What is a sensitive resistor? What are the characteristics of the types of sensitive resistors?

Sensitive resistor refers to a resistor whose resistance changes with some external conditions. There are many kinds of sensitive resistors, including thermistors, photosensitive resistors, humidity sensitive resistors, force sensitive resistors and magnetic sensitive resistors. This article has collected and collated some materials, hoping to be of great reference value to all readers.

What is a sensitive resistor?

Sensitive resistor is a special resistance sensitive to analog quantities such as light intensity, pressure and humidity. When selecting, pay attention not only to its rated power, maximum working voltage, nominal resistance value, but also to the maximum working temperature, resistance temperature coefficient and other parameters, and pay attention to the change direction of resistance value.

At present, there are many kinds of sensitive resistors, including thermistors, photoresistors, varistors, thermistors, magneto-resistors, humidity-sensitive resistors and gas-sensitive resistors. The following are briefly introduced.

1、 Thermistor

Thermistor is a kind of resistor whose resistance value is very sensitive to temperature. It is generally made of single crystal, polycrystalline and other semiconductor materials. There are many kinds of resistance. For example, according to the temperature number of resistance value, it can be divided into negative temperature coefficient thermistor whose resistance value decreases with temperature rise and positive temperature coefficient thermistor whose resistance value increases with temperature rise; For example, according to the size and speed of the change of resistance value with temperature; It can be divided into two types: slow variant type and mutant type; According to the way of heating resistor, it can be divided into direct heating type and side heating type; According to its shape and structure, it can also be divided into rod-shaped, circular, square, bead-shaped, linear tubular, thin film and thick film thermistors. The main characteristics of thermistors are high sensitivity to temperature, small thermal inertia, long life, small size and simple structure. It is widely used in temperature measurement, control, fire alarm, meteorological sounding, microwave and laser power measurement and other fields.

2、 Photosensitive resistor

Photosensitive resistor is a resistance element made according to the principle of semiconductor optical effect. Its resistance value can change with the intensity of incident light. Photosensitive resistor is generally composed of glass substrate, photosensitive layer, electrode and other parts. According to the materials used in the photosensitive layer, it can be divided into polycrystalline photosensitive resistor and single crystal photosensitive resistor. According to the spectral persistence of photosensitive resistor, it can also be divided into ultraviolet photosensitive resistor Visible light photosensitive resistor and infrared light photosensitive resistor. Ultraviolet photosensitive resistor is very sensitive to ultraviolet radiation and can be used to detect ultraviolet radiation; Visible light photoresistors are mainly used in various photoelectric automatic control systems, including selenium, cadmium sulfide, cadmium selenide, zinc sulfide and other photoresistors, which are generally used in various photoelectric automatic control systems.

3、 Varistor

Varistor is a sensitive resistor whose resistance value decreases sharply when the voltage is applied to a certain value at both ends. It can be divided into silicon carbide varistor, silicon varistor, metal oxide varistor and barium titanate varistor according to the different materials. According to its structure, it can be divided into body type varistor, junction type varistor, single particle layer varistor and thin film varistor, etc. According to its volt-ampere characteristics, it can be divided into symmetrical type varistor and asymmetrical type varistor. Its performance parameters include nominal voltage, nominal current, nonlinear coefficient, current carrying capacity and voltage temperature coefficient, etc. The varistor is mainly used in overvoltage protection and voltage stabilizing circuits.

4、 Magnetoresistance

Magnetosensitive resistance is also called magnetic control resistance. It is made by using the magnetoresistance effect. Its remarkable feature is that the relationship between the resistance and the magnetic field increases according to the square law in the weak magnetic field, and increases linearly in the strong magnetic field. The magnetoresistance has high sensitivity, but it can not judge the direction of the magnetic field, and is greatly affected by temperature. The resistance of the magnetoresistance changes with the change of the magnetic field. The displacement of the magnetic field relative to the magnetoresistance can be accurately measured by using the change of the magnetoresistance. The magnetoresistance can also be used to make contactless switches. It has great potential in measurement technology, automatic control and signal processing.

5、 Force sensitive resistor

If the pressure is applied on the semiconductor crystal, in addition to the deformation, the symmetry inside the crystal will change, that is, the conductivity of the crystal will also change due to the change of the electrical resistance of the semiconductor material caused by the external force, which is called the piezoresistance effect of the semi-conductor. This principle is also the manufacturing principle of the force sensitive resistor, which can realize the electrical conversion of physical quantities such as force, displacement and torque. Therefore, it can be used to make torque meters, extensometers, tensiometers, accelerometers, semiconductor microphones and various pressure sensors.

6、 Gas sensitive resistor

This is a kind of sensitive resistance made by taking advantage of the characteristics of semiconductor surface absorbing certain gas molecules to undergo oxidation or reduction reaction, which changes the resistivity. Generally, N-type and P-type gas-sensitive semiconductors are divided according to the proportion and structure of materials. When N-type gas-sensitive semiconductors meet with reducing gases, they are adsorbed on their surface in a positive ion state, which increases the electronic density of conduction band and reduces the resistance. The resistance of P-type metal oxide semiconductor increases when it meets the electron-generating gas, and decreases when it meets the electron-attracting oxidizing gas. Gas sensitive resistor is also a new type of semiconductor element, which can be made into various gas sensitive detectors, and has a unique role in leak detection, environmental monitoring, fire prevention and automatic control of various pipelines and sealing systems.

7、 Humidity sensitive resistor

Humidity sensitive resistor is a sensitive element whose resistance changes with the change of ambient relative humidity. It is composed of humidity sensing layer, electrode and insulating substrate with certain mechanical strength. When the moisture sensing layer absorbs the moisture in the environment, it will cause changes in the resistance between the two electrodes. This sensitive resistor is used to make hair hygrometer and psychrometer with high accuracy, so it is often used in the field of humidity measurement and control.