Many GPS devices use the NMEA protocol, which has been adopted as a standard protocol for GPS devices. The NMEA protocol is ideal for providing continuous positioning information along with a timestamp indicating when information was generated. However, often NMEA timing sentences are not generated at times consistent with the supplied timestamp. This basically means that it is difficult to obtain an accurate consistent time from an NMEA GPS device.
Many NMEA GPS devices therefore only provide an accuracy of about +/- 1 second, which is just not accurate enough for network timing purposes.
Many GPS devices also provide a pulse per second (PPS) output to provide an accurate timing reference. However, the NMEA GPS timing sentence is not synchronised to the pulse output providing poor accuracy. The pulse output is provided at a TTL (5V) signal level rather than a RS232 level that can be recognized by PC equipment. This makes it hard to integrate the GPS device with a computer system.
TimeTools T1000 and T2000 GPS Clock devices utilise an accurate GPS timing receiver with a binary protocol synchronised with a highly accurate timing pulse. This allows for a much more stable and highly accurate timing solution to be implemented.
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