7
COMMUNICATION
ES-2
7.3
Common SDI-12 Commands
Table 2 shows common SDI-12 commands that the ES-2 Sensor re-
sponds to. The ES-2 can respond to any SDI-12 command under the
SDI-12 specification version 1.3. The sensor addresses shown an ‘a.’
If a ‘?’ is substituted for ‘a’ all addresses respond.
Table 2: SDI-12 Commands
Send
Identification
aI!
a13DECAGON ES-2 316
<
CR
><
LF
>
Change Address
aAb!
b
<
CR
><
LF
>
(b is new address)
Address Query
?!
a
<
CR
><
LF
>
Start
Measurement
aM!
00013
<
CR
><
LF
>
Send Data
aD0!
a+9+22.2+0
<
CR
><
LF
>
(3 values)
7.4
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, a problem with one sensor can
bring down the entire array (though a short circuit or incorrect ad-
dress settings). If you do use a SDI-12 sensor bus, we recommend that
you make an independent junction box with wire harnesses where all
sensor wires attach to lugs so sensors can be disconnected individu-
ally if a problem arises. A single three-wire cable can be run from the
junction box to the data logger. While this method minimizes the
number of data loggers needed, it maximizes the need for personnel
to monitor the set-up.
7.5
SDI-12 Address
The SDI-12 protocol requires that all sensors have a unique sensor
address. ES-2 sensors come from the factory with a SDI-12 address
of 0. To add SDI-12 sensors to a system, the sensor address must
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