CT Lab Impedo DUO, User Manual

Page: 56 / 119

Impedo DUO User Guide
56
This is only valid when a user resets the instrument, when the
instrument shuts down due to supply reliability the RTC will
continue for longer than 6 month without validating the time
from NTP or GPS.
The Impedo Duo’s built-in real-time clock (RTC) is accurate to 10 ppm, implying that
in the worst case it can drift up to 0.864s per day (or 6s per week, 5 min per 365
days), and support leap year. To prevent time from drifting the Impedo Duo can keep
its time synchronized to 100ns of absolute time using a GPS, or 20ms of server time
using NTP. Time synchronisation is also possible with Osprey Lite but to an accuracy
of 1ms from the PC used for the clock synchronization.
The instrument will perform a gradual time change (time creep) when its time and
that of the time source differs slightly. If the difference is overly large, the time will
be stepped, causing a time jump. A time jump will cause a discontinuity in the data
and a new data segment (cf. Section 5.6.3) will be created.
Time creep will not cause a discontinuity in the recorded data. However, frequency
measurements are not valid and will not be recorded or available via
Realtime View
during time creep. Trend aggregation will take this into account and will only
aggregate frequency values that were valid.
When the time difference between the instrument and the selected time source is
negligible, the instrument is said to be time locked. Time-Master will keep the
instrument time locked as long as the time source is available.
During automatic time source selection, Time-Master will use the following sources
in order of preference when available: GPS, Network time, internal clock. Time-
Master will change from GPS to NTP time if no GPS signal was received for 30
minutes. If the NTP server time and GPS time differs sufficiently, a time jump will
occur. A time jump may also occur if the system switches from one NTP server to
another and the NTP servers had sufficiently different time.
See Section 0 for a
description of Time-Master’s configuration.