In accordance with the recent version of ISO 376:2011, the classification of the force transducers is based on the relative errors calculated from the calibration results. This classification approach doesn't take the uncertainty of measurement into consideration. It becomes one of the most important factors that must be utilized when making a classification decision based on of ISO/IEC 17025:2017. In this study a proposed approach for force proving instrument classification was developed. This approach is based on taking into account the calibration results uncertainty of the instruments as a decision rule for classifications. Since the expanded budget uncertainty is a combination of different parameters that may affect the classifications decisions so it is more realistic and more accurate for decision making. The results of this paper demonstrate a recommendation for ISO 376:2011 to modify its classification criteria for the force proving instruments in the upcoming version of this standard.

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Force and Material Metrology Department (FMMD) is a department within the National Institute forStandards (NIS), founded as early as 1963. The most important event achieved within the last few years at FMMD was constructing, evaluating & commissioning of Dead Weight Machines (DWMs), the Primary Standards for force measurements with ranges of 0.05-5kN, 0.5-50kN, 10-500kN, 500-1000kN and 100-5000kN. All are computerized and delivered by GTM Company except the 5kN machine which is a manually controlled machine, established through research works carried out by FMMD [1]. The FMMD was transferred to a new building which lead to dismantling the 5kN machine and re-assembling it in its new site. In addition, the machine was developed as a part of modernizing NIS force laboratory [2].This development entailed checking the design of machine main frame using finite element method, determining the gravitational acceleration in the new building, determining the air density surrounding the machine, adjusting the machine weights to enhance the accuracy associated with the measurement results, beside designing a full computerized control circuits to control the selection and application of the loads of the machine and finally estimating the relative expanded uncertainty of the machine.

Abstract. Force measuring systems (transducers and indicators) are usually used to calibrate force generated systems.Normally, it is not recommended to use load cells to measure forces less than 10% of its nominal capacity, thus, to offer calibration facilities for different ranges, several load cells are required, which may lead to difficulties in handling procedures in addition to the main disadvantage which is the over cost.This article illustrates conceptual design for a new introduced multi-capacity load cell showing the design parameters and the required metrological characteristic of the new load cell. Force measurement systemsA force measurement system is made up of a transducer and associated instrumentation. The transducer is subjected to the force to be measured, and the resulting change in the element is measured by the associated instrumentation. Force transducers can be distinguished accorduing to the type of output signal generated (mechanical, hydraulic, pneumatic or electrical). Mechanical Force Transducers.The most famous mechanical force transducer is the proving ring, where the deformation of the elastic element is measured via mechanical device. These transducers have the advantage of being simple and robust. The main disadvantage is the strong effect of temperature on the output. Piezoelectric Crystal load cells.These types differ from most other sensing elements in that they are active sensors. No power supply is needed and the deformation to generate a signal is very small. It had the advantage of a high frequency response of the measuring system without introducing geometric changes to the force measuring path. When a force is exerted on certain crystalline materials, electric charges are formed on the crystal surface in proportion to the rate of change of that force.