Xylem H-424MS V1.0 - Manual (Page 18)

2-2 SDI-12 Command and Response Protocol
H-424MS
Example of a H-424MS "aM!" command:
Command Response Time Values Description
------------- --------------------- ------- -------- -------------------------------
"aM!" "a0161" 16 sec 1 Wakeup the remote stations
Subsequent Command Response
--------------------------- ------------------------------------
"aD0" a+1
Where:
1 = Fixed dummy “data”.
2.2 Measure Command
The H-424MS Measure Command causes the H-424MS to wake the remote site(s) from low power
sleep. The time required to complete this process is the Wake Interval setting plus 1-second. During
this period the H-424MS transmits wakeup nulls which are detected by the remote site(s) when they
periodically wake and check for activity. To be SDI-12 compliant a dummy data value is stored in
the sensor's buffer for subsequent collection using "D" commands. The data will be retained in the
sensor until another "M", “C” or "V" command is executed.
Command Response Description
------------------ ---------------------- ------------------------------------
"aM!" "atttn" Initiate measurement
Where:
a is the sensor address ("0-9", "A-Z", "a-z", "*", "?").
M is an upper-case ASCII character
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" 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 anytime after the service request is received or the specified processing time has elapsed.