GHM DeltaOHM LPPYRA11 Manuel utilisateur

Operating manual

Albedometer

LPPYRA11

www.deltaohm.com

English

Keep for future reference.

LPPYRA11 - 2 - V1.2

TABLE OF CONTENTS

1 INTRODUCTION .................................................................................................... 3

2 WORKING RINCI LE ........................................................................................... 4

3 INSTALLATION ..................................................................................................... 6

4 ELECTRICAL CONNECTIONS .................................................................................. 8

5 MEASUREMENT ..................................................................................................... 9

6 MAINTENANCE .................................................................................................... 10

7 TECHNICAL S ECIFICATIONS ............................................................................. 11

8 SAFETY INSTRUCTIONS ...................................................................................... 12

9 ORDERING CODES .............................................................................................. 13

LPPYRA11 - 3 - V1.2

1 INTRODUCTION

The LPPYRA11 albedometer measures the net global radiation, as well as the albedo of

grounds albedo is the ratio between diffuse radiation from a determined surface and

the quantity of radiation that arrives on the surface).

The LPPYRA11 is manufactured mounting two LPPYRA10 pyranometers in one housing

only. The upper pyranometer measures the incident radiation striking the ground [ ↓ ],

while the lower pyranometer measures the reflected radiation [ ↑ ].

The output signals of the two pyranometers can be processed to get the desired phys-

ical quantity.

The LPPYRA11 can be used as a pyranometer for measuring global radiation. As a py-

ranometer, the LPPYRA11 is a Spectrally Flat Class A Secondary Standard) pyranom-

eter in accordance with ISO 9060:2018 and with the criteria of the WMO “Guide to

Meteorological Instruments and Methods of Observation”.

The albedometer is supplied factory calibrated and with a calibration report. The cali-

bration is carried out in accordance with the ISO 9847:1992 type IIc) standard: ”Cal-

ibration of field pyranometers by comparison to a reference pyranometer”. The pyra-

nometer is calibrated by comparison with the reference sample calibrated annually at

WRC World Radiation Center).

LPPYRA11 - 4 - V1.2

2WORKING RINCI LE

The LPPYRA11 albedometer is based on a pair of thermopile sensors, one of them

measuring the incident radiation on the ground [ ↓ ] and the other one the reflected

radiation [ ↑ ]. Each thermopile works as an independent pyranometer. The thermo-

pile sensitive surface is coated with a black matt paint, which allows the pyranometer

not to be selective at different wave lengths.

In order to grant the thermopile a proper thermal insulation from the wind and reduce

the sensitivity to thermal irradiance, LPPYRA11 is equipped with two concentric domes

having 50 mm and 32 mm outer diameter on each side. The domes protect the ther-

mopile from the dust, which might change spectral sensitivity if it lies on the black

surface.

The pyranometer spectral range is determined by the transmission of the two glass

domes. Thanks to the use of a new material for the manufacturing of the domes, the

spectral range has been further extended to short wavelengths starting from 283 nm.

Considering a standard solar spectrum, the portion of solar irradiation measured by

the pyranometer is greater than 99.8%. Figure 2.1 shows the relative spectral sensi-

tivity of the LPPYRA11 albedometer and a standard solar spectrum.

Fig. 2.1: L YRA11 albedometer relative spectral sensitivity (blue line) com-

pared with a standard solar spectrum (red line)

Radiant energy is absorbed by the thermopile black surface, thus creating a difference

of temperature between the center of the thermopile hot junction) and the pyranom-

eter body cold junction). Thanks to the Seebeck effect, the difference of temperature

between hot and cold junction is converted into a Difference of Potential.

A second thermopile, not accessible by light, is mounted inside the instrument. This

second thermopile, connected in anti-series with respect to the sensor exposed to

light, reduces the signals due to sudden temperature changes of the pyranometer

thermal shocks).

In order to minimize sensitivity changes with temperature, LPPYRA11 is equipped with

a passive compensation circuit. The graph in figure 2.2 shows the typical variation of

sensitivity at different temperatures. The deviations are calculated from the sensitivity

measured at 20 °C.

LPPYRA11 - 5 - V1.2

Fig. 2.2: : percentage change of L YRA11 albedometer sensitivity in the

temperature range -20…50 °C compared to the sensitivity at 20 °C

To prevent internal condensation forming on the internal side of the dome under cer-

tain climatic conditions, silica gel tablets are inserted inside the pyranometer to ab-

sorb humidity.

Fig. 2.1: scheme of principle L YRA11

ermopil

Surge

Protector

Connector

pins

Housing

To cable shield

ermopil

Surge

Protector

Tempe

rature °C)

% change of sensitivity

ermopil

Temperature

compensation

LPPYRA11 - 6 - V1.2

3INSTALLATION

Before installing the albedometer, refill the cartridge containing silica-gel crystals. Sili-

ca gel absorbs humidity in the dome chamber and prevents, in particular climatic con-

ditions, condensation on the internal walls of the domes and measurement alteration.

Do not touch the silica gel crystals with your hands while refilling the cartridge. Carry

out the following instructions in an environment as drier as possible:

1. Loosen the three screws that fix the white shade disk.

2. Unscrew the silica gel cartridge using a coin.

3. Remove the cartridge perforated cap.

4. Open the sachet containing silica gel supplied with the pyranometer).

5. Fill the cartridge with the silica gel crystals.

6. Close the cartridge with its own cap, paying attention that the sealing O-ring be

properly positioned.

7. Screw the cartridge to the pyranometer body using a coin.

8. Check that the cartridge is screwed tightly if not, silica gel life will be reduced).

9. Position the shade disk and screw it with the screws.

10. The albedometer is ready for use.

The figure below shows the operations necessary to fill the cartridge with the silica gel

crystals.

