Results of the questionnaire for remote calibration in T&F field Michito Imae Sub-Working Group under WG-GNSS
Sub-working group on remote calibration in T&F field • This sub-Working Group was created at the last TCTF meeting at Sydney. • The mission of the sub-WG is “Consider guidelines for harmonization or standardisation of remote calibration services, and for the assessment of these services for CMCs under the CIPM MRA” • For this purpose we conducted a questionnaire about remote calibration in T&F field to survey the present situation in APMP region.
Questionnaire (1) Q 1. Do you provide remote calibration services in time and frequency field from your institute? yes or no Q 2. If yes for question 1. , Q 2. 1 Please describe your remote calibration system briefly. Q 2. 2 In which category do you provide the remote calibration service, such as frequency, time, and time scale difference? " Q 2. 3 Who are the clients for your remote calibration services? Q 2. 4 Please describe the method and uncertainty of your remote calibration services? Q 2. 5 How often do you provide the certification for the remote calibration services? Q 2. 6 How many clients do you have for the remote calibration services? Q 2. 7 Does your remote calibration system covered by the quality system?
Questionnaire (2) Q 3. If "no" for question 2. Do you have any plan to start the remote calibration service in time and frequency field? Q 4. What is the main problem for the remote calibration service in the time and frequency field? Q 5. The GPS(GNSS) DOs (disciplined oscillators) are used for the traceability system in your country? Q 6. 1 If "yes" for question 5, in which layer the GPS(GNSS) DO are used for the traceability system? Q 6. 2 If “yes” for question 5, how to claim the uncertainty for the traceability system? Q 6. 3 If "no" for question 5, what is the main problem to use the GPS(GNSS) DO for the traceability system? Q 7. If you have any documents explaining your remote calibration service, please send them attached to this questionnaire.
Present situation of the remote calibration services 1. 2. 3. 4. 5. 6. 14 NMIs replied until now. 9 NMIs providing remote calibration services. 3 NMIs are planning to provide remote calibration services in future. 8 NMIs use GPS common-view method for remote calibgration service. 1 NMI provides remote calibration via GPS, and TV signal. Service categories of the remote calibration: Frequency 9 NMIs Time 1 NMI Time scale difference 2 NMIs 5 NMIs already have the quality system for the remote calibration service.
Uncertainty and certification 7. Uncertainty of the remote calibration systems using GPS(GNSS) CV method GPS common-view Frequency ･ 2 E-13 ･ 5 E-13 within 1 000 km of base-line length ・ 1. 1 E-13 – 4. 9 E-13 depend on the base-line length ･ 2 E-12 within 50 km of base-line length Time scale difference ･ 40 ns – 210 ns 8. Certification ・once a month ･once a year 4 NMIs 1 NMI
Main problem of the remote calibration services (1) A-STAR Clients are not clear about the service and its principle. A-STAR Clients have difficulty to install GPS antenna at their premises. A-STAR Very few clients use cesium clock as their standard. KRISS Installation of a GPS antenna at a remote site KIM-LIPI Equipments, knowledges MSL We have no control over what the client does with the measurements or of how they are interpreted. NICT The cost is the main problem for us; a system of the remote calibration (including a GPS receiver and a time interval counter and so on) is expensive now. NIMT Data proceeding.
Main problem of the remote calibration services (2) NMIA has been providing remote calibration services to customers to clients for over ten years. The main challenge for NMIA is the human resources required for maintaining all of these systems over a long operational life and providing measurement reports with minimum disruption. The production of measurement reports on these systems has been streamlined and automated over the past year. NMIA A secondary problem is the installation of remote calibration systems for commercial clients, where some negotiations can extend over a lengthy period (for example, legal aspects of a commercial agreement or security aspects for remote access to client networks). SCL No demand for the remote calibration service in the time and frequency in Hong Kong. SIRIM We do not have a remote calibration system that can be used for such service. TL As for the prototype system using GPS carrier phase technique, some improvements should be done to reach its commercial feasibility, and as for the system using C/A code method, its setup and test is still on-going. VMI Now, We haven’t got any equipment to do it.
