StDev

Find the time-weighted or event-weighted standard deviation of values for an attribute from a specified time range.

Syntax

StDev(attname, starttime, endtime [, pctgood, calculationBasis])

Arguments

• attname

  attribute with time series data (such as PI point data reference) enclosed in single quotes

• starttime

  time expression representing the beginning of a time range enclosed in single quotes; can be a relative time (such as'-3h') in reference to an absolute endtime

• endtime

  time expression representing the end of a time range enclosed in single quotes; can be a relative time (such as '+1h') in reference to an absolute starttime

• pctgood

  Optional. Time-weighted or event-weighted minimum time percentage during a specified time range for which the attribute had good values

• calculationBasis

  Optional. A string indicating the type of calculation to be performed enclosed in double quotes. Choose between "TimeWeighted" or "EventWeighted". If omitted, the default is time-weighted

Returns

The time-weighted or event-weighted standard deviation for attribute values from the specified time range

Exceptions

If the attribute has no good values or the pctgood minimum is not reached for the given time range, an error is returned

Notes

• Bad values are excluded from StDev calculation

• In order to configure an optional parameter, any previous optional parameter must be specified

  Note: If the attribute has very few good values during the time range, this function's result may not be trustworthy. Use the PctGood function to find out what percentage of the values is good

Example

• StDev('att1', 't', '+1h')

  [Return the time-weighted standard deviation of values for 'att1' between 12:00 and 1:00am today]

• StDev('att1', 't', '+1h', 80)

  [Return the time-weighted standard deviation of values for 'att1' between 12:00 and 1:00am today when at least 80% of the values were good]

• StDev('att1', 't', '+1h', 80, "EventWeighted")

  [Return the event-weighted standard deviation of values for 'att1' between 12:00 and 1:00am today when at least 80% of the values were good]