Fig. 3.1: filling the silica-gel cartridge

Silica

gel

cartridge

Perforated cap

Sealed sachet

of silica-gel crystals

Filling Closing the cartridge

LPPYRA11 - 7 - V1.2

•Mount the albedometer 1 – 2 m above the ground. Grass should be kept at the

same height all the year long. In snowy regions, keep the instrument above the

blanket of snow so that the distance from the albedometer to the snow be constant.

•The albedometer must be mounted in an easy-to-reach location in order to clean

the dome regularly and carry out maintenance. At the same time, make sure that

no buildings, constructions, trees or obstructions exceed the horizontal plane where

the upper pyranometer lies. If this is not possible, select a site where obstructions

in the path of the sun from sunrise to sunset do not exceed 5 degrees of elevation.

N.B.: The presence of obstructions on the horizon line affects significantly

the measurement of direct irradiance.

•The pyranometer must be located far from any kind of obstruction, which might re-

flect sunlight or sun shadow) onto the pyranometer itself.

•In compliance with ISO TR9901 standard and WMO recommendations, when the

pyranometer is used without the white shade disk, it must be positioned so that its

connector is pointed to the North Pole, if the instrument is used in the Northern

Hemisphere, and to the South Pole, if used in the Southern Hemisphere. In any

case, it is better to follow this suggestion even when the shade disk is applied.

•The mounting can be made using the rod provided with the instrument. In order to

allow an accurate horizontal positioning, the pyranometer is equipped with a level-

ling device. The mast height does not exceed the pyranometer plane to avoid

measurement errors caused by any reflection or shadow of the mast itself.

•It is preferably to thermally insulate the pyranometer from its mounting bracket

ensuring, at the same time, a good electrical contact to ground.

79.5

500

140

160

124

Fig. 3.2: fixing and dimensions

Connector

Levelling device

LPSP1

LPSP3

LPPYRA11 - 8 - V1.2

4ELECTRICAL CONNECTIONS

L YRA11 has a 8-pole connector and uses the C M12AA8... optional cables, with

8-pole connector on one side and open wires on the other side.

The metallic housing of the albedometer should preferably be

grounded ( ) locally. In this case, do not connect the wire of the

cable corresponding to the housing to prevent ground loops.

Only if it is not possible to ground locally the metallic case of the

albedometer, connect the wire of the cable corresponding to the

housing to ground ( ).

The albedometer LPPYRA11 is passive and does not require power supply. It is to be

connected either to a millivoltmeter or to a data acquisition system with at least two

inputs). Typically, the albedometer output signal does not exceed 20 mV. In order to

better exploit the albedometer features, the readout instrument should have 1 µV res-

olution.

Connector Function Color

1 Output positive +Vout) upper pyranometer [↓] Red

2 Output negative -Vout) upper pyranometer [↓] Blue

3 Not connected

4 Not connected

5 Output negative -Vout) lower pyranometer [↑] Brown

6 Housing C) White

7 Cable shield SH) Black

8 Output positive +Vout) lower pyranometer [↑] Green

456

+Vout [ ]

-Vout [ ]

+Vout [ ]¯

-Vout [ ]¯

Fig. 4.1: L YRA11 connections

The cable shield is isolated from the albedometer housing by means of two gas surge

arrestors, which prevents lightnings to damage the sensor. The shield has to be con-

nected to the same ground as the readout instrument. Best safety is achieved through

a perfect connection between housing and earth.

Connect to ground only if it is not possible to

ground locally the case of the pyranometer

CPM12AA8… cable

Albedometer

M12 male

connector

Reflected

radiation [↑]

ncident

radiation [↓]

Multi

input

data

logger

Converter

amplifier

with V or mA

output

Converter

amplifier

with V or mA

output

LPPYRA11 - 9 - V1.2

5MEASUREMENT

Each of the two pyranometer that make up the albedometer is distinguished by its

own sensitivity or calibration factor) S expressed in µV/ Wm-2) and shown in the label

on the pyranometer and in the calibration report).

The irradiance Ee is obtained by measuring with a multimeter the difference of potential

DDP at the ends of the sensor and applying the following formula:

Ee = DDP / S

where:

Ee is the irradiance expressed in W/m2;

DDP is the difference of potential expressed in µV measured by the multimeter;

S is the sensitivity of the albedometer expressed in µV/ Wm-2).

Albedo is the fraction of solar radiation that is reflected from the ground, with respect

to incident radiation:

ALBEDO = Ee [↑] / Ee [↓]

With the albedometer it is possible to calculate the net radiation making the difference

between the incident global radiation and the reflected global radiation.

LPPYRA11 - 10 - V1.2

6MAINTENANCE

In order to grant measurements high accuracy, it is important to keep the outer glass

domes clean. Consequently, the more the domes will be kept clean, the more meas-

urements will be accurate.

You can wash it using water and standard papers for lens. If necessary, use pure

ETHYL alcohol. After using alcohol, clean again the domes with water only.

Because of the high temperature changes between day and night, some condensation

might appear on the domes of the pyranometers. In this case the performed reading

is highly over-estimated. To minimize the condensation, the albedometer is provided

with a cartridge containing dessicant material silica-gel). The efficiency of the silica-

gel crystals decreases over time while absorbing humidity. Silica-gel crystals are effi-

cient when their color is yellow, while they turn white/translucent as soon as they

loose their efficiency. Read instructions at chapter 3 about how to replace the silica-

gel crystals. Silica-gel typical lifetime goes from 2 to 6 months depending on the envi-

ronment where the albedometer works.

To exploit all the albedometer features, it is highly recommended that the calibration

be checked annually.

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