Glossary · Automation fundamentals, platforms and components
DATE_AND_TIME (data type)
Also known as: DT
German: DATE_AND_TIME
In IEC 61131-3, DATE_AND_TIME (short form DT) is an elementary data type that holds a calendar date and time of day in one value. The standard also defines LDT for long date and time with higher resolution.
- Automation components
- Standards
In one sentence
DATE_AND_TIME (DT) is an IEC 61131-3 data type that holds a calendar date and a time of day in one value.
Example
When a batch ends, the PLC stores the current DATE_AND_TIME value in the batch record, for example DT#2026-09-26-14:05:30.
How it applies
- Engineering: DT is used for timestamps in logs, alarms and batch records. The internal representation and resolution depend on the controller, so conversions between vendors and to IT systems need care.
- Operation: A correct timestamp requires a synchronized clock; see Time synchronization.
- Documentation: State the time zone (local time or UTC) and daylight saving handling for all stored timestamps. Interface descriptions should give the exact format when DT values are exchanged with MES or cloud systems.
- Maintenance: After replacing a controller or its battery, the clock must be set or synchronized again, otherwise stored timestamps are wrong.
DATE_AND_TIME vs. TIME
TIME represents a duration, such as T#5s for a timer preset. DATE_AND_TIME represents a point in calendar time. Mixing them up leads to wrong calculations, for example when adding durations to dates.