LP NET 14_1
LP NET 14_2LP NET 14_3

LP NET 14 – Net Irradiance Meter

LP NET 14 is a 4-component net-radiometer for the measurement of the net
radiation between 0.3μm and 45 μm.
The net-radiometer consists of two pyranometers (one for the measurement of
the global radiation Esw↓ and the other one for the measurement of the reflected
solar radiation Esw↑) and a pair of pyrgeometers (one for the measurement of
the infrared radiation emitted by the sky EFIR↓ and the other one for the infrared
emitted by the ground surface EFIR↑).
The LP NET 14 is equipped with a temperature sensor (NTC). The measurement
of the temperature is needed for the measurement with the two pyrgeometers,
in fact, the far infrared is derived by measuring the thermopile output and by the
knowledge of the instrument’s temperature.
The net radiometer is suitable for outdoor use in all weather conditions and
requires little maintenance.

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Product Description

LP NET 14 is a 4-component net-radiometer for the measurement of the net
radiation between 0.3μm and 45 μm.
The net-radiometer consists of two pyranometers (one for the measurement of
the global radiation Esw↓ and the other one for the measurement of the reflected
solar radiation Esw↑) and a pair of pyrgeometers (one for the measurement of
the infrared radiation emitted by the sky EFIR↓ and the other one for the infrared
emitted by the ground surface EFIR↑).
The LP NET 14 is equipped with a temperature sensor (NTC). The measurement
of the temperature is needed for the measurement with the two pyrgeometers,
in fact, the far infrared is derived by measuring the thermopile output and by the
knowledge of the instrument’s temperature.
The net radiometer is suitable for outdoor use in all weather conditions and
requires little maintenance.
2) Working principle
The pyranometers that make up the LP NET 14 measure the radiation for
wave lengths between 0.3μm e 3.0μm, while the pyrgeometers measure the
irradiance in the spectral range between 4.5μm and 45μm.
The pyranometers are based on a thermopile sensor which sensitive surface
is covered by a matt black paint so to allow the instrument not to be selective
at various wavelengths. The pyranometer spectral range is determined by the
transmittance of the two glass domes type K5 (See fig. 1).
Radiant energy is absorbed by the thermopile black surface, creating a
difference of temperature between the centre of the thermopile (hot junction)
and the pyranometer body (cold junction). Thanks to the Seebeck effect, the
difference of temperature between hot and cold junction is converted into a
Difference of Potential.

Also the pyrgeometers are based on a thermopile. In this case, to protect the
thermopile, silicon discs are used. Silicon is transparent to wavelengths longer
than 1.1μm therefore on the inside of the window there is a filter to block radiation
up to 4.5- 5 μm. The silicon external surface, which is exposed to weathering, is
coated with a scratch-resistant coating (DLC) to ensure strength and durability
in all weather conditions. The anti-scratch coating offers the advantage of
cleaning the surface without risk of scratching the window.

