Campbell Scientific LoggerNet Datalogger Support Software - Manual (Page 109)

Section 4. Setting up Datalogger Networks
Table Data Dataloggers
When connected, data from table data dataloggers is updated based on the
Update Interval. (This is referred to as real time monitoring.) Note that
data can be updated no faster than the data values are being generated by
the datalogger. When not connected, data from table data dataloggers is
updated only as often as data collection is performed. (This is referred to
as passive monitoring.) Therefore, for input locations or public variables
to be updated when not connected, they must be included for scheduled
collection.
RTMC
In RTMC, data displays will be updated no more frequently than data is being
collected from the datalogger, either manually or on a schedule.
4.2.5.2 Intervals
One of the most significant considerations for setting up data collection is all of
the intervals associated with reading, storing, and retrieving data. The intervals
and their significance for data handling are described below.
4.2.5.2.1 Datalogger Program Intervals
There are two types of intervals written into the datalogger program which
affect the availability and collection of data:
• Program Execution Interval – The execution, or scan, interval
determines how often the datalogger carries out the instructions in the
datalogger program. It is specified in seconds and determines the
fundamental rate at which data is available. In typical programs the sensor
readings are taken at this rate and the values are stored in corresponding
Input Locations or variables. This execution interval is the fastest that data
measurements can be updated and data stored. (Depending on how the
program is written, sensor readings may occur at specified intervals and
not on every program execution.)
• Table Storage Interval or Output Data Interval – Most data tables or
final storage arrays are set up to store data records at regular intervals.
The data record consists of a record number and time stamp, followed by
the output processing (i.e., sample, average, min, max, etc.) of the input
location or variable values. This interval must be a multiple of the
program execution interval or storage intervals will be skipped. For
example, if the program execution interval is 5 seconds and the table
interval is set to 3 seconds, there will only be an entry in the table every 15
seconds. The interval specified determines the fastest rate the server can
collect new data that is stored to the datalogger’s final storage memory.
4.2.5.2.2 Data Collection Setting Intervals
The collection interval at which the LoggerNet server requests new data from
the datalogger is set up on the Schedule tab for that datalogger in the Setup
Screen. If the collection interval is faster than the rate at which data is being
stored to a data table by the datalogger program, data will not be collected
every call, but only at intervals when new data is available.
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