EUROMET Comparison of a 10 mh Inductance Standard at 1 khz EUROMET.EM-K3. Final Report

Transcription

1 EUROMET omparison of a 0 mh Inductance Standard at khz EUROMET.EM-K Final Report by Axel Kölling Physikalisch-Technische Bundesanstalt Bundesallee 00, D-86 Braunschweig, Germany May 0 Summary This report describes the organization, the equipment and the results of a EUROMET comparison of a 0 mh inductance standard at a frequency of khz which took place in 006. The participants were PTB (Germany, INM (Romania and NM (Bulgaria. omment: NM is now BIM, Bulgarian Institute of Metrology The participation of PTB made it possible to have a link to the key comparison EM-K. 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 omparison Reference Value (KRV, stated in the EM-K final report.

2 PTB Germany EUROMET.EM-K: 0 mh Inductance Trilateral omparison ontents ontents... Introduction.... Participants and organization.... Participants.... o-coordinator.... Time schedule Transportation...4. Travelling standard...4. Description of the standard...4. Quantities to be measured...6. Measurement instructions...6. Description of measuring methods...6. Measuring method at PTB...6. Reference standard and the traceability to the SI at PTB...7. Measuring method at INM Reference standard and the traceability to the SI at INM Measuring method at NM Reference standard and the traceability to the SI at NM Measurement results Results of the participants and degree of equivalence with respect to RV Link to the EM-K and degree of equivalence with respect to KRV orrelation Measurement uncertainty onclusion Reference...0 Appendix A Summary of uncertainty budgets... Appendix B Technical protocol...6 Page of 0

3 Introduction The comparison was organized within the framework of Phare 00 Project BG00. Strengthening of the National onformity Assessment System Technical Assistance for Standardization and Metrology, EUROPE Aid/6486/D/SV/BG. The comparison was linked to the corresponding EM comparison EM-K []. Three national metrology institutes took part in this comparison: PTB (Germany, NM (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. NM was responsible for the protocol. The comparison was accomplished in accordance with the EUROMET Guidelines on onducting omparisons and EM Guidelines for Planning, Organizing, onducting and Reporting Key, Supplementary and Pilot omparisons.. Participants and organization. Participants PTB (DE ontact persons: Names: Jürgen Melcher, Axel Kölling Address: Physikalisch-Technische Bundesanstalt (PTB Bundesallee 00 D-86 Braunschweig Germany Telephone: +49 ( Fax: +49 ( Juergen.Melcher@PTB.DE Axel.Koelling@PTB.DE NM (BG ontact person: Names: Petya Aladzhem, Georgy Simeonov Address: BIM - National entre of Metrology (NM 5-B G.M.Dimitrov blvd. 040 Sofia BULGARIA Telephone: Fax: p.aladzhem@bim.government.bg INM (RO ontact person: Name: Anca Nestor Address: National Institute of Metrology (INM sos. Vitan Barzesti sector 4 04 Bucuresti ROMANIA: Telephone: Fax: Anca.Nestor@INM.RO. o-coordinator Name: Axel Kölling Address: Physikalisch-Technische Bundesanstalt (PTB Bundesallee 00 D-86 Braunschweig Germany Telephone: +49 (

