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In the top part of the tab, an input edit filed field is placed. It serves for entering the expression, that determines the value of the historical value. The expression can contain functions, constants, attributes - but objects of Historical value type only. The expression may also contain extended syntax.
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The parameter can be defined for the archive method Filter. It allows restricting the number of evaluations of a given expression so that the expression will be evaluated once within a defined time . It is used especially in cases when the values of the objects defined in the expression are often changed, and calculating the expression is not required immediatelyto reduce CPU and disk I/O usage. It is used especially in cases when the values of the objects defined in the expression are often changed, and calculating the expression is not required immediately.
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- Continuous - continuous (on the fly) calculation. Result values are calculated on the fly and they are automatically available (depending on the system load). A disadvantage of the method is a higher demand for computing power (especially for frequent changes of primary historical values that enter into the expression).
- On demand - the calculation is executed and the result is stored in the archive on demand. The demand can be generated by the CALCONDEMANDSTAT action or by the RECALC Tell command command ).
Note: historical value calculated "on demand" should not have any depending historical values calculated continuously, because the result their results would be wrong. - On read - the calculation is executed as a result of a read request. An advantage of this method is that values are not stored in the database so they don't occupy any disk space. There is no possibility of re-calculation in case of writing delayed data into the archive. A disadvantage is the necessity to read source data and calculate it for each read request. This method should be used for objects whose values are rarely needed.
Note: historical value calculated "on read" should not have any depending historical values calculated continuously or "on demand", because the result could be wrong in some cases (due to delayed data) or the calculation could be ineffective (multiple calculations of a single "on read" object if it is used by several other historical values).
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For periodical data archiving, it is defined, defines what time data with the value for the given period will be stored into the archive. The time data can present either the beginning time - the "Period begin" option, or the end time of the interval (period) - the "Period end" option.
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Definition of the condition causing the start archiving of the given historical value.
The object representing the archiving start condition may be defined by in several ways:
- by writing the object in to into the input field,
- by selecting the object from the list of objects - the list is opened after clicking the button right from the input field,
- by creating a new object - the "Create new object button" button.
Also, it is necessary to define, for what state of the given object is the condition is valid. In the list under the object entry field, there are displayed the possible object value states are displayed. This list is different for various kinds of specific types of objects. The archiving start condition will be valid , if the object is in the chosen selected state. If the option Inverse function is enabled, the condition is valid, if the object is in a status other than the chosen state.
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Defining the condition that causes stopping the archiving of the given historical value.
The object representing the archiving stop condition may be defined by in several ways:
- by writing the object name into the input field,
- by selecting the object from the list of objects - the list is opened by clicking the button right from the input field,
- by creating a new object - the "Create new object button" button.
Also, it is necessary to define, for what state of the given object is the condition is valid. In the list under the object entry field, there are displayed the possible object value states are displayed. This list is different for various kinds of specific types of objects. The archiving stop start condition will be valid , if the object is in the chosen selected state. If the option Inverse function is enabled, the condition is valid, if the object is in a status other than the chosen state.
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When archiving into the statistical archive, it is possible to use these implemented functions.
