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).
