EUROMET Comparison of a 10 mH Inductance Standard at 1 kHz EUROMET.EM-K3 Final Report by Axel Kölling Physikalisch-Technische Bundesanstalt Bundesallee 100, D-38116 Braunschweig, Germany May 2011 Summary This report describes the organization, the equipment and the results of a EUROMET comparison of a 10 mH inductance standard at a frequency of 1 kHz which took place in 2006. The participants were PTB (Germany), INM (Romania) and NCM (Bulgaria). Comment: NCM is now BIM, Bulgarian Institute of Metrology The participation of PTB made it possible to have a link to the key comparison CCEM-K3. Although the methods of measurement differed in all participating laboratories, an agreement within the respective limits of uncertainty could be achieved by all participants. The results of each participant are referred to the Key Comparison Reference Value (KCRV), stated in the CCEM-K3 final report. PTB Germany EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison Contents Contents...................................................................................................................................................2 Introduction..............................................................................................................................................3 1. Participants and organization...............................................................................................................3 1.1 Participants.........................................................................................................................................3 1.2 Co-coordinator....................................................................................................................................3 1.3 Time schedule.....................................................................................................................................4 1.4 Transportation.....................................................................................................................................4 2. Travelling standard...............................................................................................................................4 2.1 Description of the standard.................................................................................................................4 2.2 Quantities to be measured..................................................................................................................6 2.3 Measurement instructions...................................................................................................................6 3. Description of measuring methods.......................................................................................................6 3.1 Measuring method at PTB..................................................................................................................6 3.2 Reference standard and the traceability to the SI at PTB..................................................................7 3.3 Measuring method at INM...................................................................................................................8 3.4 Reference standard and the traceability to the SI at INM...................................................................8 3.5 Measuring method at NCM.................................................................................................................8 3.6 Reference standard and the traceability to the SI at NCM.................................................................8 4. Measurement results............................................................................................................................8 4.1 Results of the participants and degree of equivalence with respect to CRV......................................8 4.2 Link to the CCEM-K3 and degree of equivalence with respect to KCRV...........................................9 4.3 Correlation.........................................................................................................................................10 5. Measurement uncertainty...................................................................................................................10 