US 6,236,623 B1 · System and method for synchronizing clocks in a plurality of devices across a communication channel

Abstract

A system and method is disclosed for synchronizing clocks in a plurality of devices connected by a communication channel. A master control device is coupled to one or more slave control devices, e.g., event recorders, across a communication channel. Preferably, the communication channel is implemented according to an RS-485 interface. By periodically interrogating and monitoring the responses of each of the slave control devices, the master control device determines the transit time, i.e., communication, delays to each of the slave control devices. Operating in conjunction with this data, the master control device can then interpret and/or adjust any event times reported by the event recorders to improve the relative time accuracy of the event recorders as compared to a time maintained by the master control device. Consequently, the control system can achieve a relative time synchronization accuracy between the master and slave times to within 100 microseconds and preferably 100 nanoseconds or less.

Claims39

Dependent claims

A system for synchronizing clocks in a plurality of slave control device interconnected via a communication channel, said system comprising:

a master control device comprising:
master clock circuitry for maintaining an essentially fixed frequency output and a master time;
a communication controller for periodically sending an interrogation signal to each of said slave control devices and receiving an acknowledgment signal from each of said slave control devices in response thereto, each said acknowledgment signal characterized by a time delay corresponding to each said slave control device;
and
an offset register for storing one or more time delay values corresponding to each said slave control device, said offset register storing said one or more time delay values between periodic interrogations of said slave control devices;
at least one slave control device comprising:
clock circuitry for maintaining a slave time;
a communication controller for receiving said interrogation signal and sending said acknowledgment signal in response thereto;
and
an event controller for operating in association with said slave clock circuitry;
and
a communication channel for providing a bidirectional communication path between said master control device and each of said slave control devices for sending and receiving said interrogation and said acknowledgment signals wherein said slave communication controller is additionally responsive to a synchronization signal sent from said master control device across said communication channel, used in conjunction with an associated time delay value in said offset register, to cause said slave time to essentially synchronize with said master time.

9 more elements

A method of synchronizing clocks in a plurality of slave control devices interconnected via a communication channel to a master control device, said method comprising the steps of:

periodically sending an interrogation message from said master control device to each of said slave control devices;
sending an acknowledgment message from said slave control devices to said master control device upon receipt of said interrogation message;
determining a time delay corresponding to each of said slave control devices;
storing a value corresponding to each of said time delays in said master control device;
periodically sending a master time globally to said slave control devices;
receiving said master time in each of said slave control devices;
and
said slave control devices setting a slave time in accordance with said received master time.

5 more elements

A method of synchronizing clocks in a plurality of slave control devices interconnected via a communication channel to a master control device, said method comprising the steps of:

periodically sending an interrogation message from said master control device to each of said slave control devices;
sending an acknowledgment message from said slave control devices to said master control device upon receipt of said interrogation message;
determining a time delay for each of said slave control devices;
sending a value corresponding to said time delay to its associated slave control device;
storing said corresponding time delay value in said associated slave control device;
periodically sending a master time globally to said slave control devices;
receiving said master time in each of said slave control devices;
and
said slave control devices setting a slave time in accordance with said received master time.

6 more elements

A method of synchronizing clocks in a plurality of slave control devices interconnected via a communication channel to a master control device, said method comprising the steps of:

periodically sending an interrogation message from said master control device to each of said slave control devices;
sending an acknowledgment message from said slave control devices to said master control device upon receipt of said interrogation message;
determining a time delay corresponding to each of said slave control devices;
storing a value corresponding to each of said time delays in said master control device;
periodically sending a master time adjusted by a corresponding time delay value of each slave control device to each of said slave control devices;
receiving said master time adjusted by said corresponding time delay value in each of said slave control devices;
and
said slave control devices setting a slave time in accordance with said received adjusted master time.

5 more elements

A system for synchronizing clocks in a plurality of slave control device interconnected via a communication channel, said system comprising:

a master control device comprising:
master clock circuitry for maintaining an essentially fixed frequency output and a master time;
a communication controller for periodically sending an interrogation signal to each of said slave control devices and receiving an acknowledgment signal from each of said slave control devices in response thereto, each said acknowledgment signal characterized by a time delay corresponding to each said slave control device;
and
an offset register for storing one or more time delay values corresponding to each said slave control device;
at least one slave control device comprising:
clock circuitry for maintaining a slave time;
a communication controller receiving said interrogation signal and sending said acknowledgment signal in response thereto;
two or more slave time registers operational in setting a slave time and alternately operational to receive signals corresponding to said master time;
and
an event controller operating in association with said slave clock circuitry;
and
a communication channel for providing a bidirectional communication path between said master control device and each of said slave control devices for sending and receiving said interrogation and said acknowledgment signals wherein said slave communication controller is additionally responsive to a synchronization signal sent from said master control device across said communication channel, used in conjunction with an associated time delay value in said offset register, to cause said slave time to essentially synchronize with said master time.

10 more elements

Dependencies are inferred from the claim text.

System and method for synchronizing clocks in a plurality of devices across a communication channel

Life of this patent

System and method for synchronizing clocks in a plurality of devices across a communication channel

Life of this patent

Abstract

Claims39