The working principle of a semiconductor thermistor
Thermistors can be divided into two classes according to the temperature properties, with the temperature rise of resistance increase as the positive temperature coefficient thermistor, whereas negative temperature coefficient thermistor.
(1) the principle of positive temperature coefficient thermistor
This thermistor with barium titanate (BaTio3) as the basic material, and adding an appropriate amount of rare earth elements, using high temperature sintering, ceramic process.Pure barium titanate is a kind of insulating material, but with the right amount of rare earths such as lanthanum (La) and niobium (Nb) and so on, into a semiconductor material
Semiconducting material, called barium titanate.It is a kind of polycrystalline material, grain interface exists between the grain, for the conduction electron, intergranular interface is equivalent to a barrier.When the temperature is low, the effect of the electric field inside because of batio3 semiconducting, conduction electron can be more easily
A barrier, so the resistance is small;When the temperature rises to the Curie point temperature (namely, critical temperature, the components' temperature control points' general barium titanate Curie point is 120 ℃), the electric field is damaged, can't help to conduction electron across the barrier, so show the resistance value
Show increased.Because this device has failed to reach before the Curie point resistance with the temperature changes very slowly, with constant temperature, temperature control and automatic temperature control function, only fever, redness, the halogen-light, nonflammable, 3 ~ 440 v ac or dc voltage, long service life, very suitable for electric
Machine electrical devices such as overheat detection.
(2) The working principle of negative temperature coefficient thermistor
Negative temperature coefficient thermistor is the manganese oxide, cobalt oxide, nickel oxide, alumina and copper oxide metal oxide as the main raw material, made by ceramic technology.The metal oxide materials have semiconductor properties, completely similar to germanium and silicon crystal materials, load in the body
Flow (electrons and holes) number less, high resistance;Temperature, increase the number of carriers in the body, the natural resistance reduced.A lot of negative temperature coefficient thermistor type, used to distinguish the low temperature (60 ~ 300 ℃), medium temperature (300 ~ 600 ℃), high temperature (> 600 ℃)
, with high sensitivity, good stability, fast response, long life, low price advantages, widely used in the need to measuring temperature of automatic temperature control circuit, such as refrigerator, air conditioner, the greenhouse temperature control system.
Thermistor with simple amplification circuit, can test once per thousand of temperature change, so and electronic instrument thermometer, can complete the high accuracy of temperature measurement.General purpose work thermistor temperature of 55 ℃ ~ + 315 ℃, the special low temperature thermistor temperature
Below and 55 ℃, can reach to 273 ℃.
Thermal resistance model
I domestic thermistor by the ministerial standard SJ1155-82 to make model, consists of four parts.
The first part: the Lord says, with the letter "M" said sensitive element.
The second part: category, expressed in the letter "Z" positive temperature coefficient thermistor, or expressed in the letter 'F' negative temperature coefficient thermistor.
The third part: use or characteristics, with a number (0-9) said.General number '1' said ordinary purposes, '2', said regulator USES (negative temperature coefficient thermistor), '3' said microwave measurement purposes (negative temperature coefficient thermistor), '4' said heater
(negative temperature coefficient) thermistor, temperature measurement purposes, '5' said '6' said temperature control purposes, '7,' said degaussing purposes (positive temperature coefficient) thermistor, '8' said linear model (negative temperature coefficient thermistor), '9,' said thermostatic type (positive temperature coefficient of the heat
Sensitive resistor), '0' said special type (negative temperature coefficient) thermistor
The fourth part: the serial number, also by the Numbers, on behalf of the specification and performance.
Often manufacturers for the difference between the special needs of the series of products, after the serial number and derived the serial number, by letters, Numbers, and '-' combination.
Example: 1 1 M Z
The serial number
Positive temperature coefficient thermistor
Three main parameters of thermistor
All sorts of thermistor working conditions must be within the scope of its factory parameter allows.Main parameters of thermistor has more than 10 items: nominal resistance, environment temperature (maximum operating temperature), is used to measure the power, rated power, nominal voltage of the maximum working voltage, work
Current, temperature coefficient, material constant, time constant, etc.The nominal resistance at 25 ℃ is zero power resistance, actually there is always a certain error, should be within + / - 10%.Ordinary thermistor temperature range is larger, can according to need from 55 ℃ to + 315 ℃ choice,
It is important to note that different types of thermistor highest working temperature difference is very big, such as MF11 flake negative temperature coefficient thermistor to + 125 ℃, and only MF53-1 to + 70 ℃, students should be paid attention to during the test (generally not more than 50 ℃).