Data Point Interval and the Retrieval Mode

By default, Proficy Portal samples the data every 10 seconds for each historical tag you select from a data source. You can control the sample interval by configuring a time property called the data point interval. This property controls the time range to use when calculating data points in the component (e.g., chart or grid). For example, if the data point interval is one minute, values are interpolated in one-minute intervals. If you set the data point interval to 30 minutes, data points represent interpolated values within a 30-minute interval.

Data values are interpolated because the Historian collectors typically compress data and store only significant data changes. The data's deadband determines what constitutes a significant change. For example, if the current value is 50 and the deadband is 10, the data value must exceed 55 or drop below 45 in order for the Historian server to store the value change.

When Historian data is compressed, every value that the Historian collector received is not stored in the Historian archive. Consequently, when the data is retrieved, Historian interpolates the values it sends to the Proficy Portal server. When Proficy Portal receives the data, it plots the values in one or more charts and connects (interpolates) each point plotted. Interpolation:

When Proficy Portal interpolates data, it assumes that the line connecting two values is a straight line. All points along that line are estimated except the starting point and the ending point.

NOTE: When setting a historical data source for a chart, if the data retrieval mode is set to Std Dev or Raw Std Dev, two values are required for the time calculation. If the collection interval and data point interval are both set to 1 second, no data will display on the chart. You can set the collection interval to a value faster than 1 second and the data point interval to 1, or set the collection interval to 1 second and change the data point interval to a time period greater than 1 second.

The following Historian retrieval modes can be selected:

Historian Retrieval Modes 

Retrieval Mode


Current Value

Retrieves the raw sample value with the newest timestamp, of any quality, received by the archiver. The timestamp is not necessarily the current time – rather it will be the timestamp on the sample sent to the archiver. If you have collector compression and have not exceeded if for some time, the timestamp may be much earlier than the current time.


Displays samples spaced on intervals other than the collection rate. Interpolation is used to produce an evenly space list of the most likely real-world values. Typically, you would use interpolated queries when data is not collected on a set time schedule, or if you want to see the results returned in an interval that is less than the collection rate. The following examples describe instances where you can use interpolated mode to make evenly spaced out values:

  • A tag is collected as "unsolicited". In this case, you do not know what the time interval is between collected values.

  • The deadband and/or archive compression for a tag results in non-evenly spaced collection intervals.

  • A tag is collected once per 8-hour shift, but you want to see it displayed in 1-hour intervals with a linear slope between points.

NOTE: For numeric data in charts, the start time point is calculated.


Displays the raw minimum and raw maximum value received during the data point interval. Available for Historian 2.0 and greater.


Displays actual collected raw values. The data value is never interpolated. Interval timestamps are the same as Interpolated sampling – it is the values that can be different. Since lab sampling will return real collected values, it is more accurate when a sufficient number of raw samples are stored. Use Interpolated sampling for highly compressed data.


Displays the average of the raw samples, but there is special logic for time weighting and for computing the value at the start of the interval. This is useful for computing an average on compressed data.


Displays the number of raw samples in the interval. This only addresses the count and not values or quantities of samples. Count is useful for analyzing the distribution of raw data samples.


Retrieves the time-weighted total for each calculation interval. The collected value must be a rate. This calculation mode determines a count from the collected rate.


Displays the minimum value in the interval. It may be a raw or an interpolated value. The minimum must be a good data quality sample.


Displays the maximum value in the interval. It may be a raw or an interpolated value. The maximum must be a good data quality sample.

Std Dev

Retrieves the time-weighted standard deviation of each calculation interval. This is useful for computing a standard deviation on compressed data.

Raw By Time

Returns all raw samples of all qualities with a timestamp greater than or equal to the start time and less than or equal to the end time.

For charts, if no data is received for the requested time range, the first value previous to the start time, and the next value after the end time are retrieved, allowing a pen to be drawn from the two values.

NOTE: For numeric data in charts, if there is no point with a timestamp that matches the start or end time, start and end time points are calculated. If there is an actual start or end time, they are provided as is.

Raw By Number

Displays all raw samples of all qualities with a timestamp greater than or equal to the start time. The end time is ignored. Unlike the RawByTime, this will return a sample if it has the same timestamp as the start time.

Raw Average

Displays the arithmetic average of the good data quality raw points in the interval. This is useful only when a sufficient number of raw samples are collected.

Raw Std Dev

Displays the arithmetic standard deviation of raw values for each calculation interval.

Time Good

Displays the amount of time (in milliseconds) during the interval when the data is of good quality and matches filter conditions if the filter tag is used. Available for Historian 2.0 and greater.

NOTE: The Maximum Points field has been removed from the iHistorian Edit Source dialog box (this field existed in Proficy Portal (infoAgent) 1.1). To limit the amount of data that is passed from the Historian archive, use the Retrieve Mode (General tab) and time range parameters (Time tab). Additionally, you can limit the data by setting the Max query tag in the config.xml file associated with the data source. The config.xml file can be found in the datasources directory (InstallDir\GE Fanuc\Proficy Portal\webapps\infoAgentSrv\config\datasources\iHistorian). Locate the particular Historian data source config.xml file. Open the file in a text editor such as Notepad, and change the value of the MAXQUERY tag. The default value is 100000. If the data request exceeds this amount, you will receive an error message.

See Also

Sampling Interval

Example: Using Interpolated Data

Retrieval Mode Supported Objects