In-situ metrology calibration device for shipboard time system
By using a shipborne timekeeping system with a high-precision, low-aging atomic clock trained by BeiDou as the reference frequency standard, the problem of frequency source aging and drift was solved, the in-situ calibration of the frequency source and the stable operation of the system were realized, and the metrological assurance capability of the frequency standard was improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MEASUREMENT & TESTING INST OF UNIT 92493 OF THE CHINESE PEOPLES LIBERATION ARMY
- Filing Date
- 2023-11-20
- Publication Date
- 2026-06-19
AI Technical Summary
The frequency source of the shipborne time synchronization system has aged and drifted during long-term use, making it impossible to achieve in-situ calibration, which affects time synchronization and timing output, and lacks effective measurement standards.
Using a Beidou-trained high-precision, low-aging atomic clock as the reference frequency standard, combined with the principle of fully digital measurement, and with a built-in standard source, it has the functions of B-code testing, time difference testing, second pulse width and frequency stability testing, and designs an in-situ metrological calibration device for shipborne time system.
It enables in-situ calibration of the frequency source of the shipborne timing system, timely detection of non-fault-related index deviations, ensures reliable and stable operation of the system, simplifies the calibration process, and improves the metrological support capability of frequency standards.
Smart Images
Figure CN117590734B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of shipborne time and system technology, and specifically to an in-situ metrological calibration device for a shipborne time and system. Background Technology
[0002] As a component of the military's overall time and frequency system, the shipborne time and frequency system provides a unified time standard for all combat units within the ship platform. Due to the inherent aging and drift characteristics of the core component's frequency standard, the system requires regular calibration and measurement. In the shipborne time and frequency system, accurate and reliable frequency is a prerequisite for precise and effective timekeeping; the frequency source is a crucial indicator of the system. The core component of the shipborne time and frequency system is the frequency source. Due to its physical nature, the frequency source experiences long-term aging and drift. Under continuous operation, the frequency source's output parameters may exceed tolerances. Therefore, the frequency source must undergo regular calibration and measurement to correct frequency deviations caused by drift.
[0003] Currently, the traditional calibration method for frequency sources involves directly comparing the source being calibrated with a reference source within the same laboratory. This method yields relatively small measurement uncertainties but cannot calibrate all metrological characteristics of the frequency source. However, for shipborne and vehicle-mounted timing systems, which require long-term uninterrupted operation, disassembly and subsequent inspection are not feasible, and the inspection cycle is lengthy, requiring numerous testing devices. Therefore, there is an urgent need for methods and means to perform in-situ calibration of frequency sources in timing systems. Furthermore, among the factors affecting the performance of shipborne timing systems, critical aspects such as time synchronization, signal processing, and timing output lack measurement standards, and there is a lack of detection and resolution methods for non-fault-related deviations that cause time synchronization failures. Summary of the Invention
[0004] Technical Objective: To address the aforementioned technical problems, this invention proposes an in-situ metrological calibration device for shipborne time systems. This device uses a BeiDou-tamed, high-precision, low-aging atomic clock as the reference frequency standard for comparison and measurement, employing a fully digital measurement principle. It has a built-in standard source and features B-code testing, time difference testing, second pulse width testing, and frequency stability testing functions, ensuring the accurate and reliable time and frequency system of shipborne or vehicle-mounted time systems.
[0005] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution:
[0006] A shipborne timekeeping system in-situ metrological calibration device includes:
[0007] The programmable switch module has multiple channels for receiving multiple externally input signals under test;
[0008] The Beidou and crystal oscillator discipline module adopts the method of disciplining the rubidium atomic clock with the Beidou ultra-stable low phase noise crystal oscillator to receive the Beidou second pulse signal remotely transmitted by the Beidou system and generate the rubidium clock signal;
[0009] The frequency standard comparison and measurement module uses a fully digital algorithm to compare the multiple measured signals with the rubidium clock signals generated by the BeiDou and crystal oscillator discipline modules to obtain the comparison and measurement results.
