700-SDI-PT-KEL-Man Rev 4 06 Jan 2020
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SDI-12 COMMUNICATION
3.1
GENERAL INFORMATION
SDI-12 protocols are based on Version 1.3.
All characters are printable ASCII characters except the response of an SDI-12 sensor which ends
with <CR><LF>
and sometimes the CRC code includes a non-printable ASCII character.
The default address of an SDI-12 sensor is always ‘0’. The sensor’s address can be changed to an
address from ‘1’ to ‘9’, from ‘A’ to ‘Z’ or from ‘a’ to ‘z’.
The option of continuous measurements is only supported with a specific extended command (X-
command).
A <CR><LF> is returned for an R-Command or with CRC switched on. It is a<CRC> <CR><LF>, unless
continuous mode is switched on and configured over the extended command aXR!
Note the following:
•
the “a” in each command should be replaced with the sensor’s address
•
every command must terminate with an exclamation mark (!)
•
the CRC
is added at the end of the message for commands with CRC
•
the measurement command must be followed by a Send Data command (
aD0!
) to view the
data
This chapter will provide basic direction on general SDI-12 Commands. Detailed direction can be
found in accordance with the document found at footnote 5.
This chapter will also provide information of some useful SDI-12 commands specific to the SDI-PT-
KEL. Detailed information on all SDI-12 communication protocols specific to the Keller Acculevel can
be found in the Keller document, “
SDI-12 communication Protocol”
.
3.2
NOTATION FOR SDI-12 COMMANDS
SDI commands are strings of characters sent to the SDI sensor by a data logger, data collection
platform or other SDI-12 master. The sensor takes action based on the command that was sent (ie.
starting a measurement) and then replies to the command with a string of characters.
Note that as cable length increases, so do noise levels which can interfere with the digital
measurement communications between the sensor and the data logger. Significant noise
levels can
1
In accordance with
“SDI-12 A Serial-Digital Interface Standard for Microprocessor-Based Sensors ver 1.3”
. Refer to:
2
Carriage Return Line Feed
3
Cyclic Redundancy Check
4
https://www.kelleramerica.com/manuals-and-software/manuals/communication_protocol_SDI-12.pdf
