LP PIRG 01_1
LP PIRG 01_3LP PIRG 01_2

LP PIRG 01 – Pyrgeometer

The pyrgeometer LP PIRG 01 is used to measure the far infrared radiation (FIR). Its
use is mainly in the meteorological fi eld. Measures are referred to radiations with
wavelength greater than 4.5 μm .
The far infrared radiation derives from the measure of the thermopile output
signal and from the knowledge of the instrument temperature. The temperature
measure is performed by a 10kΩ NTC which is inside the body of the pyrgeometer.
The pyrgeometer can be used also for the study of energy balance. In this case,
besides another pyrgeometer which measures infrared radiation upwards, it is
necessary to have an albedometer (LP PYRA 05 or LP PYRA 06) to measure short
wavelengths radiation (<3μm) .

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Product Description

The pyrgeometer LP PIRG 01 is used to measure the far infrared radiation (FIR). Its
use is mainly in the meteorological field. Measures are referred to radiations with
wavelength greater than 4.5 μm .
The far infrared radiation derives from the measure of the thermopile output
signal and from the knowledge of the instrument temperature. The temperature
measure is performed by a 10kΩ NTC which is inside the body of the pyrgeometer.
The pyrgeometer can be used also for the study of energy balance. In this case,
besides another pyrgeometer which measures infrared radiation upwards, it is
necessary to have an albedometer (LP PYRA 05 or LP PYRA 06) to measure short
wavelengths radiation (<3μm) .
2) Working Principle
The pyrgeometer LP PIRG 01 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 sensor is covered by silicon window that has two basic
purposes:
1- protect the thermopile from the weather;
2- determine the instrument spectral range: silicon is transparent to wavelengths
longer than 1.1μm, therefore on the inside of the window there is a fi lter 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 possibility 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) measure 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;
C
U E emf term. = 2
σ = Stefan-Bolzmann constant (5.6704×10-8 W m-2 K-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
(assuming emissivity ε=1) at TB temperature.
3) Installation and mounting of the pyrgeometer for the infrared radiation
measure:
Before installing the pyrgeometer you need to load the cartridge containing silica
gel crystals. The silica gel has the function of absorbing humidity present inside
the instrument; 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 three screws that fi x the white screen
2- unscrew the Silica gel cartridge by using a coin
3- remove cartridge perforated cap
4- open the envelope (included with the pyrgeometer) containing the silica gel
5- fi ll the cartridge with silica-gel crystals
6- close the cartridge with his cap, making sure that the O-ring seal is positioned
correctly
7- screw the cartridge into the body of the pyrgeometer with a coin
8- make sure that the cartridge is fi rmly screwed (if not the duration of the
crystals of silica gel is reduced)
9- place the screen and screw it
10- the pyrgeometer is ready to be used
Figure 1 shows the operations necessary to fi ll the cartridge with the silica-gel
crystals.

• The LP PIRG 01 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 the
pyrgeometer lies. 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 WMO/ISO recommendations also when the screen is used.
• For an accurate horizontal positioning, the pyrgeometer LP PIRG 01 is equipped
with a spirit level, which adjustment is by two screws with lock nut that allows
changing the pyrgeometer inclination. The fixing on a flat base can be performed
by using two 6mm diam. holes and 65 mm wheelbase. In order to access the
holes, remove the screen and re-place it back after mounting, see figure 2.

• The support LP S1 (figure 3), supplied upon request as an accessory, allows an
easy mounting of the pyrgeometer support pole. The maximum diameter of the
pole to which the bracket can be secured is 50 mm. To secure the pyrgeometer
to the bracket, remove the screen by unscrewing the three screws, fix the
pyrgeometer; once the installation is complete, fix the white screen back.

4) Electrical Connections and requirements for electronic reading:
• The pyrgeometer LP PIRG 01 does not need any power supply.
• The instrument is equipped with an 8-poles M12 output
• 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 4):

To measure the output signal from the thermopile (Chapters 1-2) the pyrgeometer
has to be connected to a data-logger or digital voltmeter (DVM). Typically the output
signal from the pyrgeometer is | Uemf|<4 mV. In order to fully exploit the features
of the pyrgeometer, the recommended resolution of the reading instrument is 1μV.
Moreover, it is necessary to read the NTC resistance so to determine the
pyrgeometer temperature.
In Figure 5 the electrical connections present inside the pyrgeometer are reported.

5) Maintenance:
In order to ensure a high measurement accuracy, it is necessary to keep clean the
silicon window, so the higher the frequency of cleaning, 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 silicon window again
with water only.
Due to the high temperature fluctuations between day and night, it is possible
that you get some condensation inside the pyrgeometer (especially on the silicon
window); in this case the reading is wrong. To minimize condensation inside the
pyrgeometer, a proper cartridge Silica gel is supplied with the instrument.
The efficiency of silica-gel crystals decreases over time with the absorption of
moisture. When crystals of silica gel are efficient their colour is yellow, while when
gradually losing efficiency their colour becomes transparent; in order to replace
them please refer to the instructions under paragraph 3. Silica gel typically lifetime
goes from 4 to 12 months 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:
According to the NTC RNTC [ohm] resistance it is possible to trace the pyrgeometer
temperature (Tb) back by using the formula 3:
=a+b·log(RNTC)+c·log(RNTC1 )3
Tb 3
Where:
a=10297.2×10-7;
b=2390.6×10-7;
c=1.5677×10-7.
Temperatura is expressed in Kelvin degrees.
N.B. In table 1 you can get the values between -25°C and +58°C; in order to
obtain the value under Kelvin degrees it is necessary to sum 273.15 to the value
read in Celsius degrees.

Once the pyrgeometer temperature in Kelvin degrees and the thermopile output
signal are known Uemf [μV], irradiation EFIR↓ [W/m2] is obtained by the formula 1:
EFIR ↓= +σTB
4 Eemf
C
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 reference
standard pyrgeometer calibrated by the World Radiation Center (WRC).
The two instruments are kept outdoors for some nights in the presence of clear
sky. The data acquired by a data logger is then processed to obtain the calibration
factor.
To take full advantage of the LP PIRG 01 features, we recommend to perform the
calibration every one, two years (the choice of calibration interval depends both
on the accuracy to be achieved and on the installation location).
7) Technical specifications:
Typical sensitivity: 5-10 μV/(W/m2)
Impedance: 33 Ω ÷ 45 Ω
Measuring range: -300÷+300 W/m2
Field of view: 160°
Spectral range: 5.5 μm ÷ 45 μm (50%)
(transmission from the silica window)
Working temperature: -40 °C ÷ 80 °C
Dimensions: figure 2
Weight: 0.90 Kg

Technical specifi cations according to ISO 9060
Response Time (95%): <28 sec
Off-set Zero (type B):
response to a change of 5K/h
of room temperature: <±4W/m2
Long-term instability (1 year): <±1.5 %
Nonlinearity: <±1 %
Spectral selectivity: <±5 %
Temperature response: <3 %
Tilt response: <±2 %
ORDERING CODES
LP PIRG 01: Pyrgeometer. Equipped with protection, silica-gel crystals cartridge,
2 richarges, level. 8-poles M12 connector and Report of Calibration ISO9001.
LP S1: Kit made of bracket for mounting pyrgeometer LP PIRG 01 to a pole with
diameter 50mm
LP SP1: Protection screen made in plastic UV resistant. LURAN S777K della BASF
LP SG: Cartridge for silica-gel crystals equipped with OR and cap
LP RING 02: Base with levelling device and adjustable holder for mounting the LP
PIRG 01 pyrgeometer in an inclined position.
LP S6: Kit for the installation of LP PIRG 01. The kit includes: 1 m mast (LP S6.05),
base fi tting (LP S6.04), graduated support plate (LP S6.01), bracket for
HD9007 or HD32MTT.03.C (HD 9007T29.1), bracket for pyranometers (LP
S6.03).
HD 2003.77/40: Clamping for mounting the LP PIRG 01 mast Ø 40mm
HD 2003.85K: Kit with adjustable height to mount pyranometers on Ø 40mm mast
(HD2003.84,HD2003.85,HD2003.79)
LP G: Pack of 5 sachets of silica-gel crystals.
CPM12 AA8.2: 8-pole cable. Length 2m. 8-pole M12 connector on one end, open
wires on the other side
CPM12 AA8.5: 8-pole cable. Length 5m. 8-pole M12 connector on one end, open
wires on the other side
CPM12 AA8.10: 8-pole cable. Length 10m. 8-pole M12 connector on one end,
open wires on the other side.

Download

Manuals and Brochures here.  

LPPIRG01.pdf

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