The measurement of body mass index (BMI) is an important indicator of preliminary assessment of human health. A higher BMI value increases the risk factor for critical diseases, e.g., high blood pressure (hypertension), cardiovascular disease, gallbladder disease, type 2 diabetes, etc. Obesity also increases the risk factor of COVID-19 in patients. BMI, the ratio of mass (in kilogram) to the square of height (in meter), is an estimation of an individual's physique. It depends upon the adult's height and mass and is intended to evaluate the tissue mass. In this article, we have described the design and developmental aspects of a temperature-compensated BMI measuring system. The developed BMI measuring system is comprised of an ultrasonic sensor for height measurement, strain gauge-based load cell for precise and accurate mass measurement, a temperature sensor to eliminate the effect of temperature, and a microcontroller with related electronics, software, and display system. The developed BMI system is capable to measure mass precisely in the range (0-200) kg with a resolution of 0.01 kg, and height in the range of (0-4) m with resolution of 0.01 m. The expanded uncertainty in height measurement is estimated as 2.8 mm. The BMI value is determined with the help of these parameters and displayed with precision of 0.01. The novelty of the developed system is temperature compensation in the height measurement using an ultrasonic sensor, which has been introduced first time. Also, system is improved for its highly precise and accurate measurements at a comparatively lower cost than the commercially available existing systems.
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