors are currently the most widely used type of sensor, including phototubes, photomultiplier tubes, photoresistors, transistors, solar cells, infrared sensors, ultraviolet sensors, fiber optic sensors, color sensors, CCDs, CMOS image sensors, and so on. Well-known domestic manufacturers include OTRON. Photosensitive elements are currently the most produced and widely used type, playing a crucial role in automatic control and non-electrical quantity inductive technology. The simplest photosensitive element is the photoresistor, which generates current at its contact point.
Gas sensors are used to monitor the concentration and composition of gases, playing a crucial role in environmental protection and safety monitoring. Gas sensors are primarily used in contact with gases of different components. Due to significant variations in temperature and humidity, as well as the presence of large amounts of dust and oil mist, their operating environment is extremely harsh. Furthermore, the gas can chemically react with the sensor material, leading to a degradation in the device's performance. Therefore, gas sensors must meet the following requirements: the ability to detect the permissible concentration of the alarm gas and other standard gas concentrations; long-term operation; high stability and repeatability; rapid response; and low influence from coexisting substances.
Sensors are characterized by miniaturization, digitization, intelligence, multifunctionality, systematization, and networking. They are the primary link in achieving automatic detection and control. The existence and development of sensors have given objects senses such as touch, taste, and smell, gradually bringing them to life. They are typically classified into ten major categories based on their basic sensing functions: thermal sensors, photosensors, gas sensors, force sensors, magnetic sensors, humidity sensors, acoustic sensors, radiation sensors, color sensors, and taste sensors.
