Apogee Instruments SQ-642-SS Owner's Manual - Page 14
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TROUBLESHOOTING AND CUSTOMER SUPPORT
Independent Verification of Functionality
Apogee SQ-642 and SQ-645 Quantum Light Pollution Sensors provide an amplified voltage 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 zero.
Compatible Measurement Devices (Dataloggers/Controllers/Meters)
-2
-1
SQ-600 Quantum Light Pollution Sensors are calibrated with a standard calibration factor of 0.08 µmol m
s
per
-2
-1
-2
-1
mV (SQ-642) or 0.04 µmol m
s
per mV (SQ-645), yielding a sensitivity of 12.5 mV per µmol m
s
(SQ-642) or 25
-2
-1
mV per µmol m
s
(SQ-645). Thus, a compatible measurement device (e.g., datalogger or controller) should have
resolution of at least 12.5 mV (SQ-642) or 25 mV (SQ-645) in order to provide photon flux density resolution of 1
-2
-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
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:
(http://www.apogeeinstruments.com/how-to-make-a-weatherproof-cable-splice/).