GHM Delta OHM LPPYRA12 User manual

Operating manual
Pyran
ometer
LPPYRA
12
www.deltaohm.com
English
Keep for future reference.
Companies / Brands of GHM
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LPPYRA12 -2-V2.2
TABLE OF CONTENTS
1INTRODUCTION.................................................................................................... 3
2WORKING PRINCIPLE........................................................................................... 4
3INSTALLATION ..................................................................................................... 5
3.1 MOUNTING THE SHADOW RING ................................................................................6
3.2 POSITIONING THE INSTRUMENT FOR THE DIFFUSE RADIATION MEASUREMENT ...........................7
4ELECTRICAL CONNECTIONS................................................................................ 11
4.1 LPPYRA12 CONNECTIONS ..................................................................................11
4.2 LPPYRA12AC CONNECTIONS...............................................................................12
4.3 LPPYRA12AV CONNECTIONS............................................................................... 12
4.4 LPPYRA12S CONNECTIONS................................................................................. 13
4.5 LPPYRA12S12 CONNECTIONS .............................................................................14
5MEASUREMENT IN THE MODELS WITH ANALOG OUTPUT....................................15
5.1 LPPYRA12....................................................................................................15
5.2LPPYRA12AC................................................................................................15
5.3 LPPYRA12AV................................................................................................15
6RS485 MODBUS-RTU OUTPUT............................................................................. 16
6.1 SETTING THE COMMUNICATION PARAMETERS.............................................................. 16
6.2 READING THE MEASURES WITH THE MODBUS-RTU PROTOCOL..........................................18
7SDI-12 OUTPUT .................................................................................................. 19
8MEASUREMENT CORRECTION ............................................................................. 23
9MAINTENANCE.................................................................................................... 26
10 TECHNICAL SPECIFICATIONS............................................................................. 27
11 SAFETY INSTRUCTIONS...................................................................................... 28
12 ORDERING CODES .............................................................................................. 29

LPPYRA12 -3-V2.2
1INTRODUCTION
LPPYRA12 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.
LPPYRA12 is equipped with a Spectrally Flat Class B (First Class) pyranometer (LPPY-
RA02) 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:
•LPPYRA12: PASSIVE
The passive version can be connected to the instruments
D09847 and HD31 by using VP 472 SICRAM module.
•LPPYRA12AC: ACTIVE with 4..20 mA CURRENT output
•LP PYRA12AV: ACTIVE with 0..1 or 0..5 or 0..10 V VOLTAGE output to be de-
fined when ordering.
•LPPYRA12S: With RS485 Modbus-RTU output.
•LPPYRA12S12: 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).

LPPYRA12 -4-V2.2
2WORKING PRINCIPLE
LPPYRA12 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. The pyranometer spectral range is determined by the
transmission of the two glass domes type K5.
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.
In order to grant the thermopile a proper thermal insulation from the wind and reduce
the sensitivity to thermal irradiance, LPPYRA12 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 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. 2.1: scheme of principle LPPYRA12 (version with mV output)
Thermopile
Surge
Protector
Connector pins
Housing
To cable shield

LPPYRA12 -5-V2.2
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

LPPYRA12 -6-V2.2
•The pyranometer must be mounted in an easy-to-reach location in order to clean
the dome regularly and adjust the height of the shadow ring. At the same time,
make sure that no buildings, constructions, trees or obstructions exceed the hori-
zontal 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
LPPYRA12 is made up of two parts: the pyranometer and the shadow ring.
Fig. 3.2: LPPYRA12 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
Screw with ring nut
Pillar
Crossbar
Graduated
sliding bar
Base
Pyranometer
support
Goniometer
Pyranometer
Shadow ring

LPPYRA12 -7-V2.2
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

LPPYRA12 -8-V2.2
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

LPPYRA12 -9-V2.2
TABLE 1A
VALID ONLY FOR LPPYRA12 (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

LPPYRA12 -10 -V2.2
TABLE 1B
VALID FOR LPPYRA12AC / LPPYRA12AV / LPPYRA12S / LPPYRA12S12
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 92 130
-22 10/1 3/12 87 125
-20 21/1 22/11 78 116
-18 29/1 13/11 68 106
-16 5/2 6/11 59 97
-14 11/2 31/10 49 87
-12 17/2 25/10 40 78
-10 23/2 19/10 30 68
-8 28/2 14/10 20 58
-6 5/3 8/10 10 48
-4 10/3 3/10 1 39
-2 15/3 28/9 9 29
0 21/3 23/9 19 19
+2 26/3 18/9 29 9
+4 31/3 12/9 39 1
+6 5/4 6/9 48 10
+8 10/4 2/9 58 20
+10 16/4 27/8 68 30
+12 22/4 21/8 78 40
+14 28/4 15/8 87 49
+16 4/5 9/8 97 59
+18 12/5 1/8 106 68
+20 20/5 23/7 116 78
+22 31/5 12/7 125 87
+23.26 21/6 130 92