# US 10,122,487 B2 · Time distribution switch

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- Number: US 10,122,487 B2
- Document ID: US10122487B2
- Status: Granted
- Kind: B2
- Application number: 15/349,526
- Filed: 2016-11-11
- Published: 2017-03-02
- Granted: 2018-11-06
- Earliest claimed: 2012-10-19
- Assignees: Schweitzer Engineering Laboratories, Inc.
- Applicants: Schweitzer Engineering Laboratories, Inc.
- Inventors: David E. Whitehead; Shankar V. Achanta; Henry Loehner
- Web page: https://patentgrep.com/patent/US10122487B2

## CPC

- H04J 3/0688: {Change of the master or reference, e.g. take-over or failure of the master}
- G06F 1/14: Time supervision arrangements, e.g. real time clock
- H03K 3/01: Details
- H04J 3/0644: {External master-clock}
- G01S 19/00: Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- H02H 7/261: {involving signal transmission between at least two stations (transmission of signals in general H02H1/0061)}
- H02H 7/28: for meshed systems
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H)

## 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

### Claim 1

A time distribution device comprising: a receiver configured to receive periodic time signals from each of first and second external 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 time sources; a memory; and a processor operatively coupled to the memory, wherein the processor is configured to execute instructions stored on the memory to cause the processor to: determine, for the first external time source, a first variation of duration between the periodic time signals from the first external time source, the first variation in duration based on a local oscillator; determine, for the second external time source, a second variation of duration between the periodic time signals from the second external time source, the second variation in duration based on the local oscillator; compare the first time source and the second time source with the lowest variation.

### Claim 2 (depends on 1)

The time distribution device of claim 1, wherein the local oscillator comprises an internal oscillator.

### Claim 3 (depends on 1)

The time distribution device of claim 1, wherein the processor is configured to execute instructions stored on the memory to cause the processor 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.

### Claim 4 (depends on 3)

The time distribution device of claim 3, wherein to detect a failure of the selected precision time source, the processor is configured to execute instructions stored on the memory to cause the processor 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.

### Claim 5 (depends on 1)

The time distribution device of claim 1, wherein the first and second external 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.

### Claim 6

A method comprising: receiving, at a time distribution device, periodic time signals from each of a first external time source and a second external time source; determining, for the first external time source, a first variation of duration between the periodic time signals from the first external time source, the first variation in duration based on a local oscillator; determining, for the second external time source, a second variation of duration between the periodic time signals from the second external time source, the second variation in duration based on the local oscillator; comparing the first variation and the second variation; selecting a best available time source as one of the first time source and the second time source with the lowest variation; and distributing the best available time source to one or more consuming devices.

### Claim 7 (depends on 6)

The method of claim 6, wherein the local oscillator comprises an internal oscillator.

### Claim 8 (depends on 6)

The method of claim 6, further comprising the steps of: detecting a failure of the best available time source; and, determining 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.

### Claim 9 (depends on 6)

The method of claim 6, wherein the first external time source and the second external time source 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.

### Claim 10

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, periodic time signals from each of a first external time source and a second external time source; determining, for the first external time source, a first variation of duration between the periodic time signals from the first external time source, the first variation in duration based on a local oscillator; determining, for the second external time source, a second variation of duration between the periodic time signals from the second external time source, the second variation in duration based on the local oscillator; comparing the first variation and the second variation; selecting a best available time source as one of the first time source and the second time source with the lowest variation; and distributing the best available time source to one or more consuming devices.

### Claim 11 (depends on 10)

The non-transitory computer-readable storage medium of claim 10, wherein the local oscillator comprises a high-accuracy oscillator.

### Claim 12 (depends on 10)

The non-transitory computer-readable storage medium of claim 10, wherein the first and second external 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.

### Claim 13 (depends on 10)

The non-transitory computer readable storage medium of claim 10, 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.