Most types of outstation have only basic or no built-in time zone support. Most outstations typically runs a single clock.
We recommend that any outstations with which ClearSCADA is to interact run in Coordinated Universal Time(UTC) whenever possible. ClearSCADA stores time values internally in UTC and therefore any time stamped data retrieved from such outstations will be stored ‘as is’, without ClearSCADA needing to perform any time conversions. (If required, time values can be displayed in Local Time on a ClearSCADA Client. With each User that requires time values to be displayed in Local Time, ClearSCADA converts its UTC time values to Local Time for display on whichever ClearSCADA Client that user is using.)
If outstations need to run in Local Time, we recommend that they run in Local Time without Daylight Saving Time. The relevant driver will convert any local time values to UTC before passing the data onto the ClearSCADA server, and vice versa whenever ClearSCADA sends time values to the outstation.
Should outstations need to run in Local Time with Daylight Saving Time, the outstation’s clock has to be set correctly at the transition from Standard Time to Daylight Saving Time and vice versa.
Ideally, all logged (time stamped) data should be retrieved from the outstation before the outstation’s clock is set forward or backward.
Care needs to be taken to ensure that the clocks of PSTN and On Demand outstations are set in a timely manner, as close as possible to the time at which the actual transition occurs. When clocks jump forward, the outstations’ clocks need to be set within the time frame by which the clocks jump. So, in time zones in which the clocks jump forward by an hour, the outstations’ clocks need to be set to the new time within 1 hour of that transition actually occurring. Providing that this is done, the data will be recorded with the correct time stamps both before and after the transition. (Any data that is reported within the 1-hour time frame is deemed to be in Standard Time, rather than Daylight Saving Time, and is time stamped as such.)
If any PSTN or On Demand outstations on your system run in Local Time with Daylight Saving Time, consider whether to use Schedules to automatically contact those outstations and change their clocks at the relevant time. For more information, see Using Schedules to Automate Regular Functions.
For further information on the effects of clock changes in outstations that run in Local Time with Daylight Saving Time, see The Effects of Daylight Saving Time Adjustments.
Example:
A PSTN outstation is configured to run in Local Time with Daylight Saving Time.
The outstation is in a time zone in which clocks jump forward by an hour in the spring, from 01:00 GMT to 02:00 BST. (In other words, from Standard Time to Daylight Saving Time.)
On the morning of the transition, the outstation logs an event at 01:30:00.000 GMT. The outstation’s clock has not yet been set to BST. The event is stored in the database as 01:30:00.000 UTC. On any ClearSCADA clients on which users view time values in Local Time, the event is shown as having occurred at 02:30:00.000 BST.
If the outstation’s clock had been set to BST before the event occurred (say at 01:00:01.000), the same event would have been:
- logged in the outstation at 02:30:00.000 BST
- stored in the ClearSCADA database with a time stamp of 01:30:00.000 UTC
- still be reported to the user as having been logged at 02:30:00.0000 BST.
Therefore, as long as the outstation’s clock is set forward correctly before 02:00:00.000 GMT, events that occur before and after the clock change will be reported and logged with the correct time stamp.
If for some reason the outstation’s clock was not updated until after 02:00:00.000 GMT, ClearSCADA would deem any time values for 02:00:00.000 onwards to be in BST rather than GMT. So if the outstation logged an event at 02:05:00.000 GMT, for example, ClearSCADA would process that data as having been logged at 02:05:00.000 BST (rather than GMT). Therefore in ClearSCADA the data would be logged with a time stamp of 01:05:00.000 UTC, and be shown on any ClearSCADA client on which users view time values in Local Time, as 02:05:00.000 BST.
If the outstation’s clock was only updated at, say, 02:30:00.000 GMT, any time stamps for 02:00:00.000 onwards would be presumed to be in BST rather than GMT. Additionally, when the outstation’s clock was adjusted forward by an hour at 02:30:00.000 GMT to 03:30:00.000 BST, a gap of one hour would appear in the data that ClearSCADA retrieves from the outstation. This is due to the 02:30:00.000 GMT clock change occurring half an hour later than the one-hour limit within which the clock’s time needed to have been set, in order for all of its time stamped data to be recorded correctly.