Campbell Scientific LI200X-L LI-COR Silicon Pyranometer - Manual (Page 14)

LI200X Pyranometer
Handle the sensor carefully when cleaning. Be careful not
to scratch the surface of the sensor. CAUTION
Recalibrate the LI200X every two years. Obtain an RMA number before
returning the LI200X to Campbell Scientific, Inc. for recalibration.
6. Calibration
LI200X pyranometers output a current that is proportional to the incoming
solar radiation. Each LI200X has a unique calibration factor. A variable shunt
resistor in the cable converts the current to the voltage measured by the
datalogger. Campbell Scientific sets the shunt resistor so that the pyranometer
outputs 5 mV kW
-1 m 2 .
The resistor value is found using Ohms law. The resistance is found by
dividing the desired output voltage by the calibrated current output. For
example, a pyranometer with a calibration of 92
μA kW -1 m 2 , will have the
resistor set to:
10
54.35 Ω = − − 5 0 092 1 2 1 2 mV kW m mA kW m . .
7. Troubleshooting
Symptom: -9999 or radiation values around 0
1. Check that the sensor is wired to the Differential channel specified by the
measurement instruction.
2. Verify that the Range code is correct for the datalogger type.
3. Disconnect the sensor leads from the datalogger and use a DVM to check
the voltage between the red (+) and the black (-) wires. The voltage
should be 0 – 5 mV for 0 to 1000 Wm
-2 radiation. No voltage indicates a
problem with the photodiode, cable, or the variable shunt resistor.
Symptom: Incorrect solar radiation
1. Make sure the top surface of the sensor head is clean, and that the sensor
is properly leveled.
2. Verify that the Range code, multiplier and offset parameters are correct
for the desired engineering units and datalogger type.