Abstract
This paper presents a developed design and construction to improve the performance and increasing the density measuring capability of the previous Hydrostatic Weighing Apparatus (HWA-NIS) at the National Institute of Standards (NIS) up to 20 kg. The previous (HWA-NIS) has been constructed up to 10 kg on 2014. The 2-Positions mass handler in the previous (HWA) was developed with 4-Positions pentagon shape to be able to make handling for individual masses in a group at once, when transferring the traceability from the primary standard “the Silicon Sphere” to the standard masses in the density scale weighing process. The weighing pan in the previous (HWA) was developed with four suspension wires with a diameter of 0.3 mm each, leads to reduce the surface tension affect on the measurement uncertainty by factor four times. The density of the standard masses in the range from 2 kg up to 20 kg were measured with an improved expanded uncertainty from 0.150 kg/m3to 0.078 kg/m3respectively due to reducing the effect of surface tension via the developed design of the weighing pan.
Highlights
Density determination is needful for accurate determination of the mass
This is reflected in the International Organization of Legal Metrology (OIML) Standard OIML R111 [1] for a mass of 1 kg E1, which gives a tolerance in the mass of only 500 mg
In the year 2014, the National Institute of Standards (NIS) designed and constructed the Hydrostatic Weighing Apparatus (HWA-NIS) which could measure the density of standard masses ranging from 2 kg up to 10 kg based on the method A2 in OIML R111
Summary
Density determination is needful for accurate determination of the mass. It is essential for the National Metrology Institutes (NMIs), accredited calibration laboratories. In the year 2014, the NIS designed and constructed the Hydrostatic Weighing Apparatus (HWA-NIS) which could measure the density of standard masses ranging from 2 kg up to 10 kg based on the method A2 in OIML R111. The development includes design and construction of a new alternative hydrostatic weighing parts, includes innovative design for a weighing pan able to carry masses up to 20 kg with four suspension wires with diameters of 0.3 mm for each one at the region of the intersection the distilled water surface with the diameter of these wires at the time of weighing in the distilled water to reduce the large uncertainty value due to surface tension effect and to be able to reach accepted standard uncertainty covers the requirements of OIML R111 for this method. A PT-100 thermometer with a resolution of 0.001 °C [12] is kept immersed in the distilled water and closed to the weighing pan to evaluate the temperature gradient of the distilled water temperature [14]
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