GPS-Disciplined Distributed Clock for Cable-Free Instrument Synchronization
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Solution Overview
Problem
Traditional methods for synchronizing data from spatially distributed sensor networks are hindered by the need for multiple cables, which can cause signal attenuation and reflections, and are prone to clock drift due to equipment and environmental constraints.
Innovation Solution
A Distributed Clock System (DCS) utilizing GPS time-based synchronization, where each DCS unit includes a single-board computer and a GPS receiver, generating a high-precision time-base that is unaffected by physical distance, and transmitting triggering signals to sampling devices to synchronize data acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple cables are run from a single function generator to each instrument, then synchronization can be achieved, but signal attenuation and reflections occur due to transmission line effects
Solution Approach 1:
The system divides the synchronization function into multiple independent DCS units distributed across the network. Each unit generates its own TTL signal locally rather than distributing a single master signal through cables, eliminating transmission line effects while maintaining synchronization through GPS-disc disciplined clocks
Solution Approach 2:
The invention introduces GPS satellite signals as an intermediary time reference that indirectly synchronizes all DCS units. Instead of directly connecting units via cables, each unit independently receives GPS timing signals and adjusts its local clock, eliminating the need for physical signal transmission between units
2Length of stationary object
If long cables are used to connect distributed sensors, then physical distance constraints are overcome, but cable length differences cause differences of arrival time and impact clock signal integrity
Solution Approach 1:
The invention replaces the mechanical/electrical cable-based synchronization system with a wireless GPS signal-based time distribution system. GPS radio waves propagate at the speed of light with minimal attenuation, eliminating cable length-related arrival time differences and signal integrity issues
3Adaptability or versatility
If independent TTL signal generation devices are used at each location, then equipment setup flexibility is improved, but clock drift occurs as sampling duration increases
Solution Approach 1:
The DCS units implement feedback control by continuously comparing their local clock time against GPS satellite time and adjusting their clock frequency accordingly. This closed-loop timekeeping mechanism eliminates clock drift while preserving the flexibility of distributed independent units
Solution Approach 2:
The system changes the operating parameter of the clock from free-running to GPS-disciplined, where the clock frequency is continuously adjusted based on GPS time reference. This parameter change maintains the independence and flexibility of distributed units while ensuring long-term clock stability
4Area of stationary object
If spatial distribution between sensors is increased, then coverage area is expanded, but sources of error such as cable length differences and signal attenuation increase
Solution Approach 1:
GPS satellite signals serve as a common intermediary time reference that reaches all distributed DCS units simultaneously. This eliminates the need for physical signal distribution cables and removes the relationship between spatial distribution and synchronization error
Solution Approach 2:
The GPS satellite system provides universal time synchronization service to all DCS units regardless of their spatial distribution. Each unit independently receives and processes the same GPS time signals, enabling scalable deployment without compromising synchronization reliability
Data Source
AI summary
A method for a distributed clock system (DCS) device that includes receiving a GPS signal, determining that a first current time equals a predetermined start time, and generating a shifted GPS signal by applying a configurable delay to the received GPS signal, the shifted GPS signal alternating between a low value and a high value. The method includes responsive to a falling edge of the shifted GPS signal, generating an ARM signal having a rising edge after a falling edge of the shifted GPS signal, and responsive to the ARM signal being high and the shifted GPS signal being high, generating an output enable signal. The method includes transmitting, while the output enable signal is high, a triggering signal, the triggering signal having one or more synchronizing pulses that cause one or more sampling devices to sample data according to the frequency associated with the raw clock signal.