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LP PHOT 02
LP PHOT 02 probe measures illuminance (lux), defi ned as the ratio between the luminous
fl ux (lumen) passing through a surface and the surface area (m2).
The spectral response curve of a photometric probe is similar to the human eye curve,
known as standard photopic curve V(»). The difference in spectral response between LP
PHOT 01 and the standard photopic curve V(») is calculated by means of the error f1
’.
It has been designed for long-time outdoor installation. The photometric measurement
probe designed for outdoor readings, is basically used for taking weather and climate
measurements during daylight.
2 Working principle
LP PHOT 02 probe is based on a solid state sensor, whose spectral response has been
corrected by means of fi lters to adapt it to the response of the human eye. The typical relative
spectral response curve is shown in fi g.1.
LP PHOT 02 is provided with a 50 mm diameter transparent glass dome, in order to protect
the sensor against atmospheric damage.
The cosine corrected response has been obtained through both the PTFE diffuser and
case particular shapes. Deviation between the theoretical response and the real one, is
shown in fi g.2.
The LP PHOT 02 cosine response allows for use even when the sun elevation is low.
Installing and mounting the probe LP PHOT 02 for global radiation measurements:
Before installing the luxmeter, the silica-gel cartridge must be refi lled. Silica-gel crystals
absorb humidity in the dome chamber and in case of particular climatic conditions, prevent
internal condensation forming on the dome inner wall, with a consequent alteration in
measurements.
Do not wet or touch the instrument with your hands while refi lling the silica-gel cartridge.
Carry out the following instructions in a dry environment:
1 Loosen the three screws that fi x the white shade disk
2 Unscrew the silica-gel cartridge using a coin
3 Remove the cartridge perforated cap
4 Open the silica-gel sachet (supplied with the probe)
5 Fill the cartridge with silica-gel crystals
6 Close the cartridge with its own cap, and check that the sealing O-Ring is in the
right position.
7 Screw the cartridge to the probe using a coin
8 Make sure the cartridge is tightly screwed (otherwise silica-gel crystal will last for
a shorter time)
9 Position the shade and tighten it with the screws
10 The photometric probe is ready for use
Fig.3 shows the operations needed to refi ll the cartridge with silica-gel crystals
• To allow cleaning the outer dome regularly and carrying out the instrument maintenance,
LP PHOT 02 should be mounted in easily reachable places. At the same time,
you should check that no building, tree, or any other obstacle exceeds the horizontal
plane where the probe is mounted. In case this is not possible, you should fi nd a place
where obstacles do not exceed 5 degrees elevation over the path followed by the sun
from rising until sunset.
• The probe should be located far from any obstacle which might refl ect sunlight (or any
shadow) onto the probe.
• For a correct horizontal placing, LP PHOT 02 is provided with a bubble level; inclination
adjustment of the luxmeter is made by means of two leveling screws. Use the two 6mmdiameter
screw holes with an interaxial distance of 65 mm, to mount the instrument on a
plane. To access the holes, remove the shade disk and reposition it after mounting (see
fi g. 4).
• LP S1 mounting kit is supplied upon demand as an accessory, and allows for an easy
mounting of the probe on a mast. The mast maximum diameter shall not exceed 50 mm.
The operator will check that the mast height does not exceed the probe plane, in order
to avoid measurement errors due to any refl ection or shadow of the mast itself. To fi x the
probe to the mounting bracket, remove the shade disk by loosening the three screws,
then fi x the probe to the bracket and mount the white shade disk again.
• The probe should be thermally isolated from the mounting bracket, and the electrical
contact with the ground must be properly made.
Electrical Connections and requirements for electronic readout devices
• LP PHOT 02 probe does not require any power supply.
• LP PHOT 02 is supplied complete with fl ying female connector:
• UV-resistant, assembled cables are available with standard length 5m and 10m.
• Also available: converter and signal amplifi ers with 4…20mA current or 0…1V, 0…5V
and 0…10V voltage output.
• LP PHOT 02 is supplied on request with a PTFE, UV resistant, braided shield and 2 wire
cable. The color code is as follows:
black ’ braided shield
red ’ (+) positive pole of the signal generated by the detector
blue ’ (-) negative pole of the signal generated by the detector (in contact
with the housing)
Fig.6 shows the wiring diagram:
• LP PHOT 02 has to be connected to a millivoltmeter or to a data acquisition system with
input impedance higher than 100k©.
Maintenance:
In order to grant the best precision and accuracy in measurements, the outer dome must
be always kept clean; the cleaner you keep the dome, the higher the accuracy in measurements
will be. Washing can be made with water and standard lens paper; in case this
wouldn’t work, use pure ETHIL alcohol. After using alcohol, the dome must be washed
with water only. Sudden rise and fall in temperature throughout day and night, might cause
condensation to appear on the luxmeter dome; in this case the performed reading is highly
overestimated. To reduce condensation, the probe is provided with a cartridge containing
desiccant material, such as Silica-gel. Silica-gel effi ciency decreases in time while
absorbing humidity. Active silica-gel crystals are yellow colored, while they turn into blue
when they gradually loose power. To replace them, see instructions. Silica-gel generally
lasts from 2 to 6 months, depending on which climatic conditions you have and where the
probe works.
Calibration and measurements:
Photometric probe sensitivity, indicated as S (or calibration factor), allows determining
illuminance by measuring a signal in Volts at the probe ends. S factor is measured in
V/klux.
• Once the difference of potential (DDP) has been measured at sensor ends, Ee illuminance
is obtained through the following formula:
Ee= DDP/S
where;
Ee: indicates Illuminance expressed in klux,
DDP: indicates the potential difference expressed in mV and measured by the
voltmeter,
S: indicates the calibration factor expressed in mV/klux and shown on the probe
label (calibration factor is also mentioned in the calibration report).
Each photometric probe is factory calibrated and has its own calibration factor. Calibration
is carried out by using a standard illuminant A, as indicated in CIE publication N°
69 “Methods of characterizing illuminance meters and luminance meters: Performance,
characteristics and specifi cations, 1987�. Calibration is carried out by comparison with a
reference luxmeter, assigned to Delta Ohm Metrological Laboratory.
To get the best performances from LP PHOT 02, we strongly recommend to check calibration
annually.
Technical specifi cations:
Typical sensitivity: 0,5 ÷ 2,0 mV/klux
Response time: