Trend - page of object PmTrend

Basic configuration of group of trends. By using the PmTrend object the PROMOTIC application becomes a trend server. In the trend server (running PROMOTIC application) it is possible to define multiple trend groups (or PmTrend objects).
Configuration items basic:
Group ID identifierIdentifier of the trend group. It is a mandatory item. The trend group represents the PmTrend object and the designer must ensure that two groups do not use the same identifier. This identifier is used for example for addressing a value in trend viewer. If, for example, group1 is set, then the internet URL address of this group data may be http://computername/group1 (if the PmTrend object enables the data for the Internet in the PmTrend > Web Server page using the PmWeb object). In such case the computername is the name of the computer where the trend server is running, and group1 is the Web component identifier in the Web Server page (this name is identical with the name in this configurator).

Macro expression can be used for input (it is evaluated while the application is launching).

This is a system name and must not contain empty string, diacritics, spaces and the first character must not be a number.
User defined name of the groupUser defined name of the group (or the PmTrend object). This name is used for viewing as user identification of the group.

Macro expression can be used for input (it is evaluated while the application is launching).

Number of records in memory cashNumber or records that are stored in memory. If the data is to be stored on the disk (i.e. the Use the data on the disc configurator is checked), then the data is stored on the 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 PmTrend objects together (for example 1000 variables in total) and for all PmTrend objects the configurator Use the data on the disc 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 data type).

Timestamp accuracy [s]Timestamp accuracy in seconds. Before the timestamp is stored in the memory/disk, the time is rounded up to the specified accuracy. This defined precision must by supported by the storage system disk itself (if the data is stored also on the disk). The maximum possible precision depends on the type of storage on disk:
Standard/local time storageTime storage type
Time is "local time" - During the daylight-saving season the time is saved as the "daylight-saving time", in the winter 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 winter 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 ensures 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 setting 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 data from existing files). In such case, the PmTrend 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 Run, RunTime methods), but other functionality remains unchanged (displaying the data by the TrendsView viewer, statistics and evaluation of the data by GetData, CreateFilter methods, saving the data into a file SaveToFile). Open methods allow dynamic connecting to requested table.

In this mode it is not needed to define the list of variables on the Data page (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 page is defined then it is synchronized with the list of columns from the database table.

See: PmTrend object in "Read only (new records cannot be written)" mode.

Macro expression can be used for input (it is evaluated while the application is launching).

Automatic value saving after launch is enabledIf checked, the automatic value saving after application launch is enabled. The PmTrend contains an internal timer (similar to the PmTimer object), allowing to save the selected values after defined time period. During each automatic saving (new record) the onAddRecord event is fired, the same way as during saving the values via the Run or RunTime methods. This event can be used for preparing the data to be saved.
Autosave period [s]Autosave period in seconds. Each time this period passes the Run method is called internally, which first generates the onAddRecord event and then saves all current values from the Data page.
Enable saving of variables on changeEnable/disable optimized value saving. In this case the values (defined in Data page) are stored (into memory, on the 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 numeric value, defined separately for each variable, see Dead band. If at least one variable defined in the Data page of the PmTrend object does not fit its insensitivity range, then all variables defined in this page are saved.
Change evaluation methodVariable change evaluation method:
simple - by variable change - The variable 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 value is evaluated as unchanged.
optimized - by 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, save after [s]Even if the new values are repeatedly evaluated as unchanged (when calling Run, RunTime), then after the defined time interval (in seconds since last data save) the data is saved during the next calling of Run, RunTime (the insensitivity is not evaluated).
See also:
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