Trend Tag Properties

Trend Tag Name

The name assigned to the trend data (79 characters maximum). If the trend tag is logging a particular variable, use a 16-character name that resembles the 32-character name of the related variable tag. This will mean an association between the two is easily recognizable. The name needs to be unique to the cluster. Trend Tag names need to adhere to the Tag name syntax. If the name is not unique or is not syntactically correct it may not be recognized. If you have many tags, use a naming convention (see Using structured tag names). This makes it easier to find and debug your tags.

Note: Trend tag names have to be unique and not identical to any SPC tag names within the cluster(s) that run this trend. Two tags accessing the same file can result in system errors which may include lost or corrupted trend/SPC data.

Cluster Name

The name of the cluster that runs this trend. If the Cluster Name is not set, then this trend will run on every defined cluster.

Expression

The logged value of the trend tag (254 characters maximum). You can log individual variables by using a variable tag. For example:

The value of the process variable LT131 is logged.

You can also log any Cicode expression or function, for example:

Trigger

The Cicode expression (or variable tag) that triggers data logging (254 characters maximum). For example:

In this example, logging occurs when the value of the variable tag (LT131) falls below 50.

For a periodic trend, data is logged only while the value of the trigger is TRUE. (The trend graph will still scroll, but will display <GATED> where the trigger is FALSE.) In the above example, data is logged continuously while the value of LT131 remains less than 50. Logging ceases when the value rises to (or above) 50. Logging does not occur again until the value of LT131 falls below 50.

You do not have to specify a trigger for a periodic trend. If you do not specify a trigger for a periodic trend, logging occurs continuously.

For an event trend, data is logged once when the value of the trigger changes from FALSE to TRUE. In the above example, one sample is logged when the value of LT131 first becomes less than 50. Another sample is not logged until the value of LT131 rises to (or above 50) and again falls below 50.

Sample Period

The sampling period of the data. You can either enter a period of your own, or choose one from the menu.

Enter sampling periods of greater than one second in hh:mm:ss (hours:minutes:seconds) format. If you enter a single digit, without the colon (:), it will be considered a second. For example, if you enter 2, it will be interpreted as 2 seconds.

Sampling periods of less than one second needs to be entered as decimals. For example, to enter a period of 200 milliseconds, you would enter 0.2.

If the sample period is less than one second, then one second needs to be divisible by the period (to give an integer). For example, a sample period of 0.05 is valid, because 1/0.05 = 20, whereas a sample period of 0.3 is not valid because 1/0.3 = 3.333... .

Note:
• Your I/O Device needs to be capable of providing data at the specified rate, otherwise gaps will appear in the trend data and/or the hardware alarm Trend has missed samples will be evoked. You can fill gaps in the file and graph using the [Trend]GapFillTime parameter. Gaps in the graph only can be filled using the TrnSetDisplayMode() function.
• If trends with a sample period of less than a second are shared by several clients across a network (distributed processingFor large applications with large amounts of data, you can distribute the data processing to reduce the load on individual computers.), enable time synchronization using the Time Synchronization configuration application This verifies that trends are synchronized with each other.

The Trigger is checked each sample period. If the Trigger is TRUE (or has just changed from FALSE to TRUE, in the case of event trends), the value of the Expression is logged.

Examples

The sampling period of the fastest trend on the page is taken as the default value for the display periodDefines the rate at which trend data is displayed on the trend page. of the page.

This property is optional. If you do not specify a sample period, the sampling period defaults to 10 seconds.

Type

The type of trend (32 characters maximum):

• TRN_PERIODIC - A trend that is sampled continuously at a specified period. You can also define a trigger to stop and start the trend (when a specified condition occurs in the plant).

• 

• TRN_EVENT - A trend that is sampled once each time the value of the trigger changes from FALSE to TRUE. Interpolation occurs between each data point to create a continuous graph.

• 

• TRN_PERIODIC_EVENT - A trend that is sampled once each time the value of the trigger changes from FALSE to TRUE. No interpolation occurs between these points, thus providing a graph which spikes at each data point.

• 

Comment

Any useful comment (48 characters maximum).

