Campbell Scientific SR50A Distance Sensor - Manual (Page 10)

SR50A Sonic Ranging Sensor
3.3 SDI-12 Operation
SDI-12 is a Serial Digital Interface standard that is used for communication
between data recorders and sensors. Most Campbell Scientific dataloggers are
SDI-12 compatible.
3.3.1 SDI-12 Wiring
It is recommended to power down your system before wiring the SR50A.
Never operate the sensor with the shield wire disconnected. The shield wire
plays an important role in noise emissions and susceptibility as well as
transient protection.
Color Function Connection
Black Power Ground Power Ground
Red +12VDC Power Power Source
Green SDI-12 I/O Recorder/Reader SDI-12 Com port or control port
White Not Used Ground
Clear Shield Shield/Earth Ground
3.3.2 SDI-12 Addresses
The SR50A can be set to one of ten addresses (0 to 9) which allows up to ten
sensors to be connected to a single digital I/O channel (control port) of an SDI-
12 datalogger.
The SR50A is shipped from the factory with the address set to 0. The address
on the SR50A can be changed by sending an SDI-12 change address command.
The change address command can be issued from most SDI-12 recorders. For
some Campbell Scientific dataloggers the SDI-12 transparent mode will need
to be entered to change the address.
When it is necessary to measure more than one SR50A, it is easiest to use a
different control port for each SR50A instead of changing the address. If
additional control ports are not available, then the address will need to be
changed.
To change the address of a sensor that has the default address of 0 to the
address of 1 the following command can be sent:
“0A1!”
Only one sensor of the same address should be connected when using the
change address command.
3.3.3 SDI-12 Commands
The SDI-12 protocol supports various measurement commands. The SR50A
can use the SDI-12 commands listed in the following table.
The SR50A needs to be powered for 1.5 s before it can receive
an SDI-12 command. NOTE
4