Metrology for next generation “Phygital Sensors”

Commonly speaking a ‘sensor’ is a device that produces an output signal quantitatively related to a certain physical phenomenon; if the output signal is provided in a digital form, it is referred in terms of ‘digital sensor’. As is known, these devices are produced in the order of million/week and are widely used for the management of “smart systems” now commonplace in everyday life, such as automotive, domotics, smart-industry, cooperative robotics (“cobots”), robotic assisted surgery, as well as for advanced monitoring of infrastructures and ecosystems; moreover, digital sensors are the foundation of the “digital twins” technology development, and support the actualization of the “Digital Earth” purposes. However, in many cases, since these sensors manage interaction processes with humans (e.g., driver assistant control, physiological data, remote surgery, environmental hazard…), their technological performance must be actually recognized as safe and trustworthy. Recently, both manufacturers and end users have begun to question the actual reliability of sensors used in particularly complex applications, and see value in traceable chain to calibration and accreditation national laboratories. Indeed, the methods applied for metrological calibration of measuring instruments, against primary or secondary standards, can allow to accurately quantify the performance of these sensors, with respect to traceable physical quantities, providing certified statements of the effective ‘sensitivity’ (and related uncertainties), as the ratio between the digital output (reaction) and the physical input (stimulus). In that meaning, once calibrated, a digital sensor can be properly considered as a physical-digital sensor, i.e. a device, interfacing the physical world, sensitive to a specific variation of a known physical quantity, and able to convert it into a digital signal output (with known accuracy, precision and reliability), readable for an observer, exploitable by interconnected instruments, and for actuators control. Currently, although no pertinent Standards are yet available for the calibration of ‘physical-digital sensors’, some National Metrology Institutes are putting into practice appropriate calibration procedures and methods to fill this important lack, as described in this paper.