RSS-2-300W Non Contact Surface Velocity Radar
User Manual

RSS-2-300W Non Contact Surface Velocity Radar

Copyright ©2023 Geolux d.o.o. All rights reserved.
Starting Point
Thank you for purchasing Geolux RSS-2-300W non-contact surface velocity radar! We have put  together the experience of our engineers, the domain knowledge of our customers, the enthusiasm of our team, and the manufacturing excellence to deliver this product to you.
You may freely rely on our field-proven radar technology. The use of top- quality components and advanced signal processing algorithms ensures that Geolux surface velocity radar can be used in various applications and environments.
Although we are certain that you are more than capable of connecting the surface velocity radar to your system, we have created this User Manual to assist you in setting up and using Geoducks surface velocity radar device.
Should there be any questions left unanswered, please feel free to contact us directly:
Federal Communications Commission (FCC) Approval
This equipment has been tested and found to comply with the limits for a class B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates, uses and can radiate radio frequency energy and if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference to ratio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:

• Reorient or relocate the receiving antenna
• Increase the separation between the equipment and receiver
•  Connect the equipment into an outlet on a circuit different from that to which the receiver is connected
• Consult the dealer or an experienced radio/TV technician for help

This equipment has been verified to comply with the limits for a class B computing device, pursuant to FCC Rules. In order to maintain compliance with FCC regulations, shielded cables must be used with this equipment. Operation with non-approved equipment or unshielded cables is likely to result in interference to radio and TV reception. The user is cautioned that changes and modifications made to the equipment without the approval of manufacturer could void the user’s authority to operate this equipment.
ISED/Canada Statement
This device contains licenceexempt transmitter(s)/receiver(s) that comply with Innovation, Science and Economic Development Canada’s licenceexempt RSS(s). Operation is subject to the following two conditions:

• This device may not cause interference.
• This device must accept any interference, including interference that may cause undesired operation of the device.

RADIATION EXPOSURE STATEMENT
The device meets the exemption from the routine evaluation limits in section 2.5 of RSS 102. This equipment should be installed and operated with a minimum distance of 20 centimeters between the radiator and users.

Introduction

Geolux RSS-2-300W surface velocity radar uses radar technology to provide precise contactless measurement of surface flow velocity. Contactless radar technology enables quick and simple sensor installation above the water surface, and requires minimum maintenance. This functionality is achieved by transmitting an electromagnetic wave in 24 GHz frequency range (K-band), and measuring the frequency shift of the electromagnetic wave reflected from the flowing water surface. The frequency shift is caused by the Doppler effect of the moving surface on the electromagnetic wave. As the relative speed between the radar sensor and the water surface increases, the detected frequency shift also increases, thus enabling the surface velocity radar to precisely determine the surface flow velocity.
The surface velocity radar is able to detect water flow traveling at speeds ranging from 0.08 m/s to 15.0 m/s with precision of 0.01 m/s. Integrated tilt sensor measures inclination angle of the sensor and the flow velocity measurement is automatically cosine-corrected according to the measured mounting tilt angle.

Electrical Characteristics

1. The electrical characteristics of the Geolux RSS-2-300W surface velocity radar are given in Table

Table 1. Electrical Characteristics

bps
Radar sensor
Frequency – EU, with CE label
Frequency – US/Can, with FCC/IC label Radiated power (EIRP)
Sensitivity
Beam-width (3dB) — Azimuth
Beam-width (3dB) — Elevation| 24.050
24.075
-108| 24.125
24.125
-110
12
24| 24.200
24.175
20
-112| GHz
GHz
dBm
dBm
°
°
Power supply voltage| 9.0| 12.0| 27.0| VDC
Current consumption 0 12 V
Active mode
Standby mode
Maximum peak current| | | 90
7.5
175| mA
mA
mA
Operational temperature range| -40| | +85| °C
Operational relative humidity range| 0| | 100| ok
Measurement range| 0.08| | 15.00| m/s
Resolution| | 0.1| | mm/s
Accuracy| | +/- 2| | %
Angle compensation| 20| 30| 60| deg.
Installation Height Above the Water| 0.5| | 25| m
Sample rate| | 10| | sps
Ingress protection rating| IP68| | |

Connector Pin-Out

The surface velocity radar uses robust IP68 circular M12 connector with 12 positions and the mating cable is also delivered with the surface velocity radar. The connector and cable details are shown in Picture 1 while Table 2 gives a detailed description of each pin. Picture 1. Surface Velocity Radar Connectors
Table 2. Connector and Cable Pin-out

Pin No.

1

| Wire Color| Pin Name

GND

| Pin Description

This pin should be connected to the ground (negative) pole of the power supply

---|---|---|---
White|
2| Brown| | +Vin| The power supply for the Radar Speed Sensor is provided on this pin. The Radar Speed Sensor power supply voltage must be in the range 9 VDC to 27 VDC, and the power supply must be able to provide at last 0.65W
3| Green| | RS232 – TxD| RS-232 data transmit signal
4| Yellow| | RS232 – RxD| RS-232 data receive signal
5| Grey| | GND| Signal ground
6| Pink| | CAN – H| CAN2.0B high signal (optional)
7| Blue| | CAN – L| CAN2.0B low signal (optional)
8| Red| | Reserved| Reserved
9| Orange| | RS485 – D-| RS-485 data transmitter/receiver low signal
10| Dark Red| | RS485 – D+| RS-485 data transmitter/receiver high signal
11| Black| | Alarm SW| Alarm – open collector switch signal max. 60mA (optional)
12| Purple| | 4 – 20 mA| Sink for 4 – 20 mA analog interface. Connect sensing device as pull-up to sink the current

