700-SDI-RADAR-300W-Man Rev 2 30 May 2022
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Part# 21370
4)
Modbus Protocol which responds to Modbus requests over the RS-485 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 the 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).
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).
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. The angle report is
sent periodically, together with RDTGT 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.
4.2.2
SERVICING PROTOCOL (RS-232)
The servicing protocol is used to retrieve and modify the device operating parameters. Various
device settings, such as unit system and filtering parameters are configured using this protocol.
Since NMEA protocol is one way (it only outputs the data), the servicing protocol is always active.
2
I
n the radar sensor setting it is possible to select km/h, mph, fps, fpm or mm/s for the speed reporting
