29
Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

Embed Size (px)

Citation preview

Page 1: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

Piezoelectric precipitation sensor from VAISALA

Atte Salmi

Project Manager

Vaisala Instruments

Page 2: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 2

Contents

Construction of the sensor

Measurement method

Sensor calibration

Errors in measurement method

Field test results

Conclusions

Page 3: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 3

Introduction

Developed for Weather Transmitter

Durable and maintenance free

Page 4: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 4

Vaisala RAINCAP

Construction

Sensor frame

Sensor cover

Piezo detector

Electronics + Software

Page 5: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 5

Vaisala RAINCAP

Measurement method

The voltage output U(t) from the piezo detector due to a drop impact is proportional to the volume of the drop.

Since, the surface area is known, the drop signals can be directly converted to accumulated precipitation.

pv = mvt

Piezo detector

Electronics Algorithm

U(t) = c(dp(t)/dt)

Precipitation P = f(U)

Page 6: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 6

Terminal velocity

Atlas et. al. (1973):

vt (D) = 9.65 - 10.30e(0.6D)

Page 7: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 7

Vaisala RAINCAP

Type calibration

Comparison of detector voltage response with precipitation readings from accurate reference instruments under different field conditions:

• light and moderate rain in Finland

• moderate and heavy rain in Malaysia

0 1000 2000 3000 4000 5000 6000 70000

10

20

30

40

50

60

70

80

Voltage sum [V]

Ref

[mm

]

Precipitation P = f(U)

Page 8: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 8

Errors in measurement method

Vaisala RAINCAP do not have systematic error sources like:

• wetting on the internal walls of the collector and the container

• evaporation from the container

• splashing of water in and out

Error sources related to Vaisala RAINCAP are more stochastic than systematic:

• variation in the shape and velocity of raindrops caused by air movements

• sensitivity variations over the sensor area, due to surface wetness

Page 9: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 9

Results - Kuala Lumpur, Malaysia

0

10

20

30

40

50

60

70

80

90

0311

20

0311

21

0311

22

0311

23

0311

24

0311

25

0311

27

0311

28

0311

29

0312

01

Date

Acc

um

ula

ted

ra

infa

ll [m

m]

WX1

WX2

TB1

TB2

Page 10: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 10

Results - FMI Observatory, Jokioinen

0

10

20

30

40

50

60

70

80

90

100

Aug-04 Sep-04 Oct-04 Nov-04

Month

Acc

um

ula

ted

ra

infa

ll [m

m]

WX1

WX2

WG1

WG2

WG3

Gauge WX1 WX2 WG1 WG2 WG3[mm] 222.7 227.5 205.4 203.9 189.6

Total accumulations during a four months test period at Jokioinen observatory.

Page 11: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 11

Results - Tokyo University, Japan

Oct 2004 - Feb 2005

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12 14

WXT510 rain accumulation [mm/10 min]

TB

rai

n ac

cum

ulat

ion

[mm

/10

min

]

WXT510 vs TB

Page 12: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 12

Results - characteristic short-interval data

Page 13: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 13

Conclusions

Due to the measurement method and construction of the sensor, the Vaisala RAINCAP is virtually maintenance free. The sensor does not suffer from systematic errors due to wetting, evaporation or splashing of raindrops. It is also capable for true real time intensity measurement.

The field results show good comparability of the sensor to traditional tipping buckets and weighing-recording gauges.

Because of its robust design with no moving parts the Vaisala RAINCAP is especially suitable for dense measurement networks.

Page 14: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 14

Contact Information

Atte Salmi

Project Manager

Vaisala Instruments

Phone +358 9 8949 2785

[email protected]

Page 15: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 15

Errors in precipitation measurement

Term Description of error component Magnitudek wind-field deformation 2 - 10 %P1 + P2 wetting on the internal walls of the collector and the container after emptying 2 - 15 %P3 evaporation from the container 0 - 4 %P4 splashing of water in and out 1 - 2 %

,)( 4321 rgk PPPPPPkP where Pk is the adjusted amount of precipitation,Pg the recorded precipitation in the gauge,k and P1 - P4 the adjustments for different error componentslisted in Table below and Pr random observational and instrumental error.

World Meteorological Organization, 2000: Precipitation Estimation and Forecasting,

Point Measurement Using Gauges. Operational Hydrology Report No. 46, WMO-No. 887, Geneva.

Page 16: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 16

Four operation modes

Precipitation Start/End mode:

Transmitter sends automatically a precipitation message 10 seconds after the recognition of the first drop. The messages are sent continuously as the precipitation proceeds and stopped when the precipitation ends.

Tipping bucket mode:

This mode emulates tipping bucket type precipitation sensors. Transmitter sends automatically a precipitation message when the counter detects one unit increment (0.1 mm/0.01 in).

Time mode:

Transmitter sends automatically a precipitation message in the update intervals defined by the user.

Polled mode:

Transmitter sends a precipitation message whenever requested by the user.

Page 17: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 17

Piezoelectric sensor

When mechanical pressure is applied to the sensor, the crystalline structure produces a voltage U(t) proportional to the pressure. Conversely, when an electric field is applied, the structure changes shape producing dimensional changes in the material.