6. Conclusion..........................................................................................................................................10 7. Reference............................................................................................................................................10 Appendix A Summary of uncertainty budgets........................................................................................11 Appendix B Technical protocol...............................................................................................................16 Page 2 of 20 Introduction The comparison was organized within the framework of Phare 2002 Project BG0201.12 “Strengthening of the National Conformity Assessment System – Technical Assistance for Standardization and Metrology”, EUROPE Aid/116486/D/SV/BG. The comparison was linked to the corresponding CCEM comparison CCEM-K3 [1]. Three national metrology institutes took part in this comparison: PTB (Germany), NCM (Bulgaria) and INM (Romania). PTB acted as the pilot laboratory and in this function was responsible for providing the travelling standard, the evaluation of the measurement results and the final report. NCM was responsible for the protocol. The comparison was accomplished in accordance with the EUROMET Guidelines on Conducting Comparisons and CCEM Guidelines for Planning, Organizing, Conducting and Reporting Key, Supplementary and Pilot Comparisons. 1. Participants and organization 1.1 Participants PTB (DE) Contact persons: Names: Jürgen Melcher, Axel Kölling Address: Physikalisch-Technische Bundesanstalt (PTB) Bundesallee 100 D-38116 Braunschweig Germany Telephone: +49 (531) 5 92 2100 Fax: +49 (531) 5 92 2105 e-mail: Juergen.Melcher@PTB.DE Axel.Koelling@PTB.DE NCM (BG) Contact person: Names: Petya Aladzhem, Georgy Simeonov Address: BIM - National Centre of Metrology (NCM) 52-B G.M.Dimitrov blvd. 1040 Sofia BULGARIA Telephone: +359 2 9702 747 Fax: +359 2 9702 735 e-mail: p.aladzhem@bim.government.bg INM (RO) Contact person: Name: Anca Nestor Address: National Institute of Metrology (INM) sos. Vitan Barzesti 11 sector 4 042122 Bucuresti ROMANIA: Telephone: +40 21 334 48 30 Fax: +40 21 334 55 33 e-mail: Anca.Nestor@INM.RO 1.2 Co-coordinator Name: Address: Telephone: Axel Kölling Physikalisch-Technische Bundesanstalt (PTB) Bundesallee 100 D-38116 Braunschweig Germany +49 (531) 5 92 2115 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison Fax: e-mail: 1.3 +49 (531) 5 92 2105 Axel.Koelling@PTB.DE Time schedule Starting date: First measurements at PTB: Measurements at INM: Measurements at NCM: Final measurements at PTB: 1.4 April 2006 From 16 to 20 February 2006 From 12 June to 7 July 2006 From 24 July to 4 August 2006 September 2006 Transportation The travelling standard was taken as carry-on luggage by aeroplane from Germany to Romania. An NCM car was used for transportation from Romania to Bulgaria. Transportation of the standard back to Germany by car was organized by NCM. The standard was accompanied by an ATA – carnet in order to solve custom formalities. 2. Travelling standard The travelling standard was an inductance standard with a nominal value of 10 mH. It is a General Radio 1482-H 10 mH inductance standard encased by a temperature-regulated enclosure. The thermostated device together with a power supply unit guarantees a constant operating temperature during the transportation . A set of batteries (2 pieces, 6 V lead storage battery) or the car’s supply system of 12 volt (in the case of transportation by car) was used. 2.1 Description of the standard Table 1: Description of the standard Type Manufacturer Serial number Nominal value of inductance Relative instability of inductance Nominal thermostatic temperature GR 1482-H Inductance Standard General Radio, enclosure ASMW №01 10 mH ± 0.1% < 1 µH/H per year 30.0 °C± 0.2 K Instability of thermostatic temperature with an instability of the ambient air temperature of 0.5 K ± 0.01 K per year Dependence of the value of inductance on the ambient air temperature in the range from 18 °C to 28 °C ≤ 0.3 ppm per K Measuring frequency Measuring voltage 1 000 Hz ≤ 0.5 V Effective resistance (DC) of the coil at an ambient air temperature of 23.0 °C ± 0.1 K 8.671 Ω Width of the HIGH and LOW connecting terminals 19 mm Connection system Two terminals (case is internally connected with LOW terminal) Power supply of thermostat: • power supply unit (230 V ± 10%; 50 Hz); • set of batteries (2 x 6 V); • 12 V supply system of a car 0.5 A at 12 V (DC) Power cable Red plug to be connected to plus, blue plug to be connected to minus Dimensions of leather bag Total mass 470 mm x 300 mm x 400 mm Approx. 