NOVUS V1.5x A - Manual (Page 88)

NOVUS AUTOMATION www.fieldlogger.net 88/103
Modbus commands to start and stop loggings, when enabled, can be sent at any time and have precedence
over the configured start and stop modes. In such a way, if a Modbus command to start loggings is sent to
the equipment, they will start up, no matter the state of the equipment in relation to the configured modes
(the only exception is a configured mode different from "circular memory" with the memory already full).
Similarly, when sending a Modbus command to stop loggings, they will stop regardless of the mode
configured for start and stop. If a stop command has been sent and then there is a start situation (as per the
configured mode), loggings will not occur, because the command has higher priority than the modes. It is
worth to point that the sent command persists even after a power outage. When sending a new logging
configuration, however, the previously sent commands are "forgotten".
When logging is done in the SD card, it is generated a folder structure whose purpose is to organize the logging data and
to ease access for the data download software to such data. The following figure shows an example of this structure:
In the root folder it is created a folder whose name is the serial number of the equipment. Inside this folder, in its turn, are
generated other folders whose name are the year and month in which the logging began. And inside of the year-months
folders, other folders are generated whose names are the days in which the loggings start up. The data files are stored
within these last folders and their names are made up by the information related to hour, minute, second and hundredths
of second of the first log in the file, followed by the extension "fl". For example, the file /00000002/201010/01/18243516.fl
was generated by FieldLogger with the serial number 00000002 on October 01, 2010, and the first log contained in this
file was held on this day at 18 hours, 24 minutes, 35 seconds and 16 hundredths.
The files generated by the registration process are composed of a header followed by periodic data blocks and
timestamps (time markers). The header carries information relevant to the logs from that file, essential for the correct
interpretation of its data. In the data block are stored values for each channel that is being logged, in floating point format
(IEEE 754) with simple precision, where each log occupies 4 bytes. The timestamps are used as time reference to
identify the moment in which the channels were logged. Periodic timestamps serve to ensure the integrity of the loggings
in time, even under power failure or fault in the SD card.
When the logging is done in internal memory, the file format is exactly the same as when it is written on the SD card.
However, by the size of the available memory, all data will be contained in one sole file.
In its internal flash memory, FieldLogger has something about 2M bytes that turns into an approximated value of 512k
(512000) loggings. The exact loggings number depends a lot on the enabled channels number for loggings and on the
configured logging interval. Logging intervals equal or bigger than 30 seconds record, on each logging instant, extra data to
indicate the time when the log happened (timestamp), and that increases memory consumption makes the total logging
capacity decrease. Therefore, speaking of logging memory usage, the worst possible scenario is logging only one channel
on slow (bigger than 30 s) intervals.
Data download consists of copying the data from the internal memory of FieldLogger or from the card to a computer. This
process, when using the configuration software, is guided and assisted. When done via USB flash drive, it is also simple
and automatic. However, when performed manually, via an FTP client, for example, one should take care that the directory
structure is kept, otherwise an error may come to occur in the interpretation of the data download.
It is not possible to download data through different interfaces at the same time. If a user starts a download through the
Ethernet interface (FTP, for example) and another user tries to download via USB flash drive, this one will not be able to
accomplish the download and must wait until the first download has been terminated.
Depending on the amount of data on this equipment, mainly when using high-capacity SD cards, the download process
can take hours. In these cases, prepare to make the download through faster interfaces and, perhaps, in more likely
times of the day.
The simultaneous data download while in logging process is based on the assumption that the download rate is faster
than the logging rate. This is particularly important when using circular memory, because, otherwise, we could never
download all the data (the logging, being faster, might eventually turn around, reaching and surpassing the download,
which would lead to data inconsistencies). Such being the case, whenever the circular memory is used with high
registration rates, you should try to use a faster interface for download.