3.1. Serial RS-232 Interface
Serial RS-232 interface is implemented as standard PC full-duplex serial interface with voltage levels adequate for direct connection to PC computer or other embedded devices used for serial RS-232 communication.
In case the RS-232 interface is connected to standard DB-9 PC connector, TxD line (green wire) is connected to pin 2 and RxD (yellow wire) is connected to pin 3. For proper operation of the serial interface, additional connection of signal GND (grey wire) is required on pin 5 of the DB-9 connector. Optionally Geolux can supply a cable with DB-9 connector connected to the cable but this must be specified as option when ordering the sensors.
Several communication protocols are available, and custom on request. Details of communication protocols are described later in this user manual.
3.2. Serial RS-485 Interface
Serial RS-485 interface is implemented as standard industrial half-duplex communication interface. The communication interface is internally short- circuit and overvoltage protected.
Depending on the receiving device, the interface can be used with only two wires (D+ dark red wire & D- orange wire) while in some cases the ground connection (signal GND grey wire) is also required. For more details please consult receiver specification.
Most common communication protocol used with RS-485 interface is Modbus-RTU but other protocols are also available. Details of communication protocols are described later in this user manual.
3.3. Analog 4 – 20 mA Output
Analog current 4 – 20 mA output is provided for easier compatibility with older logging and control systems. Output is implemented as current sink architecture with common ground. Maximal voltage applied to the sink can go up to 30 VDC, providing greater flexibility in connections of the sensor to PLCs, loggers, or data concentrators.
Signal range and function for 4 – 20 mA analog output can be configured in the setup application so the sensor will be able to signal best suitable value range with available current range. Current step in the sensor is 0.3 µA, which limits the resolution, so care has to be taken while setting the minimal value to be represented by 4 mA and the maximal value to be represented by 20 mA so the resolution is sufficient for the system requirements. Measurement of the current by the client device (logger, PLC, modem etc.) must be implemented as the high side current measurement as shown on the picture 4. If sensing resistor is used resistance should be selected from the range 10Ω to 500Ω with recommended value 100Ω for the sensing resistor. 3.4.1. Connection to Schneider TM3AM6 analog input module
The TM3AM6 analog module contains 4 analog inputs, marked I0 to I3. Each analog input consists of two connectors, marked as I+ and I-. Each analog input can be configured to work either as analog voltage input (0 – 10 V or -10 to +10 V), or as analog current input (0 – 20 mA or 4 – 20 mA). This is the wiring diagram from the TM3AM6 user manual: In order to connect the Geolux instrument to the TM3AM6 module, the first step is to configure the selected input port as analog current input operating on 4 – 20 mA range. This is done by using Schneider software. After the analog input module is configured, the second step is to connect the Geolux instrument to the TM3AM6 module, according to the following schematic diagram: It is important to note that the 4 – 20 mA wire from the Geolux instrument should be connected to negative (-), not positive (+) terminal of the analog input port.

Installing the Surface Velocity Radar

The surface velocity radar must be installed above the water surface, pointing toward the water surface at a vertical angle. Recommended minimum height above the water surface is 1 meter, with maximum height up to 20 meters. Recommended vertical angle is 45 degrees.
Picture 5 shows how the radar should be positioned relative to the water surface.  4.1. Instrument Mounting and Location Selection
To achieve the specified accuracy, it is important to properly select the measurement site and to install the sensor with proper horizontal and vertical tilt angle. The tilt angle to horizontal plane for surface velocity sensor should be between 30° and 60°, and if instrument is mounted with reasonable tolerances to the pole this should be maintained. For optimal operation and best results, the instrument should be oriented in parallel with the water flow direction. Any deviation from parallel water flow direction will introduce offset of the real measurement value, more precisely, the value will be lower than actual surface velocity of the water. It is recommended that
the instrument is pointed upstream, so that the water flows towards the instrument.
The height of the instrument above the water surface and the inclination determine area on  the surface that is covered by the radar beam. This measurement area should be clear of any obstacles. The structure holding the instrument (pole, bridge fence, etc.) must be solid and without vibrations. There should be no vegetation between the radar and the measurement area because it could affect measurement accuracy.
Water surface directly below the sensor should be clean of vegetation, rocks, sand deposition or other obstacles that could affect measurement.
Surface velocity radar beam will cover an elliptical area on the water surface. The radar reports average surface velocity of the covered area and instrument uses complex Kalman filters with physical modeling of the water flow to give stable measurements even under turbulent conditions.
However even the moderate waviness of the water surface will improve the measurement, if the water flow is strongly turbulent, fluctuations in measured data could be expected as well as somewhat reduced measurement accuracy. If strongly turbulent flow can be expected at monitoring site, then the filter length of the radar should be configured to 120 or more.
4.2. Measurement Quality Indicator
Geolux RSS-2-300W instrument is constantly calculating various parameters of the signal in the signal processing algorithms and will continuously, along with measurement data, report the measurement quality. Quality indicator value is in range from 0 (the best quality) to 3 (the worst quality) and can be used to interpret data in the analysis software with better understanding and confidence.
For example, when the radar is mounted on the railway bridge, one of common applications, measurements will be very good quality most of the time except when train is passing the bridge due to the extensive vibrations. In this case radar will still report measurements but values could be quite wrong, but also the measurement quality indicator value will go up to the higher value. It is up to every user to interpret the quality indicator value for their application, but general recommendation is that measurements with quality indicator 3 cannot be trusted, value 2 could be questionable, and values 1 and 0 are very good and accurate.
4.3. Rain and Wind
Geolux RSS-2-300W instrument has integrated internal software filters to filter out effects of rain, fog or wind both for surface velocity. These filters however have some limitations. Majority of measurement inaccuracies caused by environmental factors can be solved by proper sensor installation.
For rain and snow suppression, the most effective solution is to mount the radar so that it points upstream and the water flows towards the radar. As rain falls down and the radar is tilted downwards, rain droplets will move away from the radar, while the water flows towards the radar. The radar can then easily distinguish the water movement from rain movement. To further improve rain filtering, the radar should be configured to report only incoming direction of water flow. In this case, the radar will completely ignore all movement with direction going away from the sensor. Influence of the wind on the accuracy of measured data is, in most cases small and can be neglected. The only exception is strong wind as it will create surface waves that are traveling in different direction from the water flow. This can affect surface measurement accuracy.
4.4. Interference and Multiple Radars
Surface velocity radar operates in K band, in frequency range around 24.125 GHz. Frequency stability and phase noise of the internal oscillator is very good and always trimmed in factory to precise central frequency but even with the best possible trimming and most stable oscillators it is very unlikely that two devices will be working on the exact same frequency to cause interference. Doppler frequency shift caused by water in speed range up to 15 m/s is measured in kHz frequency shift. As this frequency shift is relatively small in comparison to the central frequency, in most cases below 0.00005%, it will be required to keep difference between central frequencies of two radars
in the same range to get interference.
Similarly, as interference from two or more surface velocity radars on the same location it is very unlikely that other radiation sources in K band will also affect radar measurements. It is possible that some wideband radiation sources can introduce small and impulse interference for the short period of time, but this should not, or is very unlikely to affect measurements reported by radar sensor continuously.
4.5. Fogging and Evaporation
Generally, radar sensors are not affected by fog or evaporation of water unless very heavy evaporation is present and water density in the air is very high. Very high amount of evaporation can introduce reflections and can affect measurement on surface velocity sensor. In the case of evaporation, the best solution for surface velocity sensor problem solving is to use outbound flow direction and to configure sensor with only downstream directional filter. As evaporation is traveling upwards from the water surface, inbound or approaching to the radar, directional filter will solve the problem in most of the cases.
4.6. Reflections
Water is very reflective medium for the radar waves and most of the power transmitted from radar transmitter will be reflected from the water surface. Reflections of the radar transmitted power beam follow the same physical laws as in optics and every time radar beam hits the surface part of the power is reflected away from the radar, part of the power is reflected towards the radar and only a small part of power is absorbed by the water. Depending on the surface roughness and incident angle ratio between power reflected in the direction away from the radar and direction back towards the radar can significantly vary.
Ratio between reflections is determined by water surface roughness and rule of thumb can be applied where more rough water surface will lead to stronger reflection inbound the radar thus easier detection and greater SNR (signal to noise) ration on the radar which enables more accurate measurement. Geolux surface velocity radar is designed with special techniques to achieve accurate measurements even in the very small SNR environments so the required surface
roughness of 1 mm is usually enough for the precise measurements.  When selecting location for surface velocity sensor additional care must be taken to avoid reflected power away from the radar (red arrow) to hit moving objects (gray cloud) on the side of water channel as this can cause additional reflection to inbound the radar and can significantly affect measurement accuracy. Installations where pedestrians, cars or other objects are moving in front of the sensor closer than 75 m should be avoided as it is proven in practice that it can cause problems.
Indoor applications are generally not recommended as it could lead to wrong readings due to the reflection of the radar beam and hitting any moving or rotating object which could cause false readings.

