3
multiplying the UVB sensor reading by a factor of 40 index-cm
2
/mW, but this is
only an estimate. The UVA sensor reading cannot be used to estimate UV index.
Examples of experiments
•
Measure the UV intensity as a function of time throughout the day. Do you need
to worry about sunscreen at 8:00 in the morning?
•
Measure the UV transmittance of various sunglasses and regular glasses. Do your
sunglasses protect your eyes from both UVA and UVB? Can you get sunburn
through a car window?
•
Measure the UV transmittance of fabrics, both wet and dry. Does a wet T-shirt
provide much solar protection?
Calibration
To collect data you can:
1.
Use the calibration supplied by the sensor EEPROM memory.
2.
Use the calibration supplied in the standard sensor library of the Coach program.
The sensor name is
UVA sensor (0388) (CMA) (0 .. 19700 mW/m2)
.
3.
Calibrate the sensor. It is quite difficult to calibrate a UV sensor to read in
absolute units, since you must have a source of known UV intensity and spectral
distribution. More often you will simply want to calibrate the sensor in terms of a
relative intensity. In that case, you will point the sensor at a UV source (most
often the sun) and define that intensity as 100%. To perform this kind of
calibration, complete the following steps for a two-point calibration:
In Coach, select the sensor you are using in the Standard Sensor Library and drag
it to the position the sensor is connected on the panel, replacing the automatically
detected sensor icon. Right click on the sensor icon and choose “Edit Properties”
Set the unit to “%” and the maximum to 100.
The first point is your zero, with no light striking the sensor. Cover the tip of the
UV sensor with a clean opaque object. Enter 0 (zero) in “Y0” (first calibration
point). Set “X0” of this point to the voltage that is measured (shown in the
dialog).
Now allow full UV intensity to strike the sensor. Since the orientation of the
sensor affects the reading, it is best to hold the sensor in place with a ring stand
or other clamp. To point the sensor directly at the sun, make the shadow of the
sensor tube as small as possible. Enter 100 in “Y1” (second calibration point) and
enter the measured voltage in “X1”.
