255-100 Novalynx
Analogue Output Evaporation Gauge
9
7. Operation
7.1 Calibration
All 255-100 ga
u
ges need to be field calibrated by the user. Field calibration
will provide the multiplier and offset for use in the datalogger program to
provide data in units of inches or centimet
re
s. The
FieldCal()
instruction may
be used to perform the calculations automatically and preserve the results in
the datalogger. Refer to the
FieldCal()
help in
CRBasic Editor
for more
information on its use. The following provides instructions on performing a
manual field calibration.
Calibration Procedure:
1.
Partially fill the evaporation pan. Measure the depth with a ruler.
2.
Measure the voltage using the ga
u
ge and the
BrHalf()
or
ExDelSE()
instruction with a multiplier of 1.0 and an offset of 0.0.
3.
Add more water to the evaporation pan and measure the depth in the pan
using the ruler.
4.
Measure the voltage at that depth using the ga
u
ge and the
BrHalf()
or
ExDelSE()
instruction with a multiplier of 1.0 and an offset of 0.0.
5.
Calculate the multiplier using the following equation:
m = (D
2
– D
1
) / (V
2
– V
1
)
Where,
m = multiplier
D
1
= initial depth measurement (inches or cm)
D
2
= second depth measurement (inches or cm)
V
1
= initial voltage measurement (mV)
V
2
= second voltage measurement (mV)
6. Calculate the offset using the following equation:
b = D
1
– m
∙
V
1
Where,
b = offset
m = multiplier
D
1
= initial depth measurement (inches or cm)
V
1
= initial voltage measurement (millivolts)
Example
This example calculates the multiplier (m) and offset (b) for a specific
evaporation ga
u
ge. Because the multiplier and offset vary with each ga
u
ge,
your numbers will be different than this example.
