MONITORING STATION INSTRUMENTATION AND MEASUREMENTS - Wind Resource Assessment: A Practical Guide to Developing a Wind Project - page 50

accesses this buffer to calculate the desired parameters, such as means and standard
deviations. The resulting data values are then stored in memory. Some data loggers
have a fixed, or firm, operating system that cannot be altered or can be only slightly
modified; others are user-interactive and can be reprogrammed for different tasks. In
older models, the operating system and data buffers are sometimes stored in volatile
memory. Their drawback is that they need a continuous power source to retain data.
Data loggers that incorporate internal backup batteries or use nonvolatile memory are
preferred because data are less likely to be lost.
4.5.1 Data Processing and Storage
Data processing and storage methods vary according to the data logger (Chapter 7).
There are two commonly used formats for recording and storing data: ring memory
and fill and stop.
1. Ring Memory. Once the available memory is filled to capacity, the newest data
record is written over the oldest.
2. Fill-and-Stop Memory. Once the memory is filled to capacity, no additional data
are archived. This stops the data logging.
In the past, the ring memory format was preferred over fill-and-stop memory
because it allowed data logging to continue if the operator was unable to retrieve
the data before the memory buffer was filled. Given the memory storage capacity of
modern data loggers, however, this is of much less concern. Today's memory buffers
are typically able to store at least 6-12 months of data, unless the recording interval
is much less than the usual 10 min.
4.5.2 Storage Devices
Most manufacturers offer several options for data storage devices. The most common
are presented in Table 4-6.
4.6 DATA TRANSFER EQUIPMENT
The selection of a data transfer and handling process and data logger model depends
on the monitoring program's resources and requirements. As a rule, the manufacturer
should be consulted to ensure compatibility between system components. It is also
recommended that a unit be purchased in advance for testing before committing to a
new monitoring system configuration.
Data are typically retrieved and transferred to a computer either manually or
remotely.