9762 papers found
Creep measurements in reference torque calibration machines cannot be performed like those in direct load calibration machines. Comparisons between creep measurements in both situations lead to recommendations for reference methods yielding results which are equivalent to results based on direct load methods. Furthermore, some effects are discussed which might affect the comparability of creep measurements.
This paper discusses an optical position sensor which can be used in balances based on the principle of electromagnetic force compensation (short used EFC) for example. Other applications are zero point detection as well as high precision positioning in the range of ± 200 μm. The position sensor consists of two infrared-LED (IR-LED) which illuminate a single photodiode via an aperture. The aperture is movable and performs a shadowing of the beams, thus shadowing changes due to the position of the aperture. The photodiode detects light from both LED. Both light sources have to be modulated...
The National Physical Laboratory, India (NPLI) is the custodian of National Prototype of the Kilogram (NPK) No. 57, which was provided by the International Bureau of Weights and Measures (BIPM), Paris, France in 1958 after its first calibration in 1955. The NPK has been recalibrated three times (1985, 1992 & 2002) so far at the BIPM. All NPL working standards (Multiples & sub-multiples of 1 kg) range from 1 mg to 20 kg are reestablished using new value of NPK through four Transfer Standards of 1 kg (two made of Stainless steel and two made of Nickel-Chromium alloy) according to defined...
Surface roughness is one of many parameters that influences on mass stability of standard weight, commonly used as a transfer standard of mass SI unit. One of the most famous non-invasive methods for determining surface roughness from a surface profile of material is a vertical scanning interferometry (VSI) with a white light source. In this research, 3-D surface profiles of 316-stainless steel, usually used as a material for standard weights, are constructed by using VSI, based on Michelson interferometer (MI). Because of its low-coherent properties, low cost, and compact light source, a...
The Vacuum Transfer System (VTS) is designed for fully automatic loading of weights into the Sartorius Prototype Mass Comparator CCL1007. The system enables the user to transfer weights from air to air/neutral gas, air to vacuum and back, as well as from vacuum to vacuum conditions. A detailed description of the technical parameters and the different operation modes will be presented.
Gas leak detection is getting more important in the last years. Primary standards for leaks can be divided into sensitive and insensitive to gas species. The method proposed by authors is insensitive to gas species. The basic principle of the method is mass comparison and detection of the difference between standard weight and the leak to be calibrated. The authors made several measurements to prove the repeatibility of the method. It can be seen that to get results with reasonable uncertainty the weekend measurement is sufficient.
Three new density measurement techniques have been devised and evaluated for the measurement of nonstandard objects, namely porous material samples, small solid samples, powders and particulates. Hydrostatic weighing has traditionally been used to determine the density of solid artefacts. This method is not, however, suitable for porous objects since they will adsorb water making weighing in water unstable and possibly detrimental to the material samples. A method, weighing the artefacts in inert gas, has been developed for this application. The density determination of small solid artefacts...
In order to further improve the metrological properties of weighing systems based on the principle of electromagnetic force compensation (EMFC) as well as quality assurance, it is necessary to determine the parameters relevant for the dynamic operation, such as measurement time and controller behavior. This determination is carried out by loading the balance system and observing the indication. Typically this is done by a load changer using different metrological weights. This method is inevitable if metrological traceability is required. However, the conventional procedure of load changing...
As the demand for measuring objects in motion is increasing the need for a system to measure vehicles has been developed to measure mass of vehicle in dynamic motion. Using the concept of measuring the inertial mass of a moving vehicle instead of gravitational mass has proven successful for a purely dynamic problem. Since the measurement of a dynamic motion requires high speed sampling a scanning speed of the signal information is set at 1μs/sample. This is to ensure the movement of the structure is captured to full extent. Using dynamics, the inertial mass correlation between the Dynamic...
This paper shows an interesting case for a national comparison where two transfer standards have been used. Participating laboratories have calibrated one transfer standard or the other, but one that calibrated both, so that can be used as a link to make a joint evalution for all the participant laboratories.