4 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison Fax: +49 ( Axel.Koelling@PTB.DE. Time schedule Starting date: April 006 First measurements at PTB: From 6 to 0 February 006 Measurements at INM: From June to 7 July 006 Measurements at NM: From 4 July to 4 August 006 Final measurements at PTB: September Transportation The travelling standard was taken as carry-on luggage by aeroplane from Germany to Romania. An NM car was used for transportation from Romania to Bulgaria. Transportation of the standard back to Germany by car was organized by NM. The standard was accompanied by an ATA carnet in order to solve custom formalities.. Travelling standard The travelling standard was an inductance standard with a nominal value of 0 mh. It is a General Radio 48-H 0 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 ( pieces, 6 V lead storage battery or the car s supply system of volt (in the case of transportation by car was used.. Description of the standard Table : Description of the standard Type Manufacturer GR 48-H Inductance Standard General Radio, enclosure ASMW Serial number 0 Nominal value of inductance 0 mh ± 0.% Relative instability of inductance < µh/h per year Nominal thermostatic temperature 0.0 ± 0. K 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 8 to 8 Measuring frequency Measuring voltage Effective resistance (D of the coil at an ambient air temperature of.0 ± 0. K Width of the HIGH and LOW connecting terminals onnection system Power supply of thermostat: power supply unit (0 V ± 0%; 50 Hz; set of batteries ( x 6 V; V supply system of a car Power cable Dimensions of leather bag Total mass ± 0.0 K per year 0. ppm per K 000 Hz 0.5 V 8.67 Ω 9 mm Two terminals (case is internally connected with LOW terminal 0.5 A at V (D Red plug to be connected to plus, blue plug to be connected to minus 470 mm x 00 mm x 400 mm Approx. 8 kg Page 4 of 0

5 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison Page 5 of 0

6 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison. Quantities to be measured The quantities to be measured were: L: inductance of the standard (two terminals; R: D resistance of the inductor coil; f: measurement frequency; T ext: the temperature ( of the environment where the standard is measured.. Measurement instructions The measurements should be performed under the following conditions: Measurement frequency: 000 Hz; Measuring voltage: <0.5 V (rms; Temperature of the environment: ± ; Relative humidity: between 0 % and 70 %.. Description of measuring methods. 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 ( is independent of frequency. But measurements at a frequency of khz require an investigation of higher order effects, i.e., lumped impedances must be taken into account. H R W G T L W W R D W D A R H L X R R W W R X 4 L L Page 6 of 0

7 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison The main arms of the bridge contain, besides the DUT, represented by the element L X and R X, the fixed capacitor, the variable capacitor A, the two fixed resistors R and R and the variable resistor R. The main bridge balance (equ. ( is achieved with components A and R. The bridge is adapted to the value of inductor L X by exchanging, R and R. L X R R ( The impedance of the resistors can be characterized by Rn( f (+ jωτ n With the impedances Z and Z the bridge equation leads to Z n ( R X + jωl X ZZ( + jω( + = Z jω Z Z ( + jω( 4 A Z + Z A ( The capacitance 4 characterizes only the stray capacitance at the bridge terminals. The inherent parallel capacitance of the inductor is not included in 4. To eliminate the main effects of the time constants τ n, a zero-substitution method is employed: Inductor L X is replaced by a relatively small inductor L X0, and is removed. The value A0 for A is obtained to balance the bridge. The Value 40 can be different to 4 because of different connection to the main measurement. This procedure results in the model equation that approximates L X within the uncertainties of the calibration. L X = ( + ω + ( 4 R 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.. Reference standard and the traceability to the SI at PTB A 40 R 4 R R R R τ τ R The reference standards are represented by the components, R and R. The capacitor is traceable to the Thompson-Lampard apacitor of PTB. The two resistors are traceable to the quantized Hall resistance via calculable A/D transfer resistors of PTB. A0 ω R R ( ( + A R R + L 40 X0 A0 (4 Page 7 of 0

8 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison. 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 0 mh reference standard using a digital LR-meter, type HP 484 A. The D resistance of the inductor coil is measured directly in four-terminal connection using a digital multimeter, type Keithley 00. This procedure results in the model equation that approximates L X within the uncertainties of the calibration. L X = ( LS + LScurrent + δlsdrift + δlst K K δlxt (5.4 Reference standard and the traceability to the SI at INM The 0 mh reference standard (serial number 860 used is an inductor built in INM in 986. 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 005 in INRIM, Italy..5 Measuring method at NM A : substitution method with inductance bridge model GR 6 A is used. The travelling and reference standards (L and L S 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 000 Hz. This procedure results in the model equation that approximates L X within the uncertainties of the calibration. * (6 All conditions mentioned in section 4 Measuring instructions from the Technical Protocol are observed..6 Reference standard and the traceability to the SI at NM The reference standard (L S model GR 48 H, Ser. 798, is part of the national group standard. The value of the national standard is traceable to PTB. The last calibration was in Measurement results L = ( L l l δl S + δld + δlts 4. Results of the participants and degree of equivalence with respect to RV Table reports the measured inductance and uncertainty given by NM, INM and PTB, along with the degrees of equivalence D i and their expanded uncertainty U Di for the participants NM 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 NM and INM. In the following calculations, the mean value of the first and second PTB result, PTB mean, 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. The degree of equivalence D i is given with respect to the PTB mean value, which is taken as the comparison reference value (RV: K T D = L L i i PTB mean (7 See a description of the single components in Appendix A Page 8 of 0

