The Basic Building Blocks in the PI System

Version 5

    This document is an excerpt from the Visualizing PI System Data Workbook v2017

     

    Objectives

    • Define the terms of PI Asset Framework (AF) Asset and its components: elements and attributes.
    • Define AF attribute types: static (none), PI Point, point array, formula, string builder, table lookup and Analysis.

     

    3-PIPointsAttributes.png

     

    What is a PI Point?

    PI Point (or PI Tag) is a unique storage point for data in the Data Archive.  It is simply a single point of measurement.  It has been the traditional storage unit in the PI Server.

    Data Archive points have a set of properties called point attributes that define the PI points. Some of these properties are commonly used in client tools for display or informational purposes and are briefly described in the following.

    Point name

    Unique name is required to create points for storage in the Data Archive. It is a common practice to name the PI Points based on the Control Systems point names. Since the point is the name that identifies the point to users, consistent point-naming convention should be used that is meaningful to people in your organization.  Knowing the naming convention can be helpful in searching for points.  For example, try to determine what the following point may refer to:

     

    Point name:  M03_E1P1_MOTDRV1202_RUNSTAT

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    It refers to: Machine3 Enclosure 1 Panel 1 Motor Drive 1202 Run Status which is not intuitive.

    Some of the other common point attributes that are often used in client tools are listed in the following table.

    Attributes

    Description

    Descriptor

    This is the human-friendly description of the Data Archive Point. The descriptor is often a search criterion since the point name is not always intuitive. Often the point name is some sort of abbreviated convention and the descriptor captures the “full name.”

    EngUnits

    Engineering units (units of measure)

    Zero and Span

    These define the minimum and maximum values and are used in a number of places. Most obvious are the upper and lower boundaries of object like the trend, bar graph, or multistate symbol.

    Point source

    Allows grouping of PI points by their interfaces that collect data and is occasionally used in point searching. It requires the knowledge of data source, which is instruments that generate the data of interest (e.g. DCS, PLC, or other sources).

     

     

    What is an Asset?

     

    In AF, each piece of equipment or process or company locations and sites is represented by an Element (Asset). It organizes all equipment into a structure that makes it easy to find information.  AF can be helpful to users of the Data Archive who know the assets and processes, but are not familiar with attribute nomenclature.  With assets, data can be located without understanding the technical details of each piece of equipment as the assets are organized hierarchically and logically.

     

    What is an AF Attribute?

    Attributes represent a unique property associated with an asset.  Attributes can hold simple values, representing fixed information, such as the diameter of a tank. An attribute can reference a PI point, a formula, a value from a relational database and more. All relevant data about an asset is tied to the element representing that asset.

     

    AF can automatically generate points as assets are created.

     

    See more examples of Assets and Elements in this video: