Campbell Scientific CS470/CS471 Compact Bubbler System - Manual (Page 43)

Appendix D. SDI-12 Sensor Support
D.3 Advanced SDI-12 Commands
All advanced SDI-12 commands begin with O (the letter not zero).
TABLE D-3. Advanced SDI-12 Commands
Command Response Description
aOXP<value>! aOXP<value><CR><LF> Activate purge function.
The parameter <value> represents the setting
defined as follows:
0 = purge function deactivated
1 = purge function activated
aOXG<value>! or aOXG! a<value><CR><LF> Set/query value for local gravitational constant.
Format:
cb.aaaaaa
c: Polarity (+ or -)
bb: Number before the decimal point
aaaaaa: Number after the decimal point
(max. 6 digits)
default setting: +9.80665
aOXT<value>! or aOXT! a<value><CR><LF> Set/query value for local water temperature.
Format:
cb.aaaaaa
c: Polarity (+ or -)
bb: Number before the decimal point
aaaaaa: Number after the decimal point
(max. 6 digits)
default setting: +3.98
The CS470/CS471 either produces a value proportional to the pressure, or an
actual water level compensated for the relative density of the water (using the
default settings).
The correct water level measurement is calculated according to the following
formula:
constant nal gravitatio Local density Water
C 4 at pressure O mH level Water
2
80665 . 9 1
∗ ∗ ° =
Where: water density = -6.017777e -6 t 2 + 0.0000408 t + 0.999841 and
t = temperature in °C
The CS470/CS471 can calculate the water density at any time using the value
for the local water temperature. You can enter the value for the local
gravitational constant using the command aOXG<value>! and the value for
the local temperature using the command aOXT<value>!.
Calculation of the correct value for the local gravitational constant
The gravitational acceleration at the earth’s surface varies between 9.78036
m/s 2 at the equator and 9.83208 m/s 2 at the poles. Also, it decreases by
D-7