IMEKO Event Proceedings Search

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Akobuije Chijioke, Richard A. Allen, Steven E. Fick, Benjamin J. Reschovsky, Jared H. Strait, Randall P. Wagner
Primary sound standard based on dynamic Fabry-Pérot refractometry

We describe an optical sound standard in which the sound pressure is measured by using a high-finesse optical cavity to observe the induced change in the refractive index of the medium (acousto-optic effect). The optical refractive index of a substance varies with density, and for a compressible substance it will therefore vary in time in an acoustic field. To accurately measure the refractive index changes due to acoustic density variations, we enhance the induced optical phase shifts using a high-finesse optical cavity. By tracking the shift in the optical cavity resonance frequency we sensitively track the shift of the refractive index of the cavity medium and thereby the acoustic pressure in the cavity. We perform the optical measurement at standard telecom wavelength (1550 nm), thereby minimizing the cost of the optoelectronic components required. We report initial measurements in an acoustic resonator, comparing the pressure indicated by the optical cavity to the pressure indicated by a condenser microphone, at 1 kHz and 2 kHz acoustic frequencies.

Sven Ehlers
Height difference measurement in PTB’s liquid column manometer

A primary liquid column manometer (LCM) is under development at PTB for use in conducting low-pressure measurements up to 2 kPa in gauge and absolute pressure. To calculate pressure, all measured input quantities of the instrument, as there are liquid density, gravitational acceleration, and length, are traceable to the International System of Units (SI), thus making the LCM a primary pressure standard. The LCM is well suited to identifying small force-induced errors, particularly those of force-compensated pressure balances with non-rotating piston in their lower measurement range, and as such to disseminating the pascal, the SI unit of pressure.
This report focuses on the measurement of the height difference inside the instrument, where homodyne plane mirror interferometry is applied using the liquid’s free surface as the reflecting mirror for the laser beam.

W. Sabuga
Recent research results on piston gauges

Since the end of 20th century, a big progress has been achieved in the pressure metrology based on piston gauges. It includes a significant reduction of measurement uncertainty, an extension of the measurement range to lower pressures for piston gauges used as primary pressure standards and new measurement techniques for different pressure types. The paper gives a review of this progress with presenting main new approaches applied and results achieved.

Yuanchao Yang, Patrick F. Egan, Tom Rubin
Working equation for a Fabry-Perot cavity based optical pressure standard

From basics of Fabry-Perot (FP) resonator and roundtrip phase, a complete working equation for a FP cavity based optical pressure standard (OPS) is derived and presented which includes corrections of reflection phase-shift, diffraction and pressure-induced distortion. The correction from diffraction, i.e. Gouy phase, is negligible. To operate an OPS as a primary standard, two unknown parameters, i.e. mirror dispersion coefficient ϵ_α and pressure distortion coefficient d_m, in the working equation should be determined independently. Methods to determine ϵ_α and d_m are described and applied to an OPS developed at the National Institute of Metrology (NIM), China. Thermodynamic effect observed in the determination of d_m is also discussed.

A. Rezki, Z. Silvestri, D. Bentouati, J.-P. Wallerand, C. Guianvarc’h, M. Himbert, P. Otal
Status and performance of the LNE-Cnam Fabry-Perot refractometer

We present the status of the single-cavity Fabry-Perot interferometer developed at the LNE-Cnam laboratory used for thermodynamic pressure measurements within the range of 100 Pa to 100 kPa. After characterizing the intrinsic parameters of the refractometer, this optical sensor is used to measure the refractivity of nitrogen. Then, using the Lorentz-Lorenz equation and knowing the refractive virial coefficients at 532 nm, it is possible to deduce its density. Measuring the temperature of the gas makes it possible to determine its pressure using an equation of state.
Once the temperature and pressure stability of the gas inside the optical sensor have been achieved at sub-mK and mPa levels, respectively, the expanded uncertainty of the sensor is evaluated to be [(𝟓𝟎 𝐦 𝐏𝐚 )^𝟐 + (𝟐𝟐 × 𝟏𝟎^−𝟔 ∙ 𝒑)^𝟐 ]^(𝟏/𝟐). In order to further decrease this uncertainty, several approaches and solutions are given, leading to more accurate and reliable pressure measurements. The developed optical cavity operates as a high-resolution pressure sensor with an objective of complementing and eventually replacing conventional pressure standards, such as the force-balanced piston gauge and capacitance diaphragm gauge, that are based on the classical definition of pressure.

