Electrex X3M, Руководство пользователя

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10.6.4 Clock / Calendar
X3M contains a clock/calendar with supporting the timezones and the transitions rules for automatic
Daylight Saving Time and Standard Time change.
The following conventional denominations are used:
−
Coordinated Universal Time
(UTC), formerly known as GMT (
Greenwich Mean Time
): this is
independent from the geographic location (hence “universal”);
−
Standard Time (ST)
: this is the local time to a given timezone, based on sun cycles (“solar
time”);
−
Daylight Saving Time (DST)
: it is the local time to a given timezone when an offset (
DST
offset) is applied to ST. This offset is usually applied (by local laws and regulations) to
increase the daylight hours during summer season.
−
Wall time
: this is the current clock time: it matches either ST or DST depending on the period
of the year.
The difference between ST and UTC is called
GMT offset.
Summarizing:
GMT offset = Standard Time – UTC
Wall Time = Standard Time + DST offset = UTC + GMT DST offset
The instrument RTC (Real Time Clock) maintains the following time information:
−
UTC Date/Time;
−
Timezone ID;
The X3M, in this way, uses its internal UTC timing to compute the local time (
Wall Time
) anywhere on
earth.
10.6.4.1 Timezones
The pertinent timezone is set by specifying a numeric
timezone index.
The correspondence between
timezone index and standard name is listed in the table available on chapter “Set up” paragraph “Clock Set
up”.
The X3M embeds a database of
timezone rules
that enables the instrument to determine the local GMT
offset and DST offset at a given time for any of the available timezones and to consequently covert them
into Universal and Local time.
The database with the
timezone rules
is compiled starting from the package published by
elsie.nci.nih.gov
(
tzdataXXXXX.tar.gz
) and it is embedded in the instrument firmware therefore an update of the timezone
rules requires upgrading of the firmware.