TH NextGen - Similarity search

You can apply the Similarity Search tool to search for events in your data that present similar profiles to an event you find interesting.

You can quickly find and analyse peaks related to unit shutdowns based on variables that are characterized by a signal shape. By doing this you can easily determine how frequently the signal shape appears in the history of your data, and hence how frequently a certain event occurs in the operation of your process.

Note: The similarity search will search through the period highlighted by the context bar. Time periods that are filtered out or not yet indexed, are excluded from the search.

How to perform a similarity search

  1. Select a set of tags and a time window that contains the behaviour of interest and visualize the event of interest in the focus chart. Only visualized tags will be considered for a similarity search.

Note: The index resolution setting determines the minimum length of a search pattern. The length of your query period needs to be a minimum of 4x the index resolution for similarity searches.

  1. Within the search menu, click "Create new" under the Similarity search option. When the similarity search option is selected, the similarity search tool will use the complete pattern highlighted within the focus chart as search query.

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  1. Change search conditions if needed (see Editing search conditions below).
  2. Press the button "Search" to start the search.

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  1. Wait for the result list to appear. By default, the results are sorted and grouped by match score (see working with the search result list to change the order of the results). 

You can visualize events by adding additional layers, just click on "Add Layer".

Editing search conditions

  • Visualized tags can be included or excluded from the search by selecting the checkbox next to the tag name.
  • For each tag, the similarity search can be performed on absolute values or on signal shape.
    • Absolute values: Select this option when the absolute level and evolution over time needs to be matched.
    • Signal shape: Select this option when the absolute level of the measurement is less important, but the signal shape or measurement evolution (up / down) needs to be matched. The signal shape option will not rescale the measurement but will allow vertical displacement of the pattern.
  • The user can change the minimum match score (default = 70% match quality). If this value increases, fewer results will be found. Decreasing the value has the opposite effect.

Check how should I interpret similarity search scores document to learn more about this score.

Weights

In some cases, a specific part of the pattern is more important for your analysis. In these cases, weights may be used to increase the importance of a selected sub-window of the query.

  1. Highlight a selected area.
  2. Use the weight buttons to set the weights. The line thickness of the trend will change accordingly. The period on which the weight is applied, and the level of the weight is also indicated in the left side panel. You can still alter the level of the weights by using the arrows next to the level indicator.

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  1. Press the button "Search" to start the search.
    The similarity search will still look for matches based on the full pattern, but mismatches in the highlighted region will be penalized more.

Note: Changing the weights on the focus chart will only take effect on the open search when editing the search conditions.

In certain cases, no results are found. This may occur when:

  • No matches with a sufficiently high score are found in the selected time range.
  • A user tries to search in a period that is not yet (fully) indexed.
  • The window of the focus covers a substantial part of the context range.
  • Filters are active that exclude significant parts of the context bar.

Add calculations

It is possible to add one or multiple calculations to the search results and the search definition, by clicking on the "Add calculation" link. Please look to the Calculations on search results document for more information about how to work with calculations.

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Saving a search

After creating or editing a search, save it following the next steps:

  1. Click on the link "Save this search" on the Search summary.

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This action will open a panel, where you can specify:

  • The search name,
  • A description,
  • The location in the Work Organizer.
  1. Click on the button "Save search" on the panel.

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Note: A similarity search can also be used as monitor once saved. To learn more about monitoring, refer to this article.

 

 

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