Sutron
Corporation
SDI
‐
TB
Users
Manual
Rev.
1.1
5/24/2018
pg.
4
2.2
Operation
IMPORTANT:
On
powering
up
the
SDI
‐
TB
for
the
first
time,
the
SDI
‐
TB
requires
about
2minutes
for
the
internal
capacitor
to
charge
up
and
the
supply
voltage
to
get
up
to
the
minimum
voltage
threshold
required
for
the
module
to
be
operational.
The
capacitor
typically
takes
about
10
hours
to
discharge
once
completely
charged
Reading
any
of
these
registers
will
initiate
a
new
measurement
and
the
measured
value
will
be
returned.
The
SDI
‐
TB
provides
a
standard
3
‐
wire
SDI
‐
12
bus
to
interface
with
any
SDI
‐
12
v1.3
compliant
logger
and
a
2
‐
wire
interface
for
connection
to
standard
Tipping
buckets.
Most
Tipping
buckets
consist
of
a
bucket
attached
to
a
simple
switch.
The
switch
makes
a
brief
contact
between
the
two
wires
as
the
bucket
tips.
The
SDI
‐
TB
increments
the
cumulative
total
and
daily
rainfall
and
raw
tip
count
for
each
tip
it
records.
The
SDI
‐
TB
can
be
configured
to
record
a
tip
on
a
falling
edge
or
rising
edge.
A
pull
‐
up
or
pull
‐
down
resistor
is
automatically
active
depending
on
whether
a
falling
edge
or
rising
edge
respectively
has
been
configured.
A
user
programmable
debouncing
duration
can
be
configured
to
filter
out
noise
during
the
voltage
transitions
as
the
switch
makes/breaks
contact.
The
SDI
‐
TB
uses
a
configurable
‘
Bucket
size’
or
a
third
order
compensation
polynomial
to
convert
tips
into
rainfall.
The
bucket
size
indicates
the
amount
of
rainfall
that
corresponds
to
a
single
tip
of
the
bucket.
By
default
(if
no
compensation
has
been
programmed)
the
SDI
‐
TB
increments
the
total
accumulation
after
each
valid
tip.
The
new
accumulations
is
calculated
using
the
formula
Since
the
bucket
takes
a
finite
amount
of
time
to
tip
over
and
start
filling
again,
some
rain
will
be
lost
before
the
bucket
is
in
position
to
collect
rain
again.
This
amount
of
rainfall
lost
will
become
more
significant
as
the
rainfall
rate
increases.
To
compensate
for
such
heavy
rainfall
rates,
the
SDI
‐
TB
supports
a
third
order
polynomial
with
user
configurable
coefficients.
The
polynomial
is
used
to
compute
the
rainfall
for
each
tip
based
on
how
frequently
the
bucket
tips.
The
polynomial
is
of
the
form
/
The
coefficients
can
be
obtained
by
plotting
the
rainfall
in
inches/hour
on
the
x
‐
axis
and
the
compensated
rain
(inches/tip)
on
the
Y
‐
axis
and
fitting
the
resultant
curve
to
a
third
order
polynomial.
The
following
plot
shows
the
curve
for
a
0.01
inch
bucket.
