GS3
5
COMMUNICATION
5
Communication
The GS3 sensor can communicate using two different methods, Se-
rial (TTL) and SDI-12. In this chapter we will briefly discuss the
specifics of each of these communication methods.
Please visit
www.decagon.com/support
for the complete Integrators
guide, which gives more detailed explanations and instructions.
5.1
Serial Communication
The GS3 communicates in both serial and SDI-12. In some applica-
tions where non-Decagon data loggers are used, SDI-12 will be the
best choice.
When excitation voltage is applied, the GS3 makes a measurement.
Within about 50 ms of excitation three measurement values are
transmitted to the data logger as a serial stream of ASCII char-
acters. The serial out is 1200 baud asynchronous with 8 data bits,
no parity, and one stop bit. The voltage levels are 0 to 3.6 V and the
logic levels are TTL (active low). The power must be removed and
reapplied for a new set of values to be transmitted.
The ASCII stream contains three numbers separated by spaces. The
stream is terminated with the carriage return character. The first
number is the dielectric permittivity (
ε
), the second number is tem-
perature in
◦
C, and the third is the electrical conductivity in
µ
S/cm.
5.2
SDI-12 Communication
The GS3 sensor can also communicate using the SDI-12 protocol,
a three-wire interface where all sensors are powered (white wire),
grounded (bare wire), and communicate (red wire) on shared wires
(for more info, go to www.sdi-12.org). There are some positive and
negative elements of this protocol. On the positive side, up to 62 sen-
sors can be connected to the same 12 V supply and communication
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