9 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison with the expanded uncertainty : i U = U + U D i PTB (8 Table : Results of the participants participants measured expanded inductance, L X uncertainty, U(L X degree of equivalence, D expanded uncertainty, U D mh mh µh/h mh PTB st NM INM PTB nd PTB mean Link to the EM-K and degree of equivalence with respect to KRV The link for NM and INM results to the key comparison reference value of EM-K 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 EM-K 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 then the systems of ASMW and PTB that are used during the EM 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 NM/INM with results of the participants in the key comparison EM-K, the Key omparison Reference Value (KRV, stated in the EM-K final report was referred to. The degree of equivalence D K,NM/INM and expanded uncertainty U K,NM/INM of NM/INM with respect to KRV is calculated as follows: D + K, NM/INM = DNM/INM DK,PTB (9 where D K,PTB and U K,PTB are the degree of equivalence and its expanded uncertainty of PTB (ASMW with respect to KRV. The degree of equivalence and expanded uncertainty of NM/INM with respect to KRV are given in Table. Table : Degree of equivalence and expanded uncertainty of NM/INM with respect to KRV participants degree of equivalence, D K,NM/INM in µh/h U = U + U K, NM/INM DNM/INM DK/PTB expanded uncertainty, U K,NM/INM µh/h in degree of equivalence, D K,PTB in µh/h (0 expanded uncertainty, U K,PTB in µh/h NM INM Page 9 of 0

10 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison 4. orrelation The result of INM is correlated to the KRV (section 5., because the reference standard of INM was calibrated at INRIM, Italy (IEN at the time of EM-K. The result of NM is correlated to the RV and the KRV, because the reference standard of NM was calibrated at PTB. The uncertainties of the INM and NM 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. onclusion The comparison EUROMET.EM-K was organized with the main objective of showing the international equivalence of the as-maintained units of inductance at NM and INM. To calculate the degree of equivalence of the results of NM and INM they were linked to EM-K. The results obtained show very good agreement with the reference value within the expanded uncertainties. 7. Reference [] H. Eckhard, Final Report of EM-K: International omparison of 0 mh Inductance Standards at khz, published online in the Key omparison Data Base: Page 0 of 0

11 Appendix A Summary of uncertainty budgets Acronym of institute: PTB Date: September 006 Remarks: Because of the two measurement periods we have to give two different groups of results. Model equation L X,A/B L H ω = π f A A0 R X0 = ( ω R ω R + ( = + = c = c = r ( + TypB = l A A0 X0 H 4H R (k R A A0 ( 40 ( + TypB ( + TypB ( + TypB R R 4H RR R R Definition of quantities quantity unit definition L + k H + L τ τ + TypB L XA/B H inductance of travelling standard F capacitance of capacitor A F capacitance of capacitor A c A F observations of capacitor A A0 F entire capacitance of zero-substitution c A0 F observations of capacitor A0 H F entire capacitance of main measurement 40 F capacitance of bridge terminals in the zero-substitution 4H F capacitance of bridge terminals in the main measurement f Hz frequency of measurement k s frequency coefficient of resistor R k s frequency coefficient of resistor R L x0 H inductance of small air coil L X0 l xo H observations of small air coil L X0 R Ω value of decade resistor R r Ω observations of decade resistor R R Ω value of resistor R R Ω value of resistor R X0 40 A0 T

