Please compare the advantages and disadvantages of contact temperature sensors and non-contact sensors.

1, non-contact temperature sensor and the measured medium does not directly contact, so do not have to consider some of the contact medium

self-physical properties, such as: adhesion, corrosion, wear and tear, etc. will not cause damage to the sensor. The contact type will have to face these

problems of additional solutions.

2, non-contact sensors are less limited by space. For some of the distance is not easy to contact the measured target can be a long distance

measurement of temperature.

3, for some inconvenient contact measurement of the target non-contact sensors can realize the measurement, such as rotating machinery, the movement of the target

standard and so on.

Temperature sensor (temperature?transducer) refers to the temperature can be felt and converted into a usable output signal sensor. Temperature

Temperature sensor is the core part of the temperature measuring instrument, a variety of varieties. According to the measurement method can be divided into two categories of contact and non-contact, according to

The sensor material and electronic component characteristics are divided into RTDs and thermocouples two categories.

Contact temperature sensor detection part and the measured object has good contact, also known as thermometer.

The thermometer achieves thermal equilibrium by conduction or convection, so that the indicated value of the thermometer can directly represent the temperature of the measured object. ? Generally measured

measurement accuracy is high. In a certain temperature measurement range, the thermometer can also measure the temperature distribution inside the object. But for the moving body, small target

or heat capacity of the object is very small will produce a large measurement error, commonly used thermometers are bimetallic thermometers, glass liquid thermometers,

pressure thermometers, resistance thermometers, thermistors and temperature difference thermocouples and so on. They are widely used in industry, agriculture, commerce and other sectors.

People also often use these thermometers in their daily lives.

With the wide application of low-temperature technology in the sectors of defense engineering, space technology, metallurgy, electronics, food, medicine and petrochemistry and

the research of superconducting technology, the low-temperature thermometers measuring the temperature below 120K have been developed, such as low-temperature gas thermometers, vapor pressure thermometers

meters, acoustic thermometers, paramagnetic salt thermometers, quantum thermometers, low-temperature RTDs and low temperature temperature difference thermocouples and so on. Low-temperature thermometers require sensing

Temperature element small size, high accuracy, reproducibility and stability. The use of porous high silica glass carburization sintered carburized glass thermoelectric

Resistance is a low-temperature thermometer is a temperature sensing element, can be used to measure the temperature within the range of 1.6 ~ 300K.

Non-contact sensor sensitive element and the object to be measured without contacting each other, also known as non-contact temperature measurement instrument. This instrument can be used to measure

moving objects, small targets and small heat capacity or rapid temperature change (transient) object surface temperature, can also be used to measure the temperature field temperature

degree distribution.

The most commonly used non-contact temperature measurement instruments are based on the fundamental law of blackbody radiation and are called radiometric temperature measurement instruments. ? Radiometric thermometry includes the bright

degree method (see optical pyrometer), the radiant method (see radiation pyrometer), and the colorimetric method (see colorimetric thermometer). Each type of radiometric thermometry

can only measure the corresponding photometric, radiometric or colorimetric temperature. Only the temperature measured for a blackbody (an object that absorbs all radiation and reflects no light)

is the true temperature. To determine the true temperature of an object, the surface emissivity of the material must be corrected. The surface emissivity of the material

depends not only on the temperature and wavelength, but also on the surface condition, coating film and microstructure, so it is difficult to accurately measure

measurement. In automated production often need to use radiation thermometry to measure or control the surface temperature of certain objects, such as metallurgy in the steel strip

rolling temperature, roll temperature, forging temperature and a variety of molten metal in the smelting furnace or crucible temperature. In these specific cases, the measurement of the surface emissivity of the object

is quite difficult.

For automatic measurement and control of solid surface temperatures, additional mirrors can be used to make a blackbody cavity with the measured surface.

The effect of additional radiation can increase the effective radiation and effective emission coefficient of the measured surface. Using the effective emission coefficient, the measured temperature

is corrected accordingly by the instrument, and the true temperature of the measured surface is finally obtained. The most typical additional reflector is the hemispherical reflector. Ball center

near the surface of the measured radiation can be reflected by the hemispherical mirror back to the surface and the formation of additional radiation, thereby increasing the effective emission coefficient of the formula ε for

material surface emissivity, ρ for the reflectivity of the mirror. ? As for the real temperature of gas and liquid media radiation measurement, can be used to insert

heat-resistant material tube to a certain depth in order to form a blackbody cavity method. The effective

emission coefficient of a cylindrical cavity in thermal equilibrium with the medium is calculated. In automatic measurement and control can be used to correct the measured cavity bottom temperature (i.e., medium temperature) and get the real temperature of the medium

Mass.

Advantages of non-contact temperature measurement: the upper limit of the measurement is not limited by the degree of temperature resistance of the sensing element, and thus there is no limit to the maximum measurable temperature in principle

System. For high temperatures above 1800 ℃, the main non-contact temperature measurement method. With the development of infrared technology, radiation temperature measurement gradually from the can

See the light to infrared expansion, 700 ℃ up to room temperature have been used, and high resolution.