Decagon Devices VP-4 Operator's Manual page 19

6 COMMUNICATION
Send
Identification
Change Address
Address Query
Start
Measurement
Send Data
SDI-12 Sensor Bus
Up to 62 sensors can be connected to the same 12 V supply and
communication port on a data logger. This simplifies wiring because
no multiplexer is necessary. However, one sensor problem can bring
down the entire array (through a short circuit or incorrect address
settings). If you use an SDI-12 sensor bus we recommend that you
make an independent junction box with wire harnesses where all sen-
sor wires attach to lugs so sensors can be disconnected individually
if a problem arises. A single three-wire cable can be run from the
junction box to the data logger.
SDI-12 Address
The SDI-12 protocol requires that all sensors have a unique address.
VP-4 sensors come from the factory with an SDI-12 address of 0.
To add more than one SDI-12 sensor to a system, the sensor address
must be changed. Address options include 0...9, A...Z, a...z. The best
and easiest way to change an address is to use Decagon's ProCheck
(if the option is not available on your ProCheck, please upgrade to
the latest version of firmware). SDI-12 addressing can be accessed
in the CONFIG menu by selecting SDI-12 Address. Addresses may
then be changed by simply pressing the up or down arrows until you
see the desired address and pushing Enter.
The SDI-12 communication protocol is supported by Campbell Sci-
entific data loggers like the CR10X, CR200, CR1000, CR3000, etc.
Table 2: SDI-12 Commands
aI! a13DECAGON VP-4 385<CR><LF>
aAb! b<CR><LF>(b is new address)
?! a<CR><LF>
aM! a0013<CR><LF>
a+1.170 + 21.5 + 0.457
aD0!
+92.25<CR><LF>(4 values)
16
VP-4