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TROUBLESHOOTING AND CUSTOMER SUPPORT
Independent Verification of Functionality
Apogee SQ-644 Quantum Light Pollution Sensors provide a 4-20 mA output that is proportional to incident photon
flux density for the 340-1040 nm wavelength range. A quick and easy check of sensor functionality can be
determined using a DC power supply and an ammeter. 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 ammeter to measure across the white wire (signal output) and green wire (signal ground). 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 4 mA.
Compatible Measurement Devices (Dataloggers/Controllers/Meters)
-2
-1
SQ-644 Quantum Light Pollution Sensors are calibrated with a standard calibration factor of 12.5 µmol m
s
per
-2
-1
mA, yielding a sensitivity of 0.08 mA per µmol m
s
. Thus, a compatible measurement device (e.g., datalogger or
controller) should have resolution of at least 0.08 mA in order to provide photon flux density resolution of 1 µmol
-2
-1
-2
-1
m
s
and resolution of at least 0.008 mA in order provide photon flux density resolution of 0.1 µmol m
s
.
An example datalogger program for Campbell Scientific dataloggers can be found on the Apogee webpage at
https://www.apogeeinstruments.com/downloads/#datalogger.
Cable Length
Shortening or splicing on additional cable in the field is generally not a problem for the current output of the SQ-
644. However, adding cable will result in a greater resistive load, which should be taken into consideration when
determining the maximum resistive load that the sensor will drive (see section above on Compatible Measurement
Devices). 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:
(http://www.apogeeinstruments.com/how-to-make-a-weatherproof-cable-splice/).