How to use the MMU-EGS Meteorological field instrumentsWHIRLING HYGROMETER (Psychrometer) Measures wet and dry bulb air temperatures. Wet bulb is covered by a cotton wick, kept saturated

How to use the MMU-EGS

Meteoro log ica l

f i e l d ins t ruments A guide to the correct field procedures for the digital

anemometer, ventimeter, whirling hygrometer and LUX meter

CONTENTS

INTRODUCTION 2

DIGITAL ANEMOMETER 3-4

VENTIMETER 5- 6

WHIRLING HYGROMETER 7-8

LUX METER 9-10

SAMPLE FIELDSHEET back cover

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INTRODUCTION Before embarking on meteorological field instruments it is useful to consider the correct proce-dures for using often fragile and expensive equipment. Sometimes the data recorded from an instrument must be transformed in order to be useful. Incorrect handling of the equipment may lead to misleading results at best, or instrument damage at worst.

There are FOUR instruments discussed in this document:

DIGITAL ANEMOMETER Measures instantaneous, mean and gust values. Based on digital calibration of impeller. Readings should be recorded as m/s

VENTIMETER

Measures instantaneous wind speeds. Based on mechanical movement of a central disk—doesn’t operate under calm conditions. Readings should be recorded as m/s

WHIRLING HYGROMETER (Psychrometer)

Measures wet and dry bulb air temperatures. Wet bulb is covered by a cotton wick, kept saturated by a distilled water reservoir. Relative humidity (% RH) is calculated from a lookup table

LUX (light intensity) METER

Measures instantaneous light level (between 320 and 730 nm) using a silicon photodiode sensor. Readings should be recorded as LUX

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Digital Anemometer

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Control buttons

Digital Anemometer

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IMPORTANT

The impeller is easily damaged by sand. When undertaking readings in coastal dune areas please ensure that sand is kept away from the impeller bearings as much as possible

Ventimeter

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Air outlet

Ventimeter

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Ventimeter

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Whirling Hygrometer

Plastic distilled water reservoir DRY bulb scale

WET bulb scale

handle

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Whirling Hygrometer

IMPORTANT Before using the instrument, make sure that the plastic distilled water reservoir is topped up with sufficient water and the sealing cap is secure. Make sure that the cotton wick is saturated prior to using the instrument.

1) Allow the temperature scales to equilibrate for a minute or so before starting 2) Holding the instrument at arms length (to minimise the effects of body temperature and

maintain a uniform height above the ground) begin to rotate the instrument by whirling with the handle at a constant rate

3) After 20 to 30 seconds stop rotation and immediately record the WET and DRY bulb temperatures—estimate to the nearest 1/10th of a degree Celsius

4) Subtract the lower WET bulb temperature from the higher DRY bulb temperature 5) Use the lookup tables below to estimate Relative humidity (%)

Field recordings should include both the WET and DRY bulb temperatures as well as the calculated %RH.

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LUX Meter

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Data recorder output

LUX Meter

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IMPORTANT The hand-held light sensor should remained covered until required with the black plastic cap— otherwise readings will be less accurate.

1) When the reading is required, switch the instrument on and select the lowest scale setting (200)

2) Remove the sensor cap and allow the readings to settle after 5 seconds or so 3) If the display shows an overload error: “-1” on the left side select a higher range 4) Make a note of the reading and cover the sensor with the black cap before switching off

the meter NOTE: Testing in 20000 range: that display value must be multiplied by 10

ENVIRONMENTAL VARIABLES DATA SHEET

SITE NAME:

DATE:

TIME (GMT):

NAME:

Wind Speed (instantaneous):

Wind Speed (average) :

metres per second

Wind Speed (gust) :

metres per second

metres per second

Instrument Used :

WET bulb temperature : º

DRY bulb temperature :

C

º

WET bulb MINUS DRY bulb :

C

º

Relative Humidity :

C

%RH

Light reading : LUX

Soil temperature : º

Air pressure :

C

Cloud cover :

millibars

Wind Direction :

Oktas

degrees

General Weather Description and additional Field Notes