Trend - tab of the PmaTrendGroup object

Basic settings of trends group.
By using the PmaTrendGroup object the PROMOTIC application becomes a trend server. In the trend server (in running PROMOTIC application) it can be defined multiple trend groups (i.e. PmaTrendGroup objects).
Configurators basic:
Trend group identifierIdentifier of trends group. It is a mandatory item. The trend group represents the PmaTrendGroup object and the designer must ensure that two groups do not use the same identifier. This identifier is used for example for addressing a variable in the trend viewer. If, for example, group1 is set, then the internet URL address of this group data may be http://computername/group1 (if the PmaTrendGroup object enables the data for the Internet on the "PmaTrendGroup > Web server" tab by means of the PmaWeb object). In this case the computername is the name of the computer where the trend server is running, and group1 is identifier of the Web component on the "Web server" tab (this name is identical with the name in this configurator).
Macro expression can be used for input (it is evaluated after the application is launched). This is a system name, so it must contain only alphanumeric and must not contain any diacritics (i.e. national dependent characters), empty string, spaces and the first character must not be a number.
Displayed group nameUser defined name of the group (i.e. of the PmaTrendGroup object). This name is used for displaying as user identifier of the group.
Macro expression can be used for input (it is evaluated after the application is launched).
Number of records in the memory cashThe number of records that are stored in the memory. If the data is to be stored to disk (i.e. the "Use the data on the disk" configurator is checked), then the data is stored to disk and the defined number of records also into memory simultaneously. When client queries are being processed the trend server does not have to load the data from the disk but it can use the current data that is also available in the memory. When setting this constant it is necessary to understand that a high number of records in the memory (>1000) may cause higher intensity of RAM memory usage.
For example if a higher number of variables is being archived by all PmaTrendGroup objects together (for example 1000 variables in total) and for all PmaTrendGroup objects the "Use the data on the disk" configurator has been set to 2000, then it causes additional requirement of about 1000*2000*8 = 16 000 000 bytes of RAM = approx. 15 MB of the RAM arises (the number 8 in the expression is the size of the Double type).
Timestamp precision [s]Timestamp precision in seconds. Before the timestamp is stored in the memory/to disk, the time is rounded up to the specified precision. This defined precision must by supported by the storage system disk itself (if the data is stored also to disk). The maximum possible precision depends on the type of storage on the disk:
Standard/local time storageTime storage type
Time is "local time" - In the daylight-saving season the time is saved as "daylight-saving time", in the standard season as "standard time". The time is saved as it has been detected for example by calling the Run method.
Time is "standard time" - In the standard season the time is saved unchanged and in the daylight-saving season the time value is decreased by 1 hour and thus it is always saved as "standard time". This approach provides correct functionality of the viewer in time of transition "standard time"/"daylight-saving time" and vice versa and therefore it is recommended.
Read only (new records cannot be written)If the "Storage type" configurator is set to any saving method other than Database Access backups (obsolete), Database MS SQL server backups (obsolete) or Promotic binary file cyclic, then this setting can be used to switch the object into the "Read only (new records cannot be written)" mode (i.e. reading the data from existing files). In this case, the PmaTrendGroup object reads the data from databases created by the PROMOTIC system, or even from databases created by other systems. The database table from which the data are to be read must include the timestamp column configured as the Date and time data type. In this mode the object does not allow writing any data (by methods Run, RunTime), but other functionality remains unchanged (displaying the data by the PmgTrendViewer viewer, statistics and evaluation of the data by methods GetData, CreateFilter, saving the data into the file by SaveToFile). The Open method allows dynamic connecting to requested table.
In this mode it is not needed to define the list of variables on the "Data" tab (list of variables is read from the file as a list of columns of the database table). If the list of variables on the "Data" tab is defined, then it is synchronized with the list of columns from the database table.
See: The PmaTrendGroup object in "Read only (new records cannot be written)" mode.
Macro expression can be used for input (it is evaluated after the application is launched).
Automatic saving after launch is enabledIf checked, then the automatic value saving after the application is launched is enabled. The PmaTrendGroup object contains an internal timer (similar to the PmaTimer object) - allows to save the selected values after defined time period. During each automatic saving (in the form of new record) the onAddRecord event is triggered, the same way as during saving the values by methods Run or RunTime. This event can be used for preparing the data to be saved.
Autosave period [s]The period in seconds. Each time this period passes the Run method is called internally, then the onAddRecord event is triggered and then saves all current values on the "Data" tab.
Enable saving of variables on changeEnable/disable optimized value saving. In this case the variables (defined on the "Data" tab) are stored (into memory, to disk) when calling the Run, RunTime method, only if the value has been changed since the last save and the difference is greater than the insensitivity range.
The insensitivity range is a number, defined separately for each variable, see the "Dead band" configurator.
If at least one variable defined on the "Data" tab of the PmaTrendGroup object does not fit its insensitivity range, then all variables defined in this tab are saved.
Change evaluation methodVariable change evaluation method:
simple - by variable change - The value change is evaluated as a difference between the new saved value and the value saved last time. If the new variable value is for example 35 and the last saved value is 34 and insensitivity range is 4, then the new value fits into insensitivity range (34-4/2,34+4/2)=(32,36) and the variable is evaluated as unchanged.
optimized - according to direction change - The value change is evaluated as the difference between the new saved value and the direction (change in Y-coordinate / change in X-coordinate) of straight line connecting the values saved so far. In this case the insensitivity range is applied to the slope of the straight line connecting the value points.
If no change, then save after [s]If the new values are repeatedly evaluated as unchanged (when calling Run, RunTime), then after the defined time span (in seconds since last data save) the data is saved during the next calling of Run, RunTime (the insensitivity is not evaluated).
See also:
PROMOTIC 9.0.27 SCADA system documentation MICROSYS, spol. s r.o.

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