How to Choose an Infrared Temperature Sensor?

The physical nature of infrared radiation is thermal radiation. The higher the temperature of the object, the more infrared radiation it emits, and the stronger the energy of the infrared radiation. The study found that the various thermal effects of the solar spectrum gradually increase from violet light to red light, and the largest thermal effect occurs within the frequency range of infrared radiation, so people turn infrared radiation into thermal radiation or heat. The infrared temperature sensor uses the radiant heat effect to cause the detection device to receive radiant energy and cause the temperature to rise, thereby changing the performance of a column in the sensor and the temperature. By detecting a change in one of these properties, radiation can be detected. In most cases, radiation is detected by the Seebeck effect. When the device receives radiation, it causes a physical change other than electricity, and it can also be measured after changing into electricity through appropriate changes. How to choose an infrared temperature sensor? We need to judge according to some of its performance indicators, including optical resolution, response time, working wavelength, temperature range, etc.

How to Choose an Infrared Temperature Sensor?

Optical Resolution

Optical resolution is determined by the ratio of D to S, which is the ratio of the sensor-to-target distance, D, to the measurement spot diameter, S. If the infrared temperature sensor must be installed far away from the target due to environmental conditions, and small targets are to be measured, a sensor with high optical resolution should be selected. The higher the optical resolution, that is, the higher the D:S ratio, the higher the cost of the thermometer.

Response Time

The response time represents the response speed of the IR temperature sensor to the temperature change being measured. The electromagnetic flowmeter is defined as the time required to reach 95% of the energy of the final reading, which is related to the time constant of the photodetector, the signal processing circuit and the display system. The response time of the new infrared temperature sensor can reach 1ms. This is much faster than the contact temperature measurement method. If the moving speed of the target is very fast or when measuring a rapidly heated target, a fast-response infrared temperature sensor should be selected, otherwise, the sufficient signal response will not be achieved, which will reduce the measurement accuracy. However, not all applications require fast response infrared temperature sensors. For stationary or thermal inertia of the target thermal process, the response time of the thermometer can be relaxed. Therefore, the selection of the response time of the infrared temperature sensor should be adapted to the situation of the measured target.

Signal Processing Function

Measuring discrete processes (such as part production) is different from continuous processes, requiring infrared temperature sensors to have signal processing capabilities (such as peak hold, valley hold, average). For example, when measuring the glass on the conveyor belt, it is necessary to use peak hold, and the output signal of its temperature is transmitted to the controller.

Environmental Conditions

The environmental conditions in which the temperature sensor is located have a great influence on the measurement results, which should be considered and properly resolved, otherwise it will affect the temperature measurement accuracy and even cause damage to the thermometer. When the ambient temperature is too high and there is dust, smoke and steam, accessories such as protective jacket, water cooling, air cooling system, and air blower provided by the manufacturer can be used. These accessories effectively address environmental influences and protect the thermometer for accurate temperature measurement. When identifying accessories, standardized services should be required wherever possible to reduce installation costs. To investigate smoke, dust, or other particles that reduce the measured energy signal, a two-color temperature sensor is the best choice. In noise, electromagnetic fields, vibration or inaccessible ambient conditions, or other harsh conditions, fiber optic dual color temperature sensors are the best choice.

Temperature Range

The temperature measurement range is one of the most important performance indicators of the sensor, and each type of sensor has its own specific temperature measurement range. Therefore, the measured temperature range must be considered accurate and comprehensive, neither too narrow nor too wide. According to the law of black body radiation, the change of radiant energy caused by temperature in the short waveband of the spectrum will exceed the change of radiant energy caused by the emissivity error.

Target Size

According to the principle, infrared temperature sensors can be divided into single-color temperature sensors and two-color temperature sensors. For a monochrome temperature sensor, when measuring temperature, the measured target area should fill the sensor field of view. The electromagnetic flowmeter recommends that the size of the measured target exceed 50% of the size of the field of view. If the target size is smaller than the field of view, the background radiant energy will enter the sensor's apparent sound branch to interfere with the temperature measurement reading, causing errors. Conversely, if the target is larger than the thermometer's field of view, the thermometer will not be affected by the background outside the measurement area.

Wavelength Range

The emissivity and surface properties of the target material determine the spectral response or wavelength of the thermometer. For high reflectivity alloy materials, there is a low or varying emissivity. In the high temperature region, the best wavelength for measuring metal materials is near-infrared, and the wavelength of 0.18-1.0μm can be selected. Other temperature zones can choose 1.6μm, 2.2μm and 3.9μm wavelengths. Since some materials are transparent at certain wavelengths, infrared energy will penetrate these materials, and special wavelengths should be selected for this material. For example, the wavelengths of 10μm, 2.2μm and 3.9μm are used to measure the internal temperature of the glass (the glass to be tested should be very thick, otherwise it will pass through); the wavelength of 5.0 μm is selected for the measurement of the internal temperature of the glass; the wavelength of 8-14μm is suitable for the low measurement area; The wavelength of 3.43μm is selected for measuring polyethylene plastic film, and the wavelength of 4.3μm or 7.9μm is selected for polyester. If the thickness exceeds 0.4mm, the wavelength of 8-14μm is selected; for example, the narrow-band 4.24-4.3μm wavelength is used to measure CO₂ in the flame, the narrow-band 4.64μm wavelength is used to measure CO in the flame, and the 4.47μm wavelength is used to measure NO₂ in the flame.