I. Key Points for Selecting Infrared Temperature Sensors
When selecting an infrared temperature sensor, the following points need to be considered:
1. Object of measurement
First, it is necessary to determine the type of object to be measured and its surface condition. For example, when measuring a metal plate uniformly coated with black paint, a filter with a reflectivity of 0.9 should be selected; when measuring a bright metal surface, a narrowband filter should be selected to avoid errors caused by multiple reflections, etc.
2. Measuring distance
Secondly, it is necessary to select the appropriate infrared temperature sensor model based on the measurement distance requirements of the actual application scenario. For example, for long-distance measurement needs, an infrared temperature sensor with a wider measurement range and higher emission power should be selected.
3. Environmental conditions
In complex environments, the measurement error of infrared temperature sensors may be affected by environmental factors. Therefore, when selecting an infrared temperature sensor, its ability to adapt to factors such as ambient temperature, humidity, and electromagnetic interference needs to be considered.
4. Response speed
Response speed is a crucial indicator of infrared temperature sensors, affecting their real-time performance and stability. Generally, response speed is inversely proportional to the temperature measurement range; therefore, an appropriate response speed must be selected based on specific requirements.
5. Accuracy Requirements
Accuracy is one of the key performance indicators for infrared temperature sensors. When selecting a sensor, it's crucial to choose an appropriate model based on the accuracy requirements of the specific application. Additionally, it's essential to consider the sources of measurement error for infrared temperature sensors, such as environmental interference and temperature drift.
6. Wavelength range of infrared temperature sensor
The emissivity and surface properties of the target material determine the spectral response or wavelength of the thermometer. High-reflectivity alloys have low or varying emissivity. In the high-temperature range, the optimal wavelength for measuring metallic materials is near-infrared, with wavelengths of 0.18-1.0 μm suitable. For other temperature ranges, wavelengths of 1.6 μm, 2.2 μm, and 3.9 μm can be used. Since some materials are transparent at certain wavelengths, infrared energy can penetrate them; therefore, specific wavelengths should be selected for these materials. For example, 10 μm, 2.2 μm, and 3.9 μm wavelengths are suitable for measuring the internal temperature of glass (the glass should be very thick, otherwise it will transmit); 5.0 μm wavelength is suitable for measuring the internal temperature of glass; 8-14 μm wavelengths are preferable for measuring low-temperature areas; and 3.43 μm wavelength is suitable for measuring polyethylene plastic film, while 4.3 μm or 7.9 μm wavelengths are suitable for polyester. For thicknesses exceeding 0.4 mm, a wavelength of 8-14 μm is selected; for example, a narrow-band wavelength of 4.24-4.3 μm is used to measure CO2 in a flame, a narrow-band wavelength of 4.64 μm is used to measure CO in a flame, and a wavelength of 4.47 μm is used to measure NO2 in a flame.
7. Response time of infrared temperature sensor
Response time refers to the speed at which an infrared thermometer reacts to a change in the measured temperature. It is defined as the time required to reach 95% of the energy at the final reading, and it is related to the time constants of the photodetector, signal processing circuit, and display system. This is much faster than contact temperature measurement methods. If the target is moving very fast or when measuring a rapidly heating target, a fast-response infrared thermometer must be selected; otherwise, insufficient signal response will reduce measurement accuracy. However, not all applications require a fast-response infrared thermometer. For stationary targets or targets with thermal inertia, the response time requirement can be relaxed. Therefore, the selection of the infrared thermometer's response time must be adapted to the characteristics of the target being measured.
II. The difference between infrared temperature sensors and temperature sensors
Infrared temperature sensors generally offer high measurement accuracy. Within a certain temperature range, thermometers can also measure the internal temperature distribution of an object. However, they can produce significant measurement errors for moving objects, small targets, or objects with very low heat capacity. Commonly used thermometers include bimetallic thermometers, glass liquid thermometers, pressure thermometers, resistance thermometers, thermistors, and thermocouples. They are widely used in industry, agriculture, commerce, and even in daily life. With the widespread application of cryogenic technology in defense engineering, space technology, metallurgy, electronics, food, medicine, and petrochemicals, as well as research into superconducting technology, cryogenic thermometers for measuring temperatures below 120K have been developed. Examples include cryogenic gas thermometers, vapor pressure thermometers, acoustic thermometers, paramagnetic salt thermometers, quantum thermometers, cryogenic resistance thermometers, and cryogenic thermocouples. Cryogenic thermometers require small-sized sensing elements, high accuracy, good repeatability, and good stability. Carburized glass resistance thermometers, which are made by carburizing and sintering porous high-silica glass, are a type of temperature sensing element in low-temperature thermometers and can also be used to measure temperatures in the range of 1.6 to 300K.
