Infrared temperature sensor can measure temperature without touching objects, so it is widely used in medical, industrial and other fields. How to design and select infrared temperature sensor? I hope that after reading this article, it can give you some inspiration.

Author: Alan Yang

Infrared temperature sensor can measure temperature without touching objects, so it is widely used in medical, industrial and other fields. How to design and select infrared temperature sensor? I hope that after reading this article, it can give you some inspiration.

Is Infrared Temperature Sensor Design Difficult?

It can be very simple. For some digital output infrared temperature sensors, many non-contact infrared temperature sensor manufacturers have calibrated the accuracy for you before leaving the factory. We just need to find an MCU to read the information in RAM through I2C. Some chips also give a sample program to call the infrared temperature sensor. For example, Melexis MLX90632, the MCU STM32F070 sample program is given in Git-Hub, which further simplifies the difficulty of software design. So we can focus more on how to reduce unnecessary noise and improve measurement accuracy.

In the context of the current shortage of infrared temperature sensors worldwide, Digi-Key offers a wide range of Digi-Key infrared temperature sensors for developers to choose from.

Infrared temperature sensor selection points

Choosing an infrared temperature sensor is the first step in a successful design.

・ Distance factor

How far is the temperature measurement distance of the infrared temperature sensor? Just asking this question is not accurate enough. Think of an infrared temperature sensor as a pair of eyes. If the object is large, we can see it even if it is far away. So a more accurate measure is the “distance factor (D:S)”, which is the ratio of the distance D from the sensor to the target to the diameter S of the thermometer’s measurement area at that distance.

Is it difficult to design and select an infrared temperature sensor? After reading this design guide, it is not difficult!

Generally speaking, what an infrared temperature sensor measures is the average temperature within the test range. Therefore, in order to ensure the measurement effect, try to make the test target larger than the test range.

Is it difficult to design and select an infrared temperature sensor? After reading this design guide, it is not difficult!

・ How to calculate the distance factor

Generally, the temperature sensor will give the parameter of field of view (FOV, field of view), that is, the range that the infrared sensor can “see”. Taking Melexis MLX90632SLD-DCB-000-RE as an example, taking the signal sensitivity of 50% as the measurement standard and the FOV of 50°, the distance coefficient ratio can be calculated. D : S =1 : 2tan25

Is it difficult to design and select an infrared temperature sensor? After reading this design guide, it is not difficult!

Digi-Key chooses infrared temperature sensor

The Digi-Key website provides detailed infrared temperature sensor parameters for screening. Under the category of Digi-Key temperature sensor, select “Digital, Infrared (IR)”, “Analog, Infrared (IR)” for the sensor type to get the corresponding results.

There are several more important parameters in the screening process, such as “detection temperature-remote”, “power supply-voltage”, “resolution”, “output type”, “accuracy” and so on. Among them, the “precision” parameter needs special care. Careful reading of the data sheet is recommended. Some infrared temperature sensors will adjust the special temperature range in some special applications.

Is it difficult to design and select an infrared temperature sensor? After reading this design guide, it is not difficult!

For example, Melexis Technologies NV MLX90632SLD-DCB-000-RE has an accuracy of ±0.2°C, which is adjusted for the temperature range of body temperature in the medical field.

Image of Is it difficult to design and select an infrared temperature sensor? After reading this design guide, it is not difficult!

・ Design skills

Ensuring that the surrounding temperature of the infrared temperature sensor device is stable and the corresponding temperature compensation is often the top priority of the design. The internal structure of the infrared temperature sensor is generally a large number of thermocouples stacked on the underlying silicon substrate. The temperature change of the cold junction of the thermocouple directly affects the test accuracy. Therefore, try to keep the infrared temperature sensor away from heat sources, such as heat-generating power chips, to ensure that the temperature around the infrared temperature sensor is stable.

・ Thermal noise

We can often see that the in-line infrared temperature sensor will have a metal casing, the main function of which is to reduce thermal noise. Without this enclosure, thermal noise from the flow of air may affect accuracy. Therefore, for some special applications, the design recommendations are as follows:

1. Put another metal casing outside the metal casing to reduce thermal noise.
2. Air is a good thermal insulator, leave a certain gap between the metal case and the plastic cover.
3. Try to prevent heat conduction on the PCB board, such as removing unnecessary PCB material around the chip to reduce the heat conduction path.

Is it difficult to design and select an infrared temperature sensor? After reading this design guide, it is not difficult!
(The above pictures and suggestions are from Melexis Infrared Temperature Sensor Thermal and Mechanical Design)

・ Thermal gradient and direction of heat source

Some infrared temperature sensors will do temperature compensation to achieve the purpose of noise reduction. For example, the Melexis MLX90614 will compensate for thermal gradients. At this time, special attention should be paid to the direction of the heat source and the placement direction of the infrared temperature sensor. Design according to the requirements of the application manual, in order to play the function of temperature compensation.

Is it difficult to design and select an infrared temperature sensor? After reading this design guide, it is not difficult!
(The above pictures and suggestions are from Melexis Infrared Temperature Sensor Thermal and Mechanical Design)

Summary of this article

As the core component of the temperature measuring gun, selecting an infrared temperature sensor is the first step in a successful design. Understanding infrared sensors in depth and designing around them can do more with less.

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