Time distribution switch

• US 9,520,860 B2
• Filed: 10/18/2013
• Issued: 12/13/2016
• Est. Priority Date: 10/19/2012
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Whitehead, David E., Achanta, Shankar V., Loehner, Henry
• Primary Examiner(s): Phan, Dao
• Application Number:
  US14/057,803
• Publication Number:
  US 20140111249A1
• Time in Patent Office: 1,152 Days
• Field of Search: 342/357.58, 342/357.63, 342/357.74, 342/374, 327/99
• US Class Current: 1/1
• CPC Class Codes: G01S 19/00 Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
• CPC Class Codes: G06F 1/14 Time supervision arrangements, e.g. real time clock
• CPC Class Codes: H02H 7/261 involving signal transmission between at least two stations transmission of signals in general H02H1/0061
• CPC Class Codes: H02H 7/28 for meshed systems
• CPC Class Codes: H03K 3/01 Details
• CPC Class Codes: H04J 3/0644 External master-clock
• CPC Class Codes: H04J 3/0688 Change of the master or reference, e.g. take-over or failure of the master

Abstract

Systems and methods for detecting the failure of a precision time source using an independent time source are disclosed. Additionally, detecting the failure of a GNSS based precision time source based on a calculated location of a GNSS receiver is disclosed. Moreover, the system may be further configured to distribute a time derived from the precision time source as a precision time reference to time dependent devices. In the event of a failure of the precision time source, the system may be configured to distribute a time derived from a second precision time source as the precision time signal during a holdover period.

Claims

1. A method comprising:

receiving, at a time distribution device, two or more consecutive time signals from a first external time source;

determining a first duration between each of the two or more consecutive time signals from the first external time source, wherein the first duration is based on an internal oscillator;

receiving, at the time distribution device, two or more consecutive time signals from a second external time source;

determining a second duration between each of the two or more consecutive time signals from the second external time source, wherein the second duration is based on the internal oscillator;

comparing the first duration and the second duration to determine a time source with the lowest variation in the duration between the two or more consecutive time signals;

selecting the time source with the lowest variation as a best available time source; and

distributing the best available time source to one or more consuming devices.

2. The method of claim 1, wherein the internal oscillator comprises a high accuracy oscillator.

3. The method of claim 2, wherein the high accuracy oscillator comprises one of:

an oven controlled crystal oscillator (OCXO);

a temperature compensated crystal oscillator (TCXO);

a voltage controlled crystal oscillator (VCXO);

a rubidium oscillator;

or an atomic oscillator.

4. The method of claim 1, wherein the first and second time sources include one or more of:

Inter-Range Instrumentation Group (IRIG) protocol, a global navigation satellite system (GNSS), a National Institute of Science and Technology (NIST) broadcast, an Institute of Electrical and Electronics Engineers (IEEE) 1588 protocol, a network time protocol (NTP), a simple network time protocol (SNTP), or a precision time protocol.

5. A time distribution device comprising:

a plurality of receivers configured to receive consecutive time signals from each of first and second external corresponding precision time sources;

an output configured to provide a precision time signal to an intelligent electronic device (IED), wherein the precision time signal is determined from a best available time source of the first and second external corresponding precision time sources; and

a time quality module configured to;

determine, for the first external precision time source, a first duration between two or more consecutive time signals of the first external precision time source, wherein the first duration is based on an internal oscillator;

determine, for the second external precision time source, a second duration between two or more consecutive time signals of the second external precision time source, wherein the second duration is based on the internal oscillator;

compare the duration between the two or more consecutive time signals for each time source to determine a time source with the lowest variation in the duration between the two or more consecutive time signals; and

select the precision time source with the lowest variation as the best available time source.

6. The time distribution device of claim 5, wherein the internal oscillator comprises a high accuracy oscillator.

7. The time distribution device of claim 6, wherein the high accuracy oscillator comprises one of:

an oven controlled crystal oscillator (OCXO);

a temperature compensated crystal oscillator (TCXO);

a voltage controlled crystal oscillator (VCXO);

a rubidium oscillator;

or an atomic oscillator.

8. The time distribution device of claim 5, wherein the first and second precision time sources include one or more of:

Inter-Range Instrumentation Group (IRIG) protocol, a global navigation satellite system (GNSS), a National Institute of Science and Technology (NIST) broadcast, an Institute of Electrical and Electronics Engineers (IEEE) 1588 protocol, a network time protocol (NTP), a simple network time protocol (SNTP), or a precision time protocol.

9. The time distribution device of claim 5, wherein the time quality module is further configured to:

detect a failure of the selected precision time source; and

determine a backup precision time source for use as the best available time source, wherein the process to determine the best available time source is repeated to determine the backup time source.

10. The time distribution device of claim 9, wherein to detect a failure of the selected precision time source the time quality module is configured to:

train an unlocked oscillator with a time signal from the best available time source;

compare the time signal from the best available time source to a drift rate of the unlocked oscillator; and

detect a failure of the best available time source in response to the comparing showing that the time signal from the best available time source varies from the drift rate of the unlocked oscillator by a defined margin.

11. The time distribution device of claim 9, wherein the time quality module is further configured to indicate a failure condition in response to detecting a failure of the best available time source.

12. The time distribution device of claim 9, wherein to detect a failure of the selected precision time source the time quality module is configured to:

receive a location based on a plurality of Global Navigational Satellite System (GNSS) signals received at the time distribution device;

compare the received location with a known location of the time distribution device; and

detect a failure of the best available time source in response to the received location and the known location differing by a defined margin.

13. The time distribution device of claim 12, wherein the known location is calculated using the plurality of GNSS signals.

14. The time distribution device of claim 12, wherein the known location is entered into the time distribution device at setup.

15. A non-transitory computer readable storage medium having instructions stored thereon, which when executed by a processor, cause the processor to perform a method for determining a best available time source, the method comprising:

receiving, at a time distribution device, two or more consecutive time signals from a first external time source;

determining, for the first external time source, a first duration between each of the two or more consecutive time signals, wherein the first duration is based on an internal oscillator;

receiving, at the time distribution device, two or more consecutive time signals from a second external time source;

determining, for the second external time source, a second duration between each of the two or more consecutive time signals, wherein the second duration is based on the internal oscillator;

comparing the first duration and the second duration for each time source to determine a time source with the lowest variation in the duration between the two or more consecutive time signals; and

selecting the time source with the lowest variation as the best available time source.

16. The non-transitory computer readable storage medium of claim 15, wherein the internal oscillator comprises a high accuracy oscillator.

17. The non-transitory computer readable storage medium of claim 16, wherein the high accuracy oscillator comprises one of:

an oven controlled crystal oscillator (OCXO);

a temperature compensated crystal oscillator (TCXO);

a voltage controlled crystal oscillator (VCXO);

a rubidium oscillator;

or an atomic oscillator.

18. The non-transitory computer readable storage medium of claim 15, wherein the first and second precision time sources include one or more of:

Inter-Range Instrumentation Group (IRIG) protocol, a global navigation satellite system (GNSS), a National Institute of Science and Technology (NIST) broadcast, an Institute of Electrical and Electronics Engineers (IEEE) 1588 protocol, a network time protocol (NTP), a simple network time protocol (SNTP), or a precision time protocol.

19. The non-transitory computer readable storage medium of claim 15, wherein the method further comprises distributing the best available time source to one or more consuming devices.

20. The non-transitory computer readable storage medium of claim 15, wherein the method further comprises:

detecting a failure of the selected time source; and

determining a backup time source for use as the best available time source, wherein the method for determining the best available time source is repeated to determine the backup time source.