LITHUANIAN NATIONAL TIME AND FREQUENCY STANDARD

Transcription

1 LITHUANIAN NATIONAL TIME AND FREQUENCY STANDARD Rimantas Miškinis Semiconductor Physics Institute A. Goštauto 11, Vilnius 01108, Lithuania Tel/Fax: ; miskinis@pfi.lt Abstract The Lithuanian National Time and Frequency Standard Laboratory is responsible for maintenance and dissemination of the national time scale UTC (LT), time and frequency units. Since June 2001, we have been contributing to TAI. The Laboratory is equipped with two HP5071A cesium atomic clocks (one with a high-performance Cs tube) and two TTS-2 multichannel GPS receivers based on Motorola VP Oncore GPS processors. One of the GPS receivers is equipped with thermo-stabilized GPS antenna. For the dissemination of the Lithuanian Time Scale UTC (LT), the NTP server Datum 2001 is used. In this paper, the main metrological characteristics and technical possibilities of the National Time and Frequency Standards are presented. INTRODUCTION On 11 March 1990, when Lithuania s independence was restored, a new phase of development the process of integration into transatlantic organizations started in our country. This meant a beginning of reorganization of the Lithuanian system of metrology as well. In , a profound analysis of metrological needs of economic entities and scientific institutions was made. After the results were summarized, it was decided to establish a decentralized Lithuanian National Metrology Institute (NMI). The NIM should include laboratories of primary standards, which would be located at various scientific institutes. It was also decided to establish the following national standards: Primary standards of time and frequency at the Semiconductor Physics Institute (SPI), Vilnius; Primary standard of temperature at the Semiconductor Physics Institute, Vilnius; Primary standards of voltage and resistance at the Semiconductor Physics Institute, Vilnius; Standard of gauge blocks Vilnius Metrology Center; Standards of the air (gas) flow and volume units - Lithuanian Energy Institute, Kaunas. On 5 April 2002, the Government of the Republic of Lithuania approved the Time and Frequency Standard Laboratory of the Semiconductor Physics Institute as the keeper of the National Time and Frequency Standards. Since May 2001, the National Laboratory of Time and Frequency Standards participates in the process of forming the International Atomic Time Scale (TAI). 191

2 Report Documentation Page Form Approved OMB No Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE DEC REPORT TYPE 3. DATES COVERED to TITLE AND SUBTITLE Lithuanian National Time and Frequency Standard 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Semiconductor Physics Institute,A. Go?tauto 11, Vilnius 01108, Lithuania, 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR S ACRONYM(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 11. SPONSOR/MONITOR S REPORT NUMBER(S) 13. SUPPLEMENTARY NOTES See also ADM th Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting, Washington, DC on 7-9 Dec ABSTRACT The Lithuanian National Time and Frequency Standard Laboratory is responsible for maintenance and dissemination of the national time scale UTC (LT), time and frequency units. Since June 2001, we have been contributing to TAI. The Laboratory is equipped with two HP5071A cesium atomic clocks (one with a high-performance Cs tube) and two TTS-2 multichannel GPS receivers based on Motorola VP Oncore GPS processors. One of the GPS receivers is equipped with thermo-stabilized GPS antenna. For the dissemination of the Lithuanian Time Scale UTC (LT), the NTP server Datum 2001 is used. In this paper, the main metrological characteristics and technical possibilities of the National Time and Frequency Standards are presented. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT a. REPORT b. ABSTRACT c. THIS PAGE Same as Report (SAR) 18. NUMBER OF PAGES 4 19a. NAME OF RESPONSIBLE PERSON Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

