Campbell Scientific LI200X LI200X-L LI-COR Silicon Pyranometer - Page 16

Appendix A. LI200S Pyranometer A.3 Input Range The following is an example of how to determine the optimum input range for a given sensor calibration and maximum expected irradiance. This is an example only. Your values will be different. This example uses the calibration provided by LI-COR, Inc. Assume that the sensor calibration is 87 µA kW-1 m2. The pyranometer outputs current which is converted to voltage by the 100 Ω shunt resistor in the cable or on the wiring panel. To convert the calibration from current to voltage, multiply the LI-COR calibration by 0.1 KΩ (shunt resistor). The example calibration changes to 8.7 mV kW-1 m2. A reasonable estimate of maximum of irradiance at the earth's surface is 1 kW m-2. Thus, an estimate of the maximum input voltage is obtained by multiplying the calibration by the maximum expected irradiance. In this example that product is 8.7 mV. Now, select the smallest input range which is greater than the maximum expected input voltage. In this case the 25 mV slow range for the CR10 and 15 mV slow range for the 21X are selected. A.4 Multiplier The multiplier converts the millivolt reading to engineering units. The most common units and equations to calculate the multiplier are listed in Table A.4-1. TABLE A.4-1. Multipliers Required for Average Flux and Total Flux Density for SI and English Units for a LI200S Pyranometer UNITS W m-2 MJ m-2 kJ m-2 cal cm-2 min-1 cal cm-2 MULTIPLIER (1/C) * 1000 t * (1/C) * 0.001 t * (1/C) (1/C) * (1.4333) t *(1/C) * (0.02389) PROCESS Average Total Total Average Total C = (LI-COR calibration) * 0.1 t = datalogger execution interval in seconds A-2