SQL Logger Group Tag Type Properties: Log Settings Tab
The Log Settings tab allows you to configure the timing for when data will be written to the database.
There are three choices of Log Type: Interval, Triggered and On Data Change. Note that all the tags attached to a particular SQL Logger Group through the associated SQL Logger tags will use these settings.
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Interval Selecting "Interval" allows you to record values every (n) seconds. Use this when you want continuous monitoring of the system, setting the interval to the number of seconds you want between each data output.
Triggered "Triggered" allows you to write values only when some condition changes. The write could be triggered by a tag changing value, or you can create an expression to define precise conditions that will cause a value to be written. Note that the trigger does not need to be activated by the same tag whose value you are recording. You could potentially record the level of a holding tank every time a pump switches on and/or off.
When logging is to be triggered, you must also choose what the trigger will be. For testing purposes you can choose Constant. This allows you to set a value of 1 for "On" or 0 for "Off".
Selecting "Expression" as the Log Trigger allows you to enter an expression using VTS's scripting language. See the VTS Programmer's Guide for more detail on writing expressions.
Selecting a Tag as the Log Trigger allows you to select any tag in your project to indicate when to write log values. The following section, "Trigger On" applies directly to using a tag as the trigger as you must also indicating what change in condition of that tag is to indicate when to write data.
The space where you see a 0 in the dialogue box above will be replaced with a selection of the tags in your project.
In almost all cases, if you are using the Triggered option for the Log Type, you will choose a tag as the trigger.
If you have chosen Triggered as the Log Type, you also have the choice of whether the trigger happens on a Value Change, a Rising Edge (from False to True) or a Falling Edge (from True to False. This applies to Constants, Expressions and Tags.
This option for log triggering passes more control over to the Logger Tags attached to this Logger Group. Essentially, you are indicating that log values are to be written when the value of the tag you are monitoring changes. See the section on the SQL Logger Tags for more information.
If using this log type, please read the following section: Log Invalids for an important note.
You have the option of whether or not to record "invalids" as part of the data being written. An invalid data value is essentially a NULL.
Note that if you select On Data Change as your trigger and you have not chosen to log invalids, then if the data changes from a valid value to invalid (or vice versa), no value will be written. You must enable Log Invalids in order to capture these data changes.
Where triggering controls the timing of data output, Enable sets whether or not data is to be output at all. Where the two controls offer the same options of "Constant", "Expression" and "Tag", the difference may seem subtle, but it is fundamentally different. Enabling the logger group means that logging is switched on or off. Triggering means that (if logging is enabled) data values are written when the trigger signals them to be.
Note: if a SQL Logger Group is disabled, then all the SQL Logger tags attached to that group are automatically disabled.
Use Coordinated Universal Time (UTC)
A switch giving you the option to record the time stamp using either local time or UTC.