Campbell CMP3-L, Инструкция по эксплуатации

Страница: 14 / 18

CMP3-L Pyranometer
Solution 1 – Change the multiplier in the instruction to (m*0.0001). This will
totalize MJ m
-2
instead of kJ m
-2
.
Solution 2 – Record the average flux density and later multiply the result by
the number of seconds in the output interval to arrive at total flux.
Solution 3 – Record the total flux using the high resolution format. The
drawback to high resolution is that it requires four bytes of memory per data
point, consuming twice as much memory as low resolution. Instruction 78 is
used to switch to high resolution in the Edlog dataloggers.
Dataloggers that are programmed in CRBasic can be programmed to store data
in IEEE4 format which can represent a wider range of numbers so this is not a
consideration for them.
6. Maintenance
Inspect and clean the outer dome at regular intervals, e.g. every week or so.
Clean any accumulated dust, etc. off the dome and pyranometer body using a
soft cloth dampened with water or alcohol. Check that there is no
condensation within the dome.
It is also important to check the data returned from the sensor as it will show
the first indication of a fault. When doing this you should be aware of several
expected phenomena that can cause strange measurements. In particular on
clear, windless nights the outer dome temperature of horizontally placed
pyranometers can fall as low as the dew point temperature of the air, due to
infra-red radiation exchange with the cold sky. (The effective sky temperature
can be 30°C lower than the ground temperature, which results in an infra-red
emission of -150 Wm
-2
). If this happens, dew, glazed frost or hoar frost can be
precipitated on the top of the outer dome and can stay there for several hours in
the morning. An ice cap on the dome is a strong diffuser and can increase the
pyranometer signal by up to 50% in the first hours after sunrise.
The calibration of the CMP3-L may drift with time and exposure to radiation.
Recalibration every two years is recommended. The sensor should be returned
to Campbell Scientific, the manufacturer, or a calibration lab with facilities to
calibrate radiation sensors.
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. 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). 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
10