地面铷原子钟稳定性和一致性研究

研究了铷原子钟的稳定性和一致性。重点对稳定度的不同表示方法进行了比较,对同一铷原子钟不同寿命时期的稳定性、同一类型多个铷原子钟的稳定性进行了比较,研究了断续工作铷原子钟的频率稳定性、漂移率和一致性。     

基于iGMAS的北斗导航卫星原子钟性能评估

星载原子钟是导航卫星系统的关键设备,星载原子钟的性能评估对导航误差分析及原子钟产品性能改进有重要参考价值。介绍了星载原子钟的主要性能参数和iGMAS钟差产品。基于iGMAS的钟差数据,分别对北斗卫星导航系统的铷原子钟和氢原子钟的准确度、漂移率和稳定度进行了评估和对比。结果表明,北斗三号原子钟的性能比北斗二号的明显提升,其中氢原子钟的长期性能更好,10天稳定度和天漂移率普遍达到10-15量级。     

合格判定在时间频率计量校准领域应用研究

为避免时间频率校准工作中对被校准设备合格判定产生错误判定,通过对频率偏差参数合格判定方法的研究,针对晶振老化或原子钟频率漂移、频率复现性及测量不确定度对测量结果影响,建立3种合格判定典型数学模型,分析造成错误判定的原因并提出解决思路;采用高稳晶振、铷原子钟等典型仪器进行试验验证和数据分析。实验表明:归纳总结出的3种方法能够在实际工作中得到运用,避免产生错误判定,为时间频率计量校准工作中合格判定提供解决思路和指导方法,具有较强的指导性和应用价值。     

基于光纤双向时间传递实时驯服铷钟的远程时间溯源

为了提高铷原子钟的远程时间溯源性能,在中国计量科学研究院TWOTFT链路的基础上,实施了对铷原子钟的高精密准实时驯服实验,驯服间隔分别为16,5,1 min,实现了基于TWOTFT的远程时间溯源原理验证.实验结果表明:在远程时间溯源中,TWOTFT相比GNSS时间频率传递效果更优,且1 min TWOTFT远程时间溯源...     

铷原子钟技术对于汞离子钟研制的借鉴性分析

谱灯光抽运被动型铷原子钟具有长寿命、极低的随机频率漂移噪声和较好的短、中期稳定度等显著的优点,在卫星导航定位系统中有着广泛的应用。但是这种铷原子钟的准确度和长期稳定度较差,已经不能满足新一代导航定位系统的要求。离子阱汞离子微波(Hg~+)钟已经达到了主动型氢原子钟的性能指标,与传统铷原子钟相比,具有更加广泛的应用前景。铷原子钟和汞离子微波钟有许多相同点和不同点,对两者差异性进行分析可以借鉴现有铷原子钟的研究,加深对汞离子微波钟工作过程的认识。本文对两者的原理和关键技术进行了比较分析,对汞离子微波钟的发展具有一定的借鉴作用。     

BDS-3卫星与其他GNSS系统卫星原子钟性能分析

星载原子钟是决定星上时间基准的基础。利用一年的事后精密钟差数据,对北斗三号(BDS-3)和其他全球卫星导航系统的准确度、漂移率和稳定度进行了分析,以评估全球卫星导航系统(GNSS)在轨原子钟性能。结果表明：BDS-3的铷原子钟准确度在2.62×10^-13～2.54×10^-11之间,氢原子钟在1.64×10^-14～6.77×10^-11之间;BDS-3氢原子钟的漂移率显著优于铷原子钟;BDS-3多数氢原子钟的稳定度可达到10^-15量级。BDS-3的稳定度表现最好,其次是全球定位系统(GPS)、北斗二号(BDS-2)、伽利略(Galileo)和格洛纳斯系统(GLONASS)。     

原子频标频率漂移率测试系统

针对铷原子频标的日漂移率的测试需求,采用时差法设计日频率漂移率检测装置。该装置通过多路分频器,将被测频标1 MHz、5 MHz、10 MHz信号分频为标准1PPS信号。GPIB接口控制时间间隔计数器测量时差数据并传输给计算机,计算测量结果。装置自动化程度高、工作稳定,实现对多台铷原子频标日频率漂移率的自动化测量。     

基于SR620时差测量系统的设计

时间间隔计数器目前广泛应用于时间频率校准中,针对铷频标和铯频标的计量特性测量,设计了基于SR620的时差测量系统,以测量相对频率偏差、频率稳定度和日频率漂移率,并绘制频率稳定度曲线和频率漂移率曲线.通过实验证明系统测量结果与预期相符,可有效应用于时间频率溯源及校准.     

铯原子钟日频率漂移率测量的不确定度评定

本文采用时刻比较测量方法,对铯原子钟长期特性参数之一——日频率漂移率进行测量,基于实际测量数据,分析了铯原子钟日频率漂移率不确定度来源,给出了合成不确定度评定过程和结果。     

基于FPGA的北斗驯服铷原子频标装置的研制

为了提高铷原子钟频率的准确度和稳定度,设计了基于FPGA技术的多路输出北斗驯服铷原子频标装置。装置采用粗测和细测的时间间隔测量方法实现铷原子频率的驯服和时间跟踪与同步。采用模块化设计和编程,提高了装置的通用性和可移植性。以铯原子钟时间频率为参照,利用该装置对铷原子钟驯服前后的数据进行多次比对测试,结果表明其频率的相对准确度达到了1.5×10^-13,相对稳定度达到6.97×10^-13,与驯服之前相比,铷原子钟频率的准确度和稳定度均得到大幅提高和改善。     

Atomic Time and Frequency Standards Development at Shanghai Observatory, China

The performance characteristics of several types of our atomic frequency standards are described. All of these standards are designed, developed, and fabricated in China. The hydrogen maser is the only type developed by the Shanghai Observatory. This paper also describes briefly the basic consideration for system implementation, calculation approach, and experiment results in the generation of the Shanghai Observatory atomic time scale AT(SO). Based on available frequency standards-one prototype laboratory model of cesium clock, three hydrogen clocks, and several (3-6) rubidium clocks-the AT(SO) was established in 1978. The laboratory cesium clock is used to provide the basic calibration reference of the second in 1979, while hydrogen clocks and rubidium clocks are used as the working clocks to ensure the continuity of the time scale.     

