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RSS-2-300W User Manual

5

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

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. 

Picture 3. Analog 4 – 20 mA Output Internal Architecture

Picture 4. High Side Current Measurement for the 4 – 20 mA Analog Output

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. 

Summary of Contents for RSS-2-300W

Page 1: ...Copyright 2021 Geolux d o o All rights reserved RSS 2 300W Non Contact Surface Velocity Radar User Manual ...

Page 2: ...ity 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 Geolux surface velocity radar device Should there be any question...

Page 3: ...nd 7 4 4 Interference and Multiple Radars 8 4 5 Fogging and Evaporation 8 4 6 Reflections 8 5 Surface Velocity Radar Settings 10 6 Data Interface 15 6 1 Serial RS 232 Interface 15 6 2 Serial RS 485 Interface 15 7 Data Protocols 16 7 1 NMEA Protocol RS 232 16 7 3 Request Response Protocol RS 485 22 7 3 1 Request Response Protocol RS 485 22 7 4 Modbus Protocol RS 485 24 8 Geolux Instrument Configura...

Page 4: ...e 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 ...

Page 5: ...Azimuth Beam width 3dB Elevation Measurement range Resolution Accuracy Installation height above the water 24 075 108 0 02 0 01 24 125 110 12 24 1 24 175 20 112 15 0 15 GHz dBm dBm m s m s m Power supply voltage 9 0 12 0 27 0 V Power Operational mode Sleep mode 950 85 mW mW Alarm output maximal current 60 mA Alarm output maximal voltage 30 VDC Analog output maximal voltage 30 VDC Operational tempe...

Page 6: ...ower supply 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 CA...

Page 7: ...rface is implemented as standard industrial half duplex communication interface The communication interface is short circuit and internally 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 specifi...

Page 8: ...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 Picture 3 Analog 4 20 mA Output Internal Architecture Picture 4 High Si...

Page 9: ...or 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 precise value will be lower th...

Page 10: ... 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 ...

Page 11: ...h 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 dire...

Page 12: ...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...

Page 13: ...rotocol 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 mu...

Page 14: ...here 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 u...

Page 15: ...ely 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 r...

Page 16: ...measurements with SNR below 6 dB should not be trusted The SNR threshold should be set accordingly Filter Length Input Value Filtered Value Filter length 50 Filter length 10 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...

Page 17: ...ich 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 mi...

Page 18: ...its 1 Parity None 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...

Page 19: ...EA 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 CR LF RDTGT The keyword sent on the beginning of each detection report This senten...

Page 20: ...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 CR LF 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 ...

Page 21: ...onfiguration 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...

Page 22: ...its 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 parit...

Page 23: ...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 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 f...

Page 24: ... 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_sensitivity 0 8 PGA sensitivity This parameter limits the maximum gain amplification level of the internal programable gain amplifier It is strongly recommended to use the default value 8 which allows the internal s...

Page 25: ...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 appli cation Please check Chapter 7 for instructions The request response protocol unlike NMEA protocol does not automatically report periodic flow measurement readings Instead when th...

Page 26: ...PEED Second possible command is send 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 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 Chec...

Page 27: ... 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 Examp...

Page 28: ...hlighted in green denote operating parameters that could be changed in the field Table 7 Retrieving Data from the Sensor Fun Register Address Data Length Data Range Details 0X03 0X0000 2 bytes 1 255 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...

Page 29: ...relative signal level 0x0010 2 bytes 0 65535 Read instantaneous speed in selected unit integer part 0x0011 2 bytes 0 65535 Read instantaneous speed in selected unit decimal part 1000 0x0012 2 bytes 0 65535 Read averaged speed in select ed unit integer part 0x0013 2 bytes 0 65535 Read averaged speed in selected unit decimal part 1000 0x0014 2 bytes 0 10000 Read instantaneous SNR level dBm 256 0x001...

Page 30: ...d 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 0x001C 2 bytes 0 15000 Velocity min mm 0x00...

Page 31: ...nd interface If RS 485 interface is selected additionally select the baud rate and the Modbus ID In case of multiple devices connected on a single RS 485 bus make sure that each device has a unique Modbus ID When the Connect button is clicked Geolux Instrument Configurator will try to establish a data link between your PC and the surface velocity radar If the connection is successful the device wi...

Page 32: ...changed The following settings are displayed Interfaces Baud rate RS 232 protocol RS 485 protocol Device ID Warm up time 4 20 mA output 4 20 mA min 4 20 mA max Processing Sensitivity level SNR threshold Filter length Direction filter Measurement Velocity unit PGA sensitivity Velocity min Velocity max A detailed description as described in Chapter 5 along with pictures from of this user manual of t...

Page 33: ...d clicking the Load echo curve button loads the current echo curve The echo curve plot shows both the incoming and outgoing directions with yellow and blue lines respectively Depending on the Direction filter selected in Settings the echo curve which is not of interest will be shown in grey If desired echo curves can be saved to a csv file Picture 9 Geolux Instrument Configurator Echo Curve Direct...

Page 34: ...cture on the open channel flows Discharge is calculated by multiplying mean flow velocity and channel cross section area The cross section area is the area of the slice in the water column made perpendicular to the flow direction Let us assume a rectangular channel profile with constant flow velocity at all points as seen in Picture 10 Picture 10 Simple Channel Diagram Q V A where Q is discharge f...

Page 35: ...ement The mean cross section flow velocity needs to be determined from measured surface flow velocity Studies performed by USGS reveal that typically the mean velocity is 80 95 of the surface velocity the average being 85 Knowing non rectangular area of the stream cross section and knowing the surface flow velocity the following formula can be used Q 0 85 V A More details about water flow measurem...

Page 36: ...n and white wires of the instrument cable The power supply must be able to deliver at least 500 mA of current 3 Check RS 232 connector The yellow green and grey wires from the instrument cable must be properly connected to the serial port on the computer Make sure that the grey wire signal ground is connected the RS 232 connection will not work if the signal ground is not connected Also make sure ...

Page 37: ...ire should be connected to D line and the orange line should be connected to D line Make sure that the D and D lines are not swapped Make sure that you have correctly identified and connected the dark red magenta wire as there is also another bright red wire that is used to provide output power for 4 20mA output It is possible to misidentify the wire and to connect the bright red wire to D instead...

Page 38: ... instrument It is not sufficient to simply attach the cable connector to the instrument connector the cable connector must be screwed into the instrument connector 2 Check power supply Make sure that the power is being supplied to the instrument A direct current voltage between 9 and 27 Volts must be connected to brown and white wires of the instrument cable The power supply must be able to delive...

Page 39: ...rtical angle is 45 degrees 2 Check that there are no obstructions between the instrument and the water surface There should be no obstructions between the instrument and the water surface so that the radar waves can freely travel from the instrument s antenna to the water surface and back 3 Check that the distance between the instrument and the water surface is within the instrument s operating ra...

Page 40: ...RSS 2 300W User Manual 37 RSS 2 300W Non Contact Surface Velocity Radar 11 Appendix A Mechanical Assembly ...

Page 41: ...2021 ...

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