Manual – Starflow Ultrasonic Doppler Instrument
Model 6526
Unidata Manual - 6526 Starflow User Manual Issue 17 01 2020.docx
Page 73
15.2.3
Reporting Computed Flow Results
When Starflow is programmed with a flow computation scheme additional flow extension channels
are available for reporting. These are:
Address
Type
Meaning
160
16 bit integer
Cross Sectional Area
162
32 bit integer
Flow Rate
166
32 bit integer
Flow
170
32 bit integer
Total Flow
Note
: Limitations within SDI-12 do not allow 32 bit integer values to be reported without loss of
resolution. Further limitations may occur in the SDI-12 Recorder’s ability to process large
numbers. It is recommended that 32 bit channels be reported as 2 x 16 bit integer values (e.g.
Flow Rate addr 162 scaled mm/s, addr 164 scale 65536 mm/s).
15.3
Starflow SDI-12 Implementation Notes
The following technical information describes Starflow’s implementation of the SDI-12 standard.
15.3.1
SDI-12 Data Recorder Commands
Two Scheme Program instructions are used to control the SDI-12 Recorder operation:
SDIGET
which collects measurements from the nominated SDI-12 sensor, and
SDICONV
which converts the collected data for use by the Log Program.
Measurements may be converted into fixed point Short Integers (for manipulation by the Scheme),
Floating Point Numbers (for logging by the Scheme) or an ASCII string.
•
Integers are two bytes.
•
Floating Point numbers are 4 bytes.
•
An ASCII string is zero byte terminated.
15.3.2
Data Recorder Coordination
Once an SDI-12 communication has commenced (SDIGET instruction executed) the SDI-12 Bus is
busy and will ignore any subsequent SDIGET commands until the active measurement transfer is
complete. The measurements are stored in memory, to be converted by a SDICONV instruction.
Converted measurements (stored on Micrologger channels) may be further processed by the
Scheme program and Logged.
Because most SDI-12 sensors (unlike the Starflow Sensor) require considerable time to make their
measurements (typically 60 seconds), the Starflow Data Recorder remains powered up awaiting a
response from the sensor. This mode of operation usually requires the Scheme Program to initiate
SDI-12 Measurements (SDIGETs) two scans prior to the desired Log Interval.
The sequencing of the SDI-12 measurements is under the control of the Scheme Program (which
is defined during Scheme Editing.
