P1-APMP.EM-S9. VNIIM/KRISS Bilateral Comparison of DC Magnetic Flux Density by Means of a Transfer Standard Coil. TECHNICAL PROTOCOL

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1 P1-APMP.EM-S9 VNIIM/KRISS Bilateral Comparison of DC Magnetic Flux Density by Means of a Transfer Standard Coil. TECHNICAL PROTOCOL 1. Introduction Po Gyu Park (KRISS, S.Korea), Vladlen Shifrin (VNIIM, Russia) The purpose of this document is to present the proposal by the D.I. Mendeleyev Metrology Institute (VNIIM) and Korean Research Institute for Standards and Science (KRISS) for a bilateral comparison of the magnetic flux density standards by means of a Transfer Standard Coil (TSC) at the highest level of accuracy. VNIIM is offered to be a pilot laboratory. Special conditions are necessary to achieve the low uncertainty levels sought in this comparison. These include: a non-magnetic laboratory located far from sources of man-made magnetic interference, an automatic system of deep compensation of the variations of the Earth's magnetic field, and means of establishing a highly uniform magnetic flux density is reproduced by transfer Standard Coil. It may well be that adequate conditions and appropriate equipment for their maintenance now are available only at the VNIIM and KRISS. Completion of this project may form a basis for follow-on multilateral APMP ccomparisons of dc magnetic flux density standards. 2. The traveling standard and expected uncertainty The transportable Tesla/A and Tesla standard, has been created by VNIIM on the basis of the quartz Garret solenoid [1] designed to produce a known magnetic flux density (MFD) and a known ratio of magnetic flux density to DC current. 1

2 A single layer two-pitch solenoid of the Garret type with a winding laid in a screw groove cut on the surface of a cylindrical quartz carcass has a length of about 400 mm and a diameter of 130 mm. The travelling standard is capable of carrying a maximum current in solenoid winding I C of 1 A, which produces a field in its centre with a MFD B 0 of about 0,95 mt. The field in the solenoid is homogeneous within in the centre spherical region of 30 mm diameter, which is sufficient to enable a narrow atomic magnetic resonance (AMR) line width for precision MFD measurements up to 1 mт. A copper thermo resistor of the value R t ~125 Ohm attached to the internal surface of a solenoid quartz carcass for use as a coil temperature reference. By varying the room temperature, the temperature coefficient of the coil conversion coefficient (coil constant) K Rt0 B = B 0 /I s with respect to the change of Rt was measured at VNIIM using an He-Cs AMR standard magnetometer. From the measured slope, the temperature dependence of the coil constant is estimated as K Rt B = K Rt0 B [1 + 8, (Rt 0 Rt)] T/A (1) As a result of this bilateral comparison, the total standard uncertainties of Т /A measuement of (1-2) 10-6 are expected. 3. Circulation of the standard According to the preliminary plan coordinated between the parties, transfer standard coil will be delivered from VNIIM in KRISS where metrological research on its comparisons with KRISS standards will be performed from June, 19th till June, 25th, Conditions and methods of measurement 4.1. Determination of the transfer standard coil constant at the pilot laboratory (VNIIM). The coil constant K В and the basic parameters of the travelling standard - long term stability, uniformity of the magnetic field in working space, dependence of the constant on temperature - were determined during long-term research carried out from2000 to 2010 using the VNIIM primary standard of magnetic units [2]. 2

3 The measurement methods provided automatic compensation of Earth magnetic field and other sources of magnetic noise, and also precision setting of DC current in the winding of TSC using a quantum direct current reference [3]. As a result of this research the value of a coils constant as a function of temperature (or thermo resistor value Rt) has been derived. K Rt B = K B0 [1 + 8, (125,0 Ω Rt)], (2) where K B0 = 0,9539 mt/a coil constant referred to Rt = 125,0 Ω, α Rt = 0,51 Ω/ 0 C ; α Kt = 4, / 0 C. The value of K B0 is represented in the VNIIM certificate of calibration. The estimated total standard deviation of the coil constant value is , MFD non uniformity in at edges of the central spherical working volume in diameter + _2 cm does not exceed , instability for a year does not exceed Measurements of the MFD coils (solenoids) at KRISS. Measurement of the travelling standard (VNIIM solenoid) coil constant Measurements should be carried out with the compensation of Earth magnetic field and other magnetic noise sources. Transfer standard coil constant T/A in its geometrical center is derived from the results of direct measurements by standard He-Cs magnetometer of the MFD B S generated by a solenoid at the applied DC current I in the solenoid winding. Measurements will be carried out at two opposite directions of a current in the winding of the solenoid to remove the effect of the uncompensated part of the Earth magnetic field. В В Solenoid constant K B is determined as: K B = B S / I. К В = К 1 К 2, (3) I where B K1 and B K2 are the values of MFD measured by a reference magnetometer at two opposite directions of current. All results of MFD measurements should be based on the newest γ p value recommended by CODATA in 2006 and the experimental determination of the gyromagnetic ratio of He4 atoms [4] as: B KR = (2π/γ He4 ) f KR He4 and B KR = K B VN I KR ( 4 ) where f KR He4,B KR and I KR are AMR frequency, MFD and current, respectively, measured by KRISS. 3

4 Comparison of the coil constants of VNIIM and KRISS solenoids The coil constants of the VNIIM and KRISS standard will be measured at different times with identical current in their windings. The ratio of the coil constants of the solenoids of KRISS (K B KR) and VNIIM (K B VN) is defined as: [K B KR / K B VN ] = [B KR / B VN ], (5) where B KR and B VN are measured values of MFD in VNIIM and KRISS solenoids. KR One series of measurements is carried out in 10 pairs of single measurements of MFD K B and K VN B В К and current I. Each pair of measurements is made at two opposite directions of current I. No less than three series of measurements of 10 pairs in each should be executed for the calculation of average value of results of measurements and their uncertainty. Measurement uncertainty The type A standard uncertainty at n-1 degrees of freedom is calculated as the experimental standard deviation of the mean of the К В measurements using the formula: u A = 1 [ n ( К В К Bi n( n 1) i 1 ) ] 2 1/ 2. (6) The type B standard uncertainty B is calculated as: u B = [u 2 (B T )+ u 2 (I) + u 2 (Bn)] 1/2, (7) where u (B T ) and u (I) are relative standard uncertainties of type B measurements of MFD and current, respectively, u (Bn) is relative standard uncertainty from MFD non uniformity. The total standard uncertainty is estimated from: u S = [u 2 A + u 2 B ] 1/2. The uncertainty of a MFD comparison using (4) should be calculated similarly. Report of the comparison 4

5 VNIIM as a pilot laboratory should prepare report within 60 days after finishing the measurements. The report should contain: - an explanation of the method; - the details of the measurement conditions; - the results; - the associated standard uncertainties (k = 1); - the number of degrees of freedom; - the detailed uncertainty budget. Coordinator and communications The contact person for the pilot laboratory and his whereabouts are: Dr. Po Gyu Park, ph:., pgpark@kriss.re.kr Prof. Vladlen Shifrin D.I. Mendeleyev Institute for Metrology( VNIIM), Laboratory of Magnetic Mtasurements Measurements, 19, Moskovsky pr., , St.Petersburg, Russia References ph: (812) , shifrin@vniim.ru 1. M.W.Garrett and S.Pissanetzky: "Polygonal Coil Systems for Magnetic Fields with Homogeneity of the Fourth to the Eigth Order", Rev. of Sci. Instr., vol.42, pp , V.Ya.Shifrin, E.B.Alexandrov, T.I.Chikvadze, V.N.Kalabin, N.N.Yakobson, V.N.Khorev and P.G.Park. Magnetic flux density standard for geomagnetometers, Metrologia, 37(3), V. Ya. Shifrin. V. N. Khorev, Po Gyu Park, "The Precise System for the Direct Current Reproduction on a Basis of Atom Magnetic Resonance in Helium-4", Metrologia, 36(3), V. Ya. Shifrin, P. G. Park, V. N. Khorev, C. H. Choi, and C. S. Kim, "A new low-field determination of the proton gyromagnetic ratio in water", IEEE Trans. Instrum. Meas.,47(3), (1998). 5. P.G. Park, V.Ya. Shifrin, V.N. Khorev, and Y.G. Kim Magnetic flux density standard for low magnetic field at KRISS, CPEM 2000 Digest, pp , V.Ya.Shifrin*, V.N. Khorev, V.N. Kalabin and P.G.Park, Experimental estimation of accuracy of modern scalar quantum magnetometers in measurements of the Earth magnetic field, Physics of the Earth and Planetary Interiors, 166, , 2008, 5