Xylem H-3551 - Manual (Page 21)

H-3551
SDI-12 Command and Response Protocol 5-3
5.2 Measure Command
The H-3351 supports three measure commands. Data values generated in response to these
commands are 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" may be 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.
The aM! causes the H-3351 to initiate a purge sequence. Upon completion of the purge the H-
3551 places a success/fail response parameter in the sensor buffer and sends a service request..
Example of a H-3551 "aM!" command:
Command Response Time Values Description
"aM!" "a2721" 272 sec 1 Initiate a purge
Subsequent Command Response Description
"aD0" a+0 Purge failed (low battery voltage)
"aD0" a+1 Purge succeeded