Delta OHM HD32MT.3, Operating Manual

Page: 26 / 62

HD32MT.3
- 26 -
V1.2
8 TIPPING BUCKET RAIN GAUGE MEASUREMENTS
The pulses generated by the tipping bucket rain gauge increase two separate counters: a par-
tial counter and a total counter. The partial counter allows to measure the amount of rainfall
from a given instant (the instant of resetting the counter) without losing information on the to-
tal amount of rainfall, the information which resides in the total counter.
The partial amount of rainfall can be recorded by the data logger inserting in the storage tables
the measure of index 29 or 30 (see paragraph 11.6).
The total amount of rain, not recorded in the storage tables, can be read with the command
RAINTOTALS (see paragraph 11.8) or calculated by the user based on the information in the
files of type T2, containing the instants of generation of the pulses by the rain gauge.
8.1 C
ORRECTION
T
ABLE ACCORDING TO THE RAINFALL RATE
If the rain gauge connected to the data logger has a measurement correction table as a func-
tion of the rainfdall rate, you can store the correction in the data logger to obtain the values of
the amount of rain compensated.
The correction is necessary because during the emptying time of the tipping bucket, rain is not
collected from the bucket and the amount of rain in the absence of correction is therefore un-
derestimated. The correction to be made is greater the higher is the rainfall rate (greater
number of cycles in the time unit).
The data logger allows you to set nine multiplication factors (k
1
...k
9
) of the nominal resolution
of the rain gauge, each corresponding to a range of rainfall rate expressed as the time interval
in seconds (T
BUCKET
) between two successive emptying of the rain gauge tipping bucket.
k
1
= multiplicative factor of the nominal resolution if T
BUCKET
< 2 s.
k
2
= multiplicative factor of the nominal resolution if 2 s

T
BUCKET
< 3 s.
k
3
= multiplicative factor of the nominal resolution if 3 s

T
BUCKET
< 4 s.
k
4
= multiplicative factor of the nominal resolution if 4 s

T
BUCKET
< 5 s.
k
5
= multiplicative factor of the nominal resolution if 5 s

T
BUCKET
< 6 s.
k
6
= multiplicative factor of the nominal resolution if 6 s

T
BUCKET
< 8 s.
k
7
= multiplicative factor of the nominal resolution if 8 s

T
BUCKET
< 10 s.
k
8
= multiplicative factor of the nominal resolution if 10 s

T
BUCKET
< 15 s.
k
9
= multiplicative factor of the nominal resolution if 15 s

T
BUCKET
< 30 s.
If T
BUCKET

30 s no correction is applied.
Example:
If you set k
4
= 1.100 for a rain gauge having 0.200 mm nominal resolution, the correct resolu-
tion will be considered equal to (0.200 x 1.100) = 0.220 mm when the rain falls with sufficient
intensity to cause two successive emptying of the bucket in 4 seconds or more but less than 5
seconds.
If in the technical data of the rain gauge the correction is expressed as a function of hourly
rainfall in mm/h, use the following formula to calculate the interval in seconds between two
subsequent emptying of the bucket as a function of the rainfall rate:
(mm/h) rate Rainfall
(mm) resolution Correct
3600 (s) T
BUCKET
 =
Example:
If a rain gauge with 0.200 mm nominal resolution has a correct resolution of 0.212 mm when
the rainfall rate is 100 mm/h, the interval in seconds between two subsequent emptying of the
bucket is equal to: