Appendix B. SDI-12 sensor
support
Serial Data Interface at 1200 baud (SDI-12 ) is a protocol developed to simplify sensor and data
logger compatibility. Only three wires are necessary—serial data, ground, and 12 V. With unique
addresses, multiple SDI-12 sensors can connect to a single SDI-12 terminal on a Campbell
Scientific data logger.
This appendix discusses the structure of SDI-12 commands and the process of querying SDI-12
sensors. For more detailed information, refer to version 1.4 (January 2019) of the SDI-12 protocol,
available at www.sdi-12.org .
For additional information, refer to the SDI-12 Sensors | Transparent Mode and SDI-12 Sensors |
Watch or Sniffer Mode videos.
B.1 SDI-12 command basics
SDI-12 commands have three components:
l
Sensor address (a) – a single character and the first character of the command. Use the
default address of zero (0) unless multiple sensors are connected to the same port.
l
Command body – an upper case letter (the “command”), optionally followed by one or
more alphanumeric qualifiers.
l
Command termination (!) – an exclamation mark.
An active sensor responds to each command. Responses have several standard forms and always
terminate with <CR><LF> (carriage return and line feed). Standard SDI-12 commands are listed
in Table B-1 (p. 25).
Table B-1: Campbell Scientific sensor SDI-12 command and response sets
Name
1
Command Response
Acknowledge active
a!
a<CR><LF>
Send identification
aI!
allccccccccmmmmmmvvvxxx...xx
<CR><LF>
Start verification
aV!
atttn <CR><LF>
MetSENS-Series Compact Weather Sensors 25
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