4 DATA STORAGE
During the data acquisition cycle, the probe not only shows acquired data in real time but also acts as a
data logger, storing the acquired data in its internal non-volatile memory. The probe is equipped with
2-GByte or bigger SD FLASH memory.
4.1 MEMORY ORGANIZATION
The probe, data memory is organized in two main areas. The first area is called “CAST”; it stores the
information about “when” and “how“ data has been acquired by the probe. The second area is called
“DATA”; it stores acquired data subdivided into data records, 4 bytes long. A data record is associated
to each physical sensor installed on the probe. The probe acquires and stores data relative to all the
installed sensors. A group of data records about all the installed sensors becomes a single ”data set”.
The probe stores and retrieves single or groups of “data sets”.
Acquired data is stored in memory in ADC counts. Only data belonging to physical installed sensors
are stored in memory. Parameters relative to derived units, like salinity, are not stored in memory. They
are immediately calculated once the operator asks to show stored data or to transfer stored data to a PC.
The conversion from ADC count into engineering units is done by means of the algorithms described
in the introduction section and by means of the sensors calibration values. A copy of calibration values
is associated to each set of data “CAST” stored in memory. A dedicated non-volatile memory stores the
copy of calibration values.
As a common-sense rule, it is important that the probe internal memory is not used as an archival
memory to keep data for very long time. It is important that stored data is transferred to a PC and then
archived there, immediately after the field campaign is concluded. Increase of the probe performance
can be obtained if, before starting a new measurement campaign, the probe memory is initialized.
Therefore, we strongly suggest that you upload data immediately after the field campaign and initialize
the probe memory immediately before starting the next field campaign.
4.1.1 Cast area
Allocated space of the “CAST” area is for 5000 casts. The number of data records, associated with a
certain number of casts, is only limited by the number of free data records. This means that a single cast
can head a set of data, which uses all the data area, or that the data stored for 5000 casts does not use all
the data area. The number of storable casts does not depend on the memory size. It is fixed at 5000.
The header information stored for each cast is:
❖ data acquisition starting time;
❖ sampling area identification code;
❖ type of data acquisition;
❖ time intervals or depth steps used to acquire and store data;
❖ number of parameters stored for each acquisition;
❖ number of data records stored for this cast;
❖ first data record stored for this cast.
❖ Indexing to the calibrations records associated to this cast
The above information is presented to operator when the [Show Memory Status] command is used (see
below).
4.1.2 Data records
Each data record is 4 bytes long. Either data record can contain a parameter value in raw format (ADC
counts) or the acquisition time expressed in hundredths of second. The number of data records that can
be stored in the probe internal memory depends on the size of the probe memory. A bigger memory
allows storing more data records.
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