Bilateral comparison. between. the FG5X-216 and the FG5-242

Transcription

1 Olver Francs Internal Report Blateral comparson between the FG5X-16 and the FG5-4 Walferdange Underground Laboratory for Geodynamcs, Luxembourg Olver Francs - Unversty of Luxembourg (UL) - Luxembourg Chrstan Ullrch Federal Offce of Metrology and Surveyng (BEV) - Austra

2 1. Introducton From June 5 th to June 9 th 014, a comparson between the absolute gravmeters of the Unversty of Luxembourg and the Federal Offce of Metrology and Surveyng (BEV) was hosted n the Underground Laboratory for Geodynamcs n Walferdange (WULG).Both absolute gravmeters have been manufactured by Mcrog-LaCoste Inc. and are workng on the same prncple [1] even f ther constructon concepts dffer from each other. The am of the project was to ensure that there s a good agreement between these two devces and to lnk the result to the CCM.G-K Key Comparson held n the WULG n November 013. Durng the Key Comparson, only one ste could be measured by the FG5-4. In the meantme, ths gravmeter went through a major mantenance. It was mportant to re-estmate the degree of equvalence of the FG5-4. The partcpants were: Prof. Olver Francs Olver.francs@un.lu Mag. Chrstan Ullrch Chrstan.ullrch@bev.gv.at Unversty of Luxembourg, Luxembourg Federal Offce of Metrology and Surveyng (BEV), Austra. Instrument descrpton The nstruments used n the context of ths project are ballstc free fall absolute gravmeters manufactured by Mcrog-LaCoste Inc. The absolute gravmeter FG5-16 of Unversty of Luxembourg s n operaton snce 001 but was upgraded to the FG5X-16 n 011. The FG-4 s operatng snce 010 and was servced a few month before the comparson. FG5X-16, UL FG5-4, BEV Fgure.1. Absolute gravmeters used durng ths comparson. 1

3 3. Test procedure The test procedure appled durng ths comparson s quet smple. From June 5 th 014 to June 30 th 014, each gravmeter was placed alternatvely on the reference statons B1 and B3 and C5 of the WULG. For each staton, the absolute value of gravty was measured by each gravmeter for at least 1 hours. Addtonally the FG5-4 measured at pllar A3. Ths latter measurement was not used for the comparson as the FG5X-16 dd not occupy that pllar. 4. Measurement results The results obtaned durng the comparson at the statons B1, B3 and C5 by the two gravmeters are summarzed n Table 4.1. The values are gven n µgal (µgal = 10-8 ms - ). Table 4.1. Gravty value measured by the two gravmeters at statons B1, B3, C5 and A3 (g offset = µgal) FG5X-16 (UL) FG5-4 (BEV) Statons g-g offset u g-g offset u (µgal) (µgal) (µgal) (µgal) B B C A3 406,5.6 The uncertanty gven n the Table 4.1 corresponds to the square root of the quadratc sum of the typcal uncertanty of an FG5, and the ste dependent uncertanty [3]. The gravty values measured by each gravmeter at each staton are graphcally represented n the Fgure 4.1. Fgures 4.1. Gravty value measured by the two gravmeters at the statons B1, B3 and C5. 5. Evaluaton of the measurement results 5.1 Compatblty ndex E n The compatblty ndex E n beng defned by,

4 E n x x j = (1) U ( x ) + U ( x j ) defnes the rato between the dfference of two estmated values and the expanded uncertanty (k=) of the dfference. An E n factor larger than one means that the dfference between the values cannot be covered by the uncertanty. Wth a perfectly repeatable transfer standard, ths mples that ether at least one of the two values s corrupted, or the clamed uncertantes are too small. For the measured values at the three statons B1, B3 and C5, the E n factors are lsted n Table 5.1. Table 5.1. E n factors at the gravty statons B1, B3 and C5 evaluated wth the extended uncertanty. B1 B3 C5 FG5X-16 FG5-4 FG5X-16 FG5-4 FG5X-16 FG5-4 FG5X FG The values of the E n factors, gven n table 5.1, shows that all measures are n equvalence. 5. Evaluaton of the reference values As descrbed by M. G. Cox [], the reference values at each gravty staton are determned by the weghted mean y.: x u ( x 1) + + xn u ( xn ) ( x ) + u ( x ) 1 y = 1 u 1 +1 N () u 1 ( y ) u ( x ) u ( x ) 1 1 = (3) 1 N where: y : weghted mean value for the gravty value at the staton u(y ): uncertanty of the weghted mean value for the gravty value at the staton x j : estmated gravty value by the gravmeter j at the staton u j : uncertanty of the gravmeter j at the staton The evaluated reference values for each staton are gven n Table 5.. 3