[0010] The B-code synchronous frequency accuracy test module is used to receive B codes and perform decoding, synchronization accuracy, and pulse delay time tests.
[0011] The pulse width and time delay test module is used to receive BeiDou second pulse signals and measure the time interval;
[0012] The platform processor receives the comparison results from the frequency standard comparison measurement module, as well as the reference information sent by the B-code frequency accuracy test module, pulse width and time delay test module.
[0013] Preferably, the BeiDou and crystal oscillator discipline module includes a BeiDou receiver, a Kalman filter, a phase detector, a digital loop filter, an A / D sampler, a central processing module, a high-precision anti-vibration rubidium clock, a crystal oscillator, a phase-locked loop module, a frequency synthesizer, an isolation distribution amplifier, a frequency divider, and a time isolation module.
[0014] The Beidou receiver is used to receive the Beidou second pulse signal transmitted remotely by the Beidou system, and the output of the Beidou receiver is connected to a Kalman filter;
[0015] The high-precision anti-vibration rubidium clock is used to generate a rubidium clock oscillation signal, the crystal oscillator is used to generate a clock signal, and the phase-locked loop module is used to receive the rubidium clock oscillation signal and the clock signal. The phase-locked loop module, frequency synthesizer, isolation distribution amplifier and frequency divider are connected in sequence. The frequency divider is used to output two rubidium clock frequency-divided second pulse signals. One rubidium clock frequency-divided second pulse signal is input to the central processing module after passing through the isolation distribution amplifier, and the other rubidium clock frequency-divided second pulse signal is input to the phase detector.
[0016] The phase detector is used to simultaneously receive the filtered Beidou second pulse signal and a rubidium clock frequency-divided second pulse signal and perform phase detection processing. The output of the phase detector is connected in sequence to a digital loop filter and an A / D sampler to adjust the frequency and control the phase error of the output signal, obtain the measurement signal and input it into the central processing module.
[0017] The central processing module is used to calculate the correction value based on the measurement signal and the rubidium clock frequency division second pulse signal, and input it into the frequency synthesizer;
[0018] The isolation distribution amplifier has multiple rubidium clock signal output terminals.
[0019] Preferably, the frequency standard comparison measurement module multi-channel dual-mixing time difference measurement module includes four test channels, a signal generation module, a reference signal channel and a phase difference measurement module. The signal generation module is used to generate a first signal input to each test channel, a second signal input to the reference signal channel and a third signal input to the phase difference measurement module.
[0020] The reference signal channel and each test channel include an isolation module, a mixer, a mixing filter module, a bandpass filter module, a beat frequency amplification module, and a zero-crossing detection module connected in sequence. These modules are used to process the received signal through isolation, mixing, filtering, amplification, and zero-crossing detection before inputting it into the phase difference measurement module.
[0021] Preferably, the signal generation module includes a control circuit, a frequency selection module, a crystal oscillator module, a frequency multiplier module, and an isolation amplifier module. The crystal oscillator module has an output terminal connected to the frequency selection module. The generated clock signal is processed by the frequency selection module to obtain a first signal or a second signal, which are respectively input to the reference signal channel or the test channel via the isolation amplifier module. The crystal oscillator module also has an output terminal connected to the frequency multiplier module. The generated clock signal is processed by the frequency multiplier module to obtain a third signal.
[0022] Preferably, the platform processor is equipped with a display, keyboard and mouse, and the platform processor is connected to a local area network.
[0023] Beneficial effects: Due to the adoption of the above technical solution, the present invention has the following beneficial effects:
[0024] The device of this invention can conveniently and effectively test and calibrate the frequency source of the time system without disassembling the shipborne time system, and perform metrological tests on many important outputs of the system. This solves the problem of inconvenient frequency source testing and calibration, and can promptly detect out-of-tolerance non-fault indicators of the time system outputs, ensuring the reliable and stable operation of the time system. Attached Figure Description
[0025] Figure 1 This is a structural block diagram of an in-situ metrological calibration device for a shipborne timekeeping system proposed in this invention.
