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Symbol For A Thermistor Characterisation Of Relevant Applications

Symbol For A Thermistor Characterisation Of Relevant Applications

September 19 , 2023 0

Thermistor is a class of sensitive components, according to the temperature coefficient is divided into positive temperature coefficient thermistor PTC) and negative temperature coefficient thermistor (NTC). Typical characteristics of thermistors are that they are temperature sensitive and exhibit different resistance values at different temperatures. Positive temperature coefficient thermistors (PTC) have higher resistance values at higher temperatures, while negative temperature coefficient thermistors (NTC) have lower resistance values at higher temperatures. Of course, they are both semiconductor devices.

The Main Characteristics Of Thermistor

1, high sensitivity, resistance temperature coefficient is 10~100 times larger than that of metal, and it can detect temperature change of 10~6C.
2, wide operating temperature range, room temperature devices for -55C ~ 315C, high temperature devices for higher than 315C (currently up to 2000C), low-temperature devices for -273C ~ -55C; -273C ~ -55C; low-temperature devices for -273C ~ -55C.
The low-temperature device is applicable to -273C~-55C.
3, small size, can measure other thermometers can not measure the temperature of the living body voids, cavities, blood vessels.
4. Easy to use, resistance value can be selected arbitrarily between 0.1 ~ 100kQ.
Easy to process into complex shapes, can be mass production.
6. Good stability, strong overload capacity.

Symbols For Thermistors

Some of the letters in the electrical symbol of thermistor are 0 and some are VM. The one with 0 is thermistor, and U is voltage-sensitive electric Yang. The resistance value of thermistor changes with the external temperature. Some have a negative temperature coefficient and are represented by NTC; some have a positive temperature coefficient and are represented by PTC. Use 0 or t to express the temperature. Its text symbol is "RT". In the circuit diagram, the symbols photoresistor and thermistor are expressed as.

Thermistor Damage

If the test with a multimeter ohm file (according to the nominal resistance value to determine the range, generally Rx1 range), can be divided into two steps: one is room temperature test (indoor temperature close to 25C), with alligator clips instead of test line. Measure the actual resistance of the two pins of the PTC thermistor and compare it with the nominal resistance. The difference between the two is normal within +202. If the actual resistance value is higher than +2 0; from the nominal resistance value, it shows that its performance is poor or has been damaged.
Secondly, on the basis of room temperature test, the second step of the test can be to perform a heating test, heating close to the thermistor heat source such as a soldering iron ", observe the universal indicator. It can be seen that the universal indicator changes as the temperature rises, indicating that the value is gradually changing (negative temperature coefficient thermistor NTC resistance will become smaller, while the positive temperature coefficient of PT (resistance will become larger). When the yang value changes to a certain value, the display data will gradually stabilise, indicating that the thermal electric yang is normal. If the yang value remains unchanged, it means that the thermal anode is damaged.
Test should pay attention to the following points.
Rt is measured by the manufacturer when the ambient temperature is 25C, so when measuring Rt with a multimeter, it should also be done when the ambient temperature is close to 25C to ensure that the test can be carried out.
Measurement power should not exceed the specified value to avoid measurement error caused by current thermal effect
Do not pinch the thermistor with your hand during the test to avoid the human body temperature shadow affecting the test
Be careful not to place the heat source too close to the PTC thermistor or directly touch the thermistor to prevent it from being burnt.

Thermistor Application Areas

Thermistor is very versatile, the main applications include, the use of non-linear characteristics to complete the voltage regulator, limiting, switching, overcurrent protection and other functions; the use of different media heat dissipation characteristics of the differences in the measurement of the flow rate, flow rate, liquid level, thermal conductivity, vacuum, etc.; the use of thermal inertia as a time delay.
Thermoelectric Yang can also be used as electronic circuit components for instrumentation line temperature compensation and temperature difference cold end temperature compensation. The use of NTC thermistor self-heating characteristics can be achieved by automatic gain control, constitute the RC oscillator amplitude stabilisation circuit, time delay circuit and protection circuit. When the self-heating temperature is much larger than the ambient temperature, the resistance value is also related to the heat dissipation conditions of the environment.
Therefore, the characteristics of thermistors are often used in flow meters, flow meters, gas analysers, thermal analyses, etc. to make special detection elements.PTC thermistors are mainly used for overheating protection of electrical equipment, non-contact relays, constant temperature, and automatic gain control.