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

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WXT510 Weather Transmitter

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Compact (only 9.5” / 24 cm tall)

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No moving parts durable and requires minimum maintenance

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Optimal life time cost

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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 ©Vaisala | date | Ref. code | Page

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WXT510 Weather Transmitter

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Ultrasonic wind sensor CPU board Pressure, temperature and humidity module Screw terminal Piezoelectric rain sensor

Weather Transmitter WXT510 - Basic Specs

Relative Humidity Range: 0…100% Accuracy: ± 3% (0-90%) ± 5% (90-100%) 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% Air Temperature Range: 52…+60°C (-60…+140°F) Accuracy* (at 20 °C): ± 0.3°C (0.5°F) Barometric Pressure Range: 600…1100 hPa Accuracy: ± 0.5 hPa (0…30°C) ± 1.0 hPa (-52…+60°C) Wind Direction Range: 0…360° Accuracy: ± 3° Liquid Precipitation Accumulation Accuracy: 5%** Intensity Range: 0…200 mm/h * for sensor element ** 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 ©Vaisala | date | Ref. code | Page

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Windcap - ultrasonic wind sensor

Durable and maintenance free •

Zero starting thresholds or distance constants virtually zero.

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No moving parts - thus sensor performance doesn’t degrade with wear nor is affected by natural contaminants such as salt, dust or sand.

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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 Unreliable measuring path Reliable measuring paths Turbulence Reliable measuring paths Unreliable measuring path Wind direction Wind direction ©Vaisala | date | Ref. code | Page

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RAINCAP



measuring principle

A raindrop hitting the piezoelectric detector generates a voltage pulse U drop volume V

i i

, whose amplitude is a function of the . Consequently, drop size can be estimated from the measured voltage: V

i

= f(U

i

) Accumulated rainfall is sum of the individual drops R [mm] = Σ f(U

i

) ©Vaisala | date | Ref. code | Page

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RAINCAP



calibration

Type calibration is based on comparison with accurate reference instruments under different field conditions: • light and moderate rain in Finland • moderate and heavy rain in Malaysia Individual production calibration using highly repeatable laser pulse equipment Rainfall R = Σ f(U i ) 80 70 60 50 40 30 20 10 0 0 1000 2000 3000 4000 5000 Voltage sum [V] 6000 7000 ©Vaisala | date | Ref. code | Page

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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 = 2 m GPRS communications unit ©Vaisala | date | Ref. code | Page

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Installation examples

Temporary battery operated WXT station near Hietaniemi Beach.

©Vaisala | date | Ref. code | Page

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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 ©Vaisala | date | Ref. code | Page

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Specifications of VRG101

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Capacity

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Collecting area Resolution Accuracy 650 mm (25 in) without automatic draining pump antifreeze charge included 400 cm 2 (62 in 2 ) 0.1 mm (0.005 in) ± 0.2 mm (± 0.01 in) of measured amount during a rain event > 0.5 mm -40 ... +60 °C (-40 - +140 °F)

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Temperature range Output Serial RS485/RS232 Pulse (tipping bucket emulation)

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Power Consumption < 30 mW (without heating)

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Problems with Liquid Precipitation: Evaporation Error

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Evaporation of collected water Problem: Evaporation from the container

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 ©Vaisala | date | Ref. code | Page

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Problems with Liquid Precipitation: Wetting Loss

Raindrops sticking on the inlet tube...

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... evaporate and are never measured Problem: Wetting loss on the gauge inlet

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.

©Vaisala | date | Ref. code | Page

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VRG101 Wind Shields XRS111 / XRS121 / XRS131

• Stabilizes the wind conditions over the gauge ©Vaisala | date | Ref. code | Page

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Installation examples

WXT + VRG101 weighing precipitation gauge at Malmi Airport ©Vaisala | date | Ref. code | Page

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