Dual source real time clock synchronization system and method
First Claim
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1. A method of synchronizing an endpoint device adapted for radio frequency (RF) communications in an automatic meter reading (AMR) system, the method comprising the steps of:
- counting elapsed time from a system timestamp by a first clock through a plurality of count cycles having a fixed count value;
counting elapsed time by a second clock through a subsequent count cycle having a fixed count value, wherein an accuracy of the second clock is higher than an accuracy of the first clock;
determining an overflow count and an offset count based on a maximum count value of the second clock, wherein the maximum count value resets when reached and the overflow count equals the number of times the maximum count value of the second clock has been reached and the offset count equals number of counts reached after the last maximum count value;
calculating a calculated count value of a final count cycle from the offset count;
compensating for a synchronization error of the first clock by adjusting the final count cycle from a nominal default count value to the calculated count value; and
using the first clock as compensated for the synchronization error as a source of clocking signals for the endpoint device in the AMR system.
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Abstract
A dual source real time clock (RTC) synchronization system and method for implementation within automatic meter reading (AMR) systems that provide system-wide device time synchronization. In one embodiment, a microcontroller-implemented RTC counts elapsed seconds from a pre-determined system timestamp using a low-speed, low-accuracy crystal. A second source is used to compensate for the low-speed, low-accuracy crystal. This second source comprises a high speed clock in one embodiment. This dual source RTC system can synchronize the endpoint device.
51 Citations
21 Claims
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1. A method of synchronizing an endpoint device adapted for radio frequency (RF) communications in an automatic meter reading (AMR) system, the method comprising the steps of:
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counting elapsed time from a system timestamp by a first clock through a plurality of count cycles having a fixed count value; counting elapsed time by a second clock through a subsequent count cycle having a fixed count value, wherein an accuracy of the second clock is higher than an accuracy of the first clock; determining an overflow count and an offset count based on a maximum count value of the second clock, wherein the maximum count value resets when reached and the overflow count equals the number of times the maximum count value of the second clock has been reached and the offset count equals number of counts reached after the last maximum count value; calculating a calculated count value of a final count cycle from the offset count; compensating for a synchronization error of the first clock by adjusting the final count cycle from a nominal default count value to the calculated count value; and using the first clock as compensated for the synchronization error as a source of clocking signals for the endpoint device in the AMR system. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A utility meter endpoint device adapted for a radio frequency (RF) communication automatic meter reading (AMR) system, the utility meter endpoint device comprising:
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a communications unit operatively coupled to a utility meter and comprising communications circuitry adapted for periodic RF communications with a reader; and a microcontroller comprising a real time clock (RTC) and a counter and electrically coupled to a power source and the communications circuitry, the RTC comprising a first oscillator and the counter comprising a second oscillator, the second oscillator having a higher accuracy than the first oscillator, wherein the microcontroller is operable to calculate an adjustable final count cycle based on the counter and the second oscillator after a plurality of fixed count cycles during a periodic RF communication and use the calculated adjustable final count cycle to compensate the RTC to maintain synchronization at an accuracy better than an accuracy of the first oscillator. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
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16. A synchronization system for an endpoint device adapted for radio frequency (RF) communications in an automatic meter reading (AMR) system, the synchronization system comprising:
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a microcontroller; a first oscillator in operable communication with the microcontroller; and a second oscillator in operable communication with the microcontroller, the second oscillator wirelessly synchronizable with an external reference time signal and having a higher speed and a higher accuracy than the first oscillator, wherein the microcontroller operably determines an offset count value of the second oscillator during a fixed count cycle and synchronizes the first oscillator to the second oscillator during an RF communication by calculating an adjustable final count cycle from the offset count value. - View Dependent Claims (17, 18, 19, 20, 21)
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Specification