Thermistor and thermocouple difference
Thermocouple and thermistor are temperature measurement of the contact temperature measurement components. Although its role is the same measure the temperature of the object, But their principles and characteristics are not the same.
First of all, introduce the thermocouple,Thermocouple temperature measurement is the most widely used temperature measurement components. Thermocouple temperature measurement instruments commonly used in temperature measurement components, It directly measures the temperature, And converts the temperature signal into a thermoelectromotive force signal. Through the electrical instrument (secondary instrument) into the measured medium temperature. This phenomenon is called thermoelectric effect, Also known as the Seebeck effect.
The thermoelectric power generated in the closed loop has two potentials; Temperature difference potential and contact potential. When there are two different conductors or semiconductors A and B to form a loop, When both ends are connected to each other, As long as the temperature at the two nodes are different. One end of the temperature T, Known as the working side or hot side, The other end of the temperature T0, Called the free end (also known as the reference side) or cold side. An electromotive force will be generated in the circuit, The direction and size of the electromotive force and the conductor material and the temperature of the two contacts. This phenomenon is known as the "thermoelectric effect". The circuit composed of two kinds of conductors is called "thermocouple" These two types of conductors are called "hot electrodes" Electromotive force generated is called "thermal emf"
Thermocouple structure has two kinds, Ordinary type and armored type. Ordinary thermocouple generally by the hot electrode, Insulation tube, Protection casing and junction boxes and other components. The armored thermocouple is the thermocouple wire, Insulation materials and metal protection casing combination of the three After assembly, After drawing processing from a solid combination.
But the thermocouple of the electrical signal is the need for a special wire to be transmitted, This kind of wire is called compensation wire. Different thermocouples require different compensation leads,Its main role is to connect with the thermocouple,S o that the reference end of the thermocouple away from power, So that the reference junction temperature is stabilized. Compensation wire is divided into two types of compensation and extension type, The chemical composition of the extended conductor is the same as the compensated thermocouple. However, in practice, Extension of the wire is not the same material and thermocouple metal, Generally used and thermocouple with the same electronic density wire instead. Compensation wire and thermocouple connection is generally very clear, The positive pole of the thermocouple connects the red wire of the compensating conductor, While the negative pole connects the remaining colors. Most of the general compensation wire material used copper-nickel alloy.
2> Thermistor basic features:
Thermistor is a kind of sensitive components, According to the temperature coefficient is divided into positive temperature coefficient thermistor (PTC) And a negative temperature coefficient thermistor (NTC). Thermistor is a typical feature of temperature-sensitive, Different temperatures show different resistance values. Positive temperature coefficient thermistor (PTC) in the higher the temperature the greater the resistance value. Negative temperature coefficient thermistor (NTC) in the higher the temperature the lower the resistance value, They belong to the same semiconductor device. Its advantages are many, Can also be far from electrical signals,high sensitivity, Stability, Interchangeability and accuracy are better. But the need for power excitation, It is not possible to instantaneously measure temperature changes.
① high sensitivity, The temperature coefficient of resistance than the metal 10 to 100 times more, Can detect the temperature change of 10-6 ℃;
② wide operating temperature range, Room temperature device for -55 ℃ ~ 315 ℃, High temperature device for the temperature above 315 ℃ (currently up to 2000 ℃), Low temperature device for -273 ℃ ~ -55 ℃;
③ small size, Can measure other thermometers can not measure the gap, The temperature of the blood vessel in the cavity and the organism;
④ easy to use, the resistance value can be arbitrarily selected between 0.1 ~ 100kΩ;
⑤ easy processing into a complex shape, can be mass production;
⑥ stability, and overload capacity.
Thermistor and thermocouple difference