Historical charts (hereinafter simply graphs), unlike trends, allow you to save your data in an database log.
To create a graph, you need to select the menu item Setup / Graphs. The creation interface here is the same as for Trend, with one exception - only registers with the option 'Save data for graphs' set will be displayed in the register list (see work with registers ). See more on this here.
When there are graphs configured, they appears in the Analytics / Graphs menu.
An example of a graph is shown on the following pictures:
Elements of the graph:
See explanation below for the spots #4, #5, #6 .
See the video:
Below is the video clearing how the curve's 4, 5, 6 parts are formed as well as min, max and avg values.
In this example, the register's property was set to use data from log and save on every change. The sinus value was calcualted in a script executed each scan. Then system scan time was changed from 50 ms to 1 seconds. Becuase graph viewing area resoluon is 1 seconds, more data saved in database log for any given point when scan was 50 ms and that was highlighted with semitransparent zone along the curve.
In the case when for a selected plot scale 1 minute or more will fit into 1 pixel of the screen, then the average values (5) of the register and the zone (4) of the range of values for estimating the distribution of the minimum and maximum peaks will be displayed on the graph. This averaging is drawn using cached data from the database, corresponding to the current scale of the view (in the database, averaging is stored for 1, 2, 5, 15 and 60 minutes). This method allows you to optimize the work with graphs when viewing large amounts of data on a different scale, while maintaining the speed of work.
When the current view time scale matches log speed of the parameter, the (6) solid lined is drawn so that there is either exact value, or its average / min / max are very close to each other.
The log depth can be adjusted in the Setup / Settings menu:
Theoretically, the volume of the archive is limited only by the size of the flash card. In practice, when the archive size is increased by more than 300MB, the 'response time' in the interface when working with WebHMI can increase and affect the comfort of the user's work. It should be said that storing large amounts of data is not the target application of the device, although it allows it to do so. These graphs should be used during the research stage of the monitoring object, keep the archive for analysis of certain situations (which after use can be deleted), etc. For long-term storage of a large amount of monitoring data, it is recommended to use a special server - fetching log data via the API or the Level2 cloud server option.