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CNR4 Net Radiometer

7. Datalogger Programming

The CNR4 outputs four voltages that typically range from 0 to 15 mV for the

pyranometers, and ± 5 mV for the pyrgeometers. A differential voltage

measurement is recommended because it has better noise rejection than a

single-ended measurement. If differential channels are not available, single-

ended measurements can be used. The acceptability of a single-ended

measurement can be determined by simply comparing the results of single-

ended and differential measurements made under the same conditions.

Additionally, one voltage excitation channel and one single-ended analog

channel are required to make the temperature measurement of the sensor body,

using the thermistor.

7.1 Sensor Sensitivity

Unlike the CNR1, the CNR4 comes with four different sensor sensitivity

values for four separate probes. The CNR4 sensor comes with two copies of

‘Certificate of Calibration’ by the manufacturer. They show the sensor serial

number and sensitivity values for four individual probes: one copy for

pyranometers, and another copy for pyrgeometers. The serial number and

sensitivity values are also shown on a label affixed to the bottom of the sensor.

If you choose to attach the CNF4, heater/ventilator unit to the CNR4, this label

showing the serial number and sensitivity values will be covered. After

attaching the CNF4 heater/ventilator, make sure to affix the extra label to the

bottom of the CNF4, heater/ventilator unit so that you will have the label on a

visible location. The extra label containing the serial number and sensitivity

values is supplied with the purchase of the CNR4. Please refer to the

Appendix B for more details.

The sensor sensitivity is in the units of μV/(W/m

). This needs to be converted

into the units of (W/m

)/mV to be used as a multiplier parameter inside the

datalogger program. To convert the units, divide the sensor sensitivity value

into 1000. For example, if the sensitivity is 7.30 μV/(W/m

), the multiplier is

1000/7.3 = 136.99 (W/m

)/mV.

7.2 Example Programs

7.2.1 Example 1, CR1000 Program Using Differential Measurements

The Program Example 1 requires four differential channels to measure the four

radiation outputs and one excitation channel and one single-ended channel to

measure the thermistor. The program measures the sensors every 1 second,

performs the on-line processing of the data and stores the following processed

data to a data table called cnr4_data once every 60 minutes. It also stores the

raw time-series data from CNR4 to data table called cnr4_ts.

Minimum Battery voltage

Sample Datalogger panel temperature

Average Short-wave radiation (pyranometer up)

Average Short-wave radiation (pyranometer down)

Average Long-wave radiation (pyrgeometer up)

Average Long-wave radiation (pyrgeometer down)

Average CNR4 thermistor temperature (degrees C)

Average CNR4 thermistor temperature (Kelvin)

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 59 60

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