[0026] Figure 2 A structural block diagram of the BeiDou system and crystal oscillator discipline module;
[0027] Figure 3 This is a schematic diagram of the dual-mixing time difference measurement principle.
[0028] Figure 4 This is a block diagram of the circuit for the dual-frequency time difference method measurement. Detailed Implementation
[0029] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
[0030] This invention proposes an in-situ metrological calibration device for a shipborne timing system, comprising a BeiDou ultra-stable low-phase-noise crystal oscillator disciplined rubidium atomic clock phase-locked reference module (BeiDou and crystal oscillator disciplined module), a frequency standard comparison measurement module, a B-code synchronization accuracy testing module, a 1pps pulse width / delay testing module, a high-isolation RF switch module, host computer automatic testing system software, and a power supply module. It supports external reference source input. The overall system block diagram is shown below. Figure 1 As shown.
[0031] This invention employs a phase-locked loop (PLL) to lock the short-term frequency stability of an ultra-stable, low-phase-noise crystal oscillator to the output of a rubidium clock module. The frequency standard comparison module meets the comparison requirements, the A / D converter performs real-time sampling and conversion, and the filter meets the required signal purity. The frequency standard comparison measurement module uses a fully digital algorithm to compare the external measured signal with the internal high-precision rubidium clock via a 4-channel RF switch. The measurement results can be displayed on a screen or printed using programmable software, making measurement convenient and operation simple.
[0032] 1. Beidou and crystal oscillator discipline module
[0033] like Figure 2 As shown, the BeiDou and crystal oscillator discipline module includes: a BeiDou receiver, a Kalman filter, a phase detector, a digital loop filter, an A / D sampler, a central processing unit, a high-precision anti-vibration rubidium clock, a crystal oscillator, a phase-locked loop module, a frequency synthesizer, an isolation distribution amplifier, a frequency divider, and a time isolation module. The central processing module is used to calculate the correction value based on the measurement signal and the rubidium clock's frequency-divided second pulse signal and input it to the frequency synthesizer. The isolation distribution amplifier is used to output multiple rubidium clock signals.
[0034] The BeiDou and crystal oscillator discipline module implements the rubidium clock discipline unit. Its principle is to use 1pps generated by the BDS receiver to calibrate the local frequency standard. While the 1pps generated by the BDS receiver has some jitter, its long-term stability is good; the local rubidium clock standard has good short-term stability but suffers from frequency drift. Therefore, using 1pps to correct the local frequency reference combines the advantages of both, possessing the good long-term stability of the BDS receiver and the good short-term stability of the local rubidium clock.
[0035] Due to the long signal transmission distance and susceptibility to interference, the 1pps output signal of a BDS receiver exhibits a certain degree of jitter. 1pps contains various error components: satellite clock error, ephemeris error, ionospheric additional delay error, tropospheric additional delay error, multipath error, and receiver inherent errors. Because of this 1pps signal jitter, measures need to be taken to mitigate it. The jitter in the 1pps output signal of a BDS receiver is mostly due to random errors. The presence of these random errors causes jitter at the leading edge of the BDS second pulse signal, reaching a maximum of 100ns, thus causing random jumps in the phase detection error. This module uses a Kalman filtering algorithm to filter out interference and noise in the phase detection error and extract the necessary information.
[0036] The process of BDS taming the rubidium clock is as follows:
[0037] a) Frequency calibration: In this stage, the 1pps signal obtained by the rubidium clock after frequency division begins to track the 1pps of the BDS. At this time, due to the existence of a certain phase difference and the fact that the adjustment control voltage of the rubidium clock has not yet been established, the frequency of the rubidium clock still has a certain deviation. In this stage, the main task is to calibrate the frequency and gradually eliminate the phase difference.
