FAQ

• Net Radiometers

  • What color code is used when there is an extended cable on the NR LITE?

    • Sometimes it happens that the colors of the cables are different when you order extended cables. Usually there is added a page in the manual where this is mentioned.
      
      Standard = extended
      White = white
      Green = blue
      Black = black
      

  • For the NR Lite, we want to use wind correction, but we don't understand the manual

    • The correction factor in the manual could indeed be written more carefully. It says dividing by (1+x.V^3/4) this refers to the calibration factor. Better is to say the output should be multiplied with a factor (1+x.V^3/4).

  • For the CNR 1, what is the ideal constant current source for the PT-100?

    • There is no general value to use but some criteria to keep in mind to select a Pt-100 current.
      
      Because the Pt-100 (unlike a thermocouple) needs current, it is advised to keep this current as low as possible to avoid self-heating of the Pt-100 by its own current. The Pt-100 measuring device (like our data loggers CC 48, CR10X) has a fixed current, in such a way that the voltage over the Pt-100 is matched with the Pt-100 (voltage) measuring input of these loggers.
      
      In general the current for a Pt-100 is indeed between 0.1 and 1 mA. This would result (@ 0ºC) in a voltage over the Pt-100 of 10 mV or 100 mV. Therefore the current can also be selected depending on the available input range of the measuring device. The error introduced by self-heating, when using a 1 mA current, is quite low (< 0.2ºC) also because the Pt-100 is very well connected to the body of the CNR1. When the heater of the CNR1 is on, the error introduced by the heater in measuring the body temperature is typical 2ºC (see manual).
      
      The benefit of a larger current (1 mA) is that electrical disturbances have less effect when the current is larger.
      
      To summarize these facts I would say, 1 mA measuring current is accurate enough, but the output voltage in this case (0.1 Volt) has to match the measuring input range.

  • What is the response time for CNR 1 sensors?

    • Response time for CNR1 sensors: 5 s (63%) en 18 s (95%)

  • Does the CNR 2 use the same sensor as the NR Lite(2) without wind-breaking domes? Or does it have separate thermopiles for short and long wave radiation?

    • Both instruments use thermopiles, but the dome over the thermopile determines what kind of radiation passes through and reaches the thermopile. A  thermopile  is normally protected by a single or double dome to reduce offsets caused by sudden temperature changes like wind.

      The CNR 2 uses two glass domes to cover the pyranometer and two silicon domes to cover the pyrgeometers. It uses TWO thermopile detectors (1 for each of the two pyranometers and 1 for each of the two pyrgeometers) and provides two separate outputs. One NETTO for short wave (solar spectrum) and one NETTO for long wave radiation.(Far Infrared spectrum).

      So yes, the CNR 2 has separate thermopiles to measure Far Infrared and Solar radiation and so do the other CNR net radiometers.

      The detector from the NR Lite(2) is not protected and I sin direct contact with the weather conditions. Therefore it cools down a lot faster by the wind, which effects the accuracy of the measurements. The NR Lite(2) uses NO dome. It uses only TWO detectors with a PTFE coating and provides ONE single output for NETTO short wave- and long wave radiation.  It uses one thermopile to measure the full spectrum of Far Infrared and solar radiation.

  • How come the NR Lite(2) specs refer to a continuous range between 200 and 100,000 nm, while the CNR 2 specs refer separately for the short and long wave radiation ranges?

    • The difference between the NR Lite(2) and CNR 2 lies in the material used to cover the thermopiles.

      CNR 2 uses glass domes for the pyranometers (that measure short wave radiation) that have a bandwidth of 300 nm to 2800 nm. It uses silicon domes for the pyrgeometers (that measure long wave radiation) that have a bandwidth of 4500 nm to 42000 nm. This leaves a gap between 2800 nm and 4500 nm. This is the so called atmospheric window where very little radiation comes in (see picture below).

       

      The NR Lite(2) uses NO domes. It uses two detectors with a PTFE coating which have a bandwidth of 200 nm to 100.000 nm.