Pulse per second
A pulse per second (PPS, or 1PPS) (also known as Pulse per Second ) is an electrical signal that lasts less than a second, has a sharp rising or falling edge, and which repeats itself precisely once per second. PPS signals are provided by radio beacons, frequency standards, or other types of precision oscillators and some GPS receivers. Precision clocks are sometimes manufactured in such a way that they generate a PPS signal and pass it to a processing unit, where the PPS signal is adjusted to the UTC second and converted into a format usable for the display unit. Atomic clocks typically have an external PPS output, although they could work internally at a different frequency (eg with 9,192,631,770 Hz. Cesium - atomic clocks (see definition of a second )).
commitment
PPS signals are used for precise timing. An increasingly widespread application is computer-aided time recording, taking into account the Network Time Protocol (NTP).
Because GPS is assumed to be a stratum 0 source , a common application is to connect the PPS signal to the PC using a low latency, low jitter connection that allows the program to synchronize over it. This turns the PC into a stratum 1 time source, which z. B. can be used in a local network (LAN) set up as an island system. However, such a local time source can also be very useful in globally connected networks, since for time references obtained via the global network, the quality problems due to the sometimes large distances and, above all, the variations due to the IP packet switching usually lead to a The quality of the time reference generated in this way lags behind the previously mentioned method. Only special networks (e.g. for scientific purposes, e.g. with glass fibers and special reinforcements) exceed the possibilities of PPS again. It should be noted that - because the PPS signal does not define the time, but it does define the start of the second - the PPS function must be combined with another time source that provides the full date and time. In this way, the time can be determined both accurately and precisely. Common GPS receivers typically provide not only a PPS signal but also the option of providing time and date information suitable for comparison at another output, for example via NMEA protocol or via manufacturer-specific extensions. Likewise, benchmarks such as pulse width or the relevant edge of the PPS signals offered on the outputs of the device can often be configured using control commands. There are also models that provide status information about the current accuracy and operating data (e.g. the feedback voltage and the current drift for an interposed PLL stage, e.g. due to changing temperature conditions) of the PPS signal.
See also
Web links
- RFC 2783 . - Pulse-Per-Second API for UNIX-like Operating Systems, Version 1.0 . March 2000. (English).
Individual evidence
- ↑ Optical atomic clocks - connected over a great distance for the first time , interview with Deutschlandfunk from August 22, 2016.