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Binding Properties to the Tag Historian

The Tag Historian binding type, which is only available for Dataset type properties, runs a query against the Tag Historian.

Selected Historical Tags

For this type of query, you must select at least one Tag path from the Available Historical Tags to query. The Dataset returned by the query will have a timestamp column, and then a column for each path that you select here.

Date Range

Choose either a Historical or Realtime query. Historical queries use a date range that must be bound in from other components on the screen, typically a Date Range or a pair of Popup Calendars. Realtime queries always pull up a range that ends with the current time, so all they need is a length.

This example uses a Historical query and two Popup Calendars for the start and end dates. The history is presented in the Table below.  

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Tag Historian Binding




Sample Size and Aggregation Mode

In places where the Tag History system can be queried, a Sample Size and Aggregation Mode can be selected that will determine how the results will be queried out and how the raw values will be aggregated.


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Tag History Aggregates


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Table – Fixed Sample Size

Aggregation Mode

The Aggregation Mode dictates what happens when multiple raw values are encountered for a given sample window (the size of which is determined by the number of requested rows, or the interval size).


Aggregation Mode

Description

Time-weighted Average The values are averaged together, weighted for the amount of time they cover in the interval.

Min/Max

The minimum and maximum values will be returned for the window. In other words, two rows will be returned. If only one value is seen in the interval, only one row will be returned.

Closest Value

The value closest to the ending time of the interval will be returned.

Basic Average

The values are summed together and divided by the number of values.

Sum

The values in the interval are summed together.

Maximum

The maximum value in the interval.

Minimum

The minimum value in the interval.

Duration On

Returns the number of seconds that the value was recorded as non-zero.

Duration Off

Returns the number of seconds that the value recorded as zero.

Count On

Returns the number of times the Tag's value went from a zero value to non-zero.

Count Off

Returns the number of times the Tag's value changed from a non-zero value to zero.

Count

Returns the number of times a value was recorded 

Percent Good

Time-weighted percentage of good values over the date range. 

Percent Bad

Time-weighted percentage of bad values over the date range.

Range

Returns the range between the highest and lowest value for the period.

Standard Deviation

Standard Deviation - Returns the standard deviation of values, or how much spread is present in the data; low standard deviation shows the values are close to the mean, and high standard deviation shows that the data points are spread out over a large range of values. Only good quality values are used when calculating

Variance

Returns the variance of values. Similar in concept to standard deviation. Only good quality values are used when calculating.

Sample Size

The sample size determines how many data points will be returned from the query.  

On Change

An On Change query will return points as they were logged, and can be thought of as a "raw" query mode. This means that the results may not be evenly spaced. Also, it is important to note that every changed value will result in a row, and therefore if you are querying multiple tags and once, you may end up with more rows than you anticipated. For example, if Tag A and Tag B both change, you would end up with [[A0, B0],[A1, B0], [A1, B1]].

If you want to essentially retrieve raw values, while coalescing them down into fewer rows, try using the Interval sample mode, with an interval set to your largest acceptable time between rows, and select "prevent interpolation" from the advanced settings.

Natural

A Natural query will look up the logging rate for the queried tags (when possible), and return results spaced apart at that rate. This means that the return size will vary with the date range.

Fixed

You can use the Sample Size and Aggregation Mode on the Tag History binding type to fix the number of records that are retrieved. The Fixed sample size will cause the binding to retrieve all records from the date range, and aggregate them evenly between a fixed number of points. This will ensure that the number of rows will remain the same without regard to the size of the dataset. In windows where users are able to select a large range of data, Fixed is recommended as it will prevent the property from loading an excessive number of records. 

In cases where the number of points can not evenly represent the data from the date range, an extra point will be added, making the final size of the dataset the fixed value + 1. 

Selecting the Min/Max aggregation mode returns two rows of data for every row requested. Each pair represents a minimum and a maximum result from the underlying data. Therefore, a table with a fixed length, would return double the requested amount with Min/Max aggregation mode selected. With Min/Max aggregation mode selected, and with a fixed row length of one, the data set returns the oldest tag value of the time range

The following image shows a Tag History Binding pulling data from the last one day. The Sample Size is configured to Fixed with a value of 100, and the Aggregation Mode is set to Basic Average. This means that the binding will query for data from the last one day, regardless of how many records there are, and create 100 time-slices that are evenly dispersed between the start and end periods of that range. Then, a basic average of the tag values are calculated for each time-slice. The resulting values are then returned to the property

Note the Insert Propertyicon next to Sample Size. This allows a property binding to determine the number of data points, so you could change the size to increase or reduce the amount data points on the chart from the client. 

Interval

Where as the Fixed sample size will calculate time slices based on the date range, the Interval sample size allows you to determine the size of the time slices. This sample size will divide the date range by the interval size to determine the size of each slice. Because of this, it is recommended to use an interval that is evenly divisible by the date range. However, in the event that the date range is dynamic or user driven, interpolation will handle any partially built slices. Even though the binding may attempt to evenly distribute the slices, there may be an extra row that represents the current values as they are building an interval. 

The image below shows a Realtime range of 60 minutes. The Aggregation Mode is set to Time-weighted Average, and the Sample Size is set to Interval 5 minutes. This means that the binding will query for data ranging from 60 minutes ago to now (or whenever the binding last executed, in the case that polling has been turned off). That 60 minute window will be divided as evenly as possible into 5 minute time-slices, so there should around 12 time-slices. Each time slice will aggregate its value based on the time-weighted average of all values within that slice. 

The example uses a Realtime range, but a Historical range could easily be used instead. 

Note the Insert Propertyicon next to Sample Size. This allows a property binding to determine the number of data points, so you could change the size to increase or reduce the amount data points on the chart from the client. 

 

Return Format

Return format dictates how the requested data will be returned. The options are "wide" (default), in which each Tag has its own column, and "tall", in which the Tags are returned vertically in a "path, value, quality, timestamp" schema.

Advanced Options

These options affect the query results in more subtle ways.

  • Ignore Bad Quality - Only data with "good" quality will be loaded from the data source.
  • Prevent Interpolation - Requests that values not be interpolated, if the row would normally require it. Also instructs the system to not write result rows that would only contain interpolated values. In other words, if the raw data does not provide any new values for a certain window, that window will not be included in the result dataset.
  • Avoid Scan Class Validation - "Scan class validation" is the mechanism by which the system determines when the Gateway was not running, and returns bad quality data for these periods of time. By enabling this option, the scan class records will not be consulted, which can improve performance, and will not write bad quality rows as a result of this check.

 

Tags Historian information is often easiest to work with in the Easy Chart component, which handles all of these options automatically.

 

Indirect Tag History Binding

The Tag History Binding can be made indirect but using indirection parameters in the Tag Paths of the Selected Historical Tags. This works similarly to the Indirect Tag Binding, which uses Indirection References within the Tag Paths to substitute something into the path. Valid Indirection references consist of a reference number within curly braces. Simply type the indirection parameters (for example, {1}) into a selected Tag path by double-clicking in the list of selected paths. All valid parameters will appear in the lower indirection table.

In this example, the Tag Path points to the Spinner component for the indirection parameters.


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Indirect Tag History Binding



 

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