Surface Velocity Radar Settings

Communication Interfaces Parameters
Baud rate Baud rate – Configures the baud rate (bits per second) for serial communication on both RS-232 and RS-485 data lines. This setting controls how many bits are sent on the communication line in one second. The available values are standardized. Using higher baud rate over longer lines may introduce errors in transferred data. The default instrument baud rate is 9600 bps.
RS-232 and RS-485 protocol RS-232 protocol – Selects the communication protocol to be used for data communication on RS-232 interface. The NMEA protocol is a GPS-like human readable messaging protocol where each data packet contains a checksum for data integrity verification. SDI-12 protocol is used for interfacing older type of Geolux SDI-12 adapters. Unless the instrument is connected to an older Geolux SDI-12 adapter, NMEA protocol must be selected.
RS-485 protocol – Selects the communication protocol to be used on RS-485 half-duplex interface. HS protocol is a simple request-response protocol for the simplest applications. Modbus RTU protocol is a standardized protocol which is commonly used in automation and instrumentation as it provides all measurements with detailed diagnostics of device operation and the possibility to change the instrument’s operating parameters.
Device ID Device ID – Configures the device (slave) ID to be used on RS-485 interface protocols (Modbus RTU or HS). Both protocols use request/response format and allow multiple instruments to be connected on the same bus. When a remote master transmits the request message, it will use the device ID as a device address. All instruments will receive the request, but only the instrument with matching device ID will answer to the received request.
Modbus settings Modbus settings – Configures the parity and number of stop bits used in communication. Parity is used in serial communication for basic error detection. When parity is set to none, no parity is used, and no error detection is possible on bit level. When parity is set to odd parity, an additional bit is added to the communication that will be set to 1 when there is odd number of bits with value 1 in the 8-bit payload byte. Similarly, when parity is set to even parity, an additional bit is added to the communication that will be set to 1 when there is even number of bits with value 1 in the 8-bit payload byte. In general, all bytes on the receiver side where the parity bit is not matching the message will be discarded. Default setting on most devices that use Modbus is even parity. Stop bits are added to the end of each data byte transferred over serial communication, to allow pause between two bytes. The default setting is even parity and one stop bit.
Warm up time Warm up time – The time after sensor power-up, during which all measurements are ignored.
This time is used to settle auto-gain parameters, Kalman filter values, averaging filter, and all other operational parameters. It is recommended to set this value to a minimum of 5 seconds. In extreme cases where a quick response after unit power-up is required, 3 seconds can be used, with a possibility of losing measurement accuracy.
4 – 20 mA output
4 – 20 mA output – this parameter is used to select the value that will be presented on the 4 – 20 mA output. When velocity is selected the output current will be proportional to the measured velocity. When none is selected the 4 – 20 mA output will be disabled.
4 – 20 mA min. and 4 – 20 mA max. 4 – 20 mA min. – To configure the 4 – 20 mA output range, the minimum measured value which will correspond to 4 mA analog output needs to be set. The value is set in the currently configured measurement unit. Example: if values measured by the instrument are expected to be within the range of 700 mm/s to 1500 mm/s, it is recommended to configure the minimum value to slightly below 700 mm/s (for example 500 mm/s). Alternatively, if the resolution is not critical, then minimum value for 4 – 20 mA output can be left to the instrument minimum of 0 mm/s.
4 – 20 mA max. – To configure the 4 – 20 mA output range, the maximum measured value which will correspond to 20 mA analog output needs to be set. The value is set in the currently configured measurement unit. Example: if values measured by the instrument are expected to be within the range of 700 mm/s to 1500 mm/s, it is recommended to configure the maximum value to slightly above 1500 mm/s (for example 2000 mm/s). Alternatively, if the resolution is not critical, then maximum value for 4 – 20 mA output can be left to the instrument maximum of 15000 mm/s.

Processing Parameters

Sensitivity level
Sensitivity level – Configures the radar sensitivity level. The sensitivity level threshold is used by the radar to determine whether the reflected signal is too low to detect any flow. If the instrument is incorrectly reporting flow when there is no water in the channel, it’s necessary to increase the value of this parameter.
SNR Threshold SNR threshold – The minimal Signal to Noise Ratio that is required to detect the surface velocity. If the actual measured SNR is lower than the threshold, the instrument will not report any surface velocity.
Setting SNR threshold to a higher value will result with more robust measurements but may also result with no measurements when the water is very smooth. As a general rule of thumb, the measurements with SNR below 10 dB may be inaccurate, and measurements with SNR below 6 dB should not be trusted. The SNR threshold should be set accordingly. The SNR is calculated according to the following formula, where A_peak is the absolute signal level amplitude at the detected peak, and A_avg is the average signal level amplitude of the complete signal, except for the detected peak:
SNR = 10 * log(A_peak / A_avg)
Filter length Filter length – The length of the averaging filter, in number of readings, to smoothen the measured values. The instrument performs 10 readings per second, so a filter length value of 50 will result in 5 second integration time. When using longer filter lengths, more measured values are used for filtering, and the resulting data will be smoother. However, when the surface velocity changes, it will take more time for the new measurement to be reported. Typically, this parameter should be set to a value between 50 and 200. For highly turbulent water, larger filter length is recommended.
Direction filter Direction filter – Direction filter is used to choose whether the instrument will detect flow in both  directions, or if it should detect only incoming or only outgoing flow. If the direction filter is set to both directions, the instrument will measure the flow velocity in any direction and will also report the actual direction of the flow. If the direction filter is set to incoming direction, then the instrument will reject all radar returns that correspond to outgoing flow, and vice versa. On monitoring sites where it is expected that the flow will always be in only one direction, it is recommended to properly configure this parameter to either incoming or outgoing, as that will improve the consistency of measurements.
Extra fast
Extra fast – Enables or disables the extra fast setting. When the radar is powered-up in normal operation mode, it will need a few seconds to self- configure in an optimal way for the current flow conditions. This is not necessary with stable flow conditions when the strength of the reflected radar signal is high (which can be checked by monitoring the reported SNR value). In that case, enabling the extra fast setting will force the radar to skip self- configuration and save a few seconds at power-up before the first measurement is reported.
Peak width
Peak width – When a velocity peak is detected, this parameter tells the radar how wide to consider the side velocities for the final velocity report. If the flow is uniform across the surface, then normal peak width can be selected.

Measurement Parameters

Velocity unit
Velocity unit – The measurement unit used to report the measured velocity value. For NMEA protocol which is used over RS-232 connection, the velocity is reported as an integer value. To preserve higher precision with integer numbers, the measured velocity will be multiplied by 10 for cm/s, m/s, km/h, mph, fps and fpm when being transferred over RS-232. When mm/s units are used, the measured values will not be multiplied by 10. Geolux Instrument Configurator application internally handles the multiplication factor which is used over RS-232 protocol, and it displays the correct values to the user.
PGA sensitivity PGA sensitivity – This parameter limits the maximum gain (amplification level) of the internal programmable gain amplifier. It is strongly recommended to use the default value 8, which allows the internal signal amplifier to use the maximum gain when the reflected radar signal is very low. Setting this value to a lower value is used only when the instrument is mounted very close to the water surface, typically less than 1 meter, and in that case this parameter should be set to a value 4 or 5.
Velocity min. and Velocity max.
Velocity min. – This parameter is used for setting up the minimum velocity value of interest.
Velocity max. – This parameter is used for setting up the maximum velocity value of interest.

Data Interface

Geolux RSS-2-300W surface velocity radar offers multiple data interfaces, in order to make the integration of the device with existing SCADA/telemetry systems easy.
6.1. Serial RS-232 Interface
Serial RS-232 interface is used for direct connection of a single surface velocity radar unit with the computer. The serial interface is used both for retrieving live flow measurements and for configuration of the surface velocity radar device. Geolux provides a PC application for unit configuration and flow monitoring free of charge.
Default communication parameters are:

A NMEA-like communication protocol is used to deliver flow measurements over RS-232 interface.
Detailed description of the protocol is given in the Chapter 7 of this user manual.
6.2. Serial RS-485 Interface
Serial RS-485 interface is used for connecting multiple surface velocity radars to a single data logger.
RS-485 interface uses a different protocol then the protocol used over RS-232 interface, in order to allow multiple surface velocity radars connected on a single RS-485 bus. The main difference from the protocol used over RS-232 interface is that the flow measurements are not reported automatically, but are instead reported only after being requested by the master device (data logger unit). Detailed description of the protocol is given in the Chapter 7 of this user manual.
Default communication parameters are:

Data Protocols

Geolux RSS-2-300W surface velocity radar supports the following data protocols:

• NMEA-like protocol on RS-232 interface that constantly outputs the detected speed and reflected signal power, and also the current measured tilt angle
• Servicing protocol on RS-232 interface for configuring the unit
• Request-response protocol on RS-485 interface that allows multiple units to be used on a single RS-485 bus
• Modbus-RTU protocol on RS-485 interface which is supported by variety of third-party data loggers

Support for additional protocols is available upon customer request.
7.1. 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 singe-direction protocol: data is only transmitted from the surface velocity radar.
At RS-232 interface the device periodically outputs following data sentences:
Direct flow measurement report
$RDTGT,D1,S1,L1*CSUM

$RDTGT: The keyword sent on the beginning of each report. This sentence is sent whenever there is detected flow.
D1: The direction of the flow, as detected by the instrument (1 incoming, -1 outgoing). Geolux Instrument Configurator displays this value as “In” for incoming and “Out” for outgoing direction.
S1: The measured surface velocity, without applying additional averaging filter (velocity is reported as velocity10 for m/s, km/h, mph, fps and fpm and as velocity1 for mm/s and cm/s). Geolux Instrument Configurator internally handles the multiplication factor and displays the correct values to the user.
L1: The relative level strength of the returned radar signal. This value is used internally by the auto-gain algorithm which adjusts the gain levels of the internal signal amplifiers.
CSUM: The check sum of the characters in the report from $ to excluding these characters.
Average flow measurement report
$RDAVG,S1CSUM
_ $RDSNR: The keyword sent on the beginning of each SNR report.
S1: Signal to Noise Ratio of the detected signal in dB. SNR is the difference between signal level corresponding to measured velocity and the noise floor level. Low SNR levels indicate that the measured value may be inaccurate.
S2:   The average Signal to Noise Ratio of the detected signal. SNR is the difference between signal level corresponding to measured velocity and the noise floor level. Low SNR levels indicate that the measured value may be inaccurate.
CSUM: _The check sum of the characters in the report from $ to excluding these characters.
Tilt angle report
$RDANG,ACSUM

sensor.  The angle is relative to the horizontal plane.
CSUM:| The check sum of the characters in the report from $ to * excluding these characters.

