How to effectively distinguish between varistor and thermistor.Infrared sensing module

　　There are three main factors to consider at this time, one is the capacitance of the varistor itself, the second is the leakage current under the system voltage, and the third is the influence of the nonlinear current of the varistor through the coupling of the source impedance on other circuits.

　　In normal use, the thermistor is divided into two types: positive temperature coefficient thermistor and negative temperature thermistor (also known as ntc thermistor).

　　They have different symbols in circuit design, thermistor is also called ntc, and varistor is called mov, which is also the most obvious way of distinguishing them in circuit design.

　　Secondly, their package colors are also different, the common thermistor has a black appearance, while the common package appearance of a varistor is blue.

　　In order to reduce the aging change of the thermistor, the environment with sudden temperature change should be avoided as much as possible.

　　Thermistor is a sensitive component with early development, many types and relatively mature development. The thermistor is composed of semiconductor ceramic materials, and the principle used is that the temperature causes the resistance change. If the concentrations of electrons and holes are n and p, respectively, and the mobilities are μn and μp, respectively, then

　　Because n, p, μn, and μp are functions that depend on temperature t, conductance is a function of temperature, so the temperature can be calculated by measuring conductance, and a resistance-temperature characteristic curve can be made. This is the working principle of the semiconductor thermistor.

　　Thermistors include positive temperature coefficient (ptc) and negative temperature coefficient (ntc) thermistors, as well as critical temperature thermistors (ctr).

　　The main features of the thermistor are: 1. High sensitivity, its temperature coefficient of resistance is more than 10 to 100 times larger than that of metal, and it can detect temperature changes of 10-6 °C.

　　If water droplets or dust are attached between the leads or on the surface of the insulator, the measurement results will be unstable and errors will occur. Therefore, attention should be paid to making the thermistor waterproof, moisture-resistant, and cold-resistant.

　　The influence of the wire resistance, the nominal resistance of the thermistor is 0.55-30kω, which is very large. Although the thermistor national standard uses two leads, the influence of the wire resistance can still be ignored.

　　The thermistor detects the fixing temperature of the machine. When it reaches a certain temperature, it will stop heating to ensure the normal operation of the machine.

　　High sensitivity, including thermistor, its temperature coefficient of resistance is more than 10 to 100 times larger than that of metal, and it can detect temperature changes of 10-6 °C.

　　Small in size, it can measure the temperature of voids, cavities and blood vessels in living organisms that cannot be measured by other thermometers.

　　Easy to use, the resistance value can be arbitrarily selected between 0.1 ~ 100kω.

　　It is easy to process into complex shapes and can be mass-produced; it has good stability and strong overload capacity.

Read recommendations:

Sensors for detecting the water temperature of intelligent toilets.Photosensitive sensor

The industry's smallest medical grade FIR sensor

HW801

Φ20 mm size

PIR Lens 8005-1