,)(

)(dt

tdpctU

where c is a constant dependent on the properties of the piezoelectric material.

Page 18: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 18

Vaisala RAINCAP

Rain drop

Hail

Page 19: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 19

Drop signal

Page 20: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 20

Drop signal

t1

t2

Page 21: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 21

Drop collapse

t1

t2

Page 22: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 22

Technical data PTU

Barometric pressure

Range 600...1100 hPaAccuracy ± 0.5 hPa at 0...30°C (+32...+86 °F)

± 1 hPa at -52...+60 °C (-60...+140 °F)Output resolution 0.1 hPa, 10 Pa, 0.001 bar, 0.1 mmHg, 0.01 inHgUnits available hPa, Pa, bar, mmHg, inHg

Relative Humidity

Range 0...100 %RHAccuracy ±3 %RH at 0...90 %RH

±5 %RH at 90...100 %RHOutput resolution 0.1 % RH

PTU Measuring IntervalMeasuring interval 3…3600 s (=60 min),

at one second steps

Page 23: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 23

Technical data liquid precipitationRainfall cumulative accumulation after the latest auto or

manual resetCollecting area 60 cm2Output resolution 0.01 mm (0.001 in)Field accuracy fordaily accumulation better than 5%*, weather dependentUnits available mm, in

*Due to the nature of the phenomenon, deviations caused by spatial variations may exist in precipitationreadings, especially in short time scale. The accuracy specification does not include possible wind inducederror.

Rain duration counting each 10-second increment wheneverdroplet detected

Ouput Resolution 10 s

Rain intensity running one minute average in 10-second steps

Range 0...200 mm/h (broader range with reducedaccuracy)

Units available mm/h, in/h

Hail cumulative amount of hits against collectingsurface

Output resolution 0.1 hits /cm2 (1 hits/ in2), hitsUnits available hits /cm2, hits/ in2, hits

Hail duration counting each 10 second increment wheneverhailstone detected

Ouput resolution 10 s

Hail intensity one minute running average in 10-second steps

Output resolution 0.1 hits/ cm2h (1 hits/ in2h)Units available hits/cm2h, hits/ in2h, hits/h

Page 24: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 24

Technical data wind

Wind speedRange 0...60 m/sResponse time 0.25 sAvailable variables average, maximum and minimumAccuracy ± 0.3 m/s or ±2 % whichever is greaterOutput resolution 0.1 m/s (km/h, mph, knots)Units available m/s, km/h, mph, knots

Wind directionAzimuth 0...360°Response Time 250 msAvailable Variables Average, maximum and minimumAccuracy ± 2°Output Resolution 1°

Measurement frame Averaging time 1…600 s (=10 min),

at one second stepson the basis of 0.25 second samples

Measuring interval 1…3600 s (=60 min),at one second steps

Page 25: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 25

Technical data general

Operation voltage 5*...30 VDC

*) Below 5.3V the measurement performance for high wind speeds may be degraded.

Average power consumption minimum 0.07 mA @ 12VDC (SDI-12)maximum 13 mA @ 30 VDC (constant measurement of all

parameters)typical 3 mA @ 12 VDC (with default measuring

intervals)

Heating voltage options: DC, AC, full-wave rectified AC

recommended ranges 12 VDC 20 %, 1.1 A max24 VDC 20 %, 0.6 A max68 Vp-p

20 % (AC), 0.6 Arms max34 Vp 20 % (f/w rect. AC), 0.6 Arms max

absolute max 30 VDC84 Vp-p (AC)42 Vp (f/w rect. AC)

Digital outputs SDI-12, RS-232, RS-485, RS-422

Communicationprotocols SDI-12 v1.3, ASCII automatic& polled, NMEA

0183 v3.0 with query option.

Page 26: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 26

Technical data general

Operating conditions

Temperature operation -52 …+60 °C (-60...+140 °F)storage -60 …+70 °C (-76...+158 °F)

Relative humidity 0...100 %RHPressure 600...1100 hPaWind 0...60 m/s

Electromagneticcompatibility EN61326: 1997 + Am 1:1998 + Am2:2001

Electrical equipment for measurement, controland laboratory use - EMC requirements;Generic environment

Materials

Radiation shield, top andbottom parts Polycarbonate + 10 % glass fibre

Precipitation sensor plate stainless steel (AISI 316)

Weight 650 g (1.43 lbs)

Page 27: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 27

The Rain Lab

Page 28: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 28

Photoacoustic principle

Page 29: Piezoelectric precipitation sensor from VAISALA Atte Salmi Project Manager Vaisala Instruments

©Vaisala | date | Ref. code | Page 29

Interface Architecture

SDI-12 v1.3

Receiver

SDI-12 v1.3

Receiver

NMEA0183 v3.0

Talker

NMEA0183 v3.0

Talker

StandardASCII

Terminal

StandardASCII

Terminalsystem level

instrument level

HW- interface 3-wire SDI-12RS232, RS485/422

data formattransmission

ASCIIPolled

ASCII Polled / Automatic

External power supply5 - 30 VDC