12 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison quantity unit definition TypB TypB L takes into account the uncertainty of the capacitance meter takes into account the uncertainty of the inductance meter TypB R takes into account the uncertainty of the decade resistor R TypB T H takes into account the uncertainty of the temperature stability of the travelling standard ω s - radian frequency of measurement π time constant of resistor R τ s time constant of resistor R τ s frequency coefficient of resistor R Uncertainty budget of the first measurement period quantity value standard uncertainty degrees of freedom sensitivity coefficient uncertainty contribution index F F H 0.8 % A F F 4 c A F F H 8.9 % A F F 4 c A F F H. % H F F F F H 0.0 % 4H F F H 0.5 % f Hz 0.89 Hz H 0.0 % k s s H 0.0 % k s s H 0.0 % L X H H l X H H H 0.0 % R Ω 664 Ω r Ω 4.5 Ω H 0.0 % R Ω Ω H 5.8 % R Ω Ω H 4.7 % TypB H 0.0 % TypB L H.6 % TypB R H 0.0 % TypB T 0.0 H H H.5 % ω 686. s -.8 s - π τ s s H 0.0 % τ s s H 0.0 % L A H H 49 The quantity (value = 0 does not make a contribution to the value of L S but rather to the uncertainty. Page of 0

13 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison Uncertainty budget of the second measurement period quantity value standard uncertainty degrees of freedom sensitivity coefficient uncertainty contribution index F F H. % A F F c A F F H -4.5 % A F. 0-5 F c A F. 0-5 F H 4.9 % H F. 0-5 F F F H 0.0 % 4H F F H 0.8 % f Hz 0.89 Hz H 0.0 % k s s H 0.0 % k s s H 0.0 % L X H H 5 l X H H H 0.9 % R Ω 664 Ω r Ω 9. Ω H 0.0 % R Ω Ω H 5.0 % R Ω Ω H 5.6 % TypB H 0.0 % TypB L H 5. % TypB R H 0.0 % TypB T 0.0 H H H 5.0 % ω 686. s -.8 s - π τ s s H 0.0 % τ s s H 0.0 % L B H H 500 Page of 0

14 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison Acronym of institute: INM Date: July 006 Remarks: Model equation ( LS + LScurrent + δlsdrift + δlst K K δ XT LX = L Definition of quantities quantity unit definition L S H certificate value of the reference standard L Scurrent H correction for the different measurement current of the reference standard δl Sdrift H time drift of the reference standard δl ST H correction for the temperature variation of the reference standard δl XT H correction for the temperature variation of the unknown inductance K c K correction factor given by systemic effects of the measurement circuit (finite resolution of the LR-meter, undesired couplings, variation of inductance of the measurement cables, etc. ratio between the indicated value of the unknown inductance and the indicated value of the reference standard inductor L X H inductance of travelling standard Uncertainty budget quantity estimate standard probability degrees sensitivity uncertainty uncertainty distribution of coefficient contribution X i x i u(x i freedom c i u i(l L S mh mh normal mh L Scurrent mh mh rectangular mh δl Sdrift mh mh rectangular mh δl ST mh mh normal mh δl XT mh mh rectangular mh K c triangular 0 mh mh K normal 9 0 mh mh L x mh mh Page 4 of 0

15 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison Acronym of institute: NM Date: September 006 Remarks: Model equation L = ( L l l δl S + δld + δlts Definition of quantities quantity unit definition L S H certificate value of the reference standard δl D H time drift of the reference standard δl TS H correction for the temperature variation of the reference standard δl T H correction for the temperature variation of the unknown inductance l K Ī K correction factor given by systemic effects of the measurement circuit ratio between the indicated value of the unknown inductance and the indicated value of the reference standard inductor L H inductance of travelling standard T Uncertainty budget quantity estimate standard probability sensitivity uncertainty uncertainty distribution coefficient contribution X i x i u(x i c i u i(l L S mh.50e-04 mh normal.0.50e-04 mh δl D mh.6e-04 mh normal.0.6e-04 mh δl TS.00E-05 mh.7e-05 mh rectangular.0.7e-05 mh δl T mh.46e-05 mh rectangular E-05 mh l K E-06 triangular mh.45e-05 mh Ī E-07 normal mh 5.60E-06 mh L mh.95e-04 mh Page 5 of 0

