Hao Fang

Bureau International des Poids et Mesures, Sèvres, Île-de-France, France

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Publications (7)7.16 Total impact

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    ABSTRACT: The Bureau International des Poids et Mesures (BIPM) is developing a watt balance to measure accurately the Planck constant h by linking it to the kilogram. The kilogram is currently the only base unit of the International System of Units still defined by a material artifact. A fixed numerical value of h could be the basis for the expected future redefinition of the kilogram in terms of fundamental constants. One main concern of the watt balance experiment is the alignment of the involved vectors. In particular, the electromagnetic force exerted on the watt balance coil needs to be carefully aligned parallel to the gravitational force exerted on the test mass. To address this requirement, we have developed an original experimental procedure that has been validated with a test coil which is a prototype for the ultimate watt balance coil. The result is accurate enough to enable a determination of the Planck constant with a relative uncertainty of about 1 . 10(-8), which is the ultimate goal of the BIPM watt balance.
    No preview · Article · Jul 2011 · IEEE Transactions on Instrumentation and Measurement

  • No preview · Article · Jan 2011
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    ABSTRACT: Since beginning the construction early in 2005, considerable progress has been made on the watt balance of the Bureau International des Poids et Mesures (BIPM). We have continued the development of a room-temperature version to test the feasibility of simultaneous force and velocity measurements. Preliminary measurements of the voltage-velocity ratio have been carried out with a reproducibility of the order of 1 part in 10<sup>4</sup>. The coil suspension has been improved to reduce the undesired coil movement in the 5 degrees of freedom different from a perfectly vertical movement. Further work on the current source has reduced its long-term drift to a few parts in 10<sup>9</sup> per minute with a satisfactory short-term stability. A technique needed to separate the voltage induced in the coil from the voltage drop due to the current flow based on the use of a second noninductive coil has been tested. The second coil is now being integrated into the apparatus. Work has started on the geometrical and magnetic characterizations of a large precision solenoid that will become the reference for the magnetic field alignment. The collaboration with a university on the fabrication of our magnetic circuit is being continued. This paper briefly outlines the main ideas of the BIPM watt balance and reports the progress to date.
    Full-text · Article · May 2009 · IEEE Transactions on Instrumentation and Measurement
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    ABSTRACT: We present the recent progress on the BIPM (Bureau International des Poids et Mesures) watt balance. The existing apparatus was transferred to the dedicated new laboratory with better thermal and vibrational conditions. The apparatus is fully operational in air. An improvement by a factor of three was achieved on the S/N ratio of both the voltage-to-velocity and force-to-current ratios. The fabrication of the parts of the new magnet is completed and its assembly is finished.
    Full-text · Article · Jan 2009 · The European Physical Journal Conferences
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    ABSTRACT: The Bureau International des Poids et Mesures (BIPM) has recently started work on a watt balance to link the kilogram with the Planck constant, in view of a future redefinition of the kilogram. This paper presents the essential ideas of the BIPM watt balance and reports the progress to date
    No preview · Article · May 2007 · IEEE Transactions on Instrumentation and Measurement

  • No preview · Article · Jan 2007
  • Alain Picard · Hao Fang
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    ABSTRACT: Improved knowledge of air density will be useful to support various experiments in the mass field. A study was carried out at the Bureau International des Poids et Mesures to reduce the uncertainty on the air density determination by comparison of the performance of the following three methods: application of the CIPM- 81/91 formula; direct determination using air buoyancy artefacts having the same surface area but a large volume difference; refractometry, exploiting the high correlation between air density and air index of refraction, using a novel refractometer well adapted to our requirements (relative determination). The coherence among the three methods was satisfactory, but a discrepancy of the order of 10<sup>-4</sup> kg·m<sup>-3</sup> was observed between the CIPM-81/91 formula and methods employing artefacts. Additional measurements made in the framework of Euromet mass project 144 confirm this difference, which needs to be clarified by future studies using gravimetric measurements and on further investigations of the air composition.
    No preview · Article · May 2003 · IEEE Transactions on Instrumentation and Measurement