Campbell Scientific SC115 CS I/O 2G Flash Memory Drive with USB Interface - Manual (Page 24)

SC115 CS I/O 2G Flash Memory Drive with USB Interface
12.2 Skipped Scans
To avoid skipped scans, ensure that the scan interval in the datalogger program
is long enough to include writing to the SC115. For example, if the program
has a single TableFile() instruction, add at least 100 ms to the scan rate to
accommodate each added TableFile() instruction.
Compile datalogger programs in pipeline mode when possible. Datalogger
programs compiled in sequential mode require a longer scan interval than
programs compiled in pipeline mode to avoid skipped scans. In pipeline mode,
the Scan() / NextScan instruction BufferOption parameter can be increased to
prevent skipped scans. In sequential mode, the TableFile() instruction must
finish before continuing to the next instruction, resulting in skipped scans
unless the scan interval is long enough to handle all communication,
measurement processing, and TableFile() tasks. Sequential mode ignores any
scan buffers that may be assigned. Programs may run as much as three times
faster in pipeline mode than in sequential mode.
12.3 SC115 with Large Data Compliment
An SC115 with a large compliment of data (either a large number of files, or a
few very large files) may respond slower than an SC115 with less data.
Compiling datalogger programs from a full SC115 may take longer than
normal.
Opening the SC115 directory in support software File Control also takes
longer if there are a large number of files within the SC115 directory. File
Control can access approximately twenty files per second when opening the
directory.
12.4 Data Collection Speed
Many factors affect collection speed in plug and pull data collection mode. As
a rough estimate, collection speed is typically 3 to 4 kB of SC115 file size per
second (TFOption = 8, SDC7 set to -115200 [autobaud], no card storage
module present). Following are descriptions of two factors that contribute
significantly to the slowing of collection speed.
12.4.1 CF Card and Collection Speed
Following is a discussion of SC115 performance expectations when it is used
in tandem (plug and pull data collection mode) with a resident CF card on a
datalogger.
Background — When an SC115 is configured for data collection mode (plug
and pull), and it is plugged into a datalogger with a resident CompactFlash
®
(CF) card, and the running program is using the CardOut() instruction, all data
present since the last collection will be automatically transferred from the data
table to the SC115 file.
How it works — When CardOut is used in a DataTable() / EndTable
declaration, the file created on the CF card becomes an extension of the table
memory. The internal memory is used as a buffer to transfer data to the CF
card. When there are enough data to warrant a write to the CF card, the data are
flushed to the card. This results in duplicate data, up to the internal table size,
that will exist on the internal memory and the CF card files. Any time the table
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