Instruction manual

CS451/CS456 Submersible Pressure Transducer
8.2 SDI-12 Commands
This section briefly describes using the SDI-12 commands.
Additional SDI-12 information is available at Appendix D, SDI-
12 Sensor Support
(p. D-1), www.sdi-12.org, or
www.youtube.com/user/CampbellScientific
.
The CS451/CS456 uses an SDI-12 compatible hardware interface and supports
a subset of the SDI-12 commands. The most commonly used command is the
aM! command, issued by the datalogger, where a represents the sensor
address. The communication sequence begins with the datalogger waking the
sensor and issuing the aM! command. The transducer responds to the
datalogger indicating that two measurements will be ready within two seconds.
Subsequent communications handle data reporting from the sensor to the
datalogger.
The SDI-12 protocol has the ability to support various measurement
commands. The CS451/CS456 supports the commands that are listed in
TABLE 8-3.
TABLE 8-3. SDI-12 Commands
SDI-12 Command Command Function Values Returned
aM! Configured settings Pressure/Level,
Temperature
aM1! PSIG, °C Pressure, Temperature
aM2! PSIG, °F Pressure, Temperature
aM3! kPa, °C Pressure, Temperature
aM4! kPa, °F Pressure, Temperature
aM5! Sensor’s Serial
Number
Serial Number
aM6! Ohms, ohms, °C
'R, Rb, Temperature (°C),
IN – DAC counts single-
ended measurement,
IN+ DAC counts single-
ended measurement,
OUT DAC counts
differential measurement
aM7! Configured settings
(provides data in less
than 0.8 seconds)
Pressure/Level
aM8! Configured settings
(provides average of
data based on user
selected samples)
Pressure/Level,
Temperature
As measurement data is transferred between the probe and datalogger digitally,
there are no offset errors incurred with increasing cable length as seen with
analog sensors. However, with increasing cable length, there is still a point
NOTE
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