Three-dimensional data: Value, time, and quality (VTQ)
- Last UpdatedMar 07, 2025
- 2 minute read
Each time Historian records a data value, it also records a corresponding timestamp and data quality rating. Together, these three things – value, time, and quality – are called a "VTQ".
Values alone: Only somewhat helpful
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For example, suppose there is a tag named "tank1.temp" that measures the temperature of a tank in the plant. The tank’s sensor would send periodic temperatures to Historian – 97 degrees, 98 degrees, 102 degrees, 108 degrees, etc. These mean little unless you know when the temperatures were taken, so each value also has a date/time stamp. |
Value + Time
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Recording each value with a timestamp allows you to see trends, pinpoint process errors, etc. Historian tracks when a record is sent by the device and when it is received by Historian. This helps to clarify the information if there is a data lag, or if values are added or updated later. |
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Value + Time + Quality
And because errors can occur – from minor mechanical hiccups to major area-wide blackouts – Historian also records a data quality indicator for each record.
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If something happens that may affect the data quality, the quality indicator reflects that. That way, you can know if the quality less than optimal for some records, and use that information to report and as accurately as possible. |
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Where there are gaps, Historian can provide a best guess of what the values were. |
