A method for synchronizing a master clock and a remote slave clock which nominally has the same pulse frequency but may be out of time-phase comprising transmitting a master pulse to the slave, measuring the time delay, Δτ, between the received pulse and the nearest succeeding (in time) slave pulse, delaying the latter slave pulse by Δτ to provide a conjugate slave pulse, transmitting the conjugate pulse to the master station and measuring the time difference Δ between time of reception of the conjugate pulse and time of generation of the original master pulse. The time Δ is equal to twice the error between the master and slave pulses. The process can also be done at the slave station if the slave pulse is transmitted to the master and a conjugate-phase master pulse is retransmitted to the slave where the measurement is accomplished. The phase of the slave pulse can then be adjusted by Δ/2 to synchronize it with the master pulse.

Conjugate-phase, remote-clock synchronizer

A system for synchronizing a first clock and a second clock includes a receiver associated with the first clock, configured to receive a remote pulse from the second clock The remote pulse has a pulse repetition frequency and spectral characteristics that are known to the local clock The system also includes a local pulse emitter configured to create a local pulse at the first clock, and optics configured to align the local pulse and the remote pulse The system further includes an interferometer configured to create an interference pattern between the local pulse and the remote pulse A controller is provided that is configured to calculate a time delay between the first clock and the second clock based on the interference pattern between the local pulse and the remote pulse

Synchronization of remote clocks

System for measuring the time difference between a master clock and a slave clock located respectively in two remote stations and synchronizing these clocks. It comprises, in the master clock station, a time base generator controlled by the master clock, a source of light, an electro-optical detector, control means depending upon the time base generator for switching on the light source and control means depending upon the electro-optical detector for switching off the light source. The slave clock station comprises a time base generator controlled by the slave clock, an electro-optical detector detecting light from the master clock station, a chronometer switched on by the time base generator and switched off by the electro-optical detector and another chronometer switched on and off respectively by the first and second output signal of the electro-optical detector. Means are provided in the slave clock station for partially receiving and partially reflecting the light to the electro-optical detector at the master clock station causing the light source to produce a luminous signal whose start and end are split by a duration equal to twice the light propagation round trip time between the two stations.

System for measuring time differences between remote clocks and for synchronizing the same

Methods and systems for synchronizing clocks used in underwater devices is described. All clocks have some drift due to frequency accuracy and this disclosure provides a method for periodically synchronizing clocks to an accurate master clock to remove long term drift. A synchronization device can use an accurate clock and hardware to transmit both a sound wave and light pulse at the same point in time. Remote slave clocks can detect the light first, and later the sound, allowing them to calculate the distance the pulse had to travel. The clocks can then synchronize their time to the master clock canceling out any drift. The synchronization device can be packaged in a waterproof housing and can be moved around on a periodic basis between the clock on an underwater robot or any other means.

Method and apparatus for synchronizing clocks underwater using light and sound

A method and apparatus for adjusting the frequency of a piezoelectric crystal oscillator. The effective frequency of the oscillator is adjusted (trimmed) by periodically inhibiting pulses to the divider stage. The pulse inhibit circuit includes a nonvolatile programmable read-only-memory (ROM) to store binary complement information corresponding to the number of oscillator pulses to be suppressed. A counter is periodically preset with the binary complement information and the count advances in response to oscillator pulses. The difference count between the complement number and the counter's maximum count controls the number of pulses periodically suppressed.

Digital frequency trimmed electronic timepiece

System for measuring the time difference between a master precision clock and a slave precision clock situated respectively in a master and a slave station remote from each other. The clocks generate timing pulses with respective frequencies very close to each other. The master station includes a laser source of light pulses generating luminous pulse signals, a local detector of these signals and means for transmitting them towards the slave station. The slave station includes a detector of the luminous pulse signals and means for reflecting the same towards said master station. Two chronometers in the master station measure the time difference between the instant of generation of a luminous pulse signal and a master clock timing pulse and the time difference between the instant of generation of a luminous pulse signal and the instant of detection of a reflected back luminous pulse signal and a third chronometer in the slave station measures the time difference between the instant of detection of a luminous pulse signal and a slave clock timing pulse.

J Boillot

Papers

System for measuring time difference between and synchronizing precision clocks