TW s at. GNSS sat. u B /CA/GNSS 26%. 20. TW: Lab K -PTB. GNSS Lab K -PTB: Ref k - Ref PTB. Unbalance: u A vs. u B ?!. u B /CA/GNSS 16%. Std B - Ref PTB. Uncertainty Type A / Type B /ns. 7. GNSS. TW k. 6. GNSS PTB. u B /C|P/GNSS/TW 44%. TW PTB. 5. 4. PTB. Std B. u A.
uB /CA/GNSS 26%
GNSS LabK-PTB: Refk-RefPTB
uB /CA/GNSS 16%
Type A / Type B /ns
uB/ TW 7%
StdB at OP
Optic fibre etc.
GPS SA ON | Off
BIPM PPS cable
2000 2003 2004 2005 20092012 201X
BIPM PPS cable
Δ=289.958 ns =
Common reference point
of the OPMT and the StdB
at OP Lab
at OP Lab
__ Method (A) Dif. ≤ 0.3 ns__
The 4 offsets in the total delays designed on different MJDs measured by the TIC SR620 and the BIPM Calibrator (P3/PPP). The mean differences is -0.2±0.3ns
Design of the experiments to evaluate the total uncertainty
The basic idea is to measure a delay using different and independent methods then to compare the results. The RMS (the root of mean squares of the differences between the methods) will provide an estimate of the total uncertainty (uM) which includes all the uncertainty sources of GPSs’, TICs’, and cable delay measurements’ etc. This plus the instabilities of the reference and the travel receivers make the total uncertainty of the METODE link calibration: UM (uB).
Evolution of Time links and
Uncertainties since 2000
The 2013 setup of the BIPM portable calibrator with two GTR50 GPS receiver-antenna systems
The 10 meter baseline between the UTC(TL) and the mobile Cs standard. The CCD are measured continuously by both METODE and a TIC SR 620. The difference is 0.7 ns.
The CCD setups of the StdB at OP of two references: the maser H889 and UTC(OP). The difference is 0.5 ns
A 25km CCD baseline experience was carried out at TL. A mobile Cs clock was transported together with the METODE calibrator developed by TL.
The RMS of the two independent data sets is 0.92 ns on average.It should be pointed out that the RMS includes the instability of the mobile Cs clock which may be up to 1 ns depending on various conditions of temperatures, transports and power etc.
BIPM StdB antennas’ supporter
Method (C) Dif. =0.9 ns
The BIPM Z12T BP0C was absolutely calibrated in 2001. The related calibration uncertainty uB is about 2.3 ns. Table below gives the differences of the calibrations results by the METODE calibrator and by the 2008 classical receiver calibrations of OPMT vs. BP0C. By PPP, the difference of the calibrations is 0.9 ns between OP Z12T OPMT and BIPM BP0C. In the table, uA is the measurement uncertainty.
Setup at OP
_ Method (D)_Dif. = 0.9 ns _
An one for all link calibration
The BIPM traveling Calibrator at OP and PTB
Prague EFTF2013 ID 515
Z Jiang1, G Petit1, L Tisserand1, P Uhrich2, G D Rovera2 and S Y Lin3
1 Time Department, Bureau International des Poids et Mesures (BIPM), Pavillon de Breteuil F-92312, SÈVRES CEDEX, France
2 Laboratoire National de Métrologie et d’Essais - Systèmes de Référence Temps-Espace, CNRS, UPMC, Observatoire de Paris (OP), France
3 National Standard Time and Frequency Laboratory, Telecommunication Laboratories (TL), Chunghwa Telecom
Four independent methods are used to test the BIPM calibrator (StdB):
(A) Use the StdB to measure the delay of the known delay cables;
(B) Comparisons between the SR620 time interval counter (TIC) and the StdB;
(C) Comparisons between A mobile Cs standard and the StdB;
(D) Comparison between the earlier calibrations and the StdB
The dominant part of the total uncertainty budget in the [UTC-UTC(k)] is from the type B uncertainty (uB) in time link calibration. In 2011, the BIPM launched a pilot experiment to reduce the uB from 5 ns at present to ≤ 2 ns and has developed a standard calibration scheme, namely METODE, associated with an integrated portable GNSS calibrator and reference receivers stationary at BIPM. Similar setups are made in TL. Using these systems, we performed a series experiments at BIPM, OP and TL to study the reachable uncertainty of METODE. The results are compared to that of the traditional differential receiver calibrations.
Keywords : UTC, Time transfer, Calibration
___ Method (B) _Dif. ≤ 0.7 ns ____
60 % uA ≤ 1 ns vs. 93 % uB ≥ 5 ns 93% u > 5 ns
The uncertainty in UTC is dominated by the uB.
The major challenge: Reduce the uB !
UTC Calibration Guidelines for RMO
Reduce uB from 5 ns to 1~2 ns by Link Calibration
- BIPM transportable time link calibrator (BIPM)
- TWSTFT mobile calibrator (TimeTech)
- GNSS receiver absolute calibration (BIPM-CNES)
Briefly, above the Tests A, B, C and D give separately the uncertainty estimates < 1.0 ns. The RMS is 0.7 ns