Bulletin 101, Issue 2
Export: 4/5/2012
Discharge Measurement System
Model RQ-30
INTRODUCTION
Special points of interest:

Easy to install

Non contact, Real-time
discharge measurement

Robust Construction

Measures Water level,
velocity and calculates
discharge

Maintenance free operation

Interfaces: 1 x SDI-12 and
1 x RS 485

Operating Temperature
-35° C to 60 °C (-31 °F to
140 °F)

FCC Approved & Certified

Adjustable Bandwidth to
suit water flow

Measurement time 0 to
240 seconds
Inside this issue:
Special point of
interest
1
Introduction
1
Specifications
2
The availability of real-time discharge data has become increasingly important to companies who require detailed data quickly for optimal watermanagement strategies. The conventional method is
the development of a relation called “stage-discharge
rating” by periodic measurements of the discharge,
using mechanical or
acoustic current meters for a range of stages. Complex
flow conditions may negate stable stage-discharge
ratings and make the use of conventional methods
impractical or impossible. These conditions include
flow reversals, backwater effects, and hysteresis effects.
The RQ-30 radar sensor measures the stage and the
flow velocity and can be used to produce discharge
records at stations where conventional methods cannot
be used. Furthermore it allows to directly calculate the
discharge in the sensor. Two techniques of contact
free radar measurement are combined in one system.
The determination of the flow velocity is based on the
principle of Doppler frequency shift. The water level
is determined by transit time measurement. The measurement values are output via a serial interface or as
analog current signals of 4 to 20mA. This allows a
simple adoption into any measurement system. The
system is installed simply without constructional
changes of the channel itself. Existing bridges or
buildings can be used to mount the system. The contact free radar technique guaranties a maintenance free
operation over years.
Hydrological Services Pty Ltd
Address:
Installation
3
48-50 Scrivener Street
Liverpool, NSW, 2170, Australia
Operation
4
Ph. 61 2 9601 2022
Fax. 61 2 9602 6971
Web: www.hydrologicalservices.com
Email: [email protected]
Distributed By:
Model RQ-30
Specification
General
Dimension
Protection
Power supply
Power consumption
Operating temperature
Storage temperature
Lightning protection
395.35 mm x 280.50 mmm x 151 mm (15.56 in. x 11.04 in. x 5.93 in.) Connector space on rear: 150 mm (5.91 in.)
IP 68
5.5 … 30 V, Reverse voltage protection, over voltage protection
Sleep mode: 1 mA Measurement: appr. 180 mA (12VDC)
-35° C to 60 °C (-31 °F to 140 °F)
-40° C to 60 °C (-40 °F to 140 °F)
Integrated lightning protection with discharge capacity 0.6 kW Ppp
Connector 1 (12 pin)
1 x RS-485
1 x SDI-12 Transmission rate (1.2 KBaud to 115 KBaud)
Various protocols
4 x 4 … 20 mA
Water level
Velocity
Discharge
AUX Sensor
1 x switching output (max. 1.5A)
1 x trigger input (0 = 0 - 0.6V) (1 = 2 – 30V)
Interface
Analog outputs
DIG OUT
Digital input
Connector 2 (4 pin connector)
1 x 4 … 20 mA (max. 20 mA for water level)
Intern Power supply for external pegel sensor (17 VDC)
GND
Analog input
Connector 3 (4 pin female)
1 x 0 to 2.5 V
Power supply for sensor (U power – 1 V)
GND
AUX IN
Velocity Measurement
Range
Accuracy
Resolution
Direction recognition
Measurement duration
Sample interval
Frequency
Distance to water surface
Horizontal inclination
0.15 to 15 m/s
± 0.02 ms; ± 0.5 %
1 mm/s
downstream flow or tide
10 to 240 sec
10 sec … 5 h
K-Band (24.125 GHz doppler technology)
0.5m to 30m
Measured internally
Water level measurement
Depth measurement
Resolution
Accuracy
Measurement frequency
Page 2
Standard operating range from RQ-30 to liquid: 0 to 15m (0 to 59,06 in.)
Optional extended operating range from transducer face to liquid:
0 to 35m (0 to 137.8 in.)
1 mm
± 2mm; ± 0.025 % FS (15m)
K-Band (26 GHz)
© Copyright 2011, Hydrological Services preserves the right to change this bulletin at any time without notice
Model RQ-30
Installation
The discharge is determined by a measurement of the surface velocity and the water level. Therefore it is important to
position the measurement at a representative location. Narrowing and widening of the channel as well as branching, inflows
or curves are not suitable for good measurements. The best results are achieved at a straight running channel with constant
width and laminar current behavior. Essential for good results is a measurement area free of disturbances as stones, rocks or
artificial constructions. Appearing swirls have a high influence on the measurement and do not allow precise determinations of
the flow velocity at the measurement surface. Velocity measurements are possible, if the wave height exceeds 3 mm, higher
waves improve the reproducibility of the measurement. The minimal measurable flow velocity is 0.3 m/s depending on the
