LP PYRA 10 AV. 1 Introduction. 2 Working Principle

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1 LP PYRA 13 1 Introduction The LP PYRA 13 pyranometer measures the irradiance on a plane surface (Watt/ m 2 ). Thanks to the shadow-ring, the LP PYRA 13 measure the diffuse solar radiation eliminating the contribution of direct irradiance, The LP PYRA 13 is equipped with a First Class pyranometer ( LP PYRA 10)in accordance with ISO 9060 standard and with the criteria of the WMO Guide to Meteorological Instruments and Methods of Observation, fifth edition (1983). The pyranometer is produced in three versions: LP PYRA 10 PASSIVE* LP PYRA 10 AC LP PYRA 10 AV ACTIVE, 4..20mA CURRENT output ACTIVE, 0..1** or 0..5 or V VOLTAGE output, to be defined at the order. * Using SICRAM Module VP 472 it is possible to connect passive pyranometer to Indicator D ** 0..1 output version can be connected to indicator HD using SICRAM Module VP 474. The indicator reads directly in W/m 2. 2 Working Principle The pyranometer LP PYRA 10 is based on a thermopile sensor which surface is covered by a matt black paint so to allow the instrument not to be selective at various wavelengths. The spectral range of the pyranometer is determined by the transmission of the two glass domes type K5. The new sensor allows a response time less than the requirements of the ISO9060 standard for classifying Secondary pyranometers (response time is generally less than 9 seconds, where ISO9060 standard requires a response time less than 15 seconds). Radiant energy is absorbed/radiated from the surface of the blackened thermopile, creating a temperature difference between the centre of the thermopile (hot junction) and the body of pyranometer (cold junction). The temperature difference between hot and cold junction is converted into Potential Difference thanks to the Seebeck effect. A second thermopile is mounted inside the instrument and not accessible by light. This second thermopile, connected anti-series with respect to the sensor exposed to light, reduces the signals of pyranometer in sudden temperature changes (thermal shock)

2 In order to minimize variations of sensitivity according to the temperature, the LP PYRA 10 is equipped with passive compensation circuit. The graph 1 shows the typical variation of sensitivity at different temperatures Variazione % della sensibilità Temperatura (C ) Grafico1:% change of the sensitivity of the pyranometer LP PYRA 10 compared to the sensitivity at 20 C in the temperature range between -20 and 50 C. The deviations are calculated from the measured sensitivity at 20 C. LP PYRA 10 has two concentric domes with external diameter of 50 mm and 30mm respectively, this to ensure a thermal insulation of the thermopile by the wind and reduce the sensitivity to radiation heat. The domes protect the thermopile from dust settling on the blackened it could change the spectral sensitivity. 3 Installation and Mounting of the Pyranometer for the Measurement of Global Radiation: Before installing the pyranometer, refill the cartridge containing silica-gel crystals. Silica gel absorbs humidity in the dome chamber and prevents (in particular climatic conditions) internal condensation forming 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 - 2 -

3 4- Open the sachet containing silica gel (supplied with the pyranometer) 5- Replace 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 Figure N.1 shows the operations necessary to fill the cartridge with the silica gel crystals. Silica-gel cartridge LP SG Sealed sachet of silica Perforated Cap A B LP G Filling Closing the cartidge C D Fig. 1 The PYRA 13 pyranometer has to be mounted in a readily accessible location to clean the outer dome regularly and to carry out maintenance. At the same time, check that no building, construction, tree or obstruction exceeds the horizontal plane where the pyranometer lays. If this is not possible, select a site where obstructions do not exceed 5 degrees of elevation, in the path followed by the sun, between earliest sunrise and latest sunset. N.B The presence of obstructions on the horizon line significantly affects the measurement of direct irradiance. The pyranometer has to be located far from any kind of obstruction, which might reflect sunlight (or sun shadow) onto the pyranometer itself. The LP PYRA 10 pyranometer is provided with a spirit level for carrying out an accurate horizontal leveling. The adjustment is made by means of two leveling screws that allow to adjust the pyranometer inclination. Use the two 6mm-diameter holes and a 65mm interaxial distance to mount the instrument on a plane. Remove the shade disk to access the holes and reposition it after mounting (see fig. 2)

4 3.1 Mounting the shadow ring. The L LP PYRA 13 is made up of two parts: the pyranometer and the shadow-ring (figure 2). The pyranometer specifications are listed in paragraph 8. Shadow Ring 570 mm 54 mm Pyranometer Goniometer Graduating sliding bar Crossbar 370 mm Base 300 mm Pillar Screw with ring nut Spirit Level 300 mm Figura 2 To make the transport easier, the shadowring is disassembled in the following 5 pieces: 1- Base (3 pieces) 1- Shadow-ring with L profile 2- Sliding bars with graduated scale 1- Pillar + crossbar + pyranometer support + goniometer (factory assembled and aligned) Mounting Instructions: 1- screw 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 (when correctly mounted, the ring axis crosses the pyranometer thermopile center). 3.2 Instrument Positioning for the Measurement of Diffuse Radiation. The shadow ring particular geometry allows to intercept the solar direct radiation during the whole day without readjustments. The LP PYRA 13 base has to be mounted parallel to the ground. The leveling screw and the spirit level allow to carry out this operation easily. The shadow-ring has to be positioned in such a way that its axis be parallel to the earth s axis (fig. 3)

5 Shadow-ring axis Earth s axis North Pole Equator Solar Radiation South Pole figure 3 For this reason, respect the following two separate steps: Align the shadow-ring along the North/South axis. Then adjust the ring tilt. To align the shadow-ring along the North-South axis, observe the following procedures: 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 (figure 4). SolarRadiation figura 4 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 shadowring along the North-South axis. Now adjust the sliding bar tilt as follows: 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 - 5 -

6 3- Position the goniometer in such a way to read on its scale the latitude of the LP PYRA 13 installation site (figure 5). Angle Reading Figura 5 4- Rotate the crossbar (after loosening the screw that locks it) until the pyranometer is parallel to the ground. Use the spirit level on the pyranometer body. 5- If these operations have been carried out properly, the shadowring axis will be parallel to the earth s axis. By now you just have to adjust the height of the sliding bars until the pyranometer big dome does not appear in the shade. To confirm that installation has been performed correctly, you can compare the reading on the sliding bar scale with that listed in table 1 (paragraph 7). If they match, the pyranometer and the shadowring have been correctly installed. 4 Electrical Connection and Requirements for Electronic Readout Devices: The LP PYRA 10 is produced in three versions, LP PYRA 10, 10 AC and LP LP PYRA PYRA 10 AV. The LP PYRA 10 is passive and does not need power. Versions LP PYRA 10 AC, AV are active and need power. The voltage required is: 8-30 VDC for the versions LP PYRA 10 AC and LP PYRA 10 AV with 0..1V and 0..5 V output VDC for the version LP PYRA 10 AV with 0..10V output. All versions are equipped with 4-pin output connector. The optional cable, ending with a connector by one side, is made in PTFE resistant to UV and is provided with 7 wires plus braid (screen), the diagram with the correspondence between cable colours and connector poles is the following (figure 6): Fig.6-6 -

7 LP PYRA 10 Connector Function Color 4 Screen ( ) Black 1 Positive (+) Red 2 Negative (-) Blue 3 Case ( ) White LP PYRA 10 AC Connector Function Color 4 Screen ( ) Black 1 Positive (+) Red 2 Negative (-) Blue 3 Case ( ) Bianco LP PYRA 10 AV Connector Function Color 4 Screen ( ) Black 1 (+) Vout Red 2 (-) Vout and (-)Vcc Blue 3 (+) Vcc White LP PYRA 10 is connected to a millivoltmeter or to a data acquisition system. Typically, the signal from pyranometer not exceed 20 mv. The recommended resolution of the instrument reading in order to take full advantage of the pyranometer, is 1μV. Termopila LP PYRA 10 Contenitore Termopila - Compesazione in Temperatura Scaricatore Blu Rosso Bianco Schermo (Nero) C B Fig. 7 D A An example of connection reading system is shown in Figure

8 LP PYRA Probe output = µv/(w/m 2 ) Red [ 1] Blue [ 2] Datalogger or 3 4 (shield) Converter/Amplifier Black [ 4] with Vor maoutput White [ 3] Fig.8 LP PYRA 10 to be connected to an AC power supply and a multimeter as shown below (Figure 9), resistance load for reading the signal must be 500 Ω: LP PYRA 10 AC Probe output = ma Red [ 1] Power Supply Vdc 2 1 Blue [ 2] ma 3 4 White [ 3] (shield) Black [ 4] Equipment with ma input Fig. 9 LP PYRA 10 AV to be connected to a power supply and a multimeter, as shown below (Figure 10), the load resistance for reading the signal must be 100 KΩ: LP PYRA 10 AV Probe output = 0...1V, 0...5V, V Red [ 1] Equipment with 0...1V/0...5V/0...10V input 2 1 Blue [ 2] 3 4 White [ 3] Black [ 4] (shield) Power Supply Vdc for 0 10V output Vdc for other versions Fig

