Sensitive components in circuit protection

What are the sensitive devices in circuit protection? In the boring work of engineers, they have to deal with devices with different functions. When protecting electrostatic current in circuits, some sensitive devices will be used. Are you ignorant of these devices? Are you sensitive? The component is an important part of the sensor. It is a special electronic component that can keenly sense certain physical, chemical, and biological information and convert it into electrical information.

Features:

Special electronic components that can keenly sense certain physical, chemical, and biological information and convert it into electrical information. Such components are usually made using some sensitive effect of the material. Sensitive components can be named according to the input physical quantities, such as heat-sensitive (see thermistor), light-sensitive, (electrical) voltage (pressure) force-sensitive, magnetic-sensitive, gas-sensitive, and moisture-sensitive components. Using sensitive components in electronic devices to sense external information can reach or exceed the functions of human sensory organs. The sensitive element is the core element of the sensor. With the rapid development of electronic computers and information technology, the importance of sensitive components is increasing day by day.

Several categories of sensitive components:

thermistor

It is a type of sensitive element, which is divided into positive temperature coefficient thermistor (PTC) and negative temperature coefficient thermistor (NTC) according to different temperature coefficients. The typical characteristic of a thermistor is that it is sensitive to temperature and exhibits different resistance values ​​at different temperatures. The positive temperature coefficient thermistor (PTC) has a greater resistance value when the temperature is higher, and the negative temperature coefficient thermistor (NTC) has a lower resistance value when the temperature is higher. They are both semiconductor devices.

Varistor

The varistor is a voltage-limiting protection device.

Utilizing the nonlinear characteristics of the varistor, when overvoltage occurs between the two poles of the varistor, the varistor can clamp the voltage to a relatively fixed voltage value, thereby protecting the subsequent circuit. The main parameters of the varistor are: varistor voltage, current capacity, junction capacitance, response time, etc.

Photoresistor

A sensitive element whose resistance value changes with the intensity of incident light (generally visible light). Generally, as the incident light increases, the resistance value decreases. The response of a photoresistor to incident light is related to the wavelength of the light and the material used. The materials used to make photoresistors are mainly cadmium compounds, such as cadmium sulfide, cadmium selenide and their eutectic ─ cadmium sulfur selenide. Secondly, there are germanium, silicon, zinc sulfide, etc. Photoresistors are used in light intensity control, photo-electric automatic control, photo-electric switches, photo-electric counting, photo-electric safety protection and smoke alarms, etc.

force sensitive element

Sensitive components whose electrical parameters change with changes in external pressure.

There are many types of force-sensitive components, such as resistive, capacitive, piezoelectric, etc. The most common ones are metal strain gauges and semiconductor strain gauges. Metal strain gauges are subject to external forces that cause the metal foil and metal wire to extend or shorten, causing the resistance value to change to complete the information conversion function. Strain materials mostly use metals and alloys such as copper and nickel. Semiconductor strain gauges are made by utilizing the piezoresistive effect of semiconductor materials.

Semiconductor strain gauges can be divided into two types: body type and diffusion type. Diffused semiconductor strain gauges are made using semiconductor planar technology, have excellent performance, and have great development prospects. The basic parameter of a force-sensitive element is sensitivity, which is the ratio of the relative change in resistance value to the amount of strain. The sensitivity coefficient of metal strain gauges is 2 to 3, while the sensitivity coefficient of semiconductor strain gauges is 20 to 200. Force-sensitive components can be used to measure mechanical quantities such as pressure, displacement, torque, acceleration, air pressure, and gas flow.

Magnetic sensitive element

A magnetoelectric conversion element includes a Hall element, a magnetoresistive element, a magneto-sensitive diode, a magneto-sensitive transistor, etc.

Hall element, also called Hall generator, is a semiconductor device made using the Hall effect. The magnetic sensitivity of the Hall element is measured in units of the ratio of the Hall voltage to the magnetic induction intensity under a given control current condition. Magnetoresistive elements work by utilizing the magnetoresistive effect of semiconductor materials. Its magnetic sensitivity is called the magnetoresistance coefficient, which is the ratio of the resistance value of the magnetoresistive element under a certain magnetic field intensity to the resistance value at zero magnetic field. Using magnetic fields as media, magnetic sensitive elements can be used to measure physical quantities such as displacement, vibration, pressure, angle, rotation, speed, acceleration, flow, current, and electrical power.

gas sensor

Sensitive components whose electrical parameters change with changes in the type and concentration of external gases.

The gas sensing effect mechanism of gas sensors is still in the exploratory stage. It is generally believed that the adsorption and desorption of gases will cause distortion of the energy band structure of the semiconductor surface, causing changes in the macroscopic resistance value. Semiconductor gas sensors have high sensitivity, simple structure, easy use, and low price. They have developed rapidly since their advent in the 1960s. Many oxide materials such as ZnO, SnO2, Fe2O3, Cr2O3, MgO, NiO, etc. have gas-sensing effects. Generally, the most commonly used gas-sensitive materials are SnO2 and ZnO, and their detection sensitivity is related to temperature. The main application fields of gas sensors are in disaster prevention and alarm, pollution prevention, detection and measurement, etc.

Humidity sensor

Sensitive components whose electrical parameters change with changes in ambient humidity.

Humidity sensors include electrolyte moisture sensors, organic polymer film moisture sensors, metal oxide moisture sensors, ceramic moisture sensors, etc. The sensitivity of a hygroscopic resistor is expressed as the rate of change in resistance value when the relative humidity changes by 1%. The resistance value of most humidity-sensitive resistors decreases as humidity increases. This type of humidity-sensitive resistor is called a negative characteristic humidity-sensitive resistor. There are also a few hygroscopic resistors whose resistance value increases with increasing humidity. Humidity sensors are mainly used for humidity measurement and control. According to the humidity measurement range, they can be divided into three categories: high humidity type, low humidity type and full humidity type. It is widely used in meteorology, food, textile, light industry sectors and environmental air conditioning and warehouse facilities. The above are the sensitive components in circuit protection. I hope it can be helpful to everyone.