Accubar SDI-12 Barometric Pressure Sensor Operations & Maintenance Manual Rev-B 30 Nov 2017
pg. 16
When the measurement is complete, the sensor does NOT issue a service request. Note: this is different
from the M and MC commands.
To request the data after a measurement,
aD0!
where a is the address character and D0 is the
command to retrieve measured data. Note: the
number zero follows D, not the letter O.
In this case, the sensor will reply with two values in the format:
avuC
where a is the address, v is the data value, u indicates
the units the value is expressed in, and C is the CRC-16
encoded into 3 ASCII characters. Both v and u have the
format of a polarity sign (
or
) followed by up to seven
digits, including a decimal point. The CRC-16 is always
the last three characters which are never a numeric digit.
The u indicates the units of the measurement. When u is 0, the value has units of mB(hPa). When u is
1, the units are inches of mercury ("Hg). When u is 9, the units depend on a user entered slope and
offset. u can also take on additional values if a station elevation offset has been entered. The following
table summarizes all the values of u.
0
units are mB (hPa)
1
units are "Hg
2
units are kPa
3
units are mmHg
4
units are Atm
5
units are psia
9
units depend on user-entered scale and offset.
If the station elevation offset is non-zero, then one of the following values of u will be returned:
10
units are mB + station elevation offset
11
units are "Hg + station elevation offset
12
units are kPa + station elevation offset
13
units are mmHg + station elevation offset
14
units are Atm + station elevation offset
15
units are psia + station elevation offset
19
user units with non-zero station elevation offset
(mB + elevation offset)
user scale + user offset
set by XE or XS
Set by XUU
In most cases, you will not set up the recorder to store this units identifier. It is provided in response to
the standard measure command to eliminate confusion as to the computation used to come up with the
final value.
