FIR Temperature Sensor

Among the many things that the COVID-19 pandemic taught us was the technique of assessing the human body temperature non-invasively. This was used in several locations, including hospitals, schools, and airports, employing an infrared sensor for measuring the surface temperature without making physical contact. Now, this is a popular method used commonly for taking body temperature. While being non-invasive, infrared thermometers also provide quick and reliable readings.

The accuracy of the infrared thermometer technique was affected by variables including the nature of the surface under measurement and its surroundings. However, scientists have largely resolved these issues, attaining medical-grade accuracy and compensation. In the process, they have also successfully lowered the size of the thermometer. Accordingly, Melexis Microelectronic Integrated Systems have developed a miniature infrared temperature sensor.

Based in Belgium, Melexis specializes in ICs and microelectronic sensors for applications involving consumer, automotive, digital health, smart devices, and energy management. For instance, Samsung is using one of Melexis’s products, the MLX90832 temperature sensor that works on FIR or far-infrared technology, for their GW5 smartwatch. The medical-grade version of the Melexis temperature sensor allows menstrual cycle tracking. Such continuous but reliable temperature monitoring opens up a vast range of newer applications in health, sports, and other domains.

The FIR sensor from Melexis is an SMD or surface-mount device that can accurately measure an object’s infrared radiation to record its temperature. The SMD packaging makes the sensor suitable for a large variety of applications, such as wearables, including hearables or in-ear devices, and point-of-care clinical applications that require highly accurate human-body temperature measurement.

Non-contact temperature measurement has several advantages over the more traditional contact methods. It can be helpful in several circumstances where making physical contact is undesirable, such as when the object is fragile, located in a dangerous area, or moving. It is helpful when a quick response is desirable, or when it is not possible to guarantee an excellent thermal contact between the object under test and the sensor. Moreover, the technique of measuring temperature without contact can be more accurate and yield results that are more reliable than contact temperature measurement methods.

The extremely small 3 x 3 x 1 mm3 QFN package of the Melexis MLX90832 is a full-solution device that incorporates the optics, a sensor element, digital signal processing, and digital interfacing, providing a quick and simple integration for a wide range of modern applications within a limited space.

With factory calibration, the MLX90832 offers high accuracy, while Melexis has ensured thermal and electrical precautions internally so that the device has adequate compensation when operating in thermally harsh external conditions. Internally, the voltage signal from the thermopile element undergoes amplification and digitization. After undergoing digital filtering, the raw measurement data resides in the RAM of the device. All the functions remain under the control of a state machine. An I2C interface makes available the results of each measurement conversion, while allowing access to the control registers of the internal state machines, the RAM for auxiliary measurement data and pixel readings, and the E2PROM for calibration constants, the trimming values, and other measurement/device settings.