HTB weather and precipitation
sensors
Mesoscale Atmospheric Network Workshop
University of Helsinki, 12 February 2007
Heikki Turtiainen
Contents
WXT510 Weather Transmitter
WXT network implementation
VRG101 Weighing Precipitation Gauge
©Vaisala | date | Ref. code | Page 2
WXT510 Weather Transmitter
• Compact
(only 9.5” / 24 cm tall)
• No moving parts durable and requires minimum maintenance
• Optimal life time cost
• Easy to use purchase, install and use
6 MEASUREMENTS IN 1 INSTRUMENT
1. temperature
2. relative humidity
3. rain fall
4. wind speed
5. wind direction
6. barometric pressure
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WXT510 Weather Transmitter
Piezoelectric rain sensor
Ultrasonic
wind sensor
CPU board
Pressure,
temperature
and humidity
module
Screw terminal
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Weather Transmitter WXT510 - Basic Specs
Relative Humidity
Range: 0…100%
Accuracy: ± 3% (0-90%)
± 5% (90-100%)
Air Temperature
Wind Speed
Range: 0…60 m/s
Accuracy:
0...35 m/s ± 0.3m/s or ± 3%,
whichever is greater
35...60 m/s ± 5%
Range: -52…+60°C (-60…+140°F)
Wind Direction
Accuracy* (at 20°C): ± 0.3°C (0.5°F)
Range: 0…360°
Barometric Pressure
Accuracy: ± 3°
Range: 600…1100 hPa
Liquid Precipitation
Accuracy: ± 0.5 hPa (0…30°C)
Accumulation Accuracy: 5%**
± 1.0 hPa (-52…+60°C)
Intensity Range: 0…200 mm/h
* for sensor element
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** Due to the nature of the phenomenon, deviations caused
by spatial variations may exist in precip. readings,
especially in short time scale. The accuracy specified does
not include possible wind induced error
Windcap - ultrasonic wind sensor
Durable and maintenance free
•Zero starting thresholds or distance
constants virtually zero.
• No moving parts - thus sensor
performance doesn’t degrade with
wear nor is affected by natural
contaminants such as salt, dust or
sand.
• Vaisala’s proprietary equilateral
triangle design solves the turbulence
problem. (1 redundant measurement
path)
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Equilateral triangle design vs. orthogonal design
Vaisala proprietary
equilateral triangle design
Orthogonal design
Turbulence
Reliable
measuring paths
Turbulence
Unreliable
measuring path
Unreliable
measuring path
Reliable
measuring paths
Wind direction
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Wind direction
RAINCAP measuring principle
A raindrop hitting the
piezoelectric detector generates
a voltage pulse Ui, whose
amplitude is a function of the
drop volume Vi. Consequently,
drop size can be estimated from
the measured voltage:
Vi = f(Ui)
Accumulated rainfall is sum of
the individual drops
R [mm] = Σ f(Ui)
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RAINCAP calibration
Rainfall R = Σ f(Ui)
Type calibration is based on
comparison with accurate reference
instruments under different field
conditions:
80
70
60
• moderate and heavy rain in Malaysia
Ref [mm]
• light and moderate rain in Finland
50
40
30
Individual production calibration using
highly repeatable laser pulse
equipment
20
10
0
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0
1000
2000
3000 4000 5000
Voltage sum [V]
6000
7000
Helsinki Testbed Weather Transmitter network
Currently 62 stations with 112 WXT510 weather transmitters.
Average distance < 10 km. Data interval 5 min.
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Cell phone base station masts utilized as meteorological
towers
Upper Weather
Transmitter
h = 40...100 m
Middle level
Weather
Transmitters h =
20-30 m
Lower Weather
Transmitter
h=2m
GPRS
communications
unit
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Installation examples
Temporary battery operated
WXT station near Hietaniemi
Beach.
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All-weather Precipitation gauges
Weighing rain gauges
• 5 pcs VRG101 all-weather
precipitation gauges
– Lahti
– Nummi-Pusula, Loukku
– Vihti, Maasoja
– Nurmijärvi, Röykkä
– Helsinki, Malmi Airport
• measure both liquid and
solid precipitation
• heated rim
• Tretyakov-type wind shield
• communications: GPRS
Lahti 5.12.2005
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VRG101 - Vaisala All Weather Precipitation Gauge
FEATURES
• Weighing principle applying high accuracy,
temperature compensated load cell
• Simple, robust design
• All weather operation with heating option
• High capacity up to 650 mm (25”)
• Large collecting area to enhance performance
in light rain and snow
• Selection of optional features for enhanced
performance and extended service interval
• Field-removable measurement unit, enabling
use of pre-calibrated measurement units. Field
check with dedicated weight.
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VRG101 Components
1=Lock
2=Collecting funnel
3=Side guide plate
4=Container (volume 30 liters)
5=Faucet
6=Collector tray
7=Spirit level
8=Load cell and electronics
9=Base plate
10=Rim
11=Top cone
12=Enclosure
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Specifications of VRG101
• Capacity
650 mm (25 in) without automatic draining pump
antifreeze charge included
• Collecting area
400 cm2 (62 in2)
• Resolution
0.1 mm
• Accuracy
± 0.2 mm (± 0.01 in)
of measured amount during a rain event > 0.5 mm
• Temperature range
-40 ... +60 °C (-40 - +140 °F)
• Output
Serial RS485/RS232
Pulse (tipping bucket emulation)
• Power Consumption
< 30 mW (without heating)
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(0.005 in)
Problems with Liquid Precipitation: Evaporation Error
Problem:
Evaporation
from the
container
Evaporation of
collected water
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VRG101 Solution: Evaporation Error
rainfall
mm
corrected
uncorrected
time
• VRG101 software filters out “negative rainfall” due to evaporation
• Use of anti-evaporation oil is not required
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Problems with Liquid Precipitation: Wetting Loss
Problem:
Wetting loss
on the gauge
inlet
Raindrops sticking
on the inlet tube...
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... evaporate and are
never measured
VRG101 Solution: Wetting Loss
The orifice/inlet geometry
minimizes wetting loss:
• Funnel shaped inner orifice
element is resting on the collector
container so that it’s mass is
measured together with the
container.
• Water sticking on the funnel
surface will be measured and
included in the cumulative rainfall
before it evaporates.
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VRG101 Solutions for Solid Precipitation
Problem 1: Uneven snow distribution in the container
Solution: The load cell technology used measures
only forces along the vertical axis. Eccentric snow
accumulation is not a problem.
Problem 2: Snow deposit on the inlet funnel surface
Solution: The mass of the funnel
element is also measured. Snow
accumulation on the funnel surfaces
does not introduce error.
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VRG101 Solutions for Solid Precipitation
Problem 3: Outblowing of snow
Solution: Optimized gauge geometry for solid
precipitation. Deep container and funnel-shaped inlet
orifice minimize outblowing of snow.
Problem 4: Evaporation error caused by heating
Problem 5: Large heating power consumption
Solution: Intelligent heating control by software
• Heating is applied only when necessary, using control
algorithm based on air temperature and precipitation
amount.
• Evaporation loss caused by heating is minimized.
• Compared to continuous heating, power consumption
on a typical winter day is decresed from over 2 kWh to
0.1 - 0.2 kWh.
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VRG101 Wind Shields XRS111 / XRS121 / XRS131
• Stabilizes the wind conditions over the gauge
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Installation examples
WXT + VRG101 weighing precipitation gauge at Malmi Airport
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