VP-3
User’s Manual
5. Communication
19
SDI-12 Communication
The VP-3 can also communicate using SDI-12 protocol, a three-
wire interface where all sensors are powered (white wire),
grounded (bare wire), and communicate (red wire) on shared
nodes (for more information on the SDI-12 protocol, visit
www.sdi-12.org). Below is a brief description of SDI-12 for
communication. If you plan on using SDI-12 for communication
with the VP-3 Sensor, please see our integrator's guide at
www.decagon.com/support/literature for detailed instructions.
SDI-12 Commands
Following are SDI-12 commands that the VP-3 Sensor responds
to. The sensor address is shown as 'a'. If a '?' is substituted for 'a'
all addresses respond.
SDI-12 Sensor Bus
Up to 62 sensors can be connected to the same 12 V supply and
communication port on a datalogger. This simplifies wiring
because no multiplexer is necessary. However, one sensor
problem can bring down the entire array (through a short circuit
Send Identification
aI!
a13DECAGON VP-3 350<CR><LF>
Change Address
aAb!
b<CR><LF> (b is new address)
Address Query
?!
a<CR><LF>
Start Measurement
aM!
a0013<CR><LF>
Send Data
aD0! a+1.17+21.5+0.456<CR><LF> (3 values)
