Sutron Corporation Satlink Operations & Maintenance Manual, Rev 8.04.2 11/3/2016 pg. 170
wind speed and direction
Sutron also offers general purpose interfaces for making analog and digital measurements via
SDI-12.
For more information on SDI-12, go to
19.2.
Wiring Guidelines
SDI enables you to connect up to 10 sensors with as many as many as 9 parameters each. The
interface is implemented using three wires: data, ground, and +12V. The ground conductor of the
SDI interface line should be large enough to keep the voltage drop between the data recorder
and the sensor to less than 0.5 volts during the maximum sensor current drain. Failure to observe
this specification will cause bad communications and/or bad data. The maximum current used on
the +12V line should not exceed 2 amps at any time.
19.3.
Connector
The connector type is not part of the SDI specification. On Satlink, the connections are made on
the terminal block: #14 (SDI-12 Data), #13 (SDI-12 PWR), and #12 (GND). Multiple sensors can be
connected to these connections.
19.4.
Setup of SDI sensors
Each SDI-12 sensor has an address from 0 to 9. This address differentiates one sensor from
another. Most sensors are factory default set to address zero (0). If/when interfacing more than
one sensor to Satlink, each sensor must be assigned a unique address. This is normally done by
setting dipswitches on the sensor or by software commands. Failure to set unique addresses for
each sensor will result in failure of the communications interface (i.e. no data logged). Consult
the sensor manufacturer’s data for information on your particular sensor(s).
When setting up multiple SDI-12 sensors, connect one sensor at a time. Once a new sensor is
connected, you must give it a unique address. To do so, either use LinkComm or the command
line. Type SDI-12 FIND to detect new sensors. Once a sensor is found, change its address by
typing SDI xAy!, where x is the old address, A is A, and y the new address. For example, SDI 0A1!
will change the address from 0 to 1.
When getting more than one parameter from a single sensor, be sure to set the measurement
schedules the same. When Satlink finds multiple parameters from a single sensor (same address),
it will only issue a measurement of the sensor once, then read each of the parameters from the
one measurement. This is important to ensure that data from one sensor is gathered at the same
time and for sensors that have multiple parameters that take a long time to process.
19.5.
Useful SDI commands
Resetting the address by software (some sensors) is normally done by sending the aAb!
command. (a A b !, where a is the current address of the sensor you want to change and b is the
address you want to change to, e.g. 0A5! changes the address of sensor 0 to address 5.)
