One of my customers uses an ION7550 V355 to modbus master and log metering data from 17 downstream Enercept and PM600 meters. There are 17 data record module inside 7550 to log data from each downstream meters, and they are set up exactly the same with a log "Depth" equal to "9120". This setup has been worked fine for the past 6, 7 years, and 7550's on-board memory was able to keep the metering data's integrity in the event of server restart or network outage.
The customer's Ethernet network went offline on Dec 7th 2016, and it was not fixed till Jan 3rd. After the comms was restored and waited after ION log inserter downloaded all the on-board logs from 7550 (data logs were "caught up"), we found that around 10 data (data recorder) had a gap between Dec 17th 2016 and Jan 3rd. At the same time, the other data recorder still logged the data without any gap.
The downstream devices are all on the same RS485 chain connected to 7550's COM2, and they were working in the whole time. All the data recorders have large enough log "Depth", so last month's data should not be FIFOed out. I pulled in question data log directly from 7550 using IONSetup to bypass ION, and it also shows that there is no data between the gap, so I suspect that it is something related to 7550 itself rather than ION DB.
Another observation is, before the network was restored, the customer cycled the control power to the 7550, and there are "power down" and "power up" events logged by 7550. My first question is, is it possbile for a 7550 meter to lose some of the logged data during a control power cycling? If 7550 stores the logging data in a DRAM area and period write it to Flash memory, when the control power is off, does it have enough time to flush all the DRAM data into Flash memory?
The answer to your first question "IS it possible to lose logged data on a controlled power cycle" is a complicated one. Technically the answer is yes if the device is triggering data records at a very high speed so that it runs out of flash credits (these are tokens used for the saving of data records). However in your case I can see that the data recorder is triggering every 15 mins, and the credits are incremented every 10 minutes, therefore in your case you will not be able to run out of credits.
To answer your second question the meter will not have saved up 3 weeks worth of data to be written to the flash. Data from all intervals would have had ample time to write to the flash.
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