The trend system can help you better understand your plant and equipment's performance. Trending can be used for dynamic visual analysis (trend and SPC graphs), production records, or for regularly recording the status of equipment for efficiency and preventive maintenance.
Using trend tags, you can specify the data you
want to collect from your I/O Device variables. This information
can be logged at regular intervals (periodic
trend
), or only when an event occurs (event trend).
Event trends are used for trending data that is not time-based, for
example, for a product as it comes off an assembly line. Trend data
is usually saved on disk for analysis or displayed on a trend
graph.
The trend system is based on real-time samples. The trend system expects a return of one data point each time it samples the data. Although gaps in the data can be filled, you will want to verify that your field device can return data values at the rate you specify (especially if you are using sample periods of less than 100 ms).
Any amount of data can be collected and stored. The only restriction on the amount of data that you can store is the size of the hard disk on your computer (an efficient data storage method is used to optimize the use of storage space on your computer's hard disk). For long term storage, you can archive the data to disk or tape (without disrupting your runtime system).
Note: If you are trending data across a
network (distributed
processing), it is recommended that you
enable time synchronization using the Time Synchronization configuration
application. This verifies that every trend is synchronized to the
same time.
You might also consider staggering your trend sample requests using the [Trend]StaggerRequestSubgroups parameter.
See Also