Signal to noise ratio (SNR) report
$RDSNR,S1,S2*CSUM

between signal level corresponding to measured velocity and the noise  floor level. Low SNR levels indicate that the measured value may be inaccurate.
S2:| The average Signal to Noise Ratio of the detected signal. SNR is the difference between signal level corresponding to measured velocity  and the noise floor level. Low SNR levels indicate that the measured value may be inaccurate.
CSUM:| The check sum of the characters in the report from $ to * excluding these characters.

Quality of signal report
$QOS,Q1,Q2*CSUM

related to the instrument vibrations. If the instrument is vibrating, the measurements may be incorrect, and the amount of vibrations is
measured and reported. Geolux Instrument Configurator color-codes  these values. Measurements can be trusted when QoS is green. Measurements may be inaccurate when the indicator is yellow or red.
Q2:| This is an indicator of the Quality of the Service (measurements) related to the radar signals. Geolux Instrument Configurator color-codes these values. Measurements can be trusted when QoS is green.
Measurements may be inaccurate when the indicator is yellow or red.
CSUM:| The check sum of the characters in the report from $ to * excluding these  characters.

Quality of signal factors and corresponding color codes:
0 – Excellent measurement quality (Green)
1 – Good measurement quality (Green)
2 – Low measurement quality (Yellow)
3 – Unacceptable measurement quality (Red)
7.2. Servicing Protocol (RS-232)
The servicing protocol is used to retrieve and modify 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. To make radar configuration easy, Geolux provides the Geolux Instrument Configurator utility application. Regular users do not need to be concerned about the servicing protocol used between the Geolux Instrument Configurator and the surface velocity radar device. Geolux Instrument Configurator is described in the Chapter 7 of this manual.
The servicing protocol listens on RS-232 serial port for incoming requests, and on each received request, it will answer back.
The following requests are recognized by the servicing protocol and every command should be followed by , or (enter):
Change interface parameters
Baud rate – Configures the baud rate (bits per second) for serial communication on both RS-232 and RS-485 data lines. This setting controls how many bits are sent on the communication line in one second. The available values are standardized. Using higher baud rate over longer lines may introduce errors in transferred data. The default instrument baud rate is 9600 bps.

• set_baud_rate = 9600

• set_baud_rate = 19200

• set_baud_rate = 38400

• set_baud_rate = 57600

• set_baud_rate = 115200

RS-232 protocol – Selects the communication protocol to be used for data communication on RS232 interface. The NMEA protocol is a GPS-like human readable messaging protocol where each data packet contains a checksum for data integrity verification. SDI-12 protocol is used for interfacing older type of Geolux SDI-12 adapters. Unless the instrument is connected to an older Geolux SDI-12 adapter, NMEA protocol must be selected.

set_proto=nmea

RS-485 protocol – Selects the communication protocol to be used on RS-485 half-duplex interface. HS protocol is a simple request-response protocol for the simplest applications. Modbus RTU protocol is a standardized protocol which is commonly used in automation and instrumentation as it provides all measurements with detailed diagnostics of device operation and the possibility to change the instrument’s operating parameters.

• set_485_proto=modbus_rtu

• set_485_proto=hs

Device ID – Configures the device (slave) ID to be used on RS-485 interface protocols (Modbus RTU or HS). Both protocols use request/response format and allow multiple instruments to be connected on the same bus. When a remote master transmits the request message, it will use the device ID as a device address. All instruments will receive the request, but only the instrument with matching device ID will answer to the received request.

set_can_id=<1-247>

Modbus settings – Configures the parity and number of stop bits used in communication. Parity is used in serial communication for basic error detection. When parity is set to none, no parity is used, and no error detection is possible on bit level. When parity is set to odd parity, an additional bit is added to the communication that will be set to 1 when there is odd number of bits with value 1 in the 8-bit payload byte. Similarly, when parity is set to even parity, an additional bit is added to the communication that will be set to 1 when there is even number of bits with value 1 in the 8-bit payload byte. In general, all bytes on the receiver side where the parity bit is not matching the
message will be discarded. Default setting on most devices that use Modbus is even parity. Stop bits are added to the end of each data byte transferred over serial communication, to allow pause between two bytes. The default setting is even parity and one stop bit.

set_485_modbus_type=0| (no parity, one stop bit)

---|---

set_485_modbus_type=1| (no parity, two stop bits)

set_485_modbus_type=2| (even parity, one stop bit)

set_485_modbus_type=3| (odd parity, one stop bit)

Warm up time – The time after sensor power-up, during which all measurements are ignored. This time is used to settle auto-gain parameters, Kalman filter values, averaging filter, and all other operational parameters. It is recommended to set this value to a minimum of 5 seconds. In extreme cases where a quick response after unit power-up is required, 3 seconds can be used, with a possibility of losing measurement accuracy.

set_dead_time=<3-100>

4-20 mA output – This parameter is used to select the value that will be presented on the 4 – 20 mA output. When velocity is selected the output current will be proportional to the measured velocity. When selecting none the 4-20 mA output will be disabled.

