Campbell CVF4 Spezifikationen PDF herunterladen (Seite 35)

CNR4 Net Radiometer

8.2 Testing the Pyrgeometer

It is assumed that the zero offset is no more than a few watts per square meter

(see second test in section 8.1).

The CNR4 body and the ambient air should be at the same temperature as

much as possible. Let the pyrgeometer rest for at least five minutes to regain

its thermal equilibrium. Set the voltmeter to its most sensitive range. To test if

the pyrgeometer is working properly, put your hand in front of the

pyrgeometer. The thermal radiation from your hand will cause the

pyrgeometer to generate a positive voltage when the surface temperature of

your hand is higher than the pyrgeometer temperature. The pyrgeometer will

generate a negative voltage if the hand is colder. The signal is proportional to

the temperature difference (see the rule of thumb in section 5.6). The radiation

that is emitted by the hand can be calculated by dividing the pyrgeometer

output by the sensor’s sensitivity value, and subsequently correcting for the

temperature, according to equation 5-2. If there are still no faults found, your

pyrgeometer is probably doing fine.

8.3 Testing the Thermistor

Using a multimeter, measure the resistance between the black and white wires

of the thermistor, and compare the value with the resistance values listed in

Table 5-1. The resistance should be around 10 k Ω at 25 °C, and the cable

resistance should add about 0.026 Ω per each foot of cable. When in doubt the

Pt-100 resistance (temperature) can be checked as well for reference.

8.4 Testing the Pt-100

Using a multimeter, measure the resistance between the two opposite wires of

the Pt-100 (gray-yellow, gray-brown, green-yellow, green-brown), and

compare the measured value with the resistance values listed in Table 5-2. The

resistance should be above 100 Ω (100 Ω at 0 °C), and the cable resistance

should add about 0.026 Ω per each foot of cable. When in doubt the thermistor

resistance (temperature) can be checked as well for reference.

9. Maintenance and Recalibration

The CNR4 is weatherproof, and is intended for a continuous outdoor use. The

materials used in pyranometer and pyrgeometer are robust and require very low

maintenance. For optimal results, however, proper care must be taken.

9.1 Cleaning Windows and Domes

The radiometer readings can be reduced if domes and windows are not clean.

The site operator should check the windows and domes of the CNR4 regularly,

and clean them as needed. Use distilled water or alcohol as cleaning solution,

being careful not to scratch the windows and domes during cleaning.

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Campbell CVF4 Spezifikationen Seite 35