On real-time optimal FIR estimation of linear TIE models of local clocks

In this paper, we present an optimal finite-impulse response (FIR) filter for the linear time-interval error (TIE) model of a local clock and compare its estimates to those obtained by the unbiased FIR filter via the global positioning system (GPS)-based sawtooth measurements. We show theoretically and verify experimentally that there is no reasonable necessity in using optimal filters for GPS-based estimation of the TIE of precision crystal, rubidium, and cesium clocks. For these clocks, the optimal FIR filter requiring four coefficients degenerates to a simple unbiased FIR filter requiring only one coefficient.     

铷原子钟光谱灯铷量测量和寿命评估

铷光谱灯灯泡的使用寿命是影响星载铷钟寿命的关键因素。为了评估铷灯泡寿命,利用一种新的灯泡赶铷方法,显著提高了差分扫描量热计测量灯泡铷量的精度。通过对长达7年铷量测试数据的理论拟合,得到了迄今为止精度最高的铷量消耗公式,进而评估了灯泡的使用寿命。结果分析表明,对于材料为Schott 8436玻璃的灯泡,充铷量超过130 μg,使用寿命即可达到50年。     

GPS在轨卫星原子钟性能评估

卫星钟在轨性能评估对于卫星钟差预报与系统完好性监测具有重要作用。利用国际GNSS服务组织发布的事后GPS精密卫星钟差数据,基于频率准确度、漂移率、万秒稳定度及天稳定度对GPS Block IIR、IIR-M、IIF与IIIA 4类卫星的星载钟性能进行评估。结果表明:1) GPS卫星钟的频率准确度与天漂移率分别在10^-13～10^-12量级与10^-15～10^-14量级;2) 星载铷钟的万秒稳定度与天稳定度分别可达10^-14与10^-15量级,比星载铯钟的同类指标高近一个数量级;3) 新型Block IIIA卫星的星载钟的天稳定度比另外3种类型卫星的星载钟的天稳定度更高,达到(3～5)×10^-15的水平;4) 无论对于不同系列卫星还是同一系列卫星,各星载钟之间均存在一定的性能差异,这种差异与卫星钟在轨运行时间长短无显著关系。     

Kalman filter-based force estimation in a clamped plate using reduced order model and noisy measurements

Deterministic techniques are available for force estimation in dynamic systems in time, frequency, and modal domain. But, these techniques are susceptible to measurement noise and require an accurate model of the system, hence, are not suitable for precise force estimation. Some combined deterministic-stochastic approaches are available in the literature for unknown input force estimations, where force estimations are performed by considering the model uncertainty and measurement noise. In the present work, one such technique is extended by incorporating reduced-order model to estimate forces in of plate structures. Kalman filter and a recursive least-squares (KF-RLSE)-based technique which uses displacement and/or velocity measurements for force estimation is used in the present work with a reduced-order model. Time-varying unknown forces acting at single/multiple locations are reconstructed using the measured responses from the plate. Numerical simulation followed by experimental verification is presented. The effect of error in model parameters on the force estimation is presented, and robustness of the input estimation technique is tested for different levels of measurement noise.     

INRIM Tool for Satellite Clock Characterization: Frequency Drift Estimation and Removal

In Global Navigation Satellite Systems (GNSS), atomic clocks are fundamental for their excellent stability. Being the distance measured from the time, any error on the measure of time leads to an error in the positioning: accurate and stable atomic clocks need to be employed on board satellites. Hence, the on board clock behaviour has to be continuously monitored and any malfunctioning has to be immediately detected. In this work, we illustrate a software tool developed at the National Institute of Metrological Research (INRIM) for GNSS clock characterization and monitoring. In particular we focus on the functionality of frequency drift estimation and removal, including the uncertainty evaluation. Actually, the frequency drift evaluation and the monitoring of its evolution over time is extremely important in GNSS applications to ensure the adequacy of the timing system to the integrity requirements of the positioning service. The software has been optimized for space clock data, which are different from the ones from timing laboratories, since often present missing data and outliers. The tool allows to easily handle satellite clock data, and get a quick estimate and graphic representation of clock key parameters, such as the clock frequency drift.     

Time synchronization using the Internet

This paper discusses a new algorithm for synchronizing the clocks of networked computers using messages transmitted over the network itself. The design is based on a statistical model of the clock and the network, and uses this model to define the parameters of a frequency-lock loop which is used to discipline the local oscillator. The design was tested by synchronizing a standard workstation to a time server located 1200 km away; the time offset between the clock synchronized in this way and UTC is 2 ms rms. This analysis also can be used to design algorithms that provide lower accuracy at lower cost.     

The NIST Automated Computer Time Service

The NIST Automated Computer Time Service (ACTS) is a telephone time service designed to provide computers with telephone access to time generated by the National Institute of Standards and Technology at accuracies approaching 1 ms. Features of the service include automated estimation by the transmitter of the telephone-line delay, advanced alert for changes to and from daylight saving time, and advanced notice of insertion of leap seconds. The ASCII-character time code operates with most standard modems and computer systems. The system can be used to set computer clocks and simple hardware can also be developed to set non-computer clock systems.