wave form.
Bad Sites
Good Sites
Site Rating
Site Top View
After a suitable measurement site has been found along the
channel. It is important that the complete measurement field
of the sensor is at a representative position in the channel.
The diameter of the measurement area depends on the
installation height and the measurement angle. The higher
the sensor is installed and the smaller the measurement
angle, the larger the diameter of the measurement area.
Note:
In specific hydraulic situations it is necessary to install more
than one RQ-30. Up to 4 RQ-30 sensors can be combined.
Every sensor calculates on part of the discharge and
transfers the result to one master RQ-30. This master adds
all the partial discharges to the resulting total discharge
quantity.
Page 3
© Copyright 2011, Hydrological Services preserves the right to change this bulletin at any time without notice
Model RQ-30
Operation
The flow velocity and the water level are measured separately and the discharge is calculated by combining the two measurements. The RQ-30
measurement system is a combination of two sensors for the measurement and an integrated
processor to calculate the quantity of discharge.
Flow Velocity
The measurement of the flow velocity is based on the
principle of the frequency shift due to the Doppler effect.
The radar sensor is installed pointing in a defined angle on
the water surface. Via the send and receive antenna a
constant frequency of 24 GHz is sent. This signal is partly
reflected at the water surface and returns with a specific
shift to the antenna. The reflected signal is recorded with a
digital signal processor and the frequency spectrum is built.
With support of spectral analysis, filters and statistical
methods the velocity is determined.
The measured velocity corresponds to the flow velocity of
the surface at that point, where the radar device is pointing
to. It is essential that a small unevenness of the water
surface for example in form of waves is present. Only then
the signal can be reflected and a velocity determined.
The radar device has to be installed in an angle of about 40
to 60 degrees, which influences the velocity determination.
Therefore the horizontal inclination of the RQ-30 is internally
measured and the velocity influence of the angle is
automatically compensated
Velocity Measurement
Water Level
The water level is measured on the principle of a transit time measurement. The radar sensor
transmits defined impulses of a length in the low microsecond range vertically to the water
surface. There the signal is reflected back to the radar sensor, where it is received. The time
span between the transmission and the receiving of the impulse is measured, which is
proportional to the distance between the sensor and the water surface.
Discharge calculation
The discharge Q is calculated corresponding to the continuity equation by multiplying the area
of the cross section A(h) and the mean velocity vm.
Q = A(h) · vm
The area of the cross section is deviated from the profile at the measurement site and the
actual water level. The radar sensor does not measure the mean velocity but the local flow
velocity vl at the water surface. The relation between the mean and the local velocity is
expressed by the k-factor. This dimensionless correction factor is also depends on the water
level.
k(h) = vm / vl
Finally the discharge is determined by the measurement parameters water level and surface
velocity and the input parameters cross section and k-factors.
Q = A(h) · vl · k(h)
Water Level
Cross section and area
The cross section of the channel at the measurement site is essential to calculate the cross section area. Since the area depends on the water
level a table for water level and cross section area is created and entered into the discharge table of the radar device. The table can for example
be generated with the program RQCommander.
k-factors
The k-factures are used to calculate the mean velocity from the measured local surface velocity. On one hand the k-factors can be determined
using reference measurements of the discharge in a specific time range at different water levels. The flow velocity and the water level are
recorded during this time. For every discharge measurement the k-factor is calculated from the discharge, the flow velocity and the water level.
This results over the time range finally in a table of water level and k-factors. On the other hand the k-factors are calculated by modeling the
measurement site (i.e. RQ Commander, SimK,… ). Any model requires the cross section and basic hydraulic parameters of the measurement
site. The k-factors depending on the water level are integrated with the cross section area in the discharge table that is entered in the radar
device.
Page 4
© Copyright 2011, Hydrological Services preserves the right to change this bulletin at any time without notice