How to use high accuracy digital temperature sensors in health monitoring wearables

Author : Rolf Horn | Applications Engineer | Digi-Key Electronics

01 October 2022

Figure 5. For accurate environmental temperature sensing, there should be a high thermal resistance between the skin & environmental temperature sensors. [image source: ams OSRAM]
Figure 5. For accurate environmental temperature sensing, there should be a high thermal resistance between the skin & environmental temperature sensors. [image source: ams OSRAM]

Accurate digital temperature measurements are important in a range of applications including wearables, medical monitoring devices, health & fitness trackers, cold chain & environmental monitoring, and industrial computing systems.

This full version of this tutorial was originally featured in the October 2022 issue of EPDT magazine [read the digital issue] and the Digi-Key Article Library. And sign up to receive your own copy each month.

While widely applied, the implementation of highly accurate digital temperature measurements frequently involves temperature sensor calibration or linearization, as well as higher power consumption, which can be an issue for compact, ultra-low power applications with multiple acquisition modes. As Rolf Horn, Applications Engineer at component distributor, Digi-Key Electronics explains here, the design challenges can quickly mount, causing cost overruns and delayed schedules…

Complicating the matter, some applications involve multiple temperature sensors sharing a single communication bus. In addition, some production test setups need to be calibrated according to the US National Institute of Standards & Technology (NIST), while verification equipment needs to be calibrated by an ISO/IEC-17025 accredited laboratory. Suddenly, what seemed a straightforward function becomes both intimidating and costly.

This article briefly describes the requirements for high accuracy temperature measurements in mobile and battery powered health monitoring applications. It then introduces a low-power, high-accuracy digital temperature sensor IC (integrated circuit) from optical sensing & lighting firm, ams OSRAM that doesn’t require calibration or linearization. It finishes with integration recommendations, including an evaluation board and a Bluetooth enabled demo kit with a companion app that makes it possible to modify sensor settings and observe the impact on power consumption...


Requirements for high-accuracy temperature monitoring

Digital temperature sensor with NIST-traceable production testing

High accuracy plus low power

Wearables integration options

Improving thermal response time

Sensing environmental temperature

Eval kit kickstarts AS6221 development

Demo kit for the AS6221

Conclusion

Designing high-accuracy digital temperature sensing systems for healthcare, fitness and other wearables is a complex process with respect to design, test and certification. To simplify the process, lower cost and get to market more quickly, designers can use highly integrated, low-power, high-accuracy sensors.

As shown, the AS6221 is one such device. It does not require calibration or linearization, and the production testing equipment is calibrated according to NIST standards by an ISO/IEC-17025 accredited laboratory, speeding the design and approval process for medical devices.

Read the full article in EPDT's October 2022 digital issue...


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