Data from tags with loggers either attached or built-in is automatically logged by VTS so that you may generate reports and/or plot archived data. This historical data is stored in encrypted binary files that cannot be edited, and cannot be read unless a report is generated or the data is plotted on the Historical Data Viewer page.
These data files are named following the syntax, "<Tag Name>.dat" (e.g. AnalogStatus_20_01.dat or 2-A-10.dat).
For VTScada applications, historical tag data is stored in a special History directory within your application directory. Inside this History directory appear a series of subdirectories labeled using the syntax, "<YYYY>-<MM>.log" (e.g. 2004-5). Within each of these subdirectories are housed the data files for each tag in your system for the specified month.
For VTS applications, historical tag data is stored directly in your application directory.
While data is being saved to a historical tag data file, the file is opened, written, and then closed. This enables the data file to be logged to a network server, and read by other applications on the network. It is for this reason that it is required that only one logger be directly configured to record values per tag. Attempting to have more than one logger attached to a tag could result in a corrupted file and reduced performance.
There is, however, a means by which you can log the data for a single tag in multiple formats using multiple function tags. Instructions on doing so can be found in Using Function Tags to Facilitate Data Logging for a Standard Tag Type.
Each record in a data file consists of the tag's value, a timestamp, and the validity status of the data.
Note: It is possible to store more than one value per record in the data file by using custom scripting code; this process requires knowledge of the VTS scripting language, and is therefore beyond the scope of this guide; however, information on doing so is described in the VTS Programmer's Guide.