38 kg Page 4 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison Page 5 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison 2.2 Quantities to be measured The quantities to be measured were: − L: inductance of the standard (two terminals); − R: DC resistance of the inductor coil; − f: measurement frequency; − Text: the temperature (°C) of the environment where the standard is measured. 2.3 Measurement instructions The measurements should be performed under the following conditions: − Measurement frequency: 1000 Hz; − Measuring voltage: <0.5 V (rms); − Temperature of the environment: 23°C ± 1°C; − Relative humidity: between 30 % and 70 %. 3. Description of measuring methods 3.1 Measuring method at PTB Inductance measurements at PTB are carried out with a Maxwell-Wien Bridge. This bridge has the advantage, that to a first order the bridge equation (1) is independent of frequency. But measurements at a frequency of 1 kHz require an investigation of higher order effects, i.e., lumped impedances must be taken into account. H RW1 CW1 R1 C1 R2 C1A T DW LW3 G D H RW3 LX R3 C4 RX CW3 L L Page 6 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison The main arms of the bridge contain, besides the DUT, represented by the element LX and RX, the fixed capacitor C1, the variable capacitor C1A, the two fixed resistors R2 and R3 and the variable resistor R1 . The main bridge balance (equ. (3)) is achieved with components C1A and R1. The bridge is adapted to the value of inductor LX by exchanging C1, R2 and R3. LX ≈ C1 ⋅ R2 ⋅ R3 (1) The impedance of the resistors can be characterized by Zn ≈ Rn (f ) ⋅ (1 + jωτ n ) (2) With the impedances Z2 and Z3 the bridge equation leads to R X + jωLX = Z2Z3 (1 + jω (C1 + C1A )Z1 ) Z1 − jωC4 Z 2Z3 (1 + jω(C1 + C1A )Z1 ) (3) The capacitance C4 characterizes only the stray capacitance at the bridge terminals. The inherent parallel capacitance of the inductor is not included in C4. To eliminate the main effects of the time constants τn, a zero-substitution method is employed: Inductor LX is replaced by a relatively small inductor LX0, and C1 is removed. The value C1A0 for C1A is obtained to balance the bridge. The Value C40 can be different to C4 because of different connection to the main measurement. This procedure results in the model equation that approximates LX within the uncertainties of the calibration. LX = (C1 + C1A )R2 R3 − C1A0 R2 R3 + LX0 − ω 2 R 2 R3C1τ 2τ 3 2 − ω 2 R22 R32(C4(C1 + C1A )2 − C40C1A0 ) (4) R22 R32 + (C4 − C40 ) R12 A potential problem in Maxwell-Wien Bridge circuits is that of stray capacitance between either connecting point of the null detector and ground potential. The best solution for solving this problem is to insert a Wagner earth. This voltage divider is designed to have the same voltage ratio and phase shift as each side of the bridge. These circuit elements have the index “W”. Because the midpoint of the Wagner divider is directly grounded, the Wagner balance forces the null detector to be at virtual ground potential, without a direct connection between the detector and the ground. 3.2 Reference standard and the traceability to the SI at PTB The reference standards are represented by the components C1, R2 and R3. The capacitor C1 is traceable to the Thompson-Lampard Capacitor of PTB. The two resistors are traceable to the quantized Hall resistance via calculable AC/DC transfer resistors of PTB. Page 7 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison 3.3 Measuring method at INM The equivalent series inductance of the standard inductor is measured in two-terminal connection by substitution against the equivalent series inductance of one 10 mH reference standard using a digital LCR-meter, type HP 4284 A. The DC resistance of the inductor coil is measured directly in four-terminal connection using a digital multimeter, type Keithley 2001. This procedure results in the model equation that approximates LX within the uncertainties of the calibration. LX = (LS + ∆LScurrent + δLSdrift + δLST ) ⋅ K ⋅ K C − δLXT 3.4 1 (5) Reference standard and the traceability to the SI at INM The 10 mH reference standard (serial number 8602) used is an inductor built in INM in 1986. This inductor is included in the group of transfer standards used to provide traceability on a regular basis. The last external calibration of this standard was performed in December 2005 in INRIM, Italy. 3.5 Measuring method at NCM A 1:1 substitution method with inductance bridge model GR 1632 A is used. The travelling and reference standards (L and LS) are measured in turn in two-wire connection using five decades of the bridge. The last digit of the measured values (missing in the uncertainty budget table) is estimated by de-balancing the bridge with a step of the last decade in plus and in minus. The measurements are made at 1000 Hz. This procedure results in the model equation that approximates LX within the uncertainties of the calibration. L = (LS + δLD + δLTS ) ⋅ l K ⋅ l − δLT * (6) All conditions mentioned in section 4 “Measuring instructions” from the Technical Protocol are observed. 3.6 Reference standard and the traceability to the SI at NCM The reference standard (LS) model GR 1482 H, Ser. № 17982, is part of the national group standard. The value of the national standard is traceable to PTB. The last calibration was in 2003. 4. Measurement results 4.1 Results of the participants and degree of equivalence with respect to CRV Table 2 reports the measured inductance and uncertainty given by NCM, INM and PTB, along with the degrees of equivalence Di and their expanded uncertainty UDi for the participants NCM and INM. The drift of the travelling standard was neglected, because the change between the first and second measurement in PTB was very small, especially compared with the uncertainties claimed by NCM and INM. In the following calculations, the mean value of the first and second PTB result, PTBmean, was taken into account. For the associated expanded uncertainty, the two PTB results were looked at, as if they were the results of two different measurements with a correlation coefficient of 1. The degree of equivalence Di is given with respect to the PTBmean value, which is taken as the comparison reference value (CRV): Di = Li − LPTBmean 1 See a description of the single components in Appendix A Page 8 of 20 (7) EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison with the expanded uncertainty : 2 U Di = U i + U PTB (8) 2 Table 2: Results of the participants measured inductance, LX expanded uncertainty, U(LX) degree of equivalence, D expanded uncertainty, UD mH mH µH/H mH PTB1st 10.00456 6.4 ·10-5 NCM 10.0044 40 ·10-5 -12.5 40 ·10-5 INM 10.0043 60 ·10-5 -22.5 60 ·10-5 PTB2nd 10.00449 5.1 ·10-5 PTBmean 10.004525 5.7 ·10-5 participants 4.2 - - Link to the CCEM-K3 and degree of equivalence with respect to KCRV The link for NCM and INM results to the key comparison reference value of CCEM-K3 is made via the PTB measurements, as PTB or PTB (ASMW) respectively participated in both comparisons. The applied travelling standard was one of the two standards that are used in the CCEM-K3 comparison. In the meantime this standard was always kept under thermostated condition. PTB has a history of the measurement values of this standard from the first measurements at ASMW up to now. The actual measuring system of PTB achieves lower uncertainties (see table 2) then the systems of ASMW and PTB that are used during the CCEM comparison. Measurements based on the mentioned standard history shows that this PTB system has an exact accordance with the old ASMW measuring system. To compare the results of NCM/INM with results of the participants in the key comparison CCEM-K3, the Key Comparison Reference Value (KCRV), stated in the CCEM-K3 final report was referred to. The degree of equivalence DK3,NCM/INM and expanded uncertainty UK3,NCM/INM of NCM/INM with respect to