UNIDATA
Unidata Manual 6293 - Precision Water Level Instruments Issue 2.1
12
•
Scan rate.
•
Log interval.
•
Log sub-interval.
The scan rate defines the frequency at which the logger “wakes-up” and
interrogates the instrument. This is typically 5 seconds, however a shorter
interval may be defined for better data definition or, a longer interval to
conserve data logger battery power.
The log interval is the time between entries saved to the logger memory. The
ideal log interval will capture adequate details for your project without wasting
memory or producing unnecessary data.
Natural water levels may change slowly for most of the time except during very
intense rainfall when rapid changes may occur. For many projects you will want
to record these extreme events and will need to select your log interval
accordingly. Key in the log interval. It must equal an even number of scans.
Logs will be aligned to logical real times, e.g. hourly data will log on the hour.
The sub-interval allows you to average data over a portion of the log interval.
For example, if you have selected a log interval of 1 hour and you enter a sub-
interval of 5 minutes, the data you log (if you select (ave)) will be the average of
all scans in the last 5 minutes of the log interval.
Event Based Logging
You can also define an event-based scheme. Event-based logging can extend the
memory endurance by only logging when specific events are detected. A simple
example of an event is; to log each time there is a level change greater than
5mm.
Water surfaces fluctuate by small amounts constantly. Avoid defining small
increments (say 1mm) or the logger memory will be quickly exhausted.
Events are defined in the Event window. Each time a defined event occurs, the
time, date and instrument value is logged.
Memory use depends on the rate at which the events occur. As a result memory
use cannot be predicted with certainty when you use Event Based Logging.
3.1.3 What to Log
You specify what data is logged by checking the boxes for each instrument
channel in the log buffer window, as shown on the next page.
The logging options are as follows:
