Deep SUNA Manual
For SUNA running firmware version 2.4 or later
4. Terminal Interface of the SUNA
on how to accurately calibrate the analog output system.
Calculating Nitrate Concentration from Voltage and Current
The inverse voltage and current equations are
C
nitrate
=
DAC
min
+
DAC
max
−
DAC
min
V
max
−
V
min
⋅(
V
−
V
min
)
and
C
nitrate
=
DAC
min
+
DAC
max
−
DAC
min
I
max
−
I
min
⋅(
I
−
I
min
)
,
using the same symbols as above.
These equation can be written more compact as
C
nitrate
=
A
0
+
A
1
⋅
V
and
C
nitrate
=
B
0
+
B
1
⋅
I
,
where
A
1
=
DAC
max
−
DAC
min
V
max
−
V
min
is the voltage scale coefficient
A
0
=
DAC
min
−
A
1
⋅
V
min
is the voltage offset coefficient
B
1
=
DAC
max
−
DAC
min
I
max
−
I
min
is the current scale coefficient
B
0
=
DAC
min
−
B
1
⋅
I
min
is the current offset coefficient
In-System Calibration
The above defined scale and offset coefficients are based on the nominal minimum and
maximum voltage and current values. In a deployed system, voltage and current may
differ, due to transmission losses. Ideally, the true low and high voltage or current values
are used instead of the nominal values.
In order to perform an in-system calibration, a Y-cable is required, that connects the
SUNA to both the data acquisition device and a computer. Please contact Satlantic for
assistance in creating or purchasing such a cable. With this cable in place, the SUNA is
tasked to generate the low DAC and then the high DAC output. The low and high
voltage or current values are measured in the data acquisition device, and used to
calculate the in-system scale and offset coefficients:
A
1
=
DAC
max
−
DAC
min
V
high
−
V
low
is the in-system calibrated voltage scale coefficient
Copyright © 2013, Satlantic LP, All rights reserved
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