700-SDI-RADAR-300WL-Man Rev 2 11 Apr Mar 2022
15
/48
Part# 21371
4)
Modbus RTU protocol on RS-485 interface which is supported by a variety of third-party data
loggers
5)
SDI-12 protocol on the SDI-12 data line
4.2.1
NMEA PROTOCOL (RS-232)
NMEA protocol is based on the standard protocol family widely used by the navigation equipment.
NMEA protocol is sentence oriented and is capable of sending multiple sentences with different
information. The sentence content is designated by the starting keyword which is different for each
sentence type. NMEA sentences are terminated with the checksum which makes this protocol
extremely reliable. NMEA protocol is single-direction protocol: data is only transmitted from the flow
meter.
At RS-232 interface the device periodically outputs the following data sentences:
Direct flow measurement report:
$RDTGT,D1,S1,L1*CSUM<CR><LF>
$RDTGT:
The keyword sent on the beginning of each detection report. This sentence is
sent whenever there is detected flow.
D1:
The detected flow direction (1 approaching, -1 receding).
S1:
The detected flow speed (speed
is reported as speed*10
for m/s, km/h,
mph,
fps, fpm and as speed*1 for mm/s).
L1:
The detected level of the signal reflection from the water surface.
CSUM:
The check sum of the characters in the report from $ to * excluding these
characters.
Average flow measurement report:
$RDAVG,S1*CSUM<CR><LF>
$RDAVG:
The keyword sent on the beginning of the report. This sentence reports
smoothed flow measurement. This is the preferred reading, since it filters
out minor fluctuations in flow speed reading due to waves.
S1:
The detected flow speed (speed
1
is reported as speed*10
for m/s, km/h,
mph,
fps, fpm and as speed*1 for mm/s).
CSUM:
The check sum of the characters in the report from $ to * excluding these
characters.
Tilt angle report:
$RDANG,A*CSUM<CR><LF>
$RDANG:
The keyword sent on the beginning of each angle report.
A:
The measured tilt angle, in degrees, 0 being horizontal.
CSUM:
The check sum of the characters in the report from $ to * excluding these
characters.
3
I
n the radar sensor setting it is possible to select km/h, mph, fps, fpm or mm/s for the speed reporting