• set_an420_type=velocity

• set_an420_type=none

4-20 mA min. – To configure the 4-20 mA output range, the minimum measured value which will correspond to 4 mA analog output needs to be set. The value is set in the currently configured  measurement unit. Example: if values measured by the instrument are expected to be within the range of 700 mm/s to 1500 mm/s, it is recommended to configure the minimum value to slightly below 700 mm/s (for example 500 mm/s). Alternatively, if the resolution is not critical, then minimum value for 4-20 mA output can be left to the instrument minimum of 0 mm/s.

set_an420_min=

4-20 mA max. – To configure the 4-20 mA output range, the maximum measured value which will correspond to 20 mA analog output needs to be set. The value is set in the currently configured measurement unit. Example: if values measured by the instrument are expected to be within the range of 700 mm/s to 1500 mm/s, it is recommended to configure the maximum value to slightly above 1500 mm/s (for example 2000 mm/s). Alternatively, if the resolution is not critical, then minimum value for 4-20 mA output can be left to the instrument maximum of 15000 mm/s

set_an420_max=

Change processing parameters
Sensitivity level – Configures the radar sensitivity level. The sensitivity level threshold is used by the radar to determine whether the reflected signal is too low to detect any flow. If the instrument is incorrectly reporting flow when there is no water in the channel, it’s necessary to increase the value of this parameter.

set_thld=<0-100>

SNR threshold – The minimal Signal to Noise Ratio that is required to detect the water flow. If the actual measured SNR is lower than the threshold, the instrument will not report any flow. Setting SNR threshold to a higher value will result with more robust measurements but may also result with no measurements when the water is very smooth. As a general rule of thumb, the measurements with SNR below 10 dB may be inaccurate, and measurements with SNR below 6 dB should not be trusted. The SNR threshold should be set accordingly.

set_thld_snr=<0-5120>

Filter length – The length of the averaging filter, in number of readings, to smoothen the measured values. The instrument performs 10 readings per second, so a filter length value of 50 will result in 5 second integration time. When using longer filter lengths, more measured values are used for filtering, and the resulting data will be smoother. However, when the surface velocity changes, it will take more time for the new measurement to be reported. Typically, this parameter should be set to a value between 50 and 200. For highly turbulent water, larger filter length is recommended.

set_filter_len=<1-1000>

Direction filter – Direction filter is used to choose whether the instrument will detect flow in both directions, or if it should detect only incoming or only outgoing flow. If the direction filter is set to both directions, the instrument will measure the flow velocity in any direction and will also report the actual direction of the flow. If the direction filter is set to incoming direction, then the instrument will reject all radar returns that correspond to outgoing flow, and vice versa. On monitoring sites where it is expected that the flow will always be in only one direction, it is recommended to properly configure this parameter to either incoming or outgoing, as that will improve the consistency of measurements.

• set_direction=in

• set_direction=out

• set_direction=both

Extra fast – Enables or disables the extra fast setting. When the radar is powered-up in normal operation mode, it will need a few seconds to self- configure in an optimal way for the current flow conditions. This is not necessary with stable flow conditions when the strength of the reflected radar signal is high (which can be checked by monitoring the reported SNR value). In that case, enabling the extra fast setting will force the radar to skip self- configuration and save a few seconds at power-up before the first measurement is reported.

set_extra_fast=0| (Disabled)

---|---

set_extra_fast=1| (Enabled)

Peak width – When a velocity peak is detected, this parameter tells the radar how wide to consider the side velocities for the final velocity report. If the flow is uniform across the surface, then normal peak width can be selected.

set_peak_width=0| (Very narrow)

---|---

set_peak_width=1| (Narrow)

set_peak_width=2| (Normal)

set_peak_width=3| (Wide)

Change measurement parameters
Velocity unit – The measurement unit used to report the measured velocity value. For NMEA protocol which is used over RS-232 connection, the velocity is reported as an integer value. To preserve higher precision with integer numbers, the measured velocity will be multiplied by 10 for cm/s, m/s, km/h, mph, fps and fpm when being transferred over RS-232. When mm/s units are used, the measured values will not be multiplied by 10. This application internally handles the multiplication factor which is used over RS-232 protocol, and it displays the correct values to the user.

• set_units=kmh

• set_units=mph

• set_units=fps

• set_units=fpm

• set_units=ms

• set_units=mms

• set_units=cms

PGA sensitivity – This parameter limits the maximum gain (amplification level) of the internal programmable gain amplifier. It is strongly recommended to use the default value 8, which allows the internal signal amplifier to use the maximum gain when the reflected radar signal is very low. Setting this value to a lower value is used only when the instrument is mounted very close to the water surface, typically less than 1 meter, and in that case this parameter should be set to a value 4 or 5.

• set_sensitivity=<0-8>

Velocity min. – Available only on devices with firmware versions above 6.3.2. This parameter is used for setting up the minimum velocity value of interest.

• set_min_velocity=

Velocity max. – Available only on devices with firmware versions above 6.3.2. This parameter is used for setting up the maximum velocity value of interest.

set_max_velocity=

Low power mode – Available only on devices with firmware versions above 6.3.2. This parameter is used for putting radar in low power mode.

radar_sleep

Reset device settings to default factory settings – This command resets all settings on the device (Interface, Processing, Measurement and Profile Settings) to default factory settings.

radar_reset_default

Retrieve current device status
#get_info
Requests the current device status. Here is an example status output:

• firmware:6.5.7

• serial:170269

• sensor_type:W

• direction:both

• baud_rate:9600

• dead_time:10

• can_id:1

• angle:89

• filter_type:2

• filter_len:50

• fft_integ_time:0

• pga_gain:10

• proto:nmea

• 485_proto:modbus_rtu

• 485_modbus_type:2

• units:mms

• sensitivity:8 (Auto)

