Duplicate 03:00 Trend Log Entries After Daylight Saving Time Change

[CraigEl]

Issue

After a Daylight Saving Time (DST) transition, interval trend logs in EcoStruxure Building Operation may display two entries with the same local timestamp, most commonly 03:00 AM, on the DST changeover day. This can be interpreted as duplicated or incorrect trend data.

Product Line

EcoStruxure Building Operation

Environment

• SmartX IP Controllers (MP/RP)
• EBO native Trend Log objects
• BACnet Trend Log objects hosted in SmartX controllers
• WorkStation and WebStation

Cause

EcoStruxure Building Operation servers and SmartX controllers operate internally using UTC (Coordinated Universal Time).

• Trend data is stored and processed in UTC
• Time zone and DST adjustments are applied only at the UI layer (WorkStation / WebStation)

It is important to distinguish between EBO native Trend Log objects and BACnet Trend Log objects used in SmartX IP controllers, as their configuration options differ.

EBO Native Trend Log Objects

• Created on Automation Servers or Enterprise Servers
• Support an Interval Time Zone setting
• The Interval Time Zone setting controls how the next interval sample is scheduled (UTC or Server Local Time), particularly for long intervals such as daily logs
• As described in the existing “Interval time zone setting in Trend log” article, using Server Local Time may result in intervals of 23 hours (DST start) or 25 hours (DST end)

This setting affects interval duration only. It does not change how timestamps are stored. All samples remain uniquely timestamped in UTC.

BACnet Trend Log Objects (SmartX MP/RP Controllers)

• Implemented as standard BACnet Trend Log objects
• Do not have an Interval Time Zone setting
• Interval sampling is based on elapsed time using UTC and is unaffected by DST changes at the controller level

During a DST fallback (Autumn), the local clock hour is repeated. As a result, two distinct UTC timestamps may be converted by the UI into the same local time when displayed. This causes two trend entries to appear with the same local timestamp (for example, 03:00 AM).

There is no duplication or ambiguity in the stored trend data. The duplicated timestamp is a local-time display effect caused by UTC‑to‑local‑time conversion during a repeated hour.

Resolution

This behaviour is expected and correct.

• Trend data remains accurate and uniquely timestamped in UTC
• Duplicate local timestamps appear only when UTC timestamps are rendered in local time during a DST fallback
• The Interval Time Zone setting does not prevent duplicate local timestamps
• BACnet Trend Log objects do not support Interval Time Zone configuration
• No supported fix exists to suppress one of the entries without discarding valid data

Customers should be advised that DST transition days may show repeated local times in trend logs