KCRV is calculated as follows: DK3,NCM/INM = DNCM/INM + DK3,PTB (9) UK3,NCM/INM = UD2NCM/INM + UD2K3/PTB (10) where DK3,PTB and UK3,PTB are the degree of equivalence and its expanded uncertainty of PTB (ASMW) with respect to KCRV. The degree of equivalence and expanded uncertainty of NCM/INM with respect to KCRV are given in Table 3. Table 3: Degree of equivalence and expanded uncertainty of NCM/INM with respect to KCRV participants degree of equivalence, DK3,NCM/INM in µH/H expanded uncertainty, UK3,NCM/INM µH/H in degree of equivalence, DK3,PTB in µH/H expanded uncertainty, UK3,PTB in µH/H NCM -16 41 -3 8 INM -26 61 -3 8 Page 9 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison 4.3 Correlation The result of INM is correlated to the KCRV (section 5.1), because the reference standard of INM was calibrated at INRIM, Italy (IEN at the time of CCEM-K3). The result of NCM is correlated to the CRV and the KCRV, because the reference standard of NCM was calibrated at PTB. The uncertainties of the INM and NCM reference values are the largest contributions to the uncertainty budgets. They are traced back via the INRIM and PTB standards to the SI. The reason for the large uncertainties is that these standards are not thermostated, so that the temperature coefficient of the standards which is not correlated with the INRIM or PTB measurements had the biggest influence on the uncertainties. Therefore, the effect of correlation was neglected. 5. Measurement uncertainty A detailed uncertainty analysis and an uncertainty budget in accordance with the ISO Guide to the Expression of Uncertainty in Measurement is given in Appendix A. 6. Conclusion The comparison EUROMET.EM-K3 was organized with the main objective of showing the international equivalence of the as-maintained units of inductance at NCM and INM. To calculate the degree of equivalence of the results of NCM and INM they were linked to CCEM-K3. The results obtained show very good agreement with the reference value within the expanded uncertainties. 7. Reference [1] H. Eckhard, “Final Report of CCEM-K3: International Comparison of 10 mH Inductance Standards at 1 kHz”, published online in the Key Comparison Data Base: http://kcdb.bipm.fr Page 10 of 20 Appendix A Summary of uncertainty budgets Acronym of institute: PTB Date: September 2006 Remarks: Because of the two measurement periods we have to give two different groups of results. Model equation LX,A/B = (C1H − C1A0 )R2R3 + LX0 + TypBT − ω 2R 2 R3C1(k2 + k3 − τ 2τ 3 ) 2 − ω 2R22R32(C4HC1H − C40C1A0 ) 2 R22R32 + (C4H − C40 ) R12 C1H = C1 + C1A ω = 2π f C1A = c1A( 1 + TypBC ) C1A0 = c1A0( 1 + TypBC ) R1 = r1( 1 + TypBR1 ) LX0 = l X0( 1 + TypBL ) Definition of quantities quantity unit definition LXA/B H inductance of travelling standard C1 F capacitance of capacitor C1 C1A F capacitance of capacitor C1A c1A F observations of capacitor C1A C1A0 F entire capacitance of zero-substitution c1A0 F observations of capacitor C1A0 C1H F entire capacitance of main measurement C40 F capacitance of bridge terminals in the zero-substitution C4H F capacitance of bridge terminals in the main measurement f Hz frequency of measurement s 2 frequency coefficient of resistor R2 k3 s 2 frequency coefficient of resistor R3 Lx0 H inductance of small air coil LX0 lxO H observations of small air coil LX0 R1 Ω value of decade resistor R1 r1 Ω observations of decade resistor R1 R2 Ω value of resistor R2 R3 Ω value of resistor R3 k2 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison quantity unit definition TypBC2 TypBL TypBR1 TypB takes into account the uncertainty of the capacitance meter 1 takes into account the uncertainty of the inductance meter 1 1 T ω takes into account the uncertainty of the decade resistor R1 H takes into account the uncertainty of the temperature stability of the travelling standard s-1 radian frequency of measurement π time constant of resistor R2 τ2 s time constant of resistor R3 τ3 s frequency coefficient of resistor R3 Uncertainty budget of the first measurement period quantity value standard uncertainty C1 1.000023240·10-9 F 276·10-18 F C1A c1A C1A0 c1A0 C1H 1.19118·10 -12 1.12176·10 -12 1.12176·10 -12 -15 C4H 200·10-15 F k3 F F F 1.00121442·10 