Knowledge Base / UTC, NTP and automatic local-time conversion

UTC, NTP and automatic local-time conversion

Understand why NTP supplies UTC, how receiving devices apply time-zone and daylight-saving rules, and what to check when local time is wrong.

Applies to: GMR, NTDS, NTP100, PCIe, RC, DA12
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NTDS/TCDS display controllers: NTP, TC (time code) or dual. LUX is part of the NTDS family.

UTC is the common time reference

Coordinated Universal Time (UTC) provides a shared time reference regardless of location. UTC does not change with a local time zone or daylight saving time (DST). Devices can therefore agree on the same instant while displaying different local clock times.

What NTP sends and what the receiver converts

Most NTP-connected devices receive UTC time from their server. The receiving device automatically converts UTC to local time using its configured time zone and DST rules. NTP synchronization does not tell the receiver which geographic time zone to use or install the local DST policy.

Automatic conversion requires the correct zone and supported DST rules to be configured, with automatic DST enabled where applicable. A device configured to display UTC will continue showing UTC. A fixed-offset configuration will not necessarily change when local DST begins or ends.

For example, 18:00 UTC displays as 12:00 at UTC−6 or 13:00 at UTC−5. Both displays represent the same instant. A region that changes between those offsets needs the corresponding DST rules on the receiver.

Locate a local-time display error

  1. Compare the receiver’s UTC time with the source’s UTC time, where the interfaces expose both. If UTC agrees but local time differs, investigate display conversion.
  2. Check the receiving device’s selected zone, DST enable state, transition rules and any manually entered offset. For a PC application, also check the operating system and application time-zone settings.
  3. After a seasonal one-hour error, check whether automatic DST is disabled, rules are outdated, or DST has been applied twice through both an automatic rule and a manual offset.
  4. Avoid shifting the server’s UTC clock to correct one client’s local display. Correct the receiving device’s conversion settings.

Time-code paths need a separate check

A time-code source can be configured to encode UTC or local time. A DA12 distributes the incoming signal; it does not apply NTP time-zone conversion. In a time-code installation, check the generator’s encoded time basis and the reader’s offset handling so the same conversion is not applied twice. See Wrong UTC time or date when using time code input.

Related articles

Article ID: KB-TIME-002
KB Version: