User Manual

Sensor Calibration
Apogee SQ-214, SQ-224 models have a standard PPFD calibration factor of exactly:
250.0 µmol m
-2
s
-1
per mA with a 4 mA offset
Multiply this calibration factor by the difference of the measured mA signal and the 4.0 mA offset to convert
sensor output to PPFD in units of µmol m
-2
s
-1
:
Calibration Factor (250 µmol m
-2
s
-1
per mA) * [Sensor Output Signal (mA) – Offset (4.0 mA)] = PPFD (µmol m
-2
s
-1
)
250 * (12.0 – 4) = 2000
Example of PPFD measurement with an Apogee
quantum sensor. Full sunlight yields a PPFD on a
horizontal plane at the Earth’s surface of
approximately 2000 µmol m
-2
s
-1
. This yields an
output signal of 12.0 mA. The signal is converted to
PPFD by subtracting the 4.0 mA offset and then
multiplying by the calibration factor of 250 µmol m
-2
s
-1
per mA.
Sensor Output
12.0 mA
Full Sunlight
(2000 µmol m
-2
s
-1
)