Delta OHM LPUVB02 Manual de usuario

Operating manual

UVB Radiometer

LPUVB02

www.deltaohm.com

English

Keep for future reference.

LPUVB02 -2-V2.0

TABLE OF CONTENTS

1INTRODUCTION .................................................................................................... 3

2WORKING PRINCIPLE........................................................................................... 4

3INSTALLATION ..................................................................................................... 5

4ELECTRICAL CONNECTIONS.................................................................................. 8

5MEASUREMENT ..................................................................................................... 9

6MAINTENANCE.................................................................................................... 10

7TECHNICAL SPECIFICATIONS ............................................................................. 11

8SAFETY INSTRUCTIONS ...................................................................................... 12

9ACCESSORIES ORDERING CODES ....................................................................... 13

LPUVB02 -3-V2.0

1INTRODUCTION

The LPUVB02 radiometer measures the global irradiance in the UVB spectral range on

a flat surface (W/m2). In particular, the instrument spectral sensitivity is centred at

304 nm with a 5 nm bandwidth (FWHM - Full Width at Half Maximum).

The global irradiance is the sum of the direct solar irradiance and the sky diffuse irra-

diance on a surface parallel to the ground. Unlike the visible spectrum, where the di-

rect component prevails over the diffuse component, in the UVB spectral region the

light is strongly diffused by atmosphere and thus the two components are equivalent;

therefore it is of primary importance to measure both the components accurately.

The probe is typically used in the following fields:

•Monitoring the ozone layer. The radiation around 295…315 nm is strongly

absorbed by ozone located in the stratosphere, therefore each small variation of the

ozone layer corresponds to an increase or decrease of the UV radiation reaching the

ground.

•Effects of UVB radiation (the most harmful to human health) on living beings.

•UVB radiation measurement in workplaces.

The radiometer requires external power supply.

The radiometer is manufactured to operate for long periods without maintenance (if

powered correctly). This characteristic makes it suitable for use in meteorological sta-

tions.

A Pt100 temperature sensor is placed inside the radiometer in order to control its

temperature. Internal temperature must remain within the specified operating range,

otherwise measurements could be affected by systematic errors higher than those

stated. Exposure to temperature higher than +60 °C can alter the interferential filters

spectral characteristics.

LPUVB02 -4-V2.0

2WORKING PRINCIPLE

The LPUVB02 radiometer is based on a solid state photodiode whose spectral response

was adapted to that desired by using special interferential filters. In particular, the

used photodiode and filters have exceptional stability characteristics, both in tempera-

ture and over time. This allowed manufacturing of an instrument that does not need

heating, thus reducing energy consumption.

Particular attention has been given to filter design so as to make the instrument com-

pletely blind to wavelengths outside the pass-band of interest. The solar energy within

the 302 nm – 308 nm spectral band is only 0.01% of the total energy from the sun

reaching Earth's surface.

The relative spectral response curve is shown in Fig. 2.1 (in linear scale) and Fig. 2.2

(in logarithmic scale).

Fig. 2.1 Fig. 2.2

The LPUVB02 is provided with a 50 mm external diameter dome in order to supply a

suitable protection of the sensor to the weather agents. Quartz was chosen due to its

optimum transmission in the UV range.

The response in accordance with the cosine law has been obtained thanks to the par-

ticular shape of the diffuser and of the housing. The deviation between the theoretical

response and the measured one is shown in the Fig. 2.3.

Fig. 2.3

The excellent relation between the response of the radiometer and the cosine law al-

lows using the instrument also when the sun has a very low raising (the UVB diffuse

radiation increases as the sun moves away from the zenith, therefore the error on the

direct radiation, due to the imperfect response according to the cosine law, becomes

negligible on the measurement of the global radiation).

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

290 295 300 305 310 315 320

Lambda (nm)

Risposta Spettrale Relativa

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

290 310 330 350 370 390

Lambda (nm)

Risposta Spettrale Relativa

-2

010 20 30 40 50 60 70 80

Angle

% departure from theoretical response

Relative spectral response

% deviation from theoretical response

LPUVB02 -5-V2.0

3INSTALLATION

Before installing the radiometer, refill the cartridge containing the silica-gel crystals.

Silica gel absorbs humidity in the dome chamber; in case of particular climatic condi-

tions this humidity can cause condensation on the internal side of the dome and then

modify the measurement.

Do not touch the silica gel crystals with your hands and do not wet them while refilling

the cartridge. Carry out the following instructions in an environment as drier as possi-

ble.

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 sachet containing the silica gel (supplied with the radiometer).

5. Fill the cartridge with the silica-gel crystals.

6. Close the cartridge with its own cap, paying attention that the sealing O-ring is

properly positioned and undamaged.

7. Screw the cartridge to the radiometer body using a coin.

8. Check that the cartridge is screwed tightly (if not, the silica-gel life will be re-

duced).

9. Position the shade disk and tighten it with the screws.

10. The radiometer is ready for use.

The following picture shows the operations necessary to fill the cartridge with the sili-

ca-gel crystals.

Fig. 3.1: filling the silica-gel cartridge

Silica-gel cartridge

Sealed sachet of sili-

ca-gel crystals

Closing the cartridge

Filling

Perforated cap

LPUVB02 -6-V2.0

•The radiometer must be mounted in an easy-to-reach location in order to clean the

dome regularly and carry out maintenance. At the same time, make sure that no

buildings, constructions, trees or obstructions exceed the horizontal plane where

the radiometer lies. If this is not possible, select a site where obstructions in the

path of the sun from sunrise to sunset do not exceed 5 degrees of elevation.

