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Apulse per second (PPS or1PPS) is anelectrical signal that has a width of less than one second and a sharply rising or abruptly falling edge thataccurately repeats once persecond. PPS signals are output by radio beacons,frequency standards, other types of precisionoscillators and someGPS receivers.[1][2] Precision clocks are sometimes manufactured by interfacing a PPS signal generator to processing equipment that aligns the PPS signal to theUTC second and converts it to a useful display.Atomic clocks usually have an external PPS output, although internally they may operate at9,192,631,770 Hz.[3] PPS signals have an accuracy ranging from 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.
PPS signals are usually generated as aTTL signal capable of driving a 1-kiloohm load. Some sources use line drivers in order to be capable of driving 50-ohmtransmission 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.
PPS signals are used for precise timekeeping and time measurement. One increasingly common use is in computer timekeeping, includingNTP. Because GPS is considered astratum-0 source, a common use for the PPS signal is to connect it to a PC using a low-latency, low-jitter wireconnection 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.
Sites that describe how to use the PPS signal to set precise time on a PC: