Xylem H-5223 - Manual (Page 55)

Ž All ASCII-Hex commands, arguments and data values are transmitted most significant digit
first.
B.2 Standard SDI-12 Command Set
All SDI-12 sensors should incorporate a set of standard commands. These commands are used
for making measurements, collecting data, identifying the sensor and verifying the sensor is
working properly. Since all sensors use the same basic commands it is easy to memorize and use
these commands on any sensor. The H-5223 has a built in menu that allows for a single key
press to activate the standard commands for testing purposes. There is also an option to edit and
send out non standard commands as each sensor could have a set of commands specific only to
its operation. When using the H-5223 with SDI-12 sensors it is important to have a manual
available for each sensor to see the exact response from the sensor for each command.
B.2.1 Measure Command
The Measure Command causes a measurement sequence to be performed. Data values generated
in response to this command are stored in the sensor's buffer for subsequent collection using "D"
commands. The data will be retained in the sensor until another "M" or "V" command is
executed.
Command Response Description
------------------ ---------------------- ------------------------------------
"aM!" "atttn<cr><lf>" Initiate measurement
Where:
a Is the sensor address ("0" to "9", "A" to "Z", or "*").
M Is the command indicator, M for Measure, and must be in upper case.
ttt Is a three digit integer (000-999) specifying the maximum time, in seconds, the
sensor will take to complete the command and have measurement data available
in its buffer.
n Is a single digit integer (0-9) specifying the number of values that will be placed in
the data buffer. If "n" is zero (0), no data will be available using subsequent "D"
commands.
Upon completion of the measurement, a service request "a<cr><lf>" is sent to the data recorder
indicating the sensor data is ready. The data recorder may wake the sensor with a break and
collect the data any time after the service request is received or the specified processing time has
elapsed.
B-2 SDI-12 Command and Response Protocol
H-5223