Han Wook Song, Jong Ho Kim, MinKy Seo, Sungwan Cho, Sam Yong Woo
Development of the optical vacuum standard system in KRISS

Recently, ‘a new realization of the Pascal’ by using photon technology showed comparable results in terms of performance compared to the existing primary standard based on a mercury manometer. In this study, we describe KRISS optical vacuum standard system uses a 633 nm He-Ne laser, specially made by KRISS, as a light source, and a double channeled Fabry-Perot (FP) cavity made from ZERODUR. Hardware construction for KRISS optical pressure standard system has been completed. Currently, as the first step, it is aimed at calculating the pressure according to the frequency in the pressure range of 1 Pa to 10 kPa using nitrogen gas. Using the measured beating frequency, we determined the internal pressure in the cavity considering the refractive index virial coefficients (AR, BR and CR) and density virial coefficients (Ap, Bp and Cp), the Boltzmann constant kB, and the thermodynamic temperature. The uncertainty is currently in evaluation taking into account the uncertainty factor.

Karl Jousten
ISO standards for vacuum metrology

During the last decade, several important standards and technical specifications (TS) for vacuum metrology have been published by the International Organisation for Standardisation (ISO) or are under development. The pressure ranges for high and ultra-high vacuum have been redefined, and extreme high vacuum has been defined internationally for the first time. Basic standards describing vacuum gauge calibration equipment and methods, as well as the uncertainties associated with a calibration, are supplemented by specific standards for characterising or calibrating specific vacuum gauges. Procedures have also been developed for the characterisation of quadrupole mass spectrometers for partial pressure measurement and for the measurement of outgassing rates in a traceable and comparable manner. A TS for the design of a high-precision ionisation vacuum gauge has recently been published. Reliable vacuum measurement is also important for characterising the performance of vacuum pumps.

D. Mari, S. Pasqualin, M. Zucco
Experimental determination of molar polarizability of nitrogen by a multi-reflection inteferometric technique

A novel optical pressure standard, based on a multi-reflection interferometric technique, has been recently developed. It is based on the measurement of the refractive index of a gas through an unbalanced homodyne interferometer (UINT) and is able to measure pressure with a relative standard uncertainty of 10 ppm at 100 kPa [1]. In this work, the interferometer was used to measure the molar polarizability of nitrogen, which resulted in agreement with recent previous determinations, paving the way for using photonic pressure standards as accurate and fast transfer standards of the pascal.

J. Halbey, M. Bernien, T. Rubin, K. W. Madison, H. Dittus, J. Grosse
Towards a dual species cold atom based pressure sensor

This article describes the conceptual design of a dual species cold-atom based pressure sensor to be built at the Center of Applied Space Technology and Microgravity (ZARM) in cooperation with the Physikalisch-Technische Bundesanstalt (PTB) and supported by the University of British Columbia (UBC). It shall be capable of pressure measurements based on the loss rate of magnetically trapped rubidium and potassium atoms and shall lay the foundation for commercial applications of this measurement method.

Tim Sparkes, Stefan Berdej, Christopher Roberts, Neculai Moisoi
Negative gauge pressure calibration methods using a PACE CM3 pressure controller

The development of pressure controllers has seen a great focus and their technical characteristics have improved over the last few decades, specifically in terms of their metrological capabilities. This advancement now makes them a suitable candidate to measure negative gauge pressure, either directly or in conjunction with other devices such as pressure balances. The Druck PACE in conjunction with CM3 (control module) has demonstrated performance characteristics in line with those required to complete negative gauge pressure calibrations. Three different calibration methods were developed within the Druck Ltd laboratory, from which two of them used a 200 kPa absolute pressure CM3, containing TERPS© (Trench Etched Resonant Pressure Sensor). The unit under test was a PACE1000 indicator built with a piezoresistive sensors with a pressure range from -100 to 100 kPa. The expanded uncertainty was evaluated for each method, as well as identifying the advantages and shortcomings of each method. As the calibrations were performed for gauge mode (not differential), the calibration range was -950 to -50 hPa.

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