Xylem H-340SDI - Manual (Page 12)

1-6 H-340SDI Introduction
H-340SDI
Other related equations of interest:
RATE
RAINFALL
N
in
hr
inches
hr
= ×
min
min 60
RAINFALL
RAINFALL
N
inches
tip
inches
tips
=
1.9 User Calibration
The “smart bucket” processor uses a fixed polynomial to compute each bucket volume as a
function of rainfall rate. The factory calibration should be sufficiently accurate for all rainfall
rates from 0 to 25 inches/hour. If the user requires an exact calibration at a rate other than 4.0
inches/hour, or if the tipping bucket mechanism is damaged or changed the bucket mechanism
may need to be recalibrated. The procedure for adjusting the counterweight is included below.
Please note that the “smart bucket” feature is calibrated somewhat differently than a normal
tipping bucket device. With a simple tippling bucket, a known amount of water is passed
through the gauge and the number of bucket tips is recorded. The counter weight is then adjusted
for the desired number of tips. With the H-340SDI “smart bucket” feature, the number of bucket
tips is not used in the calibration, instead, the SDI-12 measurement value is used. This is
different because the H-340SDI's microprocessor is using a non-linear polynomial expression to
compute the volume. With the aid of the polynomial you can get an accurate field calibration
without using the constant flow apparatus which is used at the factory. Just remember to use the
SDI-12 “aM” measurement values and not the number of bucket tips.