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 pyrgeometer (cold junction). The
temperature difference between hot and cold junction is converted into Potential
Difference thanks to the Seebeck effect.
If the pyrgeometer temperature is higher than the radiant temperature of the
portion of sky framed by the pyrgeometer, the thermopile will irradiate energy
and the output signal will be negative (typical situation of clear sky) vice versa if
the pyrgeometer temperature is lower than that portion of sky framed, the signal
will be positive (typical situation of cloudy sky).
Therefore, for the calculation of the ground infrared (EFIR ↓), besides the
thermopile output signal, is necessary to know the T temperature of the
pyrgeometer, as reported under the formula 1:
EFIR ↓=Eterm.+σTB
4 1
Where:
Eterm = net radiation (positive or negative), measured by the thermopile [W m-2)],
the value is calculated by the sensitivity of the instrument (C) [μV/ (W m-2) ]
and by the output signal (Uemf ) from formula 2;
Eterm. =
C
Uemf 2
σ = Stefan-Bolzmann constant (5.6704×10-8 W m-2 K-4);
LP NET 14
NET IRRADIANCE METER
160
74
52
EA-34
• The LP NET 14 has to be installed in a location easily accessible for periodic
cleaning of the silicon window. At the same time you should avoid buildings,
trees or obstacles of any kind exceed the horizontal plane on which lies the
instrument. In case this is not possible it is advisable to choose a location
where the obstacles are lower than 10 °.
• Usually the instrument is placed so that the cable comes out from the side of
the NORTH pole, when it is used in the NORTHERN hemisphere; from the side
of the SOUTH pole when it is used in the SOUTHERN hemisphere, according
to the standard ISO TR9901 and other WMO recommendations. In any case,
it is preferable to comply with these recommendations also when the screen
is used.
• For an accurate horizontal positioning, the LP NET 14 has to be fi xed on a
support pole by using the fi xing bracket (see fi g. 4).
TB = pyrgeometer temperature (K), obtained by the reading of the NTC
(10kΩ) resistance. In the manual (Table 1) is reported the resistance value
according to the temperature for values included between -25°C and
+55°C.
The fi rst term of the formula 1 represent the net radiation, that is to say the
difference between ground infrared radiation and the pyrgeometer emission,
while the second term is the radiation emitted by an object (taken with
submissiveness ε=1) at TB temperature.
3) Installation and mounting of the net-radiometer for the infrared radiation
measure:
Before installing the net-radiometer you need to load the cartridge containing
silica gel crystals. The silica gel has the function of absorbing humidity present
inside the instrument; in particular climatic conditions this humidity can lead to
condensation on the inner surface of the silicon window. While loading silica gel
crystals, avoid touching it with wet hands. The operations to perform (as much
as possible) in a dry place are:
1- unscrew the six screws that fi x the inner cap of the net-radiometer.
2- remove (if present) the old cartridge and the marker
3- open the envelope containing the silica gel and the marker
4- insert the cartridge in the salts-compartment
5- insert the marker so that it can easily be checked without opening the saltscompartment
6- tighten the six screws on the lid, make sure that the seal is positioned
correctly.
7- the net-radiometer is ready for use

4) Electrical Connections and requirements for electronic reading:
• The net-radiometer LP NET 14 does not need any power supply.
• The instrument is equipped with two M12 8 pole connectors.
• The optional cables end with an 8 pole connector on one side and open wires
at the other side. The cable is made in UV-resistant PTFE and is provided with
7 wires plus braid (screen), the diagram with the correspondence between
wire colours and connector poles is the following (fi gure 5):

In order to obtain a measure, it is necessary to acquire simultaneously the signal
of the four thermopiles and the NTC.
To measure the output signals of the four thermopiles, the four channels have
to be connected to a millivoltmeter or a data logger. In order to fully exploit
the features of the net-radiometer, the recommended resolution of the reading
instrument is 1μV.
Moreover, it is necessary to read the NTC resistance so to determine temperature
of the two pyrgeometers.
Under fi gure 6 the electrical connections necessary to read the signal of the four
thermopiles and the NTC are reported.

5) Maintenance
In order to ensure a high measurement accuracy, it is necessary to always keep
clean the silicon window and the glass domes of the net-radiometer, so the
higher the frequency of cleaning is the best measurement accuracy will be.
Cleaning can be done with normal tissues for cleaning photographic objectives
and water, if not possible, simply use pure ethyl alcohol. After cleaning with
alcohol, it is necessary also to clean the domes again with water only.
Due to the high temperature fl uctuations between day and night, it is possible
that you get some condensation inside the pyrgeometers and pyranometers
(especially on the silicon window); in this case the reading is wrong. To minimize
condensation inside the pyrgeometers, a proper cartridge with absorbent
material is inside: Silica gel.

