Historization attributes

<Attribute>.ForceStoragePeriod

The time interval, in milliseconds, after which the value must be historized, even if the value has not changed, or if a Value Deadband is specified, has not changed more than the Value Deadband. A value of 0 disables this feature. The force storage period is intended for use where data changes infrequently, as compared with the Engine scan rate.

Since the interval is set in milliseconds, a setting of 3,600,000 indicates the value must be stored once per hour, measured from the time the object was last put onscan (60 seconds/minute x 60 minutes/hour x 1000). If this value is less than the scan period of the host object, forced storage occurs at every scan period.

When enabled (by setting a value other than 0), the forced storage period artificially updates the timestamp on an older value that has not changed, and allows the Historian to store that value again with the artificial timestamp. Changes in value that exceed the Value Deadband are timestamped by the source system (e.g., PLC) and that time is applied to the historized values. Values historized because of the force storage period are stored with the system time of the Engine scan which exceeded the period. Depending on communications latency, clock differences and detailed Engine timing, this can cause force storage period values to be historized out of order or overlapping with normally stored values.

Disable (set to 0) the forced storage deadband in cases where the value normally updates frequently. In cases where the value rarely changes, set the forced storage period to a much longer time period, for example, to a value between 1 and 48 hours (3,600,000 to 172,800,000 ms).

<Attribute>.TrendHi

The default top of the trend scale for clients. This value must be greater than or equal to the low value for the trend. If this value is changed at run time, the maximum engineering unit change is not reflected in the historian until you redeploy the object. This attribute only applies to numeric data types.

<Attribute>.TrendLo

The default bottom of the trend scale for clients. This value must be less than or equal to the high value for the trend. If this value is changed at run time, the minimum engineering unit change is not reflected in the historian until you redeploy the object. This attribute only applies to numeric data types.

<Attribute>.ValueDeadBand

The threshold value, measured in engineering units, that the absolute value of the difference between the new and last-stored values must differ before the value is historized. The value deadband is provided as means to filter low levels of noise in the signal, and allows reduced requirements for storage and processing. Setting a value deadband to reduce processing and storage requirements area must balanced against having a complete data set. A value of 0 means that there is no deadband, and thus any value change forces a storage. When combined with the force storage period, new values are compared with the last historized value, regardless of whether historization occurred because the value deadband or the force storage period was exceeded. Note that changes in quality of the attribute always are always historized, regardless of this setting. This attribute only applies to numeric data types.

<Attribute>.Description

The brief description for the attribute that is stored to history. You can use descriptive text or a reference to another string attribute containing the history description. If an attribute reference is used, it must be in the form: "me.AttrName". If you do not provide a description, the object description is used.

<Attribute>.InterpolationType

The method used by the Historian to interpolate analog historical data. The interpolation type determines which analog value is selected during a Historian data retrieval cycle. Interpolation types include System Default, Stairstep, or Linear. The default interpolation type is System Default. For Stairstep, the last known value is returned with the given cycle time. If no valid value can be found, a NULL is returned to the Historian. For Linear, Historian calculates a new value at the given cycle time by interpolating between the last known value prior to the cycle time and the first value after the cycle time. For System Default, the Historian system-wide interpolation setting is used. The system-wide setting must be either stairstep or linear interpolated.

<Attribute>.SampleCount

Obsolete. Do not use.

<Attribute>.RolloverValue

A positive integer value that represents a tag’s reset limit when the Historian operates in counter retrieval mode. In counter retrieval mode the Historian uses a tag's rollover value to calculate and return the delta change between consecutive retrieval cycles. The default value is 0.0. The rollover value applies only to numeric attributes. The rollover value is disabled if the historical attribute data type is Boolean or a string.

<Attribute>.EnableSwingingDoor

Enables or disables the swinging door rate deadband. The default is disabled. The swinging door deadband is not applicable to Boolean or string data types. If you provide a valid swinging door rate deadband, the force storage period is now the deadband override period.

<Attribute>.RateDeadBand

The percentage rate of change deadband based on the change in the slope of incoming data values to the Historian. For example, specifying a swinging door rate deadband of 10 percent means that data is saved to the Historian if the percentage change in slope of consecutive data values exceeds 10 percent. The default is 0.0, which indicates a swinging door rate deadband is not applied. Any percentage greater than 0.0 can be assigned to the rate deadband.