Campbell CNR4 Instrukcja Obsługi Pobierz pdf (Strona 25)

CNR4 Net Radiometer

TABLE 7-1. Resistance values versus CNR4’s thermistor temperature in °C

Temperature

[

Resistance

[

Ω

]

Temperature

[

Resistance

[

Ω

]

Temperature

[

Resistance

[

Ω

]

–7

–6

–5

–4

–3

–2

–1

41070

39140

37310

35570

33930

32370

30890

10840

10410

10000

9605

9227

8867

8523

3504

3385

3270

3160

3054

2952

2854

Relatively small errors occur when the CNR4 is not in thermal equilibrium.

This happens for example when the heater is on, or when the sun is shining.

When the heater and ventilator are on, the largest expected deviation between

the real sensor temperature and the thermistor reading is 1 degree. This results

in a worst case error for the pyrgeometer of 5 W/m

. When the sun is shining,

the largest expected deviation between the real sensor temperature and the

thermistor reading is again 1 degree. This results in a worst case error for the

pyrgeometer of 5 W/m

The thermistor will not give a good indication of ambient air temperature; at

1000 W/m

solar radiation, and no wind, the instrument temperature will rise

approximately 5 degrees above the ambient temperature.

The offsets of both the pyranometers and the pyrgeometers might be larger

than 5 W/m

if large temperature gradients are forced on the instrument (larger

than 5 K/hr); for example, when rain hits the instrument. This occurrence can

be detected using the thermistor readout, and can be used for data filtering.

The thermistor measurement is calculated by the datalogger, using the Half-

Bridge Measurement instruction, which requires one voltage excitation and

one single-ended analog channel.

Alternatively, you can use the Pt-100 to make the temperature measurement.

In order to make the temperature measurement, using the Pt-100 sensor, you

will need one current excitation channel, and one differential analog channel.

TABLE 7–2 shows the Pt-100 resistance values as a function of temperature.

Please refer to Appendix B.4, CR3000 Program for Measuring Pt-100

Temperature Sensor, for a sample program to measure Pt-100.

1 2 ... 20 21 22 23 24 25 26 27 28 29 30 ... 69 70

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