Rockwell Automation FactoryTalk Historian Classic User Guide - Manual (Page 132)

Chapter 7 Creating RSBizWare Custom Analysis Tools
Usually, RSBizWare custom analysis tools are used to analyze
time-series data sets. Before looking in-depth at how to build a
custom analysis tool, it is essential to understand what a time-series
data set looks like, as you will need to interpret the parameters that
will be passed into your
Calculate()
function.
Generally, time-series data is made up of three parameters: a data
point (or tag) name, a timestamp and a value. However, the
Information Services Manager has the built-in ability to sample large
data sets on the server side when querying a large number of records.
For example, if you are collecting a data point called Pressure every
10 seconds in a year's time, you will have over 3 million records for
that data point stored in the FactoryTalk Historian Classic
time-series database. Obviously, it is not feasible or useful to send all
3 million records to an RSBizWare client for display. Therefore, the
Information Services Manager uses a sampling algorithm to return
only the number of records necessary to display the data set
accurately on the RSBizWare client. The necessary number of
records to send to an RSBizWare client is actually part of the client’s
request and depends on the size and resolution of the display device
that the client is using. It is based on the number of horizontal
screen pixels the time-series chart will occupy.
When using a sampling algorithm, the RSBizWare server will divide
the requested time range into a number of equally spaced time
buckets. To accurately display the data in the RSBizWare client, the
server then finds the minimum and maximum value of the requested
data point for each time bucket and also finds the number of data
point records that are part of each bucket. The number of data point
records in a sample may be important when developing weighted
analysis tools when the data point is not uniformly sampled. All of
this information is returned to the Configuration Console, and this
same information is passed into the custom analysis tool
What a Time-series Data Set
Looks Like
132 Rockwell Automation Publication HIST-UM001K-EN-E-June 2014