Appendix D. SDI-12 Sensor Support
D-4
D.2.7 Start Concurrent Measurement Commands (aC!
…
aC9!)
A concurrent measurement (
aC!
) command follows the same pattern as the
aM!
command with the exception that it does not require the data logger to
pause its operation, and other SDI-12 sensors may take measurements at the
same time. The sensor will not issue a service request to notify the data logger
that the measurement is complete. The data logger will issue the
aD0!
command during the next scan after the measurement time reported by the
sensor has expired. To use this command, the scan interval should be 10
seconds or less. The response to each command has the form
atttn<CR><LF>
,
where
a
= the sensor address
ttt
= time, in seconds, until the measurement data is available
nn
= the number of values to be returned when one or more subsequent
D
commands are issued.
See the following example. A data logger has three sensors wired into terminal
C1
. The sensors are addresses X, Y, and Z. The data logger will issue the
following commands and receive the following responses:
TABLE D-3. Example aC! Sequence
XC!
The data logger makes a request to
sensor X to start a concurrent
measurement.
X03005<CR><LF>
Sensor X immediately indicates that
it will have 5 (05) values ready for
collection within the next 30 (030)
seconds.
YC!
The data logger makes a request to
sensor Y to start a concurrent
measurement.
Y04006<CR><LF>
Sensor Y immediately indicates that
it will have 6 (06) values ready for
collection within the next 40 (040)
seconds.
ZC!
The data logger makes a request to
sensor Z to start a concurrent
measurement.
Z02010<CR><LF>
Sensor Z immediately indicates that it
will have 10 values ready for
collection within the next 20 (020)
seconds.
ZD0!
After 20 seconds have passed, the
data logger starts the process of
collecting the data by issuing the first
D
command to sensor Z.