GPS(GNSS) DO (1) A-STAR A 5. Yes, many testing laboratories use GPS(GNSS) DO in this way. A 6. 1 The GPS(GNSS) DO is used as a working standard. A 6. 2 Some testing laboratories send their GPS(GNSS) DO to us for calibration. Our calibration result is used by them for uncertainty claim KIM-LIPI A 5. Yes A 6. 1 I don’t understand in this question A 6. 2 List from BIPM KRISS A 5. Yes A 6. 1 Those are also calibrated like a frequency standard or a general frequency source.
GPS(GNSS) DO (2) MSL A 5. Possibly. What the client does with our measurements depends upon the technical assessment of the laboratories quality system. Most of them have either Cs or Rb standards A 6. 1 Second level laboratories. A 6. 2 Depends upon the technical assessment of the laboratories quality system NICT A 5. . Yes. But only the remote calibration can be traceable. A 6. 1 They can be used in any layer, except for the national standard. A 6. 2 It is estimated by a (remote) calibration. NIM A 5. Yes A 6. 1 second A 6. 2 Please see CMC table NIMT A 5. No. For quality system is not allow.
GPS(GNSS) DO (3) NMIA A 5. No A 6. 3 There main concern regarding the use of GPSDO systems as standalone time and frequency references is the reliability and integrity of these systems: in our experience they can be adversely affected either by firmware errors or by failure of local tracking, and the client is not always aware that a failure has occurred. For applications requiring high integrity and continuous operation, it is strongly recommended to either compare the GPSDO output to a separate independent reference or to maintain a complete record of tracking and reception conditions. NMIA does maintain two monitoring sites (Melbourne and Perth) where GPS signal reception can be tested against a local clock, but the geographical size of Australia means that it is impossible for NMIA with its current resources to fully monitor signal reception in all parts of Australia. In the future, as other GNSS and augmentation systems become fully operational (particularly GLONASS, Galileo and also QZSS), it may become easier to validate a GPSDO (for example) using a separate system tracking a separate satellite constellation, and this may give sufficient independence to support the required degree of reliability and integrity of operation.
GPS(GNSS) DO (4) NMIJ A 5. No. (Only in the case monitored by remote calibration service continuously. ) A 6. 3 Nobody can provide the uncertainty of the reference signal of GPS DO by itself. There are possibility to allow to use the GPS-DO in the traceability system with a type approval and limited uncertainty. . SCL A 5. No A 6. 3 The internal method for steering the disciplined oscillators is generally unknown from the instrument manual.
GPS(GNSS) DO (4) SIRIM A 5. Currently, there accredited laboratories that used GPS DOs as reference standards, but the traceability of such oscillators is to UTC(GPS) maintained by USNO. As the reference laboratory, we provide verification and calibration services of DOs with and without GPS locking. However, that is done in our laboratory, not by remote. We published daily GPS satellites integrity table for their use. A 6. 1 As answered above, such layer is in the customer or accredited laboratories premises. A 6. 2 Measurement uncertainty is evaluated, post-processed from the satellites data on the USNO web pages, but this is done by the laboratory. Not by NML-SIRIM. Evaluation is quite problematic, because the actual performance of free running GPSDO without GPS locking is evaluated but Allan Variance value never used or applied, as compared to other oscillators when sent for calibration. A 6. 3 Traceability is not to national frequency standard or time scale. Only those with knowledge of UTC(GPS) or USNO time scale performance will be able to claim traceability.
GPS(GNSS) DO (5) TL A 5. No A 6. 3 We think it’s not easy to establish the traceability chain from a remote site to a NMI while using GPS(GNSS) DO. VMI A 5. The GPS receiver systems are using for the traceability system in my country. A 6. 1 The GPS receiver systems are used for GPS common-view time transfer method in layer two of our the traceability system. 6. 2 From the BIPM’s Circular-T we claimed the uncertainty for the traceability system.
Summary of the questionnaire • Many NMIs already provides remote calibration services for their clients. • Almost all NMIs use GPS(GNSS) common-view method for their remote calibration services. • Various ways are existing for uncertainty concepts for their systems. • GPS(GNSS)-DO is widely used for the industry purposes. • The policies for GPS(GNSS)-DO are different among the NMIs.
Action plan for 2008 -2009 1. Discuss and create (if possible) a guideline of the remote calibration service in T&F field. 2. Discuss and create (if possible) a guideline of the use of GPS(GNSS)-DO in the traceability system in T&F field. To perform item 1. and 2. , we need some members to discuss precisely and to make the draft of the guidelines.
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