Messing about in trend view I noticed an odd behavior. I am controlling a pair of outputs according to a schedule. Basically leave them on all the time, but turn them both off at a scheduled time using DTCMP, for a set duration. As part of commissioning, I started a trend to confirm that the instruction was doing what it was supposed to, and to my surprise, the trend showed that the DTCMP was triggering 2 seconds before the scheduled time every time. Watching the trigger happen in real time, you could see that it was working as intended, but the trend report (CSV) always showed it happening 2 seconds early. A light bulb went on, and I wondered if the DMD Trend used the PLC clock or the clock of the PC it was running on? Lo and behold, the PLC clock is 2 seconds ahead of the PC clock. Therefore the PLC says it say 23:00 hours, but the PC says its 22:59:58. So the Trend view says the event happened at 22:25:58. So I learned that the Trend View in DMD uses the PC time, while the PLC of course uses its own. Here is the kicker. The PLC is set to sync to an NIST server once a day, and the PC syncs to the Microsoft server once a day. As long as I do this, the two times are never closer than 1 or 2 seconds apart. Once I changed the PC to an NIST server, the two times are right together. I wonder where the Microsoft server gets its time? 2 seconds in this case has no real significance really, just found it interesting. Anyway, I thought I would share this in case anybody else runs into this little quirk commissioning or qualifying a piece of equipment.
Topic: Odd Quirk DMD Trend View (Read 6951 times)