3 LABORATORY DESCRIPTION The Lithuanian National Laboratory of Time and Frequency Standards is a unit within the Metrology Department of the Semiconductor Physics Institute. The Laboratory occupies three rooms with a total area of 150 m 2. The rooms in which the cesium atomic clocks and equipment for comparison and distribution of time signals operate are electrically screened. A temperature of 21±1ºC is maintained in these rooms by air conditioning and control systems. A scheme of links between the laboratory equipment is provided in Figure 1. The most important equipment in the laboratory are the cesium nuclear clocks HP5071A and AGILENT5071A. The AGILENT5071A atomic clock, which has operated in our laboratory since April of 2003, is equipped with a high-performance Cs tube. We use two TTS-2 Time Transfer Systems with Motorola VP Oncore GPS multichannel receivers for comparing time signals. The systems were produced and calibrated by the Astrogeodynamical Observatory of the Space Research Center, Polish Academy of Sciences. A platform of GPS antennas has been installed on the roof of the institute building and is securely joined with the construction elements of the building. The coordinates of the sockets of GPS antennas were measured in the ITRF97 system of coordinates with a 0.5 cm uncertainty. The measurement was carried out by the experts of the Institute of Geodesy of the Vilnius Gediminas Technical University. GPS3 GPS1 GPS2 D A T U M ExacTime TTS-2 N o1. TTS-2 N o.2 Cs clocks IRIG HP5071A (standard) Agilent 5071A (high perf.) Sensors (T and RH) 1PPS 100 khz 1 MHz 5 MHz Switching device Time counter SR620 RS232 Computer PC-1 GPIB GPIB 100 Base-TX 100 Base-TX 1PPS 100 khz 1 MHz 5 MHz To laboratory computer network Signal distribution devices 100 khz, 1 MHz, 5 MHz,, IRIG Figure 1. Schematic representation of laboratory equipment. 192

4 At the present time, the main HP5071A atomic clock is connected to the first TTS-2 time transfer system. The data are collected by the microprocessor of the first TTS-2 time transfer system using the common view method and sent to the Time Division of BIPM. Figure 2 reveals the weight factor of the main LT clock from the time it joined in the formation of TAI until now. The second TTS-2 time transfer system was installed in May of It has been supplied with a thermo-stabilized GPS antenna. 0,35 0,30 LT clock weight, % 0,25 0,20 0,15 0, , , MJD Figure 2. LT clock weights ( Intrinsic technical parameters of atomic clocks as well as environmental condition (temperature T and relative humidity RH) are registered by the computer PC1. The layout of the Laboratory s computer network is given in Figure 3. ROUTER and NTP POCKET DUMP PC NTP server DATUM GPS IRIG Cs GPS 3 DATUM ExacTime Ethernet Hub Laboratory server PC 1 PC 2 PC n Figure 3. Computer network layout. 193

5 In February of 2003, a quality system according to ISO/IEC was implemented by the Laboratory. In September of 2003, the implementation was recognized by the Quality Forum of EUROMET in Istanbul. The quality system is assessed annually by experts of European accreditation bodies. TIME SERVICE The Laboratory operates a TymServe 2100 NTP server manufactured by Datum, Inc. The server receives 1 second pulses (PPS) from a laboratory s atomic clock. Exact time signals generated by the Laboratory at the beginning of each hour are transmitted to Lithuanian Radio. OTHER ACTIVITIES COOPERATION Besides participation in the activities of the Time Division of BIPM, the Lithuanian National Time and Frequency Laboratory cooperates with the Polish Central Office of Measures (GUM) in the formation of the independent atomic time scale TA (PL). DISSEMINATION OF KNOWLEDGE During qualification courses, lectures on different topics of the metrology of time and frequency are given to the technical personnel of calibration laboratories. FUTURE PLANS The Laboratory s plans in the near future include implementation of technologies for the generation and dissemination of an authorized electronic time stamp to promote the use of electronic signature in Lithuania. We plan to develop methods for the investigation of metrological characteristics of frequency sensors whose operation is based on surface acoustic waves. ACKOWLEDGMENTS The author would like to express his thanks to Wlodzimierz Lewandowski of the Bureau International des Poids et Mesures; Jerzy Nawrocki of the Astrogeodynamical Observatory of the Space Research Center, Polish Academy of Sciences; Andreas Bauch of PTB; and all his colleagues of the Polish Central Office of Measures (GUM) for their continuing support and advice. 194