| Function | Meaning |
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| None | No function. |
| Average * | Arithmetical average of all archive object values. |
| W-Average * | Weighted arithmetical average of all archive object values. |
| Integral | Time integral of historical values. |
| Sum | Sum of archive object values. |
| Maximum | Maximum of archive object values. |
| Minimum | Minimum of archive object values. |
| Count | Number The number of archive object values. |
| Filter | Applying a filter for value storing into the statistical archive. |
| Increment | If the newer value is greater than the older one, then the difference between the values, otherwise the newer value (the function is useful to process counter values that oveflow overflow and start from zero again). |
| Delta | Delta between values. Parameter (Compare value) – the weight of impulse. The result will be the impulse multiplied by its weight. Weight A weight of 1 will ensure standard behaviourbehavior. |
| EcoAvg | Average of the object values within the elapsed time period (Period parameter in Time parameters tab) according to the methodology based on flags of individual values entering the statistic. The same purpose is fulfilled by the function %EcoAveR, that which is implemented for eval tags. |
| GT Time (>) | The function calculates the time, during which the value of the historical value was greater than the entered constant (Compare value). |
| GE Time (>=) | The function calculates the time, during which the value of the historical value was greater or equal to the entered constant (Compare value). |
| LT Time (<) | The function calculates the time, during which the value of the historical value was lower then than the entered constant (Compare value). |
| LE Time (<=) | The function calculates the time, during which the value of the historical value was lower or equal to the entered constant (Compare value). |
| Maximum in time interval | Obsolete - do not use! |
| Minimum in time interval | Obsolete - do not use! |
| Number of local maximums | The number of local maximums in a given time interval. |
| Number of local minimums | The number of local minimums in a given time interval. |
| Sum of positive Sum of positive values | Sum of positive values of the historical value. |
| Sum of negative values | Sum of negative values of the historical value. |
| Average of positive values | Arithmetical average of positive values of the historical value. |
| Average of negative values | Arithmetical average of negative values of the historical value. |
| Sum of increments | Sum of increments for a given time interval. If the new value is less than the old value, the increment is 0. Parameter (Compare value) – the weight of impulse. The result will be the impulse multiplied by its weight. Weight of 1 will ensure standard behaviourbehavior. |
| Time slice** | Object value in given time moments. |
| Sample standard deviation | The function calculates the sample standard deviation of all values of the archive object. |
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The difference among the functions INCREMENT, DELTA, and SUM OF INCREMENTS is shown in the following figures.
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- DELTA = 5-10 = -5
- INCREMENT = 5 (because 5 <105<10)ADDITIONAL AMOUNT
- SUM OF INCREMENTS = 0 (because 5 <105<10)
In the third case
- DELTA = (10 - 5) + (2 - 10) + (10 - 2) = 5
- INCREMENT = (10-5) + 2 (because 5 <105<10) + (10-2) = 15
- ADDITIONAL AMOUNT SUM OF INCREMENTS = (10-5) + 0 (because 5 <105<10) + (10 - 2) = 13
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- Continuous - continuous (on the fly) calculation. Result values are calculated on the fly and they are automatically available (in dependence depending on the system load). A disadvantage of the method is a higher demand on the for computing power (especially for frequent changes of primary historical values that enter into the expression).
- On demand - the calculation is executed and the result is stored to in the archive on demand. The demand can be generated by the the CALCONDEMANDSTAT action CALCONDEMANDSTAT or by the Tell command RECALC command ).
Note: historical value calculated "on demand" should not have any depending historical values calculated continuously, because the result their results would be wrong. - On read - the calculation is executed as a result of a read request. An advantage of the this method is that values are not stored in the database so they don't occupy any disk space. There is no chance possibility of wrong re-calculation in case of writing delayed data into the archive. A disadvantage is a the necessity to read source data and calculate it for each read demandrequest. This method should be used for objects whose values are rarely needed.
Note: historical value calculated "on read" should not have any depending historical values calculated continuously or "on demand", because the result could be wrong in some cases (due to delayed data) or the calculation could be ineffective (multiple calculations of a single "on read" object if it is used by several other historical values).
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The value of the parameter Validation criteria defines the value percentage in the primary archive (used fro for the calculation of values stored into the statistical archive) that has to be valid, in order to acquire a valid result. If there were less fewer valid values than stated in the Validity criteria, the result will be Weak_Value.
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Statistical time period defines the time interval, the set of historical values, that will be processed by the particular statistical function. By default, the interval is equal with to the archiving period. If it is necessary to enter a different period, check the option Time interval different from archiving period and enter the required period into the parameter Interval. The time period must be greater than 0 [s].
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The system allows to archive considerable value changes archiving significant changes in the values of the archive archived object. This archiving method represents defining of three deadband levels, that are possible to set various values of significant changesmethod of archiving represents the definition of three sensitivity bands in which it is possible to enter different values of a significant change.
Values of filtering:
- High limit - defining the high limit for filtering.
- Low limit - defining the low limit for filtering.
- Above limit - defines a significant change of the archive object for value above the high limit.
- In limit - defines a significant change of the archive object for value within the the lower and high limits.
- Below limit - defines a significant change of the archive object for value below the low limit.
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