5 Table 5.. Reference gravty value at the statons B1, B3 and C5 (g offset = µgal). Staton Weghted mean g ref -g offset u ugal ugal B B C Degree of equvalence For both gravmeters, the degree of equvalence of the measured gravty values has been evaluated. Equvalence between nsttute and the reference value The degree of equvalence between the nsttute and the reference value s gven by: d = x x (4) U = ) u ( d ) = u ( x ) u ( x ) (5) ref ( d) u( d ref The obtaned values are gven n table 5.4. Table 5.4. Degree of equvalence between the dfferent nsttutes and the reference values Staton UL BEV d 16 U(d 16 ) d 4 U(d 4 ) µgal µgal µgal µgal B B C Mean Equvalence between nsttute and nsttute j The degree of equvalence between the nsttutes s gven by: d j = x x (6) j U d ) = u( d ) u ( d ) = u ( x ) + u ( x ) (7) ( j j The obtaned values are gven n table 5.5. j j 4

6 Table 5.6.Degree of equvalence between the gravmeter at the three statons B1, B3 and C5. B1 B3 C5 µgal µgal µgal D 4 -d Lnk to CCM.G-K Key Comparson To lnk ths comparson to the results of the CCM.G-K Key Comparson held n the WULG n November 013 [5], the Key Comparson Reference Values (KCRVs) at the statons B1, B3 and C5 have been adjusted for the gravty change observed wth the relatve superconductng gravmeter OSG-CT040 between November 13 and June 014. An uncertanty of 1 mcrogal has been assgned to the observed gravty change to take the uncertanty on the SG nstrumental drft estmate nto account (Table 6.1). Table 6.1. KCRVs from the Key comparson n November 013, CRVs of the present comparson and the KCRVs corrected for the observed gravty change wth the OSG-CT040. Staton KCRV 11/013 CRV 06/014 Gravty changes from the OSG- CT040 g U KCRV corrected for gravty change G U g U g U B B C Fgure 6.1. Comparson between the KCRVs n 013 corrected for the observed gravty change observed wth the superconductng gravmeter OSG-CT040, the CRVs of ths comparson and the g-values measured wth the FG5X-16 and FG5-4, respectvely. It demonstrates that the KCRVs and the CRVs of the present comparson and the measured g values by the FG5X-16 and FG4-4 are coherent. Based on ths, we can consder that the lnk between these two comparsons s acceptable. 5

7 7. Concluson The measurements of the FG5X-16 and FG5-4 are n agreement (or n equvalence) between themselves and wth the Key Comparson Reference Values of the CCM.G-K Key Comparson. 8. Lterature [1] Nebauer T M, Sasagawa G S, Faller J E, Hlt R and Kloppng F 1995 Metrologa [] Cox, M.G., The evaluaton of key comparson data, Metrologa, 00, 39, [3] Results of the Seventh Internatonal Comparson of Absolute Gravmeters ICAG-005 at the Bureau Internatonal des PodsetMesures, Sèvres, GGEO-008. [4] Pearson, E. A., Hartley, H. O., Bometrka Tables for Statstcans, Vol , table 8, [5] Francs, O., Baumann, H., Ullrch, C., Castelen, S., Camp, M. V., Sousa, M. A. D., Melhorato, R. L., L, C., Xu, J., Su, D., Wu, S., Hu, H., Wu, K., L, G., L, Z., Hseh, W.-C., Pálnkás, P. V., Kostelecký, J., Mäknen, J., Näränen, J., Merlet, S., Santos, F. P. D., Gllot, P., Hnderer, J., Bernard, J.-D., Mogne, N. L., Fores, B., Gtlen, O., Schllng, M., Falk, R., Wlmes, H., Germak, A., Bolcat, E., Orgla, C., Iacovone, D., Baccaro, F., Mzushma, S., De Plaen, R., Klen, G., Sel, M., Radnovc, R., Sekowsk, M., Dykowsk, P., Cho, I.-M., Km, M.-S., Borreguero, A., Sanz-Maza, S., Calvo, M., Engfeldt, A., Agren, J., Reudnk, R., Eckl, M., Westrum, D. V., Bllson, R., & Ells, B., CCM.G-K key comparson,metrologa,5(1a), 07009,