Campbell Scientific LI190SB LI-COR Quantum Sensor - Manual (Page 11)

LI190SB Quantum Sensor
5.1 Input Range
An example showing how to determine the optimum input range for a given
sensor calibration and maximum photosynthetically active radiation (PAR) is
given below. This is an example only. Your values will be different.
-Sensor Calibration: Assume the sensor calibration is 8 µA/1000 µmoles
s
-1 m -2 (1000 µmoles = 1 mmole). The LI190SB outputs amperage which is
converted to voltage by a 604 ohm shunt resistor in the cable. To convert the
calibration from µA to millivolts, multiply the calibration by 0.604. The
example calibration changes to 4.83 mV/mmole s
-1 m -2 .
-Maximum PAR: A reasonable estimate of maximum PAR is 2 mmoles
s
-1 m -2 .
-Input Range Selection: An estimate of the maximum input voltage is
obtained by multiplying the calibration by the maximum expected PAR. That
product is 9.66 mV for this example. Select the smallest input range which is
greater than the maximum expected input voltage. In this case, the 15 mV
range for the 21X and CR7, and the 25 mV range for the CR10(X) and CR500
are selected.
Measurement integration time is specified in the input range parameter code.
A more noise free reading is obtained with the slow or 60 Hz rejection
integration. A fast integration takes less power and allows for faster
throughput.
MULTIPLIER
The multiplier converts the millivolt reading to engineering units. Commonly
used units and how to calculate the multiplier are shown in Table 5-1.
TABLE 5-1. Multiplier Required for
Flux Density and Total Fluxes
UNITS MULTIPLIER
µmole s -1 m -2 1000/C (flux density)
mmoles m -2 (1/C)*t (total fluxes)
C = (LI-COR calibration)*0.604
t = datalogger program execution interval in
seconds
Unit Conversions
microEinstien/µmole
(6.02 x 10 17 photons s -1 m -2 )/(µmoles s -1 m -2 )
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