File Name

The file where the data is to be stored (253 characters maximum). Specify the full path or use path substitution.

When data is collected from your plant floor, it is stored in a file on the hard disk of your computer which is then used to display a trend or SPC graph (a separate file is used for each trend tag).

By default, CitectSCADA stores the file in the [DATA] directory on the hard disk where you installed CitectSCADA. The default name of the file is the trend tag name. However, you can specify an alternate file name like this:

where [DATA] specifies the disk and path for the data. Use path substitution to make your project more 'portable'.

Notes:

• You can no longer store trend files in the bin, runtime, backup or user directories or any subdirectories of these. If you have existing Version 3.xx or 4.xx projects that use these directories to store trend files, the path for these will have to be changed to the Data directory.
• The trend system will buffer the acquired data before saving it to a file. The [Trend]CacheSize parameters determine the buffer sizes for returned data.
• The File Name property is optional. If you do not specify a file name, the file name defaults to [DATA]:<Name> on the hard disk where you installed CitectSCADA. Where <Name> is the trend Tag Name.

• If you use the File Name property, ensure that no other SPC tags or trend tags use the same filename. Two tags accessing the same file can result in system errors which may include lost or corrupted trend/SPC data.

  UNINTENDED EQUIPMENT OPERATION If using the File Name property, ensure that the trend tag uses a unique file name. Two tags accessing the same file can result in system errors which may include lost or corrupted trend/SPC data. Failure to follow these instructions can result in death, serious injury, or equipment damage.

• Do not use a file extension when specifying a file name. If you edit this property (change the file name or path) in an existing project, existing trend data is ignored.

Storage Method

Select Scaled or Floating Point (64 characters). Scaled is a 2-byte data storage method; floating point uses 8 bytes.

Floating point storage has a dramatically expanded data range in comparison to scaled storage, allowing values to have far greater resolution. However, you need to consider that it also uses a lot more disk space. Use scaled where compatibility with pre-V5.31 trend history files is necessary.

If you do not specify a storage method, it is set to Scaled by default.

No. Files

The number of history files stored on your hard disk (for this tag) (4 characters maximum). The maximum number of files you can specify per trend tag is 999. Performance and storage will be severely impacted by having a large number of history files per trend.

If you do not specify the number of files, 2 history files are stored on your hard disk.

Time

The time of day to synchronize the beginning of the history file, in hh:mm:ss (32 characters maximum). If you do not specify a time, the file is synchronized at 0:00:00 (i.e. midnight). The time needs to be specified in Greenwich Mean Time, not the local time zone.

Period

The period of the history file, in hh:mm:ss (32 characters maximum). Alternatively, you can:

• Specify a weekly period by entering the day of the week on which to start the history file, for example Monday, Tuesday, Wednesday, etc.
• Specify a monthly period by entering the day of the month on which to start the history file, for example 1st, 2nd, 3rd, 4th, 5th, etc.
• Specify a yearly period by entering the day and the month on which to start the history file, for example 1st January, 25th February, etc. The day and month needs to be separated by a space.

• If you do not specify a period, the period defaults to Sunday (weekly).

  When deciding on a period setting, be aware that the performance of a trend viewer (be it the existing CitectSCADAclientA computer that accesses shared network resources provided by another computer called a server. 's client-server based architecture is designed to distribute the processing tasks and optimize performance. or Process Analyst) may be impacted by the size of a trend file. This is particularly true when displaying event-based trend data.

Extended forms fields

The following fields are implemented with extended forms (press F2).

Privilege

The privilege necessary by an operator to display the trend data on a trend.

Area

The areaA large application can be visualized as a series of discrete sections or areas. Areas can be defined geographically (where parts of the plant are separated by vast distances) or logically (as discrete processes or individual tasks). to which the trend data belongs.

Eng Units

The engineering units of the variable/expression being logged (8 characters maximum). The engineering units are used by the trend scales and trend cursor displays.

Format

The format of the variable/expression being logged (11 characters maximum). The format is used by the trend scales and trend cursor displays.

This property is optional. If you do not specify a format, the format defaults to ####.#.

Deadband

The value that Trend Tag need to return to before the Trend becomes inactive.