effi ciency of silica-gel crystals decreases over time with the absorption
of moisture. Typically the duration of silica gel ranges from 4 to 12 months
depending on environmental conditions the instrument operates in. In order to
evaluate easily the effi ciency status of the salt, within each charge there’s a
marker added, to be placed at the bottom of the salt compartment so that it can
be seen. When it indicates the presence of humidity, it is necessary to replace
the salts. Hail of particular intensity or dimension may damage the silicon
window, therefore, after an intense storm with hail, it is recommended to check
the status of the window.
6) Calibration and measurements:
Each pyranometer and pyrgeometer that composes the instrument is calibrated
individually
The calibration factor S is given in μV/(Wm-2).
• Once the potential difference (DDP) has been measured at sensor ends, Ee
irradiance is obtained through the following formula:
Ee= DDP/S
where;
Ee: indicates the irradiance expressed in W/m²,
DDP: indicates the potential difference expressed in μV and measured by the
multimeter.
S: indicates the calibration factor expressed in μV/(W/m²) and shown on the
net radiometer label (calibration factor is also mentioned in the calibration
report).
Each net radiometer comes factory calibrated and has its own calibration factor.
The measurement with the two pyrgeometers ha to be performed as follows:
According to the NTC RNTC [ohm] resistance it is possible to trace the pyrgeometer
temperature (Tb) back by using the formula 3:
Tb
1 = a+blog(RNTC)+c(RNTC)3 3
Where:
a=10297.2×10-7;
b=2390.6×10-7;
c=1.5677×10-7.
Temperature is expressed in Kelvin degrees.
N.B. The values between -25 ° C to +58 ° C are tabulated in Table 2, to obtain
the value in degrees Kelvin, use the appropriate conversion

Once the pyrgeometer temperature in Kelvin degrees and the thermopile output
signal are known Uemf [μV], irradiance EFIR↓ [W/m2] is obtained by the formula 1:
C
U E emf FIR ↓= +σTB
4 4
Where:
C = pyrgeometer calibration factor [μV /(W/m2)] reported on the calibration
report;
σ = Stefan-Bolzmann constant (5.6704×10-8 W m-2 K-4).
Each pyrgeometer is individually calibrated at the factory and is distinguished
by its calibration factor.
Pyrgeometer calibration is performed outdoors, by comparison with a sample

pyrgeometer calibrated by the World Radiation Centre (WRC).
The two instruments are kept outdoors for a few days and nights in the presence
of clear sky. The data acquired by a data logger is then processed to obtain the
calibration factor.
To fully exploit the features of the probe LP NET 14, it is recommended
to perform the calibration verifi cation every one or two years (the choice of
calibration interval depends both on the accuracy to be achieved and on the
installation location).
7) Technical specifi cations
PYRANOMETERS
II° Class pyranometer according to ISO 9060
Typical sensitivity: 10 μV/(W/m2)
Impedance: 33 Ω ÷ 45 Ω
Measuring range: 0-2000 W/m2
Field of view: 2π sr
Spectral range: 305 nm ÷ 2800 nm (50%)
(dome transmission) 335 nm ÷ 2200 nm (95%)
Working temperature: -40 °C ÷ 80 °C
PYRGEOMETERS
Typical sensitivity: 5-10 μV/(W/m2)
Impedance: 33 Ω ÷ 45 Ω
Measuring range: -300 ÷ +300 W/m2
Viewing fi eld: 160°
Spectral range: 5.5 μm ÷ 45 μm (50%)
(silicon window transmission)Choose from the most used Product tags
Working temperature: -40 °C ÷ 80 °C
ORDERING CODES
LP NET 14: Net-radiometer equipped with:
bracket Ø=16 mm length 400 mm, 2 bird spikes, 2 recharges of desiccant
(composed of 5 silica-gel cartridges and one marker), level, 2 8-pole M12
connectors and Calibration Report.
ACCESSORIES
LPG2: 2 Recharges composed of 2 silica gel cartridges.
CPM12AA8.5: Cable with 8-pole M12 connector, 5 meters long.
CPM12AA8.10: Cable with 8-pole M12 connector, 10 meters long.

Download

Manuals and Brochures here.  

LPNET14.pdf

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