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PTP (IEEE 1588) provides sub-millisecond precision time synchronization over an Ethernet network. The first Cyber Sciences products to use PTP are the CyTime SER-3200/2408 Event Recorders.
One CyTime SER can serve as PTP master to sync all other SERs as PTP slaves. The first SER can get its own GPS time reference via IRIG-B or DCF77, or even NTP or Modbus TCP. In turn, an SER can output a legacy protocol to sync other devices which do not yet support PTP.
Precision Time Protocol (PTP) per IEEE 1588
Precision Time Protocol (PTP) per IEEE 1588 enables highly precise time synchronization over an Ethernet network, due primarily to time-stamping embedded in the 1588 Ethernet hardware. Most power industry papers have focused on the Power Profile and PTP’s potential to achieve microsecond accuracy in electric utility substation automation applications. However, the resulting cost and complexity are unnecessary for most commercial/industrial power system applications, where 1-µs is not needed.
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Tech Notes (White Papers)
IEEE Std 1588 defines the Precision Time Protocol (PTP) with a goal of achieving very high precision for time-synchronization over a packet-based network such as Ethernet. PTP takes advantage of special Ethernet hardware for precise time-stamping of the Ethernet frame send and receive times. In addition, PTP includes a very precise mechanism to correct for delays introduced in the network path from the master clock (time reference), through multiple levels of switches, to the slave clocks (time consumers).
The most important innovation of IEEE 1588 is the introduction of hardware-assisted time stamping embedded in the PTP messages using special 1588-compliant Ethernet hardware. Time-stamping is achieved within the IEEE-1588 Ethernet physical interface (PHY) itself. In this way, there is no loss of accuracy between the time-stamp as it is sent or received and the application layer (special 1588 code). The standard does allow a “software-only” PTP implementation, but without hardware-assisted time-stamping, the achievable accuracies are equivalent to those already possible with NTP/SNTP.
The Simple PTP Profile (SPTP)
CyTime SER-3200/2408 Event Recorders use a "Simple PTP" Profile (dubbed "SPTP") optimized for commercial/industrial power system applications (including data centers, hospitals and microgrids). SPTP is intended to achieve time sync over Ethernet with accuracy of at least 100 µs, taking advantage of the same Ethernet network infrastructure used for power monitoring—without requiring special PTP-compliant Ethernet switches (transparent clocks). There is no need for special prioritization of PTP packets in managed switches, nor any constraints on network topology.
To accomplish time synchronization, SPTP uses the PTP delay request-response mechanism (also called End-to-End). Other simplifications include using UTC as its timescale (instead of TAI) and longer message intervals (e.g., updates every 32s) to minimize network traffic. Though the Simple PTP Profile is proposed by Cyber Sciences, it is not proprietary; SPTP is based on the IEEE 1588 Default Profile defined in its Annex J. Therefore, devices using SPTP are interoperable with others set to use this profile.
SPTP: Hi-Res Time-Sync over Ethernet—This Changes Everything
Electrical Power Monitoring Systems (EPMS) for commercial/industrial power systems have improved dramatically over the past 25 years. Modern EPMS have capabilities unimaginable in 1990. The only aspect that has not kept pace is the treatment of one of its essential elements: time. Incredibly, million-dollar systems and single-meter systems still rely on timestamps to the nearest second. SPTP eliminates the cost barriers that may have prevented power system engineers from obtaining the benefits of 1-ms precision: root-cause analysis, breaker opening time measurement, verifying automatic controls timing, arc-flash calculations and time-current coordination to name a few. Don't settle for EPMS circa-1990s. This is power monitoring at the speed of NOW.