[0038] b) Frequency Locking: After obtaining the frequency difference, an adjustment value is generated based on the frequency control characteristics of the rubidium frequency standard. This adjustment value is used to adjust the local frequency source. Depending on the characteristics of the local frequency source, there are various adjustment methods. When the local rubidium clock is voltage-controlled, or can be adjusted within a small range using voltage, the output adjustment amount is voltage. Typically, a D / A conversion module is used to implement the control voltage. Since the D / A conversion rate requirement is not high, a serial D / A chip is generally sufficient. To reduce costs, some literature proposes obtaining the control voltage by controlling the RC charging time. When the local frequency source is a DDS output, the frequency control word is adjusted according to the adjustment value.
[0039] Once the frequency calibration phase is complete, the rubidium clock frequency is essentially calibrated, maintaining a small difference from the BDS 1pps signal. At this point, the frequency locking phase begins. This phase primarily addresses the deviation in control voltage caused by circuit instability and the frequency drift of the rubidium clock itself. During this phase, because the rubidium clock frequency is calibrated, its output 1pps signal has high stability, while the BDS 1pps signal exhibits some jitter. Therefore, it is necessary to reduce the impact of the BDS 1pps jitter.
[0040] During the frequency locking phase, frequency adjustments are made within a small range. To avoid abrupt phase changes, the frequency adjustment should be performed slowly. During this phase, the control of the BDS 1pps signal should be weakened, and this can be achieved by adjusting the corresponding control parameters, such as the proportional and integral parameters in PI feedback control. After the frequency calibration phase is completed, the rubidium clock's control voltage value remains stable. Changing the proportional-integral coefficient at this point will cause a change in the control voltage; to prevent abrupt changes in the control voltage value, the coefficient changes should be performed gradually. Therefore, there is a parameter adjustment phase between the frequency calibration and frequency locking phases.
[0041] After taming the rubidium atomic frequency standard, BeiDou maintained the short-term stability of the rubidium clock and the relative frequency deviation of the BeiDou system, achieving a relative frequency deviation tamping value better than 1×10⁻⁶. -12 (Under stable conditions, it can reach 5×10) -13 ).
[0042] 2. Frequency Standard Comparison Measurement Module
[0043] The most basic principle of frequency measurement is to compare the signal to be measured with a known standard signal, i.e., a reference signal, to obtain the frequency of the signal being measured. As the frequency accuracy of various frequency standards becomes increasingly higher, the requirements for the resolution of the measurement system also become increasingly stringent.
[0044] like Figure 3 As shown, the present invention employs a dual-mixing time difference method. By introducing a medium frequency standard (or common frequency standard) as a common source, the frequency standard under test and the reference frequency standard are mixed with the medium frequency standard to transform into two beat signals. After passing through a low-pass filter and a zero detector, the signals are fed to a time interval counter to measure the time phase difference between the two signals.
[0045] like Figure 4 As shown, the present invention designs a multi-channel dual-mixing time difference measurement module, including four test channels, a signal generation module, a reference signal channel and a phase difference measurement module. The signal generation module is used to generate a first signal input to each test channel, a second signal input to the reference signal channel and a third signal input to the phase difference measurement module.
[0046] The reference signal channel and each test channel include an isolation module, a mixer, a mixing filter module, a bandpass filter module, a beat frequency amplification module, and a zero-crossing detection module connected in sequence. These modules are used to process the received signal through isolation, mixing, filtering, amplification, and zero-crossing detection before inputting it into the phase difference measurement module.
[0047] The signal generation module includes a control circuit, a frequency selection module, a crystal oscillator module, a frequency multiplier module, and an isolation amplifier module. The crystal oscillator module has an output terminal connected to the frequency selection module. The generated clock signal is processed by the frequency selection module to obtain a first signal or a second signal, which are respectively input to the reference signal channel or the test channel through the isolation amplifier module. The crystal oscillator module also has an output terminal connected to the frequency multiplier module. The generated clock signal is processed by the frequency multiplier module to obtain a third signal.