• thld:124

• thld_snr:1024

• an420_type:9

• an420_min:0.000

• an420_max:10000.000

• min_velocity:0.000

• max_velocity:15000.000

• border_velocity:500.000

• extra_fast:0

• power_save:0

7.3. HS Protocol (RS-485)
A different data protocol is used on RS-485 interface which allows connection of multiple units on the single RS-485 line. Before the units are connected on the single RS-485 bus, each unit must be configured with a different device identifier. The device identifier is configured by using the PC application. Please check Chapter 7 for instructions.
The HS protocol is a request-response protocol which, unlike NMEA protocol, does not automatically report periodic flow measurement readings. Instead, when the unit is polled form the data logger, it responds the measurement.
The request is sent from the data logger to the surface velocity radar: <0x25> ID CSUM
0x25: The first byte sent in the request is ‘%’ character. Its ASCII value in HEX is 0x25.
ID: Exactly two bytes long. This is the unit ID written as two ASCII characters. For example, if the polled unit ID is 2, then ID will be sent as “02”. In HEX representation it is the following two bytes: <0x30><0x32>.
CSUM: Checksum, calculated by adding in modulo 256 the two byte values of the ID. If the device ID is 2, then ID was sent as <0x30><0x32>. Checksum is then 0x30+0x32 = <0x62>.
0xA5: The first byte sent in the response is byte with HEX value of 0xA5.
ID: Exactly two bytes long. This is the unit ID written as two ASCII characters. For example, if the unit ID is 2, then ID will be sent as “02”. In HEX representation it is the following two bytes: <0x30><0x32>.
SPEED: The speed readout in currently selected units, formatted as real (float) number with exactly three digits after the decimal dot separator. For example, if the current averaged speed is 5.7143, it will be reported as 5.714, or in
HEX values: <0x35><0x2E><0x37><0x31><0x34><0x33>.
CSUM: Checksum, calculated by adding in modulo 256 the two byte values of the ID and all byte values from the SPEED.
The second possible command is sent from the data logger to the surface velocity radar:
< 0x2b> ID CSUM
0x2b: The first byte sent in the request is ‘+‘character. Its ASCII value in HEX is 0x2b.
ID: Exactly two bytes long. This is the unit ID written as two ASCII characters. For example, if the polled unit ID is 2, then ID will be sent as “02”. In HEX representation it is the following two bytes: <0x30><0x32>.
CSUM: Checksum, calculated by adding in modulo 256 the two byte values of the ID. If the device ID is 2, then ID was sent as <0x30><0x32>. Checksum is then 0x30+0x32 = <0x62>.
After receiving the request, device goes to power save mode.
The third possible command is sent from the data logger to the surface velocity radar:
< 0x2d> ID CSUM
0x2d: The first byte sent in the request is ‘-‘character. Its ASCII value in HEX is 0x2d.
ID: Exactly two bytes long. This is the unit ID written as two ASCII characters. For example, if the polled unit ID is 2, then ID will be sent as “02”. In HEX representation it is the following two bytes: <0x30><0x32>.
CSUM: Checksum, calculated by adding in modulo 256 the two byte values of the ID. If the device ID is 2, then ID was sent as <0x30><0x32>. Checksum is then 0x30+0x32 = <0x62>.
After receiving the request, device goes to normal operation mode from power safe mode.
7.4. Modbus Protocol (RS-485)
When configured in Modbus operation mode, the unit responds to Modbus requests over RS-485 data line. The baud rate and device ID configured through the PC application, and 1 stop bit, even parity, 8 data bits configuration is used.
Modbus registers that are accessed by Modbus protocol are 16-bit (2-byte) registers. Any number of registers can be read or written over Modbus.
Modbus is a request-response protocol where a master (such as data logger) sends out requests, and slave devices (such as RSS-2-300W sensor) responds. The request and response format, with examples is given in tables 3-6.
In each request, the master can either ask the slave to retrieve value of one or more registers, or the master can set the value of one or more registers. Each register holds one 16-bit value.
Table 3. Master Request Format

Name| Address| Fun| Data Start Address| Register Count| CRC16
---|---|---|---|---|---
Length| 1 byte| 1 byte| 2 bytes (H,L)| 2 bytes (H,L)| 2 bytes (L,H)
Example| 0x01| 0x03| 0x00| 0x00| 0x00| 0x01| 0x84| 0x0A

Table 4. Request Example

Table 5. Slave (sensor) Response Format

Table 6. Response Example

Table 7 defines the data returned by the unit when the master requests register is read. Table 8 defines how to write device configuration. Rows highlighted in blue denote the important values measured by the sensor. Rows highlighted in green denote operating parameters that could be changed in the field. In Tables 7 and 8, field Fun corresponds to Modbus function codes, i.e. 0x03 – Read holding register and 0x06 – Write holding register.
Table 7. Retrieving Data from the Sensor

Fun| Register Address| Data Length| Data Range| Details
---|---|---|---|---
0x03| 0x0000| 2 bytes| 1 – 247| Read device ID
0x0001| 2 bytes| 0 → 9600
1 → 38400
2 → 57600
3 → 115200
4 → 19200| Read baud rate
0x0002| 2 bytes| 0  → mm/s
1  → m/s
2  → mph
3  → km/h
4  → fps
5  → fpm
6  → cm/s| Read velocity unit type
0x0003| 2 bytes| 0 – 15000 (mm/s)| Read instantaneous velocity
0x0004| 2 bytes| 0 – 15000 (mm/s)| Read average velocity
0x0005| 2 bytes| 0 – 360| Read tilt angle
0x0006| 2 bytes| 0  → incoming
1  → outgoing| Read flow direction
0x0007| 2 bytes| 1 – 512| Read filter length
0x0008| 2 bytes| 0 – 8| Read defined PGA gain sensitivity
0x0009| 2 bytes| 0  → both
1  → incoming
2  → outgoing| Read flow direction filter setting
Fun| Register Address| Data Length| Data Range| Details
---|---|---|---|---
0x03| 0x000A| 2 bytes| 0 – 100| Read sensitivity level
0x000B| 2 bytes| 0| Read device type, always 0
0x000C| 2 bytes| 0 – 3840| Read SNR threshold (dBm 256)
0x000D| 2 bytes| 600 – 700| Read firmware code (e.g. 6.3.9)
0x000E| 2 bytes| 1,2,5,10,20,50,100,200| Read current PGA gain level
0x000F| 2 bytes| 0 – 2047| Read relative signal level
0x0010| 2 bytes| 0 – 65535| Read instantaneous speed in selected units (integer part)
0x0011| 2 bytes| 0 – 65535| Read instantaneous speed in selected units (decimal part 1000)
0x0012| 2 bytes| 0 – 65535| Read averaged speed in select- ed units (integer part)
0x0013| 2 bytes| 0 – 65535| Read averaged speed in selected units (decimal part 1000)
0x0014| 2 bytes| 0 – 10000| Read instantaneous SNR level (dBm 256)
0x0015| 2 bytes| 0 – 10000| Read averaged SNR level (dBm