F 100·10 k2 F -9 C40 f F 100.0·10 -18 100.0·10 -18 s 2 s 2 0.8 % 10·106 17·10-9 H 8.9 % -10·106 -21·10-9 H 22.2 % 1.73·10 F 4 2.06·10 -15 F 4 2.06·10 -15 F 4 1.75·10 -15 F 4 -15 F ∞ -76 -44·10-12 H 0.0 % 577·10-15 F ∞ -3900 -2.2·10-9 H 0.5 % 0.289 Hz ∞ 57.7·10 -18 57.7·10 -18 s 2 ∞ s 2 ∞ ∞ lX0 4.07·10-6 H 2.07·10-24 H 4 R1 1.148560·106 Ω 664 Ω ∞ r1 1.1485600·10 Ω 24.5 Ω 4 R2 999.94214 Ω 1.42·10 Ω R3 10000.14037 Ω 9.82·10 Ω -9 -3 -3 5200 1200 -1.4·10 -12 400·10 3 400·10 3 10·10 1.0·10 -6 ∞ -15·10-12 -9 5.77·10 H ∞ H 0.0 % 23·10 -12 H 0.0 % 0.0 % -6 4.1·10 577·10-6 23·10 -320·10-18 H ∞ 0.0 0.0 % -13·10-18 ∞ TypBR H -12 0.0 % -3 1.44·10 -410·10 0.0 H 57.7·10 0.0 -15 0.0 -6 TypBL 0.0 H 2.8·10-9 H 4 5.87·10 H TypBT 10·106 F 4.07000·10 H 0.0 index -15 LX0 6 uncertainty contribution 1.73·10 577·10 1000.500 Hz sensitivity coefficient -15 -6 TypBC 690·10 -9 -6 -9 35.8 % -9 24.7 % 14·10 H 9.8·10 H 40·10 -12 H 0.0 % 5.9·10 H 3.6 % -8.8·10-15 H 0.0 % -9 -9 1.0 5.8·10 H 3.5 % ω 6286.33 s π 3.1415926535898 τ2 800·10-12 s 2.02·10-9 s ∞ -320·10-6 -640·10-15 H 0.0 % τ3 800·10-12 s 2.02·10-9 s ∞ -320·10-6 -640·10-15 H 0.0 % LA 2 1.19118·10 -12 degrees of freedom 26 -1 0.0100045577 H 1.81 s -1 -9 30.9·10 H ∞ 49 The quantity (value = 0) does not make a contribution to the value of LS but rather to the uncertainty. Page 12 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison Uncertainty budget of the second measurement period degrees standard quantity value of uncertainty freedom C1 1.000023240·10-9 F 276·10-18 F 26 C1A c1A C1A0 c1A0 C1H C40 C4H f 1.20880·10 -12 1.20880·10 -12 1.15363·10 -12 1.15363·10 -12 F F F F -9 1.00123204·10 F 100·10 -15 200·10 -15 F 2 1.18·10 F 2 1.32·10 -15 F 2 1.32·10 -15 F 2 1.22·10 -15 F 2 -15 F ∞ F ∞ -15 577·10 1000.500 Hz s F -15 577·10 F -18 1.19·10 -15 2 ∞ 0.289 Hz 100.0·10-18 s2 57.7·10-18 s2 ∞ LX0 4.05500·10-6 H 6.53·10-9 H 52 lX0 4.05500·10 H 2.89·10 H 2 R1 1.149537·10 Ω 664 Ω ∞ r1 1.1495367·10 Ω 19.2 Ω 2 R2 999.94562 Ω 1.41·10 Ω R3 10000.19615 Ω 9.82·10 Ω 6 10·106 2.8·10-9 H 1.2 % 10·106 17·10-9 H -4.5 % -10·106 -13·10-9 H 4.9 % -76 -44·10-12 H 0.0 % -9 -3900 -1.4·10 -2.2·10 H -12 400·10 k3 6 index ∞ 100.0·10 -9 s uncertainty contribution 2 k2 -6 57.7·10 -18 sensitivity coefficient -3 -3 5200 1200 3 0.0 % 1.0 2.9·10-9 H 0.9 % -13·10-18 -250·10-18 H 0.0 % 10·10 1.0·10 -6 -6 ∞ 550·10 -9 TypBL 0.0 1.44·10-3 ∞ 4.1·10-6 0.0 -6 577·10 ∞ -12 -9 ∞ 5.77·10 H ω 6286.33 s π 3.1415926535898 τ2 800·10-12 s τ3 LB -12 800·10 -1 s 0.0100044907 H -15·10 32·10 -12 H 0.0 % 5.9·10-9 H 5.2 % -8.7·10 -15 H 0.0 % 5.0 % -640·10-15 H 0.0 % ∞ -320·10-6 -9 ∞ -6 -9 2500 Page 13 of 20 35.6 % 9.8·10 H 5.8·10 H 2.02·10-9 s 25.7·10 H 51.0 % -9 14·10 H 1.0 ∞ 2.02·10 s -9 -9 1.81 s -1 0.0 % 23·10-12 H 57.7·10 0.0 H H 400·103 -6 23·10 -12 0.0 % 0.0 TypBT -410·10 0.8 % H TypBC TypBR -15 -320·10 -15 -640·10 H 0.0 % EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison Acronym of institute: INM Date: July 2006 Remarks: Model equation LX = (LS + ∆LScurrent + δLSdrift + δLST ) ⋅ K ⋅ K C − δLXT Definition of quantities quantity unit definition LS H certificate value of the reference standard ∆LScurrent H correction for the different measurement current of the reference standard δLSdrift H time drift of the reference standard δLST H correction for the temperature variation of the reference standard δLXT H correction for the temperature variation of the unknown inductance Kc correction factor given by systemic effects of the measurement circuit (finite resolution of the LCR-meter, undesired couplings, variation of inductance of the measurement cables, etc.) K ratio between the indicated value of the unknown inductance and the indicated value of the reference standard inductor H LX Uncertainty budget quantity estimate inductance of travelling standard standard probability degrees sensitivity uncertainty uncertainty distribution of coefficient contribution freedom ci ui(L) Xi xi u(xi) LS 10.00204 mH 0.00015 mH ∆LScurrent -0.00017 mH 0.00001 δLSdrift 0.00002 mH δLST δLXT ∞ 1 0.00015 mH mH rectangular ∞ 1 0.00001 mH 0.00015 mH rectangular ∞ 1 0.00015 mH 0.00008 mH 0.00001 mH 8 1 0.00001 mH 0.00000 mH 0.00000 mH rectangular ∞ -1 -0.00000 mH Kc 1.00000 0.00002 triangular ∞ 10 mH 0.00016 mH K 1.000230 0.000001 normal 29 10 mH 0.00001 mH Lx 10.00427 mH 0.00027 mH normal normal Page 14 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison Acronym of institute: NCM Date: September 2006 Remarks: Model equation L = (LS + δLD + δLTS ) ⋅ lK ⋅ l − δLT Definition of quantities quantity unit definition LS H certificate value of the reference standard δLD H time drift of the reference standard δLTS H correction for the temperature variation of the reference standard δLT H correction for the temperature variation of the unknown inductance lK correction factor given by systemic effects of the measurement circuit Ī ratio between the indicated value of the unknown inductance and the indicated value of the reference standard inductor L H inductance of travelling standard Uncertainty budget quantity estimate standard probability sensitivity uncertainty uncertainty distribution coefficient contribution ci ui(L) Xi xi u(xi) LS 9.9999 mH 1.50E-04 mH normal 1.0 1.50E-04 mH δLD -0.0002 mH 1.16E-04 mH normal 1.0 1.16E-04 mH δLTS 3.00E-05 mH 1.73E-05 mH rectangular 1.0 1.73E-05 mH δL T 0.0000 mH 3.46E-05 mH rectangular -1.0 -3.46E-05 mH lK 1.000 000 2.45E-06 triangular 10.0000 mH 2.45E-05 mH Ī 1.00046 5.60E-07 normal 10.0000 mH 5.60E-06 mH L 10.0044 1.95E-04 mH mH Page 15 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison Appendix B Technical protocol The original text of the TECHNICAL PROTOCOL below was edited. TECHNICAL PROTOCOL EUROMET project 889 EUROMET.EM-K3 Trilateral comparison of a 10 mH inductance standard June 2006 Page 16 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison 1. Introduction The comparison is organized within the framework of Phare 2002 Project BG0201.12 “Strengthening of the National Conformity Assessment System – Technical Assistance for Standardization and Metrology”, EUROPE Aid/116486/D/SV/BG. Three national institutes of metrology are taking part in this comparison: PTB (Germany), NCM (Bulgaria) and INM (Romania). PTB is responsible for providing the travelling standard and the evaluation of the measurement results. NCM is responsible for the protocol and the final report. It is planned to complete this comparison in September 2006. 2. Description of travelling standard 2.1. The travelling standard is an inductance standard having the nominal value of 10 mH. It is constructed starting from a General Radio 1482-L 10 mH inductance standard, encased in a thermostated enclosure. The thermostatic device guarantees a constant operating temperature using a power supply unit. During the transportation a set of batteries (8 pieces, LR 20 type) or the car’s supply system of 12 volt (in the case of transportation by car) can be used. 2.2. Specifications Nominal value of inductance Relative instability of inductance Nominal thermostatic temperature Instability of thermostatic temperature with an instability of the ambient air temperature of 0.5 K Dependence of the value of inductance on the ambient air temperature in the range from 18 °C to 28 °C Measuring frequency Measuring voltage at the standard Effective resistance (DC) of the coil at an ambient air temperature of 23.0 °C ± 0.1 K Width of the HIGH and LOW connecting terminals Connection system Power supply of thermostat: • power supply unit (230 V ± 10%; 50 Hz); • set of batteries (2 x 6 V); • 12 V supply system of a car Power cable Dimensions of leather bag Total mass 10 mH ± 0.1% < 1 ppm per year 30.0 °C± 0.2 K ±0.01 K per year ≤ 0.3 ppm per K 1 000 Hz ≤ 0.5 V №01 – 8.671 Ω 19 mm Two terminals (case is internally connected with LOW terminal) 0.5 A at 12 V (DC) Red plug to be connected to plus, blue plug to be connected to minus 470 mm x 30 mm x 400 mm Approx. 38 kg 2.3. Accessories − Power supply unit; − Set of batteries (2 pieces); − 1 adapter cable for connection to a 12 V car supplies system Page 17 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison 3. Quantities to be measured − − − − L: inductance of the standard (two terminals); R: DC resistance of the inductor coil; f: measurement frequency; Text: the temperature (°C) of the environment where the standard is measured. 