The Provision of Mass Calibrations for Micro/Nano Force Measurements

The accurate force measurement is a problem of a great importance in industry, research and society because of extremely wide range of force relating applications. Over the last decade, increasing attention has been paid among the National Institutes of Metrology (NMIs) worldwide in measurement of small forces, which play a more important role in micro or nanotechnology and other significant areas (medicine, energy, environment). The equipments used to make such measurements must have metrological traceability to a realization of SI unit of force, within the required uncertainty. In this respect, the NMIs have started to study methods for completing a hierarchy of SI-traceable force metrology at low force level. As it is known, one of the ways to achieve traceability route to SI units for force measurements is through the definition of mass, length and time. For this purpose, the known method for force calibrations or measurements is the use of deadweight machines, based on masses suspended in the Earth's gravitational field (force generated by a known mass in a known gravitational field). Another way for measuring small forces is based on the comparison of a force transducer with the indication of a balance, which works on the Electromagnetic Force Compensation (EMFC) mode. Starting from these two methods, the Mass laboratory of National Institute of Metrology (INM) from Romania considered it necessary to extend the dissemination of mass unit below 1 mg, in order to meet current needs in the field of small forces measurements. In this respect, the article deals with the provision of mass calibrations for low force measurements, consisting in (1) calibration of micromass standards having nominal values between (100…500) µg, corresponding to approx. (1....5) µN, and (2) metrological characterization of a weighing instrument that works on the principle mentioned above and has a resolution of 0.1 µg (corresponding to approx. 1nN).