electrical signal
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
that has a width of less than one second and a sharply rising or abruptly falling edge that accurately repeats once per second. PPS signals are output by radio beacons,
frequency standard
A frequency standard is a stable oscillator used for frequency calibration or reference. A frequency standard generates a fundamental frequency with a high degree of accuracy and precision. Harmonics of this fundamental frequency are used to p ...
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
receivers. 'ICD-GPS-060B: GPS User Equipment (Phase III) Interface Control Document for the Pecise Time and Time Interval (PTTI) Interface'', Global Positioning System Joint Program Office, 2002 Precision clocks are sometimes manufactured by interfacing a PPS signal generator to processing equipment that aligns the PPS signal to the UTC second and converts it to a useful display.
Atomic clock
An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwe ...
s usually have an external PPS output, although internally they may operate at 9,192,631,770 Hz. PPS signals have an accuracy ranging from a 12 picoseconds to a few microseconds per second, or 2.0 nanoseconds to a few milliseconds per day based on the resolution and accuracy of the device generating the signal.
Physical representation
PPS signals are usually generated as a TTL signal capable of driving a 1 kilohm load. Some sources use line drivers in order to be capable of driving 50-ohm transmission lines. Because of the broad frequency contents, along the transmission line can have a significant impact on the shape of the PPS signal due to dispersion and after delivery effects of the dielectric of the transmission line. It is common to set t0 at the voltage level of the steepest slope of a PPS signal. PPS signals are therefore notoriously unreliable when time transfer accuracies better than a nanosecond are needed, although the stability of a PPS signal can reach into the picosecond regime depending on the generating device.
Uses
PPS signals are used for precise timekeeping and time measurement. One increasingly common use is in computer timekeeping, including NTP. Because GPS is considered a stratum-0 source, a common use for the PPS signal is to connect it to a PC using a low-latency, low- jitter wire connection and allow a program to synchronize to it. This makes the PC a stratum-1 time source. Note that because the PPS signal does not specify the time, but merely the start of a second, one must combine the PPS functionality with another time source that provides the full date and time in order to ascertain the time both accurately and precisely.
Inter-Range Instrumentation Group The Inter-Range Instrumentation Group (IRIG) is the standards body of the Range Commanders Council (RCC). The group publishes standards through the RCC Secretariat at White Sands Missile Range.
The best known IRIG standard is the IRIG timecode used ...
(IRIG) time codes
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Precise Time and Time Interval Precise Time and Time Interval (PTTI) is a Department of Defense military and Global Positioning System standard which details a mechanism and waveform for distributing highly accurate timing information.Square wave
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Timecode
A timecode (alternatively, time code) is a sequence of numeric codes generated at regular intervals by a timing synchronization system. Timecode is used in video production, show control and other applications which require temporal coordinatio ...