DF Time versus PC time


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I have read the article on using Usertime.dll to synch DaqFactory to the PC time. I notice that for my systems that run for very long periods (many months without re-starting) DF time drifts e.g. in one at present it is 15 minutes fast.

All my PC's have the time clock adjusted auotmatically, regularly (at least once per day). I realise the downside to using the PC time and having it adjusted it may set off alarms etc. but is there any way to use DF time and have it adjusted - I guess the same comments apply about alarms, double logs etc.

The only other alternative is to stop and re-start DF on a regular basis e.g. weekly, monthly.



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First, userTime replaces the internal time. The normal DF time uses the high precision crystal, but as you've seen, can drift over long periods. It reads the absolute time on startup, then the high precision crystal the rest of the time. UserTime uses the windows system clock. Its less precise (15ms or so), but of course holds truer to the actual time, especially if you have Windows making corrections for you.

The issue with using UserTime is when it gets changed by a lot. Having windows adjust the time automatically (using a network time server) is probably not going to cause issues because the time shifts are quite small, usually less than a second. The big problem is daylight savings time, because that's a full hour shift. So, if you want to user UserTime and don't want to figure around DST, simply turn DST off on your computer. Otherwise, it doesn't matter what software you use, you are going to have to take careful consideration for when the clock suddenly shifts by an hour.

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Yup, unless you need high precision (i.e. < 20ms) time stamps. I know people want their systems to display the actual time (with DST), but I can tell you from personal experience working with large data sets, that you should always log your data without DST, and ideally in UTC.

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