Xylem H-4280 - Manual (Page 15)

H-4280
SDI-12 Command and Response Protocol 3-3
3.2 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", " 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 any time
after the service request is received or the specified processing time has elapsed.
Example of a H-4280 "aM!" command:
Command
Response Time Values Description
"aM!" "a0038" 3 sec 8 Make measurement
Subsequent Command Response
"aD0" a+A.AAA+B.BBB+C.CCC+D.DDD
"aD1" a+E.EEE+F.FFF+G.GGG+H.HHH
Where: A.AAA = Channel 0 Voltage
B.BBB = Channel 1 Voltage
C.CCC = Channel 2 Voltage
D.DDD = Channel 3 Voltage
E.EEE = Channel 4 Voltage
F.FFF = Channel 5Voltage
G.GGG = Channel 6 Voltage
H.HHH = Channel 7 Voltage