TROUBLESHOOTING AND CUSTOMER SUPPORT
Independent Verification of Functionality
Apogee SU-200 sensors are self-powered devices and output a voltage signal proportional to incident UV-A
radiation. A quick and easy check of sensor functionality can be determined using a voltmeter with millivolt
resolution. Connect the positive lead of the voltmeter to the white wire from the sensor and the negative lead (or
common) to the black wire from the sensor. Direct the sensor head toward the sun and verify the sensor provides
a signal. Blocking all UV radiation from the sensor should force the sensor signal to zero.
Compatible Measurement Devices (Dataloggers/Controllers/Meters)
SU-200 UV-A sensors are calibrated with a standard calibration factor of 10.0 W m
-2
per mV, yielding a sensitivity of
0.1 mV per W m
-2
. Thus, a compatible measurement device (e.g., datalogger or controller) should have resolution
of at least 0.1 mV to provide a measurement resolution of 1 W m
-2
.
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/
