OPC Date

OPC Date expressions let you define dynamic time values without typing exact timestamps. This is useful when selecting periods in trends.

What OPC Date Means

An OPC Date expression combines:

1. A base time, for example NOW or DAY.
2. An optional positive or negative offset, for example -1D or +2H.
3. An optional fixed clock time, for example +08:00.

This lets you create reusable time expressions such as:

NOW
NOW-1D
DAY+08:00
WEEK+1W
MONTH+15D
YEAR+6MO

Base Keywords

Offset Units

Positive Offsets

NOW+1D
DAY+8H
MONTH+15D

Negative Offsets

NOW-1D
NOW-3H
YEAR-2MO

Chained Offsets

Multiple duration segments may be combined:

NOW+1Y-2MO+3D+4H

Evaluation occurs sequentially.

Example:

NOW
  + 1 year
  - 2 months
  + 3 days
  + 4 hours

This sequential behavior is important because month/year calculations depend on calendar boundaries.

Time-of-Day Offsets

A fixed time can be supplied using:

HH:mm

Examples:

DAY+08:00
DAY+17:30
MONTH+12:00

Meaning:

DAY+08:00

→ Start of current day at 08:00 AM

Examples

Assume:

Date 2025-01-15T14:30:45

Important Notes

Case Insensitive

All expressions are normalized to uppercase:

now-1d
Now-1D
NOW-1D

are equivalent.

Time Offset Format

Only:

HH:mm

is supported.

Examples:

08:00
17:30
23:59

Seconds are not supported in the expression syntax, although the internal timestamp parser can handle them if supplied directly.

Example Use Cases

Start of Business Day

DAY+09:00

Previous Day

NOW-1D

First Day of Current Month

MONTH

Midday of Current Month

MONTH+12:00

One Week From Start of Current Week

WEEK+1W

Six Months Into Current Year

YEAR+6MO