Due to perfect stability, deionized water is usually used as one important reference material for density and volume calibration. To evaluate suitability of pure water density formulas for deionized water, one measurement system based on Archimedes’s principle was designed, and silicon ring was used for density standard to measure the density of deionized at 20°C. The experimental result shows that The Tanaka equation can be used to calculate the density of deionized water with deviation 5ppm. The uncertainty budget of measurement is analyzed, and the combined relative uncertainty is 4.09ppm (k=2).
The standard near-silicon liquid (2329kg/m3) is a mixture liquid of tribromopropane and dibromoethane in a certain proportion. This liquid is used to measure the density of single crystal silicon spheres by a static suspension method and the analysis of the difference in the micro density between two silicon spheres. Measuring the difference in the micro-density of the silicon spheres is of great significance for the new definition of the new mass of kilograms. In order to obtain the micro-density difference of the silicon spheres, it is necessary to calculate the static pressure value and the temperature by separately adjusting the singlecrystal silicon spheres to the same suspension state and the compression coefficient of the near-monocrystalline silicon density liquid. Through the adjustment of the same hydrostatic suspension state of a single silica ball in different suspension states, the linear constants measured by the linear model are analyzed to calculate the liquid compression coefficient. For this purpose, a static suspension measuring device for a single crystal silicon ball was designed to maintain the water bath within a range of ±0.1mk within 3 hours, and the position control of the silicon ball was determined by controlling the pressure of the upper computer.
Glass hydrometers are simple but effective instruments for measuring the density of liquids. Glass hydrometers calibration based on the Archimedes law, using silicon ring as a reference standard solid density, n-tridecane with density stability and low surface tension as the standard working liquid, based on hydrostatic weighing method designs a glass hydrometer calibration system. Glass hydrometer calibration system uses CCD image measurement system to align the scale of hydrometer and liquid surface, with positioning accuracy of 0.01 mm. Surface tension of the working liquid is measured by Whihemy plate. According to twice glass hydrometer weighing in the air and liquid can calculate the correction value of the current scale. In order to verify the validity of the principle of the hydrostatic weighing method of glass hydrometer calibration system, for measuring the density range of (770-790) kg/m3, with a resolution of 0.2 kg/m3 of hydrometer. The results of measurement compare with the Physikalisch-Technische Bundesanstalt(PTB) ,verifying the validity of the calibration system.
In order to overcome the shortcoming of significant influence of evaporation capacity on gravimetric method and meet the requirement of online measurement, dual-wavelength photometric method is introduced for measuring microliquid volume. Based on Lambert-Beer law, this paper introduces the dual-wavelength photometric method (DWP method) at 520 nm and 730 nm, which can measure the microliquid volume through the linear relation between the concentration of dilute solution and the absorbance. Comparing to gravimetric method, an experimental system for dual-wavelength photometric method was designed. Experimental results indicate that the test result obtained by using DWP method was better than obtained by using gravimetric method, and met the technical requirement of ISO 8655. Compared with the gravimetric method, the non-gravimetric methods can provide a better solution for microliquid volume measurement, which was less stringent for measurement environment, easy to realize the online calibration and capable of reducing the influence of liquid evaporation.
Liquid volume is one important metrology method for commercial transaction in international trade, and vertical tank is
used as main metrology tool. One non-contact optical measurement system was raised by using laser scanning method.
The coordinates of vertical tank shell were acquired by phase-shift ranging method and angular measurement, and the set
of coordinates is named as data cloud. The measurement errors of distance and angle are 2mm and 2" respectively.
Wavelet was applied to noise reduction and curve feature extraction for data cloud. Iterative method was used to deduce
the radius at each course height. One 1000m3 vertical tank used as test object, comparison experiment was carried out
with strap method (international arbitral standard). The experimental results show that the noise due to tank shell surface
characteristics and laser scanning devices could be filtered satisfactorily, and the local curve features of tank shell were
Metal tanks are generally used for the measurement of liquid petroleum products for fiscal or custody transfer
application. One tank volume precise measurement method based on data cloud analysis was studied, which was
acquired by laser scanning principle. Method of distance measurement by laser phase shift and angular measurement
by optical grating were applied to acquire coordinates of points in tank shell under the control of a servo system.
Direct Iterative Method (DIM) and Section Area Method (SAM) were used to process measured data for vertical and
horizontal tanks respectively. In comparison experiment, one 1000m3 vertical tank and one 30m3 horizontal tank
were used as test objects. In the vertical tank experiment, the largest measured radius difference between the new
laser method and strapping method (international arbitrary standard) is 2.8mm. In the horizontal tank experiment, the
calibration result from laser scanning method is more close to reference than manual geometric method, and the
mean deviation in full-scale range of the former and latter method are 75L and 141L respectively; with the increase
of liquid level, the relative errors of laser scanning method and manual geometric method become smaller, and the
mean relative errors are 0.6% and 1.5% respectively. By using the method discussed, the calibration efficiency of
tank volume can be improved.