Delta OHM LP PHOT 02 Manual De Instrucciones página 3

LP PHOT 02
LP PHOT 02 probe measures illuminance (lux), defined as the ratio
between the luminous flux (lumen) passing through a surface and the surface area
(m ).
2
The spectral response curve of a photometric probe is similar to the human eye
curve, known as standard photopic curve V(λ). The difference in spectral response
between LP PHOT 01 and the standard photopic curve V(λ) is calculated by means
of the error f .
'
1
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 filters to adapt it to the response of the human eye. The
typical relative spectral response curve is shown in fig.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 fig.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 refilled. 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 refilling the silica-gel
cartridge. Carry out the following instructions in a dry environment:
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 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 refill 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 find 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 reflect 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 6mm-diameter 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 fig. 4).
• LP S1 mounting kit (fig. 5) 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 reflection or
shadow of the mast itself. To fix the probe to the mounting bracket, remove the
shade disk by loosening the three screws, then fix 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.
• Two models of LP PHOT 02 are available:
with a 5 m output cable (LP PHOT 02-5)
with a 10 m output cable (LP PHOT 02-10).
• LP PHOT 02 is supplied with a PTFE, UV resistant, braided shield and 2 wire
cable. The color code is as follows:
braid → 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 100kΩ.
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 efficiency 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, E
illuminance is obtained through the following formula:
where;
E : indicates Illuminance expressed in klux,
e
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 specifications, 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 specifications:
Typical sensitivity:
Response time:
Impedance:
Measuring range:
Viewing angle:
Spectral range:
Operating temperature:
Error f'
1
Cosine response/directional error:
Long term instability (1 year):
Non-linearity:
Temperature response:
Weight:
Dimensions:
E = DDP/S
e
0,5 ÷ 2,0 mV/klux
<0.5 sec (95%)
0.5 ÷ 1 KΩ
0-200 klux
2π sr
Standard photopic curve
-40 °C ÷ 80 °C
<9 %
< 8 % (between 0° and 80°)
<±3 %
<1 %
< 0.1%/°C
0.90 Kg
fig. 4
e