[0048] The frequency standard comparison and measurement module of this invention enables the measurement of four 5MHz and 10MHz frequency standards, satisfying not only the testing requirements of shipboard timing systems but also the verification and calibration of general frequency standards. By selecting a high-stability crystal oscillator as the common source oscillator for the multi-channel dual-mixer time difference measurement system, and choosing a common source frequency of 9.999990MHz or 4.999995MHz depending on whether the measured signal frequency is 10MHz or 5MHz, the generated beat signal frequency is 10Hz or 5Hz. This ensures a frequency difference amplification factor of 10 regardless of whether the measured frequency is 10MHz or 5MHz. 6 .
[0049] The beat signal frequency is 10Hz or 5Hz. For a 10MHz measurement signal, the sampling time is an integer multiple of 100ms; for a 5MHz signal, the sampling time is an integer multiple of 200ms.
[0050] Furthermore, the basis for selecting the measurement bandwidth is: bandwidth ≥ 5 / τ, where τ is the required sampling time. For example, if the minimum sampling time is 1s, then the bandwidth should be ≥ 5Hz. In this invention, the measurement bandwidth is set to 10Hz to ensure the validity of the measurement results when the sampling time is ≥ 1s. For the four measurement channels, the phase difference between the reference signal and the measured signal at the zero-crossing point is recorded respectively. Due to frequency deviation, the number of zero-crossing points for the reference and the measured signal are different. The periodic ambiguity phenomenon can be resolved by the control circuit, ensuring accurate comparison measurement of the frequency standard over a long period of time.
[0051] This invention's frequency standard comparison and measurement module's frequency conversion circuit can transform a standard frequency standard signal of 5MHz or 10MHz into a 1MHz reference frequency signal, ensuring the stability of the entire system. It employs digital comparison technology, and its mixing and phase detection function is implemented using IQ demodulation, offering a wide operating frequency range unaffected by temperature and high consistency. The bandpass filter uses a narrowband filter implemented via a DSP. Due to the high flexibility of DSP-implemented filters, it can automatically switch the bandwidth of the loop filter. Through Hilbert transform, the reference signal is phase-shifted by 90 degrees to form I and Q signals. Quadrature demodulation of the measured output signal yields the frequency difference and phase difference between the reference signal and the measured signal, which are used as the output of the phase detector module to calculate stability. The frequency multiplier circuit utilizes the characteristics of higher-order frequency multiplication to multiply the frequency of the measured frequency standard signal and the frequency of the reference (standard) frequency standard by N and N-1 times respectively, before mixing them in a mixer. The frequency multiplier circuit is required to have high stability and low noise characteristics.
[0052] After the device of this invention was developed, it was tested and evaluated using a cesium atomic frequency standard device. The test results showed that the relative frequency deviation reached 5E-13 (GNSS locked) and 3E-12 (within 24 hours after the GNSS antenna was disconnected); the frequency stability was 3E-12 / 1s; 2E-12 / 10s; 1E-12 / 100s; 1E-12 / 1d; and the comparison uncertainty of the frequency standard comparison module was 1.8E-13 / 1s; 2.2E-14 / 10s; 3.2E-15 / 100s. Furthermore, using the 5585B cesium clock as the standard and the TR2001 rubidium clock as the test subject, the test results showed that all technical indicators met the requirements of the rubidium clock. The device of this invention has been tested and used in various units such as naval vessels, base sites, and military metrology stations. Practice has proven that the equipment has good applicability, strong measurement and control capabilities, stable and reliable operation, and convenient operation, which greatly saves time and improves the metrological support capabilities and support levels of the time system and frequency standards.
[0053] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.
