In-Situ Win-Situ 4 / Pocket-Situ 4 Operators Manual - Manual (Page 99)

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rev. 003 11/04
LOG
Logarithmic (or simply “log”) sampling optimizes data collection speed and
memory usage for pump and slug tests. These tests characteristically
begin with very rapid changes in values, and end with very slowly
changing values. If you were to program a very fast linear rate, you could
characterize the early stages of the test, but you would be quickly
inundated with excessive data during the later stages of the test, possibly
running out of memory before the test is complete. Conversely, a slower
linear rate would allow you to run a test longer, but would not provide
enough early-time information to properly characterize the data.
Log sampling solves this problem with a schedule where the measure-
ments begin closely spaced and the interval between measurements
continuously increases. The sensor is measured at a logarithmically de-
creasing rate (i.e., continually increasing time interval between any two
points), taking 40 log-normally distributed measurements per log decade
of time.
For reference, the entire log schedule out to the 218th data point is shown
iin Appendix D.
Linearization Interval
The interval between measurements will continually lengthen, but your
specified Measurement Interval serves as a “linearization” value such that
the interval between measurements will never become greater than this
value. For example, with a Measurement Interval of 20 minutes, the
logger’s sampling interval lengthens until a 20 minute interval is reached,
then it begins to sample linearly from that time on at 20-minute intervals.
APPENDIX B: TEST MEASUREMENT SCHEDULES