0x0016| 2 bytes| 3 printable characters| Read serial number [0-2]
0x0017| 2 bytes| 3 printable characters| Read serial number [3-5]
0x0018| 2 bytes| 0 → excellent
1 → good
2 → low
3 → unacceptable| Read QoS – angle, vibrations – first byte

__

Read QoS – signal – second byte

0x0019 – 0x001A| 2 bytes| 0| Reserved, always 0
0x001B| 2 bytes| 0 → very narrow 1 → narrow
2 → normal
3 → wide| Read peak width
0x001C| 2 bytes| 0 – 15000| Read velocity min. (mm)
0x001D| 2 bytes| 0 – 15000| Read velocity max. (mm)
0x001E| 2 bytes| 0 → turned off 1 → turned on| Read extra fast setting
0x001F| 2 bytes| 0| Reserved, always 0
0x0051| 2 bytes| 0 → turned off 1 → turned on| Read low power mode

Table 8. Writing Data To The Sensor

Fun| Register Address| Data Length| Data Range| Details
---|---|---|---|---
__ 0x06| 0x0000| 2 bytes| 1 – 247| Change device ID
0x0001| 2 bytes| 0 → 9600
1 → 38400
2 → 57600
3 → 115200
4 → 19200| Change baud rate
0x0002| 2 bytes| 0  → mm/s
1  → m/s
2  → mph
3  → km/h
4  → fps
5  → fpm
6  → cm/s| Change velocity unit type
0x0007| 2 bytes| 1 – 512| Change filter length
0x0008| 2 bytes| 0 – 8| Change PGA gain sensitivity
0x0009| 2 bytes| 0  → both
1  → incoming
2  → outgoing| Change flow direction filter type
0x000A| 2 bytes| 0 – 100| Change sensitivity level
0x000C| 2 bytes| 0 – 3840| Change SNR threshold (dBm * 256)
0x001B| 2 bytes| 0 → very narrow 1 → narrow
2  → normal
3  → wide| Change peak width
0x001C| 2 bytes| 0 – 15000| Change velocity min. (mm)
0x001D| 2 bytes| 0 – 15000| Change velocity max. (mm)
0x001E| 2 bytes| 0 → turned off 1 → turned on| Change extra fast setting
0x0051| 2 bytes| 0 → turned off 1 → turned on| Change low power mode

7.4.1. Modbus Input Registers
Modbus input registers are read-only registers. By reading the Modbus input registers the user can view the device type and the firmware version, as well as real-time measurement values in 32-bit integer or 32-bit float format. Since the native Modbus registers are 16-bit registers, to store 32-bit values, two subsequent registers are used. In order to easily check the byte- order and word-order, two pairs of test registers with fixed constant values are provided. One register pair containts a fixed value of 1234567 in 32-bit integer format, and the other register pair contains a fixed value of -123.4567 in 32-bit float format.
Table 9 defines the data returned by the instrument when the master requests that the input register is read (Modbus function code 0x04). Rows highlighted in blue denote the values of interest, while the rows highlighted in green represent reserved registers which can be read but the returned value will always be equal to 0.
Table 9. Retrieving Data from Modbus Input Registers

Fun| Register Address| Data Length| Data Format| Details
---|---|---|---|---
**** 0x04| 0x0001| 2 bytes| 16-bit integer| Device type ID
0x0002| 2 bytes| 16-bit integer| Firmware version
0x0003| 2 bytes| | Reserved – always 0
0x0004, 0x0005| 2 bytes, 2 bytes| 32-bit integer| 32-bit integer control register pair containing a fixed value of 1234567
0x0006, 0x0007| 2 bytes, 2 bytes| 32-bit float| 32-bit float control register pair containing a fixed value of -123.4567
0x0008 – 0x0011| 2 bytes| | Reserved – always 0
0x0014, 0x0015| 2 bytes, 2 bytes| 32-bit float| Average surface velocity
0x0016, 0x0017| 2 bytes, 2 bytes| 32-bit float| Current surface velocity
0x0018 – 0x001F| 2 bytes| | Reserved – always 0
0x0020, 0x0021| 2 bytes, 2 bytes| 32-bit float| Surface velocity sensor tilt angle
0x0022 – 0x0023| 2 bytes| | Reserved – always 0
0x0024, 0x0025| 2 bytes, 2 bytes| 32-bit float| Surface velocity SNR
0x0026, 0x0027| 2 bytes, 2 bytes| 32-bit float| Surface velocity signal strength
0x0028, 0x0029| 2 bytes, 2 bytes| 32-bit float| Surface flow direction
0x002A – 0x0083| 2 bytes| | Reserved – always 0
0x0084, 0x0085| 2 bytes, 2 bytes| 32-bit integer| Average surface velocity
0x0086, 0x0087| 2 bytes, 2 bytes| 32-bit integer| Current surface velocity
0x0088 – 0x008F| 2 bytes| | Reserved – always 0
0x0090, 0x0091| 2 bytes, 2 bytes| 32-bit integer| Surface velocity sensor tilt angle
0x0092 – 0x0093| 2 bytes| | Reserved – always 0
0x0094, 0x0095| 2 bytes, 2 bytes| 32-bit integer| Surface velocity SNR
0x0096, 0x0097| 2 bytes, 2 bytes| 32-bit integer| Surface velocity signal strength
0x0098, 0x0099| 2 bytes, 2 bytes| 32-bit integer| Surface flow direction

7.5. SDI-12 Protocol
Supported SDI-12 commands are:
In all commands, ‘a’ represents the device address. Blue rows indicate that parameters can be set using this command.
Table 11. SDI-12 Commands

default address is 1
Ping Sensor| a!| a| Device will respond if its address is ‘a’
Address Change| aAb!| b| Device will respond if its address is ‘a’ with its new address ‘b’
Send Identification| aI!| a13GEOLUX 2300Wfff| a – address
SDI-12 version – 1.3
vendor identification – GEOLUX
sensor model – 2300W
sensor version – fff, where fff is firmware version
Start Verification Send Data| aV! aD0!| a00001 a+d| One value is ready imminently
d – verification:
0->not ready , 1->ready
Additional Data| aD1! .. aD9!| a0| No values are returned for additional data.
Start Measurement| aM!/aMC!| ammm5| 5 values are ready within mmm seconds for M command
Send Data| aD0!| a a| val0 → a±f±f+d+d+d