•The radiometer must be located far from any kind of obstruction, which might re-

flect sunlight (or sun shadow) onto the radiometer itself.

•For fixing, use the holes on the radiometer body (remove the shade disk to access

the holes and reposition it after mounting) or the suitable accessories (see the fig-

ures below). In order to allow an accurate horizontal positioning, the radiometer is

equipped with a levelling device: the adjustment is made by means of the two lev-

elling screws that allow adjusting the radiometer inclination. The mast height does

not exceed the radiometer plane to avoid measurement errors caused by any re-

flection or shadow of the mast itself.

•It is preferably to thermally insulate the radiometer from its mounting bracket en-

suring, at the same time, a good electrical contact to ground.

Fig. 3.2: fixing holes and levelling device

Fixing holes ∅6 mm

Levelling

device

LPUVB02 -7-V2.0

Fig. 3.3: fixing accessories

LPUVB02 -8-V2.0

4ELECTRICAL CONNECTIONS

LPUVB02 has a 8-pole connector and uses the CPM12AA8U... optional cables.

The metallic housing of the radiometer should preferably be

grounded ( ) locally. In this case, do not connect the wire of the

cable corresponding to the housing to prevent ground loops.

Only if it is not possible to ground locally the metallic case of the

radiometer, connect the wire of the cable corresponding to the

housing to ground.

The radiometer has two analog outputs: one for temperature, normalized 0…1 V cor-

responding to -40…+60 °C, and one for UV irradiance, not normalized corresponding

to SV/(Wm-2), where S is the radiometer sensitivity.

The radiometer has to be connected to a power supply (7…30 Vdc) and instruments

with voltage input as shown in fig. 4.1. The load resistance of the instrument reading

the signal must be ≥10 kΩ.

Connector Function Color

Analog outputs ground (SGND)

Red

+Vout UV

Blue

Not connected

Cable shield (SH)

Shield

Power supply negative (GND)

Brown

6 +Vout Temperature White

Housing (C)

Black

Power supply positive (+Vdc)

Green

Fig. 4.1: LPUVB02 connections

Radiometer M12

male connector

CPM12AA8U… cable

Power supply

Instrument

with

voltage input

Instrument

with

voltage input

LPUVB02 -9-V2.0

5MEASUREMENT

Each radiometer is distinguished by its own sensitivity (or calibration factor) S ex-

pressed in V/(Wm-2) and shown in the label on the radiometer (and in the calibration

report).

The irradiance Eeis obtained by measuring with a multimeter the output voltage

Vout UV (difference of potential between +Vout UV and SGND) and applying the fol-

lowing formula:

Ee= Vout UV / S

where:

Eeis the irradiance expressed in W/m2;

Vout UV is the difference of potential expressed in V measured by the multimeter;

Sis the sensitivity of the radiometer expressed in V/(Wm-2).

It is possible that an offset of some tenths of millivolts (0.3 - 0.4 mV) be present on

the output signal. In this case it is recommended that the data be acquired also at

night and subtract the night-measurement offset from the performed measurements.

In the presence of a possible offset OFS (in Volt), the previous formula becomes:

Ee= (Vout UV – OFS) / S

Typically, the radiometer output signal, when exposed to the sun, does not exceed 1 V.

In order to fully exploit the radiometer features, the readout instrument should have 0.1

mV resolution.

The temperature Tin °C is obtained by measuring with a multimeter the output volt-

age Vout Temp (difference of potential between +Vout Temp and SGND) and apply-

ing the following formula:

T= (100 x Vout Temp) - 40

For example, supposing to read a voltage Vout Temp = 0.532 V, from the previous

formula we obtain that the radiometer internal temperature is:

T = (100 x 0.532) - 40 = 13.2 °C

Notes on the radiometer calibration:

The calibration factor of the radiometer is factory-determined by measuring the out-

put signal when the radiometer is hit by a parallel and homogeneous beam of light

over the entire surface of the diffuser. Calibration is performed with monochromatic

light at 304 nm.

Currently no international calibration standards for this type of radiometer exist;

therefore, the calibration coefficient only makes sense if the procedure followed to ob-

tain it has been specified. The user has to consider that the same radiometer calibrat-

ed with different procedures can have different sensitivity factors, as explained in the

article "Source of Error in UV Radiation Measurements", T. C. Larason, C. L. Cromer

issued in the "Journal of Research of the National Institute of Standards and Technol-

ogy" Vol. 106, Num. 4, 2001 (The article is available free of charge on the NIST web

site at the following address: https://nvlpubs.nist.gov/nistpubs/jres/106/4/j64lar.pdf).

LPUVB02 -10 -V2.0

6MAINTENANCE

In order to grant measurements high accuracy, it is important to keep the glass dome

clean. Consequently, the more the dome will be kept clean, the more measurements

will be accurate.

You can wash it using water and standard papers for lens. If necessary, use pure

ETHYL alcohol. After using alcohol, clean again the dome with water only.

Because of the high temperature changes between day and night, some condensation

might appear on the radiometer dome. In this case the performed reading is highly

over-estimated. To minimize the condensation, the radiometer is provided with a car-

tridge containing dessicant material (silica-gel). The efficiency of the silica-gel crystals

decreases over time while absorbing humidity. Silica-gel crystals are efficient when

their color is yellow, while they turn white/translucent as soon as they lose their

efficiency. Read instructions at chapter 3 about how to replace the silica-gel crystals.

Silica-gel typical lifetime goes from 2 to 6 months depending on the environment

where the radiometer works.

To exploit all the radiometer features, it is highly recommended that the calibration be

checked annually.

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