Manual – Starflow Ultrasonic Doppler Instrument
Model 6526
Unidata Manual - 6526 Starflow User Manual Issue 17 01 2020.docx
Page 72
15.2
Using Starflow as An SDI-12 Sensor
To use the Starflow as an SDI-12 Sensor, you must first set its SDI-12 Configuration as per
“Configuring the Starflow as an SDI-12 Sensor’ on page 28
The Starflow will continue to operate at its pre-set scan rate and will perform all the normal logging
functions. Starflow measurements, RS-232 communications and data logging, coexist with SDI-12
interrogation.
Whenever an SDI-12 Data Recorder issues a START MEASUREMENT/SEND DATA sequence,
Starflow immediately responds with the latest parameter readings.
In this mode, the SDI-12 command START MEASUREMENT does not initiate a new measurement
cycle and the data is always valid and available for immediate retrieval by the Data Recorder.
15.2.1
Theory of Operation
When the Data Recorder sends a “break signal”, the Starflow wakens and captures the SDI-12
command following the break signal. If the command is valid, the Starflow reads its address
setting to see whether or not its address is in fact being called, or if the address of some other
device (at another location) is being sought. If the Data Recorder is looking for a different address,
the Starflow will go back to sleep until another break signal is received.
If the address being sent belongs to the Starflow, it will scan the instructions coming from the Data
Recorder to see what action is required.
The two most important commands at this time are:
Measure
: If the Starflow receives the START MEASUREMENT command, it will report back to the
Data Recorder the number of parameters enabled for measurement, and that these parameters
are available to be sent to the Data Recorder immediately.
Data
: If the Starflow receives the SEND DATA command, it will send the last parameter readings
measured to the Data Recorder for storage.
15.2.2
Data Reported by Starflow Sensor
Starflow will respond to an SDI-12 interrogation with up to five parameters. Each parameter
represents a Starflow 16-bit integer channel value (e.g., Water Velocity). The parameter is
reported as a five (5) digit fixed point, signed integer.
For example:
2100
means 2100mm/s positive flow
-350
means 350mm/s reverse flow
The implied parameter scaling is the same as defined for Starflow channels:
Velocity
mm/s
Depth
mm
Temperature
.01°C
Voltage
.01V
