What is infrared temperature?
This is a non-contact temperature measurement method that measures the surface temperature of a target object by infrared radiation. It is based on the Stefan-Boltzmann law, which states that the energy radiated from the surface of an object is proportional to the fourth power of its absolute temperature. Therefore, by measuring the infrared radiation on the surface of a target object, its surface temperature can be deduced.
How infrared temperature works?
Depending on the temperature of the object, the wavelength of infrared radiation is different. According to Planck’s law of radiation and Wien’s law of displacement, when the temperature of an object increases, the wavelength of infrared radiation becomes shorter; when the temperature of an object decreases, the wavelength of infrared radiation becomes longer.
When the temperature of an object is near absolute zero, it radiates in the long-wave infrared range (wavelengths of about 10 micrometers to 1,000 micrometers). When the temperature of an object increases to a few hundred degrees Celsius, the wavelength of its radiation is shortened to the mid-wave infrared range (wavelengths of about 1 micron to 10 microns). As the temperature of the object continues to rise to thousands of degrees Celsius, the wavelengths it radiates shorten to the short-wave infrared range (wavelengths of approximately 0.1 micrometers to 1 micrometer).
Benefits of infrared temperature measurement
1. High accuracy
Infrared temperature measurement uses special optical lenses and sensors that can accurately capture the infrared radiation signals emitted by the object to measure the temperature of the surface of the object. This technology can realize high-precision measurement with an error of only 0.1℃, which is much higher than contact temperature measurement.
2. Non-contact
Infrared temperature measurement is a completely non-contact method of temperature measurement. This advantage makes the measurement easier and more convenient, and can even be carried out in high temperature or dangerous environment without any damage to the measured object.
3. High efficiency
Infrared temperature measurement does not need to touch the object, so it can complete the measurement in a very short time. In addition, it can measure multiple objects at once without waiting for the instrument to cool down, greatly improving work efficiency.
4. Safety
Because this is a non-contact method, there is no contact with the measured object, thus ensuring the safety of the operator. In addition, it can also measure the temperature at a distance, which can avoid the operator to enter the dangerous place.
How to choose an infrared temperature sensor?
Temperature measurement range: Infrared temperature sensors all have different temperature measurement ranges, neither too narrow nor too wide. Generally speaking, the narrower the temperature range, the higher the resolution of the output signal to monitor the temperature, the more reliable the accuracy. Conversely, a temperature range that is too wide will reduce the measurement accuracy.
Working wavelength: According to the law of blackbody radiation, the radiation change caused by temperature in the short wave of the spectrum will exceed the radiation change caused by the emissivity error. Therefore, temperature measurement should try to use short-wave, but also need to consider the emissivity of the object to be detected.
In the high-temperature zone, the wavelength of measuring metal materials is near infrared, can choose 0.8 ~ 1.0 μm, other temperature zones can choose 1.6, 2.2 and 3.9 μm. Some materials are transparent at specific wavelengths, infrared will penetrate these materials, special wavelengths should be selected. Such as measuring the internal temperature of the glass wavelength 1.0, 2.2 and 3.9 μm, 5.0 μm to measure the surface temperature of the glass, the best choice of 8 ~ 14 μm to measure the low-temperature zone.
Spot Size: The area of the measuring spot of an infrared temperature sensor is called the “spot size”. In order to obtain a temperature reading, the sensor should be at a suitable distance from the test target. The farther away from the target, the larger the spot size. The ratio of distance to spot size (also known as D:S) should be observed when using the device. Failure to do so will affect the accuracy of the reading.
Response time: refers to the response speed of the infrared temperature sensor to measure the temperature change of the object. It is related to the time constant of the photodetector, signal processing circuit and display system. If the object’s movement is very fast or when measuring fast-heating objects, choose a fast response infrared thermometer. For stationary objects or slowly heating objects, you can choose the normal corresponding infrared thermometer. Therefore, the response time should be selected according to the characteristics of the object to be measured, mainly depending on the speed of movement of the object and the speed of temperature change.
Signal processing functions: As discrete processes (such as parts production) and continuous processes are different, infrared temperature sensors are required to have a variety of signal processing functions (such as peak hold, valley hold, average value). For example, when measuring the temperature of bottles on a conveyor belt, it is necessary to use the peak hold function to transmit the output signal of their temperature to the controller, otherwise the device will read out the lower temperature value between the bottles.
Protective accessories: The working environment not only affects the measurement results, but also affects the accuracy of the infrared temperature sensor and even leads to damage. When there is a lot of dust or steam in the environment, you can use the manufacturer’s protective sleeve, air cooling system, air blowers and other accessories. These accessories can effectively protect the sensor, but also to ensure the accuracy of the measurement results.
Window material: When measuring the material inside a container or vacuum chamber, the infrared pyrometer needs to measure through a window. The window material must be strong enough and able to pass through the operating wavelength of the pyrometer. Therefore, it is necessary to choose a suitable installation position and window material to avoid mutual influence.
Infrared temperature technology application
1. In the steel industry
Infrared thermometers are widely used in the steel industry. Because steel plates are in motion and at very high temperatures, contact measurements are not applicable. Reheating steel at a stable temperature is important to prevent it from deforming, so infrared thermometers can be used to measure the internal temperature of the return heaters. In high-temperature rotary mills, it is also possible to monitor whether the product temperature is within a reasonable temperature range.
2. In the glass industry
In the glass industry, the product is also in motion and it takes a very high temperature to melt the glass. Infrared thermometers can be used to monitor the temperature in the furnace and adjust the temperature at the furnace opening by measuring the temperature of the melted glass. In the production process, temperature changes too quickly or incorrectly controlled can affect the quality of the product, so infrared pyrometers are needed to monitor the temperature in real time.
3. In the plastics industry
In the plastics industry, infrared temperature technology is used to measure the temperature of dynamic objects and plastics to avoid product tarnishing. In order to maintain the integrity and thickness of the plastic, the temperature is tightly controlled, and infrared thermometers monitor the temperature, allowing the operator to adjust the heating and cooling.
4. In the petrochemical industry
In the petrochemical industry, coking agglomeration leads to higher ignition rates in the furnace, which in turn leads to higher tube temperatures, and frequent exposure to such high temperatures reduces the service life of the tubes. This coking prevents the product from absorbing the heat from the tube evenly. When using an infrared thermometer, the surface temperature of the tubes in the coking area may be higher than the surface temperature of the tubes in other areas.
