Clock Synchronization for Downhole Logging Phase Measurement
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Solution Overview
Problem
Existing downhole logging tools face challenges in accurately measuring the phase of signals when transmitter and receiver circuits use separate clocks, leading to clock synchronization and drift issues, which affect the precision of formation property measurements during drilling operations.
Innovation Solution
A method is introduced to determine the phase of a signal by calculating a correction factor based on the discrepancy between separate clocks, using a measured time of arrival and a drift factor, allowing for either absolute synchronization or independent clock operation, and a disciplined clock system is implemented with an update subsystem and synthesis subsystem to synchronize clocks accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If separate clocks are used in transmitter and receiver circuits, then device complexity is reduced and ease of manufacture is improved, but measurement precision deteriorates due to clock synchronization errors
Solution Approach 1:
A synchronization signal is introduced as an intermediary element between the transmitter and receiver. This signal carries timing information that allows the receiver to adjust its clock phase relative to the transmitter clock, thereby maintaining measurement precision without requiring the clocks to be physically synchronized or manufactured with identical frequencies.
Solution Approach 2:
The system implements feedback by continuously monitoring the phase difference between transmitted and received synchronization signals. The receiver uses this feedback information to dynamically adjust its clock phase, compensating for frequency offsets and drift, thus maintaining accurate phase measurements despite using separate, independently manufactured clocks.
2Measurement precision
If clock synchronization is implemented, then measurement precision is improved, but device complexity increases due to additional synchronization circuitry
Solution Approach 1:
Instead of continuous complex synchronization, the system uses periodic synchronization signals transmitted at regular intervals. These discrete timing markers provide sufficient information for phase correction without requiring continuous synchronization circuitry, thereby limiting the increase in device complexity to only the necessary periodic signal generation and processing components.
3Measurement precision
If clock drift is compensated using correction factors, then measurement precision is improved, but calculation complexity increases
Solution Approach 1:
The system performs preliminary action by pre-calculating and storing correction factors based on expected clock drift characteristics. These pre-computed correction values are applied during phase measurement without requiring complex real-time calculations, thus improving measurement precision while minimizing the increase in computational complexity through the use of lookup tables or pre-characterized drift models.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise phase measurement and clock synchronization, improving the accuracy of formation property determination and reducing errors caused by clock discrepancies, thereby enhancing the effectiveness of downhole logging tools during drilling.
Implementation Method 1
Electromagnetic (EM) wave propagation in a medium is characterized by the magnetic permeability of the medium (μ) and the complex dielectric permittivity (∈*)
Implementation Method 2
if the phase of the received signal is also measured, one can additionally solve for the real and imaginary part of the complex permittivity
Implementation Method 3
The phase is determined using a measured time of arrival of the signal, the determined discrepancy, and the determined correction factor
Data Source
AI summary
The present disclosure relates to a method to determine a clock signal when separate clocks are used. In one embodiment, a disciplined clock system comprising an update subsystem and a synthesis subsystem is provided. A first clock phase estimate is provided to the update subsystem and used, along with the update subsystem, to determine a frequency offset estimate and a phase offset estimate. The clock signal is determining using the frequency offset estimate, the phase offset estimate, and the synthesis subsystem. Alternatively, two clocks can be synchronized by generating a signal associated with a first clock; modulating the signal; transmitting the modulated signal; receiving the modulated signal by a receiver associated with a second clock; correlating the received signal; determining the time of arrival of the received signal; determining the time difference between the two clocks; and synchronizing the two clocks.