OTT SVR 100, Operating Instructions Manual

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4 Introduction
The OTT SVR 100 radar sensor is used for continuous contactless measurement of
the surface velocity of a flowing waterway (= index velocity).
A connected data logger can use this index velocity (preferably measured in the
area of the maximum velocity) to calculate the flow using the "velocity index
method". The water level that is also required for this calculation can be deter-
mined using any water level sensor (e.g. pressure probe or OTT RLS radar level
sensor). To obtain accurate flow values, the entire measuring system must be cali-
brated during commissioning, e.g. using the "OTT Prodis 2" software.
The functional principle of the OTT SVR 100 is based on the physical Doppler
effect. A transmission aerial emits radar pulses with a typical frequency of 25.3
GHz at a nominal angle of 30 degrees to the horizontal. The alignment must be
parallel, and ideally against the main flow direction of the waterway. If the water
surface is moving and has a minimum roughness, the radar pulses are reflected
with a slight frequency shift and are received by a reception aerial on the
OTT SVR 100. From the frequency shift, the radar sensor uses a trigonometric
function to calculate the average flow velocity within the radar footprint projected
onto the water surface. The exact tilt angle necessary for the calculation is pro -
vided by an integrated tilt sensor.
In addition, a vibration sensor transmits a specific vibration index for every mea-
sured velocity value. This index indicates whether measured values have potential-
ly been impaired by vibration of the device. For example, vibrations can be
caused by traffic on bridges or the influence of wind on the cantilever arms.
A physical RS-485 interface is available to connect the OTT SVR 100 to a data
logger or peripherals, and communication with the radar sensor is via the SDI-12
or Modbus transmission protocol
1)
. In addition, the OTT SVR 100 has an RS-232
interface for service purposes (e.g. firmware updates).
The radar sensor can be configured using SDI-12 transparent mode on a data
logger or via the OTT USB/SDI-12 interface (accessory), or alternatively via the
RS-232 interface using special service software.
1)
set using the "OTT SVR 100 Operating Program"; see Appendix E
Fig. 1: Schematic representation of the
velocity index method.
Q : Flow [m
3
/s]
A : Cross-sectional area [m
2
]
k : Correction factor [1]
Q = v
m
· A = v
i
· k · A
v
m
: Average flow velocity [m/s]
v
I
: Index velocity at the surface [m/s]
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