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This is important to ensure that data from one sensor is gathered at the same time and for sensors that
have multiple parameters that take a long time to process.
18.5
Useful SDI commands
Resetting the address by software (some sensors) is normally done by sending the aAb! command. (a A b !,
where a is the current address of the sensor you want to change and b is the address you want to change
to, e.g., 0A5! changes the address of sensor 0 to address 5.)
Another useful SDI-12 command is the aI! (where a is the address of the sensor, e.g., 3I! for sensor at
address 3) command. 4I! will return an identification string from the sensor at address 4, which includes
the SDI version number, vendor's name, sensor model number, sensor version number, and serial number.
This is a quick way to see if the sensor is responding properly.
A way to verify data collection (manual data collection) is to issue the aM! command. For example, 7M!
would collect data from the sensor at address 7. The sensor will respond with a 5-digit code -- the first
digit is the address, the next 3 digits are the required time for measurement in seconds, and the last digit
is the number of data values returned. Wait for the number of seconds. Then issue the aD0! (address, D,
zero, !) the sensor should respond with one or more data values. You may issue further aD1!
…
aDn! till
you get all of the data.
If the SDI sensor is version 1.3 (version number can be found out by sending the ?I! command; the version
is returned as the second and third characters of the response), then make sure to use the CRC
measurement commands. These commands work just like normal measurement commands, except that
they use an error checking mechanism that minimizes errors. So, instead of 0M!, use 0MC!. Instead of
0M1!, use 0MC1!. This will ensure reliable SDI communication.
18.6
SDI Clock Synchronization
Certain Sutron SDI-12 sensors (such as the SDR, RLR, and the CF Bubbler) support a command to set the
time of the sensor via SDI-12. The system takes advantage of that feature, and periodically sets the clock
of the sensors using an SDI-12 command, ensuring that all devices share a common time.
When recording is enabled, and every 24 hours thereafter, the station performs a time sync with all the
Sutron devices that support the XDT! command. The time sync is started by sending an I! command to
every SDI-12 device that has been set up. If the device replies favorably to the I! command, an XDT!
command is issued t
o the device. The system then decides whether to sync that device’s clock based on
the time difference between the system and the device.
This process is automatic and cannot be disabled.
The XDT set time command takes the format
aXDTYYYY/MM/DD HH:MM:SS!
a is address
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