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7.
MEASUREMENT PROGRAMMING EXAMPLES
This
section
some
examples
of lnput Programming for common sensors used with
the
21X.
These
examples
only the
connections, lnput, Program Control, and Processing Instructions necessary
to
pertorm
and store the data
in engineering
units
in lnput
Storage.
Output Processing
lnstructions
pre
omitted.
lt is teft
for
the
user
to
program
the
necessary instructions to obtain the
final
data
in the
desired. NO
OUTPUT
TO
FINAL
STORAGE WILL TAKE PLACE WITHOUT
ADDITIONAI- PROGRAMMING.
The examplQs
given
in
this
section would likely be only fragments of larger
programs.
ln
general, the
examples
atp
written with the measurements made by the lowest numbered
channels, the
instructions
lt
the beginning of
the
program table, and low number lnput Storage locations used
to
store the
dala. lt is unlikely that an application and 21X configuration exactly duplicates that assumed
In
an
THESE
EXAMPLES
ARE
NOT
MEANTTO BE USED VERBATIM; SENSOR
AND
INPLJT
LOCATIONS SELECTED MUST BE ADJUSTED FOR
THE
ACTUAL
CALIBRA
UNLESS OTHERWISE
NOTED,
ALL
EXCITATION CHANNELS ARE
ANALOG OUTPUT.
7.1
DIFFERENTIAL VOLTAGE
.
LI2OOS
SILICON PYRANOMETER
The
silicon pyranometer puts out
a
current which
is
dependedt upon the solar radiation incident
upon
the
sehsor. The current
is measured as
the voltage
across
a
fixed
resistor. The
Campbell
Ll200S uses a 100 ohm
resistor.
calibration supplied
by Ll-COR,
the
int
.
The
calibration
in
terms of volts
is
rers
of
the pyranometer, is given
determined
py multiplying the pA calibration by
the resistanbe
of
the
fixed resistor.
The calibratfon
of
the pyranometer used
in
this
example is
{ssumed to be 76.9pA/kW/m2, which
when
multillied by
100
ohms equals
7.69mV/kWfm2. The multiplier used to convert
the voltage feading
to kWm2
is
1
17
.69mV
lklv
/
m2
=
0.
1
3004.
Most LI-COR
calibrations run between 60 and
90uA/kWnl2,
which correspond to calibrations
of 6.0
to
9.dmV/kWm2.
Above
the earth's
atmospherd, the flux density
through a surface
normal to
the solar beam is 1.36kWm2;
radiation on earth
will be
less
than
this.
Thus,
the
1SmV
soale provides an
adequate range
(g.omv/kwm2 x 1.36 kWm2 <
15mV).
CONNECTIONS
The pyranqneter output is measured with a
differential
{oltage
measurement on
channel
3.
The low sidp of signal
is
jumpered
to datalogger
ground
to hold the signalwithin common mode
range (Section 14.3-2).
FIGURE
7.1-1. Wiring Diagram for Ll200S
PROGRAM
01:
P2
Volt (DIFF)
01:
1
Rep
02:
2
15
mV
slow Range
03:
3
lN Chan
04;
1
Loc
[:RAD
kWm2]
05:
.13004
Mult
06:
0
Offset
7.2
DATALOGGER AND SENSOR WITH
A
COMMON EXTERNAL POWER
SUPPLY
Some sensors either
contain or require active
signal conditioning circuitry
to provide an easily
measured analog voltage
output.
Generally,
the
output is referenced to the sensor
ground. The
associated current drain usually requires
a
power source external to
the
21X.
A typical
connection scheme where
AC power is not
available and both the 21X and sensor are
powered by an external battery is shown
in
WHITE
OR
CLEAR
7-1
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