Daylight Saving Time Home

Attention New Zealand 2007:  17-Aug-2007: New Zealand will follow new DST rules starting September 30, 2007. OSIsoft will post a bulletin on the Home Page of the Tech Support website when a new localhost.tz file is available. You will also need to update your OS. See Microsoft's website for OS updates.

Attention U.S.A. and Canada 2007: Please see support bulletin regarding new DST rules for 2007.

Attention users with customized LOCALHOST.TZ files: Please see support bulletin regarding a known bug that can cause the localhost.tz file to be overwirtten.

Daylight Saving Time (DST) is a system whereby clocks are adjusted for part of the year to create more daylight in the evening hours.  At the beginning of the DST period in the Spring, clocks are turned forward an hour, effectively moving an hour of daylight from the morning to the evening.  When the DST period ends in the Fall, the clock is moved back one hour, thus returning the clock to Standard Time (ST).

DST is an issue that PI System Managers must grapple with twice a year.  PI 3 Servers observe DST settings, so there is very little a PI 3 system manager should need to do to prepare for DST.  However, PI 2 Servers and PINet nodes do not observe DST settings; therefore, system managers must manage the DST time changes on PI 2 Servers and PINet nodes using the appropriate utility or batch file as described in the appropriate sections on the right.

For all machines that are part of the PI system, it is important to make sure the time is set correctly and synchronized to the PI Server. In addition, all Windows machines should have the proper time zone settings and should be set to automatically adjust clock for daylight saving changes (see the “Date and Time” control panel). When there are offsets between the nodes, there may be short time periods where data are lost, duplicated, or inserted with timestamps off by an hour. If time changes for DST are disabled this can result in data loss.

Click on the appropriate links to the right for more details on issues that affect PI Systems during DST transitions. 

PI Time Stamps
PI 3 Servers store data time stamps in seconds since 1970 in Coordinated Universal Time (UTC). This is why it’s so important that the time and time zone be properly set on the PI Server operating system and all interface nodes and clients in your PI system.

For most current interfaces using the extended PI API, events are sent to the server with UTC timestamps.  As a result, DST and time zone differences are properly considered when storing data on the PI Server.

PI SDK-based clients, such as ProcessBook and DataLink 3.x and higher, utilize the UTC timestamps directly from the PI Server, whereas PI API-based clients, such as ProcessBook and Datalink 2.x and earlier, use server local timestamps.

• Appendix C on "PI Time Conversions" in the PI Server Reference Guide version 3.4. This appendix includes discussion on how time zone adjustments and UTC translations are applied, and tables on conversion of PI 2 timestamps to PI 3 systems.
• The PI SDK Help file (pisdk.chm) for details on PI timestamp structure (look for "PITIMESTAMP structure" in the Index).