Claims
1. An in-situ metrological calibration device for a shipborne timing system, characterized in that, include: The programmable switch module has multiple channels for receiving multiple externally input signals under test; The Beidou and crystal oscillator discipline module adopts the method of disciplining the rubidium atomic clock with the Beidou ultra-stable low phase noise crystal oscillator to receive the Beidou second pulse signal remotely transmitted by the Beidou system and generate the rubidium clock signal; The frequency standard comparison and measurement module uses a fully digital algorithm to compare the multiple measured signals with the rubidium clock signals generated by the BeiDou and crystal oscillator discipline modules to obtain the comparison and measurement results. The B-code synchronous frequency accuracy test module is used to receive B codes and perform decoding, synchronization accuracy, and pulse delay time tests. The pulse width and time delay test module is used to receive BeiDou second pulse signals and measure the time interval; The platform processor receives the comparison results from the frequency standard comparison measurement module, as well as the reference information sent by the B code same-frequency accuracy test module, pulse width and time delay test module; The BeiDou and crystal oscillator discipline module includes a BeiDou receiver, a Kalman filter, a phase detector, a digital loop filter, an A / D sampler, a central processing module, a high-precision anti-vibration rubidium clock, a crystal oscillator, a phase-locked loop module, a frequency synthesizer, an isolation distribution amplifier, a frequency divider, and a time isolation module. The Beidou receiver is used to receive the Beidou second pulse signal transmitted remotely by the Beidou system, and the output of the Beidou receiver is connected to a Kalman filter; The high-precision anti-vibration rubidium clock is used to generate a rubidium clock oscillation signal, the crystal oscillator is used to generate a clock signal, and the phase-locked loop module is used to receive the rubidium clock oscillation signal and the clock signal. The phase-locked loop module, frequency synthesizer, isolation distribution amplifier and frequency divider are connected in sequence. The frequency divider is used to output two rubidium clock frequency-divided second pulse signals. One rubidium clock frequency-divided second pulse signal is input to the central processing module after passing through the isolation distribution amplifier, and the other rubidium clock frequency-divided second pulse signal is input to the phase detector. The phase detector is used to simultaneously receive the filtered Beidou second pulse signal and a rubidium clock frequency-divided second pulse signal and perform phase detection processing. The output of the phase detector is connected in sequence to a digital loop filter and an A / D sampler to adjust the frequency and control the phase error of the output signal, obtain the measurement signal and input it into the central processing module. The central processing module is used to calculate the correction value based on the measurement signal and the rubidium clock frequency division second pulse signal, and input it into the frequency synthesizer; The isolation distribution amplifier has multiple rubidium clock signal output terminals.
2. The in-situ metrological calibration device for a shipborne timekeeping system according to claim 1, characterized in that: The frequency standard comparison measurement module multi-channel dual-mixing time difference measurement module includes four test channels, a signal generation module, a reference signal channel and a phase difference measurement module. The signal generation module is used to generate a first signal input to each test channel, a second signal input to the reference signal channel and a third signal input to the phase difference measurement module. The reference signal channel and each test channel include an isolation module, a mixer, a mixing filter module, a bandpass filter module, a beat frequency amplification module, and a zero-crossing detection module connected in sequence. These modules are used to process the received signal through isolation, mixing, filtering, amplification, and zero-crossing detection before inputting it into the phase difference measurement module.
3. The in-situ metrology calibration apparatus for shipboard time system as claimed in claim 2, wherein: The signal generation module includes a control circuit, a frequency selection module, a crystal oscillator module, a frequency multiplier module, and an isolation amplifier module. The crystal oscillator module has an output terminal connected to the frequency selection module. The generated clock signal is processed by the frequency selection module to obtain a first signal or a second signal, which are respectively input to the reference signal channel or the test channel through the isolation amplifier module. The crystal oscillator module also has an output terminal connected to the frequency multiplier module. The generated clock signal is processed by the frequency multiplier module to obtain a third signal.
4. The in-situ metrology calibration apparatus for shipboard time system as claimed in claim 1, wherein: The platform processor is equipped with a monitor, keyboard, and mouse, and is connected to a local area network.