Campbell Scientific CMP6-L, CMP11-L, and CMP21-L Pyranometers - Manual (Page 33)

CMP6-L, CMP11-L, and CMP21-L Pyranometers
9. Troubleshooting
Symptom: NAN, –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. Measure the impedance across the red and blue sensor wires. This should
be around 100 ohms plus the cable resistance (typically 0.1 ohm•m –1 ). If
the resistance is very low, there may be a short circuit (check the wiring).
Resistances somewhat lower than expected could be due to water ingress
into the sensor or enclosure connectors. If the resistance is infinite, there
is a broken connection (check the wiring).
4. Disconnect the sensor cable and check the voltage output from the sensor.
With the sensor located 8” below a 60 W incandescent light bulb the
voltage should be approximately 2.5 mV. No voltage indicates a problem
with the sensor.
Symptom: sensor signal is unrealistically high or low
1. Check that the right calibration factor has been properly entered into the
datalogger program. Please note that each sensor has its own individual
calibration factor.
2. Check the condition of the sensor cable.
Symptom: sensor signal shows unexpected variations
1. Check for the presence of strong sources of electromagnetic radiation
(radar, radio, etc.).
2. Check the condition and the connection of the sensor shield wire.
3. Check the condition of the sensor cable.
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