Latest Single-Point Update

A single-point update operation is essentially an insert with a limited time span. The value existing before the start of the update will become visible again after that time span expires. The update time span is specified by the EndDateTime property of the HistorianDataValue class, which is not used for any other purpose.

Consider a single-point update applied to the history fragment shown in the following figure.

From time t_K to time t_L, a continuous signal of value K (the single-point update) is visible.  After time t_L, the original value F is restored.

Because F was the original value covered by the update, it will continue to be visible at time t_L (the end time of the single-point update). When performing a single-point update, the instance of HistorianDataValueList must have the parameter HistorianDataCategory.RevisionUpdateSingle included. Additionally, EndDateTime for the VTQ must be specified to indicate the end of the single-point update.

Example

HistorianDataValueList myVTQs =
    historian.CreateHistorianDataValueList(HistorianDataCategory.RevisionUpdateSingle);

HistorianDataValue myVTQ = new HistorianDataValue(tagKey, HistorianDataType.DoubleByteString);
myVTQ.StringValue   = "K";
myVTQ.StartDateTime = new DateTime(2012, 9, 1, 11, 00, 00);
myVTQ.EndDateTime   = new DateTime(2012, 9, 1, 11, 30, 00);
if (!myVTQs.Add(myVTQ, out error))
    Console.WriteLine("Failed to add update: {0}", error.ErrorDescription);           

while (!historian.SendValues(myVTQs, out error))
{
    // the same code here as in the previous code sample
}

Retrieving with wwVersion = 'LATEST' returns the following result, {A at  t_A, K at t_K, F at t_L, C at t_C}, while retrieving with wwVersion = 'ORIGINAL' will produce the same result as before, {A at  t_A, F at t_B, C at t_C}.