4. Measurement instructions 4.1. Measurements should be performed under the following conditions: − Measurement frequency: 1000 Hz; − Measuring voltage: 0.5 V (rms); − Temperature of the environment: 23°C ± 1°C; − Relative humidity: between 30 % and 70 %. 4.2. Set-up of the standard: Under laboratory conditions the standard is supplied by the power supply unit. The red lamp signals readiness for operation. The green lamp indicates that the heater of the thermostat is switched on. In order to avoid electromagnetic interference during inductance measurement, the power supply unit must be placed as far as 2 meters away from the inductance bridge and may be switched off during the inductance measurements, but for no longer than 5 minutes. The participating laboratories are asked to follow the Operating Instructions of the travelling standard. 5. Reporting of results A report should be sent to the pilot laboratory within one month after the measurements are completed. The report should include: – Description of the measurement method; – The reference standard; – The traceability to the SI; – The results of the quantities to be measured (list of section 3); – The associated standard uncertainties, the effective degrees of freedom and the expanded uncertainties; The measurement frequency, the applied voltage and the environment conditions must also be reported. 6. Uncertainty of measurement The uncertainty must be calculated following the ISO “Guide to the expression of uncertainty in measurement” (GUM), 1995 and the complete uncertainty budget must be reported. Page 18 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison 7. Transportation The travelling standard must be transported in the travel leather bag and protected from mechanical loads, vibration etc. A transport box suitable for transport by plane or car is provided. This box is equipped with tilt and squeeze indicators. It has to be handled carefully and kept the right way up. The travel box contains the following items: – leather bag, – inductance standard, – power supply unit, – set of two batteries (6 V lead storage battery, Hoppecke) with connection cable and fuse, – spare fuse, – 1 adapter cable for connection to a 12 V car supply system, – mechanical temperature recorder (Metrawatt Thermoscript 838012), – spare strip charts for the temperature recorder (initially 3 coils), – operating instructions of the travelling standard (this document), – operating instructions for the temperature recorder (in German, in case of difficulties consult PTB), When it is transported by car, the standard must be connected by the adapter cable to the 12 V power system of the car. Carrying the standard by air or rail requires the connection to the set of batteries. The batteries have to be charged with an appropriate power supply (not included in the box). Standard 4 mm banana plugs can be used to connect the batteries. During transport the temperature recorder has to be switched on. If the operation of this recorder has to be interrupted or if a new strip chart coil is used, the date and time of both the stop and start of operation have to be written on the paper by hand. The total recording time per coil is about 30 days. The transport box always has to be carried and kept upright. It internally contains internal eyelets which shall be used to fix the leather bag inside the box. Page 19 of 20 EUROMET 889 - EUROMET.EM-K3: 10 mH Inductance Trilateral Comparison 8. Participants Table 1. List of participants and contact information. Laboratory address Contact name, e-mail Physikalisch-Technische Bundesanstalt (PTB) Electricity Division, FB 2.1 Bundesallee 100 38116 Braunschweig GERMANY Jürgen Melcher Juergen.Melcher@ptb.de National Centre of Metrology (NCM) 52-B G. M. Dimitrov Str. 1797 Sofia BULGARIA Petya Aladzhem ncm@sasm.orbitel.bg National Institute of Metrology (INM) sos. Vitan Barzesti 11 sector 4, 042122 Bucuresti ROMANIA Anca Nestor anca.nestor@inm.ro 9. Schedule Table 2. List of the participants, measurement dates and report dates. Laboratory PTB - Germany INM - Romania NCM - Bulgaria PTB - Germany Measurement dates April 2006 12 - 29 May 2006 2 - 16 June 2006 July 2006 Page 20 of 20 Report date June 2006 July 2006

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