GHM Delta OHM LPPYRA13 Manual de usuario

Operating manual

Pyranometer

LPPYRA

www.deltaohm.com

English

Keep for future reference.

Companies / Brands of GHM

LPPYRA13 -2-V2.3

TABLE OF CONTENTS

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

2WORKING PRINCIPLE........................................................................................... 4

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

3.1 MOUNTING THE SHADOW RING................................................................................. 7

3.2 POSITIONING THE INSTRUMENT FOR THE DIFFUSE RADIATION MEASUREMENT ........................... 8

4ELECTRICAL CONNECTIONS................................................................................ 12

4.1 LPPYRA13 CONNECTIONS ................................................................................... 12

4.2 LPPYRA13AC CONNECTIONS................................................................................ 13

4.3 LPPYRA13AV CONNECTIONS................................................................................ 13

4.4 LPPYRA13S CONNECTIONS.................................................................................. 14

4.5 LPPYRA13S12 CONNECTIONS .............................................................................. 15

5MEASUREMENT IN THE MODELS WITH ANALOG OUTPUT.................................... 16

5.1 LPPYRA13 ..................................................................................................... 16

5.2LPPYRA13AC ................................................................................................. 16

5.3 LPPYRA13AV ................................................................................................. 16

6RS485 MODBUS-RTU OUTPUT............................................................................. 17

6.1 SETTING THE COMMUNICATION PARAMETERS............................................................... 17

6.2 READING THE MEASURES WITH THE MODBUS-RTU PROTOCOL .......................................... 19

7SDI-12 OUTPUT .................................................................................................. 20

8MEASUREMENT CORRECTION ............................................................................. 24

9MAINTENANCE.................................................................................................... 27

10 TECHNICAL SPECIFICATIONS............................................................................. 28

11 SAFETY INSTRUCTIONS...................................................................................... 29

12 ORDERING CODES .............................................................................................. 30

LPPYRA13 -3-V2.3

1INTRODUCTION

LPPYRA13 pyranometer measures the irradiance on a flat surface (W/m2). Thanks to

the shadow-ring, LPPYRA12 measures the diffuse solar radiation eliminating the con-

tribution of direct irradiance.

LPPYRA13 is equipped with a Spectrally Flat Class A (Secondary Standard) pyranome-

ter (LPPYRA10) in accordance with ISO 9060:2018 and with the criteria of the WMO

“Guide to Meteorological Instruments and Methods of Observation”.

The pyranometer is available in the following versions:

•LPPYRA13: PASSIVE

The passive version can be connected to the instruments

D09847 and HD31 by using VP 472 SICRAM module.

•LPPYRA13AC: ACTIVE with 4..20 mA CURRENT output

•LP PYRA13AV: ACTIVE with 0..1 or 0..5 or 0..10 V VOLTAGE output to be de-

fined when ordering.

•LPPYRA13S: With RS485 Modbus-RTU output.

•LPPYRA13S12: With SDI-12 output.

The pyranometer 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).

LPPYRA13 -4-V2.3

2WORKING PRINCIPLE

LPPYRA13 pyranometer is based on a thermopile sensor. The thermopile sensitive sur-

face is coated with a black matt paint, which allows the pyranometer not to be selec-

tive at different wavelengths.

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

the sensitivity to thermal irradiance, LPPYRA13 is equipped with two concentric domes

having 50 mm and 32 mm outer diameter. The domes protect the thermopile 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 LPPYRA13 pyranometer and a standard solar spectrum.

Fig. 2.1: LPPYRA13 pyranometer 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, LPPYRA13 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.

LPPYRA13 -5-V2.3

Fig. 2.2: : percentage change of LPPYRA13 pyranometer sensitivity in the

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

The shadow ring prevents the direct solar radiation to reach the sensor the whole day

long, so that only the diffuse solar radiation will be measured. Because the elevation

of the sun changes day by day, it is necessary to change the height of the shad-

ow ring at least every two days.

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. 2.3: scheme of principle LPPYRA13 (version with mV output)

Thermopile

Surge

Protector

Connector pins

Housing

To cable shield

Temperature (°C)

% change of sensitivity

Thermopile

Temperature

compensation

LPPYRA13 -6-V2.3

3INSTALLATION

Before installing the pyranometer, refill the cartridge containing silica-gel crystals. Sil-

ica gel absorbs humidity in the dome chamber and prevents, in particular climatic

conditions, condensation on the internal walls of the domes and measurement altera-

tion.

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 pyranometer 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

LPPYRA13 -7-V2.3

•The pyranometer 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 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.

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

ter the measurement of diffused light.

•In order to allow an accurate horizontal positioning, the pyranometer is equipped

with a levelling device: the adjustment is made by means of the levelling screws

that allow adjusting the pyranometer inclination.

3.1 MOUNTING THE SHADOW RING

LPPYRA13 is made up of two parts: the pyranometer and the shadow ring.

Fig. 3.2: LPPYRA13 dimensions and description

To make the transport easier, the shadow ring is disassembled in the following pieces:

•Base (composed of three spokes).

•Shadow ring with “L” profile.

•Sliding bars with graduated scale.

•Pillar + crossbar + pyranometer support + goniometer (factory assembled and

aligned).

Mounting Instructions:

1. Screw the three spokes of the base to the pillar.

2. Screw the two sliding bars to the shadow ring.

3. Insert the sliding bars of the ring in the two slots at the crossbar ends (if correct-

ly mounted, the ring axis crosses the pyranometer thermopile center).

Levelling device

Screwwithringnut

Pillar

Crossbar

Graduated

sliding bar

Base

Pyranometer

support

Goniometer

Pyranometer

Shadow ring

LPPYRA13 -8-V2.3

3.2 POSITIONING THE INSTRUMENT FOR THE DIFFUSE RADIATION MEASUREMENT

The shadow ring particular geometry allows intercepting the solar direct radiation dur-

ing the whole day without adjustments.

The base of the instrument has to be mounted parallel to the ground by adjusting the

screw with ring nut and with the aid of the levelling device integrated in the instrument.

The shadow ring has to be positioned in such a way that its axis be parallel to the

earth axis. To do this, follow two separate steps: first align the shadow ring along the

North-South axis and then adjust the ring tilt.

Fig. 3.3: positioning the instrument

Aligning the shadow ring along the North-South axis:

1. Wait for solar midday.

2. On the goniometer where the pyranometer is mounted there is a groove, rotate the

shadow ring base until the sunbeams pass through the groove from both sides of

the goniometer.

Fig. 3.4: shadow ring North-South alignment

As you get closer to the equator, this method involves an increasing uncertainty. For

installations in sites nearby the equator, it is suggested to use a map to align the

shadow ring along the North-South axis.

Shadow ring axis

Earth axis

North Pole

South Pole

Equator

Solar radiation

Sunrays

LPPYRA13 -9-V2.3

Adjusting the shadow ring tilt:

1. Check that the sliding bars and the long side of the pyranometer support be parallel

(instruments are supplied factory aligned).

2. Mount and fix the pyranometer to the goniometer.

3. Position the goniometer in such a way to read on its scale the latitude of the instal-

lation site.

Fig. 3.5: shadow ring tilt adjustment

4. Rotate the crossbar (after loosening the screw that locks it) until the pyranometer

is parallel to the ground. Use the levelling device on the pyranometer body.

5. If the operations have been carried out properly, the shadow ring axis will be paral-

lel to the earth axis.

By now you just have to adjust the height of the sliding bars (loosening the locking

screws) until the pyranometer big dome appears completely in the shade. To confirm

that installation has been performed correctly, you can compare the reading on the

sliding bar scale with the value listed in tables 1A and 1B. If the values match, the py-

ranometer and the shadow ring have been correctly installed.

The shadow ring position has to be adjusted at least once every two days.

Angle reading

LPPYRA13 -10 -V2.3

TABLE 1A

VALID ONLY FOR LPPYRA13 (no AC/AV/S/S12 versions)

The table shows the values to which the graduated sliding bars must be set for the

different solar declinations and for the two hemispheres.

Solar

declination Date

day/month

Value to be set on the

sliding bars (mm) if

installed in the

Northern hemisphere

Value to be set on the

sliding bars (mm) if

installed in the

Southern hemisphere

-23.26 21/12 101 121

-22 10/1 3/12 96 116

-20 21/1 22/11 87 107

-18 29/1 13/11 77 97

-16 5/2 6/11 68 88

-14 11/2 31/10 58 78

-12 17/2 25/10 49 69

-10 23/2 19/10 39 59

-8 28/2 14/10 29 49

-6 5/3 8/10 19 39

-4 10/3 3/10 10 30

-2 15/3 28/9 0 20

0 21/3 23/9 10 10

+2 26/3 18/9 20 0

+4 31/3 12/9 30 10

+6 5/4 6/9 39 19

+8 10/4 2/9 49 29

+10 16/4 27/8 59 39

+12 22/4 21/8 69 49

+14 28/4 15/8 78 58

+16 4/5 9/8 88 68

+18 12/5 1/8 97 77

+20 20/5 23/7 107 87

+22 31/5 12/7 116 96

+23.26 21/6 121 101

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