16 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison Appendix B Technical protocol The original text of the TEHNIAL PROTOOL below was edited. TEHNIAL PROTOOL EUROMET project 889 EUROMET.EM-K Trilateral comparison of a 0 mh inductance standard June 006 Page 6 of 0

17 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison. Introduction The comparison is organized within the framework of Phare 00 Project BG00. Strengthening of the National onformity Assessment System Technical Assistance for Standardization and Metrology, EUROPE Aid/6486/D/SV/BG. Three national institutes of metrology are taking part in this comparison: PTB (Germany, NM (Bulgaria and INM (Romania. PTB is responsible for providing the travelling standard and the evaluation of the measurement results. NM is responsible for the protocol and the final report. It is planned to complete this comparison in September Description of travelling standard.. The travelling standard is an inductance standard having the nominal value of 0 mh. It is constructed starting from a General Radio 48-L 0 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 0 type or the car s supply system of volt (in the case of transportation by car can be used... Specifications Nominal value of inductance 0 mh ± 0.% Relative instability of inductance < ppm per year Nominal thermostatic temperature 0.0 ± 0. K Instability of thermostatic temperature with an instability of the ambient air temperature of 0.5 K ±0.0 K per year Dependence of the value of inductance on the ambient air temperature in the range from 8 to 8 0. ppm per K Measuring frequency 000 Hz Measuring voltage at the standard 0.5 V Effective resistance (D of the coil at an ambient air Ω temperature of.0 ± 0. K Width of the HIGH and LOW connecting terminals 9 mm onnection system Power supply of thermostat: power supply unit (0 V ± 0%; 50 Hz; set of batteries ( x 6 V; V supply system of a car Power cable Dimensions of leather bag Total mass.. Accessories Power supply unit; Set of batteries ( pieces; adapter cable for connection to a V car supplies system Two terminals (case is internally connected with LOW terminal 0.5 A at V (D Red plug to be connected to plus, blue plug to be connected to minus 470 mm x 0 mm x 400 mm Approx. 8 kg Page 7 of 0

18 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison. Quantities to be measured L: inductance of the standard (two terminals; R: D resistance of the inductor coil; f: measurement frequency; T ext: the temperature ( of the environment where the standard is measured. 4. Measurement instructions 4.. Measurements should be performed under the following conditions: Measurement frequency: 000 Hz; Measuring voltage: 0.5 V (rms; Temperature of the environment: ± ; Relative humidity: between 0 % and 70 %. 4.. 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 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 ; 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, 995 and the complete uncertainty budget must be reported. Page 8 of 0

19 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison 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, adapter cable for connection to a V car supply system, mechanical temperature recorder (Metrawatt Thermoscript 880, spare strip charts for the temperature recorder (initially 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 V power system of the car. arrying 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 0 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 9 of 0

20 EUROMET EUROMET.EM-K: 0 mh Inductance Trilateral omparison 8. Participants Table. List of participants and contact information. Laboratory address Physikalisch-Technische Bundesanstalt (PTB Electricity Division, FB. Bundesallee Braunschweig GERMANY National entre of Metrology (NM 5-B G. M. Dimitrov Str. 797 Sofia BULGARIA National Institute of Metrology (INM sos. Vitan Barzesti sector 4, 04 Bucuresti ROMANIA ontact name, Jürgen Melcher Juergen.Melcher@ptb.de Petya Aladzhem ncm@sasm.orbitel.bg Anca Nestor anca.nestor@inm.ro 9. Schedule Table. List of the participants, measurement dates and report dates. Laboratory Measurement dates Report date PTB - Germany April 006 INM - Romania - 9 May 006 June 006 NM - Bulgaria - 6 June 006 July 006 PTB - Germany July 006 Page 0 of 0