Xylem H-3521 - Manual (Page 34)

5-4 SDI-12 Command and Response Protocol
H-3521
5.2 Concurrent Measurement Command
This is a new command since the release of Version 1.2 SDI-12 Specification. A concurrent
measurement is one which occurs while other SDI-12 sensors on the bus are also taking
measurements. This command is similar to the “aM!” command, however, the nn field has an
extra digit and the sensor does not issue a service request when it has completed the measurement.
Communicating with other sensors will NOT abort a concurrent measurement. 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
"aC!" "atttnn" Initiate measurement
Where:
a is the sensor address ("0-9", "A-Z", "a-z", "*", "?").
C 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.
nn is a two digit integer (00-99) 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.
The data recorder may wake the sensor with a break and collect the data anytime after the
specified processing time has elapsed.
Example of a H-3521 "aC!" command:
Command
Response Time Values Description
"aC!" "a00604" 6 sec 04 Make measurement
Subsequent Command Response
"aD0" a+AA.AA+BB.BBBB+CC.C+DD.D
Where:
AA.AA = Stage (feet, inches, meters etc.)
BB.BBBB = Pressure (PSI)
CC.C = Temperature (C)
DD.D = Power Supply Voltage (Volts)