UVP UVX Radiometer - Manual (Page 15)

UVX Radiometer 15
Sensor Details
Sensor Characteristics
Solarization of Filters
Shortwave ultraviolet radiation causes a decrease in sensor output that is proportional to total exposure.
This is due to changes in the transmission properties of the filters; a phenomenon called solarization.
Solarization is especially noticeable in the 254nm sensors. Only a small amount is seen in the midrange
(310nm) sensors and virtually none in the longwave (365nm) sensors. In typical shortwave sensors
operating at 254nm, solarization begins immediately and reduces the sensor output at a rate of about
0.4% per mW-h/cm
2
.
To correct this problem, the UVX shortwave (254nm) filters incorporate a new design
that significantly reduces the short term solarization effect. This is shown in Figure 5 where it can be seen
that solarization does not begin to take effect until after 50mW-h/cm
2
total dosage and then at the reduced
rate of 0.1% per mW-hcm
2
.
Spectral Response Curves
Figures 6, 7 and 8
show the typical spectral response characteristics of the UVX 25, 31 and 36 Series
Sensors (respectively). In each case the absolute response curve is typical. Individual sensors may
exhibit variations in response at wavelengths distant from the calibration wavelength, but all are
accurately calibrated to a response of 1.00 at the specified calibration wavelength.
Sensor Temperature Coefficient
An added feature of the UVX Series Sensors is that special circuitry has been incorporated to reduce the
temperature induced errors present in all solid state detectors. The result is a sensor with a nominal
overall temperature coefficient of only ±0.04%/°C from 0 to 40°C.
Sensor Response Versus Incidence Angle
The UVX Series Sensors incorporate a unique diffuser at the incident surface. This diffuser enables the
sensor to detect radiation to incidence angles of ±81 from the normal. Figure 9 shows the real response
of the UVX Series Sensors, as compared to the perfect cosine response curve, with sufficient detail that
analytical corrections can be made where accurate measurements of large UV sources are required.
Calibration Information
Authorized Calibration Service
Please note this section refers to the calibration of sensors, not the Radiometer. UVP maintains a
calibration laboratory to recalibrate UVX Series Sensors. A nominal fee is charged for this service. To
verify such a recalibration, the date of the most recent calibration is placed on the label attached to the
sensor and a certificate of calibration is included with the returned sensor. It is suggested that the first
recalibration take place 6 months after the initial unpacking and use of the use of the unit, not 6 months
from the initial calibration date on the sensor. Periods of time spent sealed on the dealer's shelves have
negligible effect on the accuracy of the calibration.