Glossary

NI CompactRIO Device Drivers Help

Edition Date: December 2017

Part Number: 373197L-01

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Clear view of the sky There is no strict definition for a clear view of the sky, but a suitable guideline is that the GPS antenna should have a clear line of sight to the sky in all directions (360°) down to an imaginary line making a 30° angle with the ground. Locations far from trees and tall buildings that could block or reflect GPS satellite signals are best.
GPS Global Positioning System
Leap second A one-second adjustment to UTC (with respect to TAI) with the intent of keeping the UTC timescale close to mean solar time. Leap seconds can be added or subtracted, though to date, they have only been added. The occurrence of leap seconds is not regular; they are announced up to 6 months prior to the occurrence, and they can only occur at 23:59:59 UTC on 30/June or 31/December.
Location fix Computation of latitude, longitude, and altitude of a location based on the signals received from GPS satellites.
PPS Pulse per second
Self-survey Method used by the GPS module to determine its precise geographic location. During the self-survey period, the GPS module acquires a new location fix every second. At the end of the self-survey period, all location fixes are averaged to obtain a more precise estimate of the current location.
TAI International Atomic Time (TAI, from the French name Temps Atomique International). Timescale based on atomic clocks distributed around the world, and thus not adjusted by leap seconds. The reference for TAI is 1/Jan/1970 00:00:00.
UTC Coordinated Universal Time. Time used in most civilian clocks, based on TAI and adjusted with leap seconds.

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