9 5 Maintenance: -The shadowring position has to be adjusted at least once every two days. Adjustment procedure: Loosen the two screws that lock the sliding bars and position the two bars at the height indicated in table 1. If the sky is bright and there is the sunshine, the adjustment can be carried out directly looking at the shadow of the ring on the pyranometer. Adjust the two sliding bars in such a way that the shadow entirely covers the outer dome. Once the correct position of the sliding bars has been set, tighten the fixing screws and proceed with measurements. It is important to keep the outer glass domes clean to grant measurement best accuracy. Consequently, the more the dome will be kept clean, the more measurements will be accurate. Washing can be made using water and standard papers for lens, or, in some cases, using pure ethyl alcohol. After using alcohol, clean again the dome with water only. Because of the high rise/fall in temperature between day and night, some condensation might appear on the pyranometer dome. In this case the performed reading is highly over-estimated. To minimize the condensation growth, the pyranometer is provided with a cartridge containing dessicant material: Silica gel. The efficiency of the Silica gel crystals decreases in the course of time while absorbing humidity. Silica gel crystals are active when their color is yellow, while they turn blue as soon as they loose their power. Read instructions at paragraph 3 about how to replace them. Silica gel typical lifetime goes from 2 to 6 months depending on the environment where the pyranometer works. 6 Calibration and Measurements: The pyranometer S sensitivity (or calibration factor) allows to determine the irradiance by measuring a signal in Volts at the thermopile ends. The S factor is measured in μv/(wm -2 ). Once the difference of potential (DDP) has been measured at the ends of the sensor, the E e irradiance is obtained applying the following formula: E e = DDP/S Where: E e : is the Irradiance expressed in W/m 2, DDP: is the difference of Potential expressed in μv and measured by the multimeter, S: is the calibration factor in μv/(w/m 2 ) shown on the pyranometer label (and mentioned in the calibration report). Pyranometers are factory calibrated one by one and they are marked by their own calibration factor. To get best performances from your LP PYRA 13 it is strongly recommended that the calibration be checked annually. The instruments and the equipment of Delta Ohm Photo-Radiometry meteorological laboratory grant the calibration of pyranometers according to the WMO specifications and assure that measurements are traceable to the international standards

10 7 Corrections to be Applied: Diffuse radiation is measured by eliminating the contribution of direct radiation through the shadow-ring. As besides the direct radiation the shadow-ring intercepts part of the diffuse light, it is necessary to correct measured values. The percentage of diffuse radiation intercepted by the shadow ring changes during the year, because the position that the ring has with respect to the pyranometer changes. In tables 2 and 3 there are the correction factors to be applied to measurements over the whole year and at different latitudes (Northern Hemisphere: table 2, Southern Hemisphere: table 3). In order to get the real value (E e v ) of diffuse irradiance, it is necessary to multiply the measured value by the correction coefficient listed in the following tables: E e v =E e C where: E e, is the measured diffuse irradiance, obtained according to the procedure mentioned at paragraph 6 C, is the correction factor mentioned in tables 2 and

11 Table 1: FOR LP PYRA 13 This table shows the values to be used to set the graduated sliding bars for the different declinations of the sun. Sun s Declination Date Day/month Value to be set on the sliding bars (mm) / /1 3/ /1 22/ /1 13/ /2 6/ /2 31/ /2 25/ /2 19/ /2 14/ /3 8/ /3 3/ /3 28/ /3 23/ /3 18/ /3 12/ /4 6/ /4 2/ /4 27/ /4 21/ /4 15/ /5 9/ /5 1/ /5 23/ /5 12/ /

12 Table 2: Correction factors C for installation of LP PYRA 13 in northern hemisphere Northern Latitudine Declination of the sun

13 Table 3: Correction factors C for installation of LP PYRA 13 in southern hemisphere Southern Latitudine Declination of the sun

14 8 Technical Specifications: Typical sensitivity: 10 μv/(w/m2) LP PYRA ma ( W/m2) LP PYRA 10AC 0..1,5,10V ( W/m2) LP PYRA 10AV Impedance: Campo di misura: Field of view: 500 Ω 1000 Ω W/m2 2π sr Spectral range: 305 nm 2800 nm (50%) (trasmission of domes) 335 nm 2200 nm (95%) Working temperature: -40 C 80 C Dimensions: figure 1 Weight: 0.90 Kg Specifications according to ISO Response time: <9 sec (95%) 2- Off-set Zero: a) response to a thermal radiation of 200W/m2: b) response to a change of 5K/h in the room temperature: <7 W/m2 < ±2 W/m2 3a- Long-term instability: < ±0.8 % (1 year) 3b- Nonlinearity: < ±0.5 % 3c- Response according to Cosine law: < ±10 W/m2 3d- Spectral selectivity: < ±3 % 3e- Temperature response: <2 % 3f- Tilt response: < ±0.5 %

15 SHADOW RING Weight: Ring diameter: Ring height: Base diameter: 5.90 Kg 570 mm 54 mm 300 mm 8 Ordering Codes

16 ORDERING CODE LP PYRA 13 LP PYRA 13 AC LP PYRA 13 AV CP AA 1.5 CP AA 1.10 LP SP1 LP SG LP G Secondary Standard Pyranometer according to ISO Complete with shade disk, shadowring for diffuse radiation, dessicant sachet with silica gel crystals, 2 silicagel cartridges, 4 pole plug and Calibration Report. Secondary Standard Pyranometer according to ISO Complete with shade disk, shadowring for diffuse radiation, dessicant sachet with silica gel crystals, 2 silicagel cartridges, 4 pole plug and Calibration Report ma signal Output Secondary Standard Pyranometer according to ISO 9060.Complete with shade disk, shadowring for diffuse radiation, dessicant sachet with silica gel crystals, 2 silicagel cartridges, 4 pole plug and Calibration Report. 0..1V, 0..5V, 0..10V signal output (to be defined when order) 4 pole plug with UV proof cable, L=5m. 4 pole plug with UV proof cable, L=10m. UV resistant plastic shade disk (BASF LURAN S777K) Desiccant sachet with silica gel crystals, complete with inner O-ring and cap. Pack of 5 cartridges of silica gel crystals