History samples

When data is collected for a history tag, a history sample is produced. A history sample is the basic unit of historical data for a history tag, composed of:

• A value – one of the DeltaV data types
• A time stamp – the date and time when the history tag had this value
• A parameter status value – an Ff style (.ST field) status value
• A history status value – with information such as whether the historical data stream was broken and the type of break

DeltaV supports the following data types for history sample values:

• 32-bit float
• 32-bit signed integer; smaller, DeltaV signed integer parameter fields are converted to this type
• 32-bit unsigned integer; smaller, DeltaV unsigned integer parameter fields are converted to this type
• UNICODE string, up to 512 characters
• Byte-enum, holding both number and state name for a DeltaV named set parameter