TROUBLESHOOTING AND CUSTOMER SUPPORT
Independent Verification of Functionality
Apogee SU-202 and SU-205 sensors provide an amplified voltage output that is proportional to incident UV-A
radiation. A quick and easy check of sensor functionality can be determined using a DC power supply and a
voltmeter. Power the sensor with a DC voltage by connecting the positive voltage signal to the red wire from the
sensor and the negative (or common) to the black wire from the sensor. Use the voltmeter to measure across the
white wire (output signal) and black wire. Direct the sensor head toward a light source and verify the sensor
provides a signal. Increase and decrease the distance from the sensor head to the light source to verify that the
signal changes proportionally (decreasing signal with increasing distance and increasing signal with decreasing
distance). Blocking all radiation from the sensor should force the sensor signal to zero.
Compatible Measurement Devices (Dataloggers/Controllers/Meters)
SU-202 UV-A sensors are calibrated with a standard calibration factor of 0.04 W m
-2
per mV, yielding a sensitivity of
25 mV per W m
-2
, and the SU-205 UV-A sensors are calibrated with a standard calibration factor of 0.02 W m
-2
per
mV yielding a sensitivity of 50 mV per W m
-2
. Thus, a compatible measurement device (e.g., datalogger or
controller) should have resolution of at least 25 mV or 50 mV to provide a measurement resolution of 1 W m
-2
respectively.
An example datalogger program for Campbell Scientific dataloggers can be found on the Apogee webpage at
http://www.apogeeinstruments.com/content/UV-Sensor.CR1
Zero Offset Error
With the use of certain dataloggers it is possible to measure a non-zero voltage (zero offset) when the sensor
output should be zero (no UV irradiance incident on diffuser). This offset can be corrected by adding or subtracting
the measured offset from the sensor output. However, if the offset is substantial, and your sensor is outputting
unrealistic values then it may need to be recalibrated. In this case, contact Apogee customer support to recalibrate
the sensor.
Cable Length
When the sensor is connected to a measurement device with high input impedance, sensor output signals are not
changed by shortening the cable or splicing on additional cable in the field. Tests have shown that if the input
impedance of the measurements device is greater than 1 mega-ohm there is negligible effect on the calibration,
even after adding up to 100 m of cable. All Apogee sensors use shielded, twisted pair cable to minimize
electromagnetic interference. For best measurements, the shield wire must be connected to an earth ground. This
is particularly important when using the sensor with long lead lengths in electromagnetically noisy environments.
Modifying Cable Length
See Apogee webpage for details on how to extend sensor cable length at
http://www.apogeeinstruments.com/how-to-make-a-weatherproof-cable-splice/
