TN Hist204 Historian Edge Detection Graphical Representation
Description
How to use data edge detection capabilities in the Wonderware Historian using the trend tool and SQL from InSource.
Below are a few pictures to illustrate the difference between the various types of edge detection.
- Author: Lewis Talley
- Published: 03/23/2015
- Applies to: Historian 10.x +
Details
An event is the moment at which a detection criterion is met on historical tag values in the Wonderware Historian. At a basic level, anything that can be determined by looking at stored data can be used as an event.
When detecting events, it is useful to pinpoint rows in a result set where the satisfaction of criteria in a WHERE clause changed from true to false, or vice versa. For example, you may want to know when the temperature of something was when something else was true. The WHERE clause in a query for this example might be Value = True. As the value approaches true, the criterion does not return true. Only when the value crosses the line from not satisfying the criterion to satisfying it, does the event actually occur. This imaginary "line" where the change occurs is called the edge.
Over a period of time, there may be many instances where the criteria cross the "edge" from being satisfied to not satisfied, and vice-versa. The values on either side of this "edge" can be detected if you configure your event tag to include this information. There are four possible options for edge detection: none, leading, trailing, or both. You will get differing results based on which option you use:
The edge is the blue line and represents the value = 1 in the following 2 queries.
