FAQ

  • Atmospheric Science Instruments

      • Scintillometers

        • How does WINLAS correct for an incorrect potentiometer setting?
          • In case the path length has been set incorrectly during the installation of an LAS scintillometer, WINLAS can correct the Cn2 data.

            In order to do so please use the following procedure.

            Step 1: 

            After entering the relevant info in the parameters section, enter the path length setting set with the potentiometer of the LAS receiver in meters and enter the correct path length in the input field below.

             

             Select OK

             Step 2:

             Select ‘Run…’  in the WINLAS file menu.

             Result:

            WINLAS will now process the Scintillometer Cn2 data using a correction algorithm for the actual path length.

             Theoretical background

             WINLAS corrects the path length in the following way:

            Using the following equation to derive the intensity fluctuation data from the recorded Cn2 values calculated by the LAS using the incorrect path length setting.

                                            (Wang et al., 1978)

             

            Where 

            D

            Aperture diameter    ~ 15cm



            L    

            Initial path length

            σlnI

            Variance of log intensity

             The equation is re-written to yield the variance of the intensity fluctuations:

                            

            And finally re-calculate Cn2 with the correct path length:

                            

            End of FAQ.

        • How can I calculate the Cn2 Saturation limit for my LAS MkI Scintillometer?
          • A scintillometer measures the path weighted structure parameter of air, Cn2, using an optical transmitter and receiver.

            In certain cases of relatively high Cn2 values the signal can become saturated depending on the diameter of the lens, wavelength and path length.

            The so called saturation limit for Cn2 can be derived using the following formula (Ochs and Hill 1982)

            Cn2 < 0.18.D5/3.L-8/3.λ2/6

            Where:

            D

            the diameter of the scintillometer

            [0.15m or 0.3 m]

            L

            the path length

            [m]

             

            λ

            the emitted wavelength

            [880 nm]

            In the calculation tool below, you can calculate the saturation limit for the LAS and X-LAS scintillometer as a function of Path length.

            Path length [m]
            Saturation Limit LAS (10cm) in m-2/3

             

            Saturation Limit LAS (15cm) in m-2/3

             

            Saturation Limit X-LAS (30 cm) in m-2/3

             

             

        • How do I set the path length using the Potentiometer on the LAS MkI receiver?
          • Once the LAS has been installed and properly aligned the Path Length dial knob at the receiver control panel must be set for the correct distance between the transmitter and the receiver. The Path Length dial knob has 10 turns maximum with a vernier counter and a locking mechanism.

            These graduations are NOT in units of distance! The precise path length must first be converted to a dial knob setting (Pot) using the following relationship for the LAS. The equations below can be used to find the correct Potentiometer setting as a function of pathlength for the LAS and X-LAS.

            In addition you can use the calculation tool below to calculate the correct potentiometer setting for the (X)LAS.

            LAS:

                        

            X-LAS:

                       

             

            Path length [m]
            Potentiometer Setting [LAS]

             

            Potentiometer Setting [X-LAS]

             

             

        • How do I connect an (X)LAS MkI to a CR10x or CR1000 data logger?
          • The LAS and X-LAS scintillometer can be connected to the CR10x and CR1000 data loggers from Campbell Scientific.

            Configuration examples for these data loggers can be viewed on this page, here:

            CR10x

            CR1000

             

            Campbell CR10x Data Logger

            A (X)LAS scintillometer can be connected to a Campbell CR10x data logger using a 2:1 voltage divider like VDIV2.1 from Campbell. The reason for this is the fact that the LAS has an output of 0..-5V and the standard input range of the CR10x is ± 2.5V. 

            The procedure is as follows:

            1. Upload the example CR10x configuration file (or your own) to the data logger. Please note that this will erase pre-existing data! The example configuration file can be downloaded here: LAS_CR10x.CSI.
            2. Connect the LAS to the CR10x using the following wiring diagram:

            Collect data using the data logger and check for normal operation of the Scintillometer data collection.

            Campbell CR1000 Data logger

            The connection procedure for the CR1000 is similar to the CR10x. The same connection to the terminals for differential measurement of the LAS signals can be used. However, the input range of this data logger is ± 5V so a voltage divider is not required.

            A example configuration for the CR1000 in LoggerNet format can be found here: LAS_CR1000.CR1

             

            End of FAQ.

        • I would like to measure atmospheric turbulence, Cn2 – what do I need?
            • LAS MkII or XLAS MkII (includes transit case)
            • Plus two 12 VDC power supplies (CVP1 LAS MkII power supply x2), and for mounting, two tripods (heavy duty tripod package x1) or secure mounting structure, if required.

        • I would like to measure sensible heat flux – what do I need?
            • LAS MkII or X-LAS MkII (includes transit case)
            • Meteorological sensor kit
            • Plus two 12 VDC power supplies (CVP1 LAS MkII power supply x2), and for mounting, two tripods (heavy duty tripod package x1) or secure mounting structure, if required.

        • What applications can scintillometry be used for?
            • Surface energy balance / radiation budget studies
            • Validating satellite data / ground truth
            • Weather forecasting
            • Irrigation / water management (shortage) - evaporation from rivers, crops and water storage
            • Hydrology
            • Micro-meteorology / turbulence studies
            • Land-atmosphere exchange / boundary layer meteorology
            • Agriculture, forestry, Biology, plant evapotranspiration, plant interactions and geosciences
            • Forest fire warning
            • Optical propagation conditions
            • Turbulence, including defense and laser propagation

        • What are the advantages of the LAS Method?
            • No absolute instrument calibration is needed
            • Low maintenance, no moving parts
            • Low power consumption
            • Integral data logging

            Remote measurement:

            • Path-averaged Cn2 measurements up to 4.5km
            • Representative for large area
            • Comparable to grid box size of numerical models and pixel size of satellite images
            • No structure / tower influence on measurements (spatial weighting function / no flow distortion by instrument). A tower, building or valley sides can be used to gain height, and they (the support structure) has no or little effect on the measurements as the LAS responds more strongly to the middle of the path and not at all at the ends.
            • Easy installation - Can measure over terrain which is difficult to access, or which you do not want to disturb.
            • Does not disturb the measurements and measurement area (such as a protected wildlife area).

            Rapid measurements:

            • Allows study of fast processes, such as plant transpiration and canopy resistance, which change on a timescale of a minute with changing solar radiation and clouds

            Point measurements (alternative methods to LAS)

            • Eddy-Covariance method (need averaging of at least 30 minutes to catch all the eddy sizes. Measures the inner scale of turbulence i.e. the momentum flux, so can be combined with gas flux measurements easily)
            • Bowen-Ratio Energy Balance method
            • Flux-profile method (MOST)
            • Results extremely localised
            • Influence of structure / flow distortion

        • What are the advantages of the Kipp & Zonen LAS MkII?
          • The LAS MkII Large Aperture Scintillometer provides continuous measurements over path lengths from 100 m up to 4.5 km. It is the only scintillometer currently available with a built-in display and control-pad. It has internal digital processing to make calculations in-situ and to store data and results. Measurements are on a comparable scale to the pixel size of satellite instruments, making LAS MkII ideal for ground-truthing applications. The LAS MkII is convenient to use due to low power consumption, integrated data logger, accurate reference time from GPS, and works reliably in cold environments.

            The advantages of the LAS MkII are the following:

            • Low power consumption due to the use of single LED and good collimation of the beam so little light is thrown away. This makes it practical for use with solar panel / battery electrical supply in field applications.
            • Contains an integrated lens heater to avoid freezing of the instrument or condensation on the window, and provides good data in cold environments.
            • More compact design with integrated datalogger, display and setup buttons which allows the configuration of the LAS without the need of an additional computer and cables / power supplies, and nothing needs to be taken apart. This makes transport and installation much easier.
            • Direct connection of the meteorological sensor kit to the receiver instead of to a separate interface or data logger.
            • Operates over the full data range of Cn2 of 1x10-17 to 1x10-11 (= 6 orders of magnitude).
            • The transmitter (as well as the receiver) can be tilted to align for optimum signal gain, and minimal power usage.
            • A supplied GPS antenna, mounted on the receiver, results in very accurate time from the satellites of the Global Positioning System, logged with the measured data.
            • The complete LAS MkII system is shipped in one rugged aluminium transport case, which can be used in the field to store equipment if needed as the case is waterproof. Lined with custom fitted foam, it protects the LAS instrument from repeated shocks of 10 to 20g without losing calibration or alignment.
            • A certificate is supplied with each instrument detailing a calibration against a reference instrument, performed outdoors for 2 weeks at the factory.
            • A large aperture scintillometer (LAS) has less saturation problems compared to a laser scintillometer, or one with a smaller beam diameter, and so can be used over longer distances.

        • I have an older version of the LAS150 or XLAS300. Can I use the latest Evation to process my data into fluxes?
          • Yes you can, but there are a few points you have to take care with as the analogue data output has changed in format.

            See appendix H of the latest manual, for details of the conversion of the analogue voltage output, UCn2. Note, the manual is written for the improved LAS MkII with GPS, so there will be differences in the hardware, and there are a couple of data formatting issues that are different (voltage ranges).

            Most likely the format of your UCn2 data is incorrect for the latest version of Evation, as the software was developed to work with the LAS MkII, which has a different analogue voltage output (positive instead of negative).

            For the LAS MkI, the Cn2 voltage output, UCn2, is output as -5 to 0V, where:

              -5V analogue voltage output is equivalent to a Cn2 of 1 x 10^-17  [m-2/3]

               0V is equivalent to 1 x 10^-12 (m^-2/3)

            Cn2  (m^-2/3) = 10^(-12+ UCn2)  (this applies to the LAS150, not to the LAS MkII !)

        • What is the latest version of the software used to process fluxes from a LAS?
          • The latest version of the Evation software V2R5 and the new manual (vs1511) which explains the use of Evation, are available online, under downloads:

            http://www.kippzonen.com/Product/193/LAS-MkII-Scintillometer#.VkyHt2eFOoA

             [The manual is now very comprehensive and covers all the recent improvements to the LAS MkII, such as the time from GPS, new firmware and processing software. It also includes clearer instructions for operation of the instrument and software, and several appendixes to cover additional information such as logging the serial or analogue output with an external logger, such as from Campbell Scientific.]

        • How do I determine the height of the LAS?
          • To derive fluxes of sensible heat (H) from the LAS measurements (Cn2), one needs to know the height of the LAS beam above the ground, also known as the effective height. Because the flux is almost linearly related to the height it is important to determine the effective height as accurate as possible (see Appendix F of the LAS manual). Over flat terrain it is relative easy to determine the LAS height: take the average of the height of the transmitter unit and receiver height (i.e. the height between the centre of the beam and the ground).

            Over non-flat terrain it is a bit more complicated, because now we also need to consider the path-weighting function of the LAS. This weighting function reveals that the centre of the LAS path contributes more to the measured Cn2 data, than near the transmitter and receiver units. This calculation is easily done by using the effective height calculator built-in to the Evation software, which takes care of the weighting function.

            Note: for very long path lengths (> 5km), such as when using the XLAS it is also important to consider the earth’s curvature (decreases the height in the centre of the path by approx. 2 m over a path length of 10 km.

            More detailed information of deriving the effective height of scintillometers over complex terrain and the effect of atmospheric stability on the effective height can be found in: Hartogensis et al., Derivation of an Effective Height for Scintillometers: La Poza Experiment in Northwest Mexico, Journal of Hydrometeorology, 2003.

        • Can I place the transmitter and receiver units behind glass windows?
          • Yes, the LAS transmitter and receiver unit can be placed inside behind glass or Perspex windows, preferably at normal incidence to minimise light loss and refraction of the beam. However, it must be noted that windows absorb a fraction of the light beam (~8 to 25%) thereby limiting the maximum path length of the LAS or XLAS.

        • How precisely do I have to measure the path length of the LAS?
          • An error in the path length L of 1% results in an error of 3% in Cn2 (and thus H). This shows that the path length should be determined accurately.

            The effective height or height of the LAS beam should be measured to 1 cm (a tape measure can be used for this).

             

        • Is the LAS sensitive to tower vibrations?
          • The measurement principle of the LAS is based on the scattering of EM radiation by the turbulent atmosphere that result in fluctuations of the intensity of light. The turbulent eddies that produce these scintillations have a size of the order of the aperture diameter of the LAS (or XLAS). The figure below shows that in general these fluctuations lie mostly between 1 and 10 Hz (exact positing of the curve with respect to the x-axis is slightly dependant on the crosswind). The bandwidth of the LAS electronics is set around these fluctuations (0.1 Hz to 400 Hz). In this way electronic noise (> 400 Hz) and low frequency fluctuations related to absorption by the atmosphere (< 0.1 Hz) are removed.

             

             

            Figure 1: Theoretical spectrum of a 0.15 m LAS (path length = 1 km, wind speed = 1.5 m/s).

            Any type of fluctuations, e.g. caused by tower vibrations that lie within this bandwidth, in particular the ones that lie between 0.5 to 10 Hz can have significant effects on the measurements. It is therefore, strongly recommended to use stable and robust mounting platforms for the LAS units.

        • Can a LAS MkII be used to measure crosswind?
          • Yes, this is possible by logging the analogue output with a fast (500 Hz) data logger, and looking at the shift in the peak of the scintillation spectrum (the scintillation power spectrum shifts linearly along the frequency domain as a function of the crosswind). In the optical microwave sintillometer, the raw data is already logged at 500Hz, so this could be implimented. Built-in data processing to calculate the crosswind may be added in the future.

            See the following publication for more information: van Dinther, D., O. K. Hartogensis, and A. F. Moene, 2013: Crosswinds from a single-aperture scintillometer using spectral techniques. J. Atmos. Oceanic Technol., 30, 3–21.

        • If I am using an external data logger which signals of the LAS do I have to measure?
          • The LAS MkII includes an inbuilt data logger, but sometimes you may which to add the data to an existing meteorological station with its own data logger.

            The LAS transmitter and receiver both have multiple analogue output signals, which can be measured by most standard data loggers. These signals allow the user to monitor the internal temperature as well as some raw signals to check the performance of the electronics. In most experiments these signals don’t have to be measured.

            For general flux measurements two signals are important: the Cn2 signal and Demod signal. Both signals are measured at the receiver unit. The first signal, re-scaled Cn2, provides information of the turbulent intensity of the atmosphere and is used to derive the sensible heat flux (H). It’s range lies between 0 to 2.4 V for the LAS MkII (-5 and 0 Volt for the LAS150). The second signal: the demod signal is a measure of the signal strength and it’s range lies between 0 to 2 V for the LAS MkII (-2 and 0 Volt for the LAS150). The more positive (more negative for the LAS150), the more signal the receiver has. In general the signal strength depends on the distance between the transmitter and receiver and the opacity of the atmosphere.

            The reason it is advised to measure the demod signal is that it can help with the interpretation of the Cn2 signal. In some cases the Cn2 can be difficult to understand, e.g. during rainy and foggy periods, while the demod signal shows clearly whether or not the receiver has a signal, or some signal is lost due to the weather.

        • I want to derive fluxes from the LAS data, what kind of additional meteorological data do I need?
          • The LAS instrument provides the structure parameter of the refractive index of air, Cn2. The latter can be considered as a parameter that describes the turbulent intensity of the atmosphere, in particularly related to the turbulent temperature fluctuations. This is way the LAS can be used to measure the sensible heat flux. However, the derivation of the sensible heat flux requires some steps. In each step additional meteorological data is required (see also processing data in the LAS manual):

            Step 1: from Cn2 to CT2 requires data of:

            • Air temperature
            • (Relative Humidity)
            • Air pressure
            • Bowen-ratio ( )

            Step 2: from CT2 to the sensible heat flux H requires data of:

            • Air temperature
            • Wind speed at 1 level

            Step 3: from H to evaporation requires data of:

            • Net radiation
            • Soil heat flux (preferably measured as closely to the soil surface as possible).

            In additional the gravitational acceleration, surface roughness and sensor heights are required.

            It is recommended to have the additional data at the same measurement interval as the LAS data.

            Step 4: selection of unstable or stable solution H:

            For land surface the typical diurnal course of H shows positive values during the day and negative values at night. Explanation: during (sunny) daytime conditions (roughly between sun rise and sun set) the earth’s surface heats up the atmosphere from below. This means H is pointed upward and defined positive. This situation is known as the unstable period. At night (roughly between sun set and sun rise) the surface cools due to long wave radiative cooling. As a result heat from the atmosphere is transported downwards to the surface. Hence, H is negative. This situation is defined as the stable period. The LAS is able to measure the magnitude of the sensible heat flux (H) but not the sign, i.e. is H directed upward (> 0) or downward (< 0)?

            There several ways to choose either the unstable or stable solution of H:

            Net radiation: During most situations when the net radiation is positive, the atmosphere is unstable. Once the net radiation becomes negative the atmosphere becomes stable. Note that this option is not applicable over intensively irrigated fields.

            Global/solar radiation: Although less accurate than net radiation data, but still useable. When the global radiation is higher than approximately 20 Wm-2, the atmosphere is unstable. When it drops below 20 Wm-2, assume stable conditions. The exact values are site/surface dependant.

            Temperature profile data: for example air temperature data collected at 0.25m and 3m height. During daytime close to the surface (0.25m) it is warmer than higher up in the atmosphere (3m), i.e. unstable conditions (dT/dz < 0). At night the situation is opposite, cold close to the surface and warm at higher levels, the condition is stable (dT/dz >0). This method is the most reliable one, but requires accurate temperature measurements.

            Cn2 data: During clear sunny days the Cn2-signal shows a very distinctive behaviour. Every time the atmosphere changes transition, the Cn2-signal drops to a very small value (® 1e-17). By determining the exact time when this occurs, the average time periods of unstable and stable conditions can be simply determined. During cloudy conditions the exact transition times are difficult to detect and is therefore difficult to automate.

        • How can I determine the surface roughness length?
          • The LAS manual shows a terrain classification for typical landscapes with corresponding surface roughness lengths. General meteorological literature can provide more detailed information of surface roughness length for specific surfaces and/or crops.

            The surface roughness can also be determined experimentally, using e.g. eddy-covariance stations or from wind profile measurements.

        • Can the LAS be used to measure evaporation of lakes?
          • This has been done, see publication by: McJannet, D. L., F. J. Cook, R. P. McGloin, H. A. McGowan, and S. Burn (2011), Estimation of evaporation and sensible heat flux from open water using a large‐aperture scintillometer, Water Resour. Res., 47, W05545, doi: 10.1029/2010WR010155.

            But there are several reasons why LAS measurements of open water is rather complicated:

            1. In general the sensible heat flux (H) is small over lakes compared to the evaporation. As a result the derivation of CT2 from Cn2 becomes sensitive to fluctuations that are the produced by turbulent humidity fluctuations instead of temperature fluctuations. This correction can be expressed as a function of the Bowen-ratio ( ). The smaller the Bowen-ratio the larger the correction. Over water bodies evaporation is (in most cases) dominant over H, resulting in small Bowen-ratio values. It is advised to have accurate Bowen-ratio data.
            2. Typical diurnal course of H over land shows positive values during the day and (small) negative values at night. In this way it is relative easy to select either the unstable or stable solution when processing fluxes (in the Evation software) as the LAS itself cannot see the sign of the flux (and thus stability). Properties of water, such as the ability to store heat (i.e. heat capacity) are very different from land. As a result it is more complicated to predict the diurnal (seasonal) cycle of H. Instead it is advised to measure the gradient of temperature over water in order to determine the sign of H.
            3. For the derivation of the sensible heat flux from CT2, the wind speed and surface roughness are required. As the surface roughness of open water bodies is dependant of the wave height (and thus wind speed) the standard applied flux-profile relationships cannot be used. Instead air-sea relationships have to be considered.
            4. To derive the evaporation from the LAS measurements (i.e. H) the soil heat flux term has to be known, i.e. the amount of heat stored in the ground or in this case stored in the water (G). For land surfaces so-called heat flux plates can be used to measure G. For water bodies this term is very difficult to determine.

             

        • Can I measure latent heat flux, such as the evaporation from lakes or rice paddies directly?
          • To measure both evaporation / latent heat flux and sensible heat flux directly (and without the restrictions when using a LAS on it own), a combined optical and microwave scintillometer can be used. This system measures both CT2, Cq2, and the co-variant term, CTq, between them, so no assumptions are made. Along with meteorological data from the receivers side mounted weather station, latent heat and sensible heat fluxes are calculated internally. See the Optical Microwave Scintillometer system page for more details.

             

        • How often do I have to check the alignment of the LAS?
          • How frequent the alignment has to be checked is dependent on the installation set-up. Tripods fixed in the ground can have the tendency to move, in particularly as the soil can become soft after periods of rain. In that case the alignment has to be checked at a regular interval. Once steel constructions are used on top of buildings, or tripods on a concrete foundation, the setup is much more stable and has to be checked less frequently.

            In-case one has the ability to check the data in real-time, the demod signal can help to monitor the alignment. A slow decreasing trend of the demod signal can suggest possible changes in the optical alignment (ignoring degradation of the LED).

        • I am leaving my LAS unattended in the field for a period, how should I secure it?
          • For a long term installation, stable steel constructions such as a steel frame or post, on a concrete foundation, are recommended to avoid vibration or miss-alignment. If tripods are used for field work, they should be fixed or tied to the ground when left unattended for a period to avoid damage from storms nocking the tripod over. To do this a ground anchor can be screwed into the ground under the tripod, and the tripod tied to this using a ratchet or cargo strap. Insure the tripod feet are firmly pushed into the ground first.

            If there are animals in the area protect the equipment from being pushed over, disturbed, or the cables chewed, by surrounding the installation with electric fencing.

        • Brewer Spectrophotometer

          • When and how should I clean the Brewer’s azimuth tracker drive?
            • The Brewer azimuth tracker has a driving mechanism based on friction between the drive shaft and the drive plate. These items will get dirty over time and the azimuth tracker is likely to slip. This can be noticed by a tracker discrepancy after AZ or SR tests.

              The drive mechanism can be cleaned by using a clean lint-free cloth with alcohol or with “garage” soap (soap with grains of sand in it). Switch the tracker power off! Remove the rear tracker cover (the cover on the side opposite to the power switch). Use the cloth with alcohol or soap to rub the dirt off the drive plate and the drive shaft. Rotate the tracker to clean the entire drive plate. Be careful not to break the wire of the safety switch. After cleaning the entire drive plate and shaft, rub them once more with a dry piece of clean lint-free cloth to remove any remaining residue of soap/alcohol.

              When this is done, rotate the tracker to aim the Brewer approximately at the sun . Put the tracker cover back on and switch on the tracker power. Now the Brewer needs to perform some tracker resets. In the Brewer software, type “PD AZ SR 10” to perform these resets. Watch the data to check that the tracker resets without discrepancies and then put the Brewer software back into its normal schedule.

          • How does the Brewer compensate Ozone measurements for temperature?
            • The Brewer instrument is capable of operating in different conditions from the tropics to the Antarctic. As the Brewer is used outside the whole year round, its Ozone measurements should not have any temperature dependency.

              During the factory testing of the Brewer it undergoes a test in the temperature chamber from 0°C to +45 °C. Standard Lamp measurements are taken throughout this entire temperature range. This is a simulated Ozone measurement based on the halogen lamp inside the Brewer. Although the intensity of the lamp does change with temperature, the wavelength shift is negligible.

              After the temperature test, the data of the SL measurements is analysed. During the analysis, the temperature correction coefficients are created. These coefficients compensate for the change in spectral response of the Brewer at the Ozone wavelengths. With the coefficients installed in the Brewer software, the Ozone measurements will not be affected by the temperature of the instrument.

          • The Brewer software says “LAMP NOT ON, HG TEST TERMINATED”. Should I replace the lamp?
            • The Brewer software will give this error message when it tries to make a HG measurement but cannot see the light of the Mercury lamp. There are several causes why the Brewer could give this error message. One of the motors could be in an incorrect position, so that the Brewer does not see the light. The PMT could not be measuring correctly or the lamp could need replacement.

              The first step in troubleshooting is doing a full reset (RE command) in the Brewer software. Then try to perform the HG test again.

              If the HG test still returns the error message one should find out if this also occurs for tests with the standard lamp. Type SL<enter> in the Brewer software.

              If Both the HG test and the SL test fail, then either a motor is not moving correctly or there is a problem with the PMT/photon counting circuitry. Use the maintenance manual for further troubleshooting.

              If the SL works but the HG fails, then there might be a problem with your lamp. For single board Brewers: Type AP to get the voltage of the Mercury Lamp (HG lamp). The voltage should be around 10 V. If the Voltage is off by 2 Volts, one should inspect the lamp.

              The HG or mercury lamp is the lowest lamp in the lamp housing. Usually, if the lamp needs replacement, the glass will have black spots or the filament will be broken.

              If the lamp needs to be replaced, do not touch the quartz envelope with your hands. Use a tissue or a piece of cloth. The lamp should be tightened firmly. Also, from the top, both filaments should be visible.

          • How often should my Brewer be calibrated?
            • For the Brewer spectrophotometer, regular recalibration is necessary for the reliability of the Brewer’s Ozone measurements. The World Meteorological Organisation (WMO) recommends that each Brewer is calibrated at least once every two years. The Brewer is a stable instrument and drifts in the instruments can be monitored and corrected because of the diagnostic tests such as Standard Lamp and Dead Time measurements.

              Some Brewer users prefer to have their Brewers calibrated every year. By doing this, they assure their Brewer data is of the highest quality. Drifts in the instrument are corrected sooner and the regular check with a reference Brewer increases the reliability of the data.

              If you would like to discuss calibration of your Brewer at the factory or at your location please contact us.

        • Solar Instruments

          • How does instrument temperature effect radiometer accuracy?
            • The temperature dependence of the sensitivity is a function of the individual CHP 1. For a given instrument the response lies in the region between the curved lines in Error! Reference source not found. The temperature dependence of each pyrheliometer is characterized and supplied with the instrument. Each CHP 1 has built-in temperature sensors to allow corrections to be applied if required.

              Typical Radiometer temperature dependence

          • RaZON+

            • Pyranometers

              • How can I check if there are interferences from the cable?
                • When we calibrate the sensors there is no signal bounce other than the time that the pyranometer needs to reach its final value (time constant) if however there are electrical inferences and the shielding of the cable and data logger is not good then you can expect noise. A good way of testing this is by connecting a dummy pyranometer with the same cable (length and position) to the data logger. (Dummy pyranometer is a 1 kOhm resistor) This will show any interference coming from the cable.

              • Negative output during nighttime measurements?
                • This error is related to the zero offset type A. Normally this zero offset is present when the inner dome has a different temperature from the cold junctions of the sensor. Practically this is always the case when there is a clear sky. Because of the low effective sky temperature (<0 °C) the earth surface emits roughly 100 W/m2 longwave infrared radiation upwards. The outer glass dome of a pyranometer also has this emission and is cooling down several degrees below air temperature (the emissivity of glass for the particular wavelength region is nearly 1). The emitted heat is attracted from the body (by conduction in the dome), from the air (by wind) and from the inner dome (through infrared radiation). The inner dome is cooling down too and will attract heat from the body by conduction and from the sensor by the net infrared radiation. The latter heat flow is opposite to the heat flow from absorbed solar radiation and causes the well known zero depression at night. This negative zero offset is also present on a clear day, however, hidden in the solar radiation signal.

                  Zero offset type A can be checked by placing a light and IR reflecting cap over the pyranometer. The response to solar radiation will decay
                  with a time constant (1/e) of 1 s, but the dome temperature will go to equilibrium with a time constant of several minutes. So after half a minute the remaining signal represents mainly zero offset type A.

                  Good ventilation of domes and body is the solution to reducing zero offsets even further. Kipp & Zonen advises the CVF 3 Ventilattion Unit for optimal ventilation and suppression of zero offset type A. Using the CVF 3 zero offset type A will be less than 3 W/m2.

              • Solar radiation at the site was greater than 1400 W/m²! Is this reasonable?
                • It is indeed possible to reach a value of 1400 W/m² or slightly higher. The maximum radiation from the sun above the atmosphere is 1367 W/m². However at high altitudes with a clear sky and some bright white cumulus clouds (not covering the sun) it is possible to get above the 1400 W/m². These clouds will act like a mirror and reflect (extra) solar radiation to the sensor and through this effect reach these high values. So it is possible, but only under these extreme conditions. Under a clear sky without clouds the radiation is definitely below the 1367 W/m².

              • What is the directional or cosine response?
                • Radiation incident on a flat horizontal surface originating from a point source with a defined zenith position will have an intensity value proportional to the cosine of the zenith angle of incidence. This is sometimes called the ‘cosinelaw’ or ‘cosine-response’ and is illustrated in figure 11. Ideally a pyranometer has a directional response which is exactly the same as the cosine-law. However, in a pyranometer the directional response is influenced by the quality, dimensions and construction of the domes. The maximum deviation from the ideal cosine-response of the pyranometer is given up to 80° angle of incidence with respect to 1000 W/m2 irradiance at normal incidence (0°).

              • What parameters or errors should we take into account if the source of light comes from a certain angle?
                • If the Pyranometer remains horizontal the error involved is the directional error listed in the Pyranometer brochure.

                  For CMP 3 < 20 W/m2  and for CMP 22 < 5 W/m2

              • Can I use a pyranometer under water?
                • The CMP series can also be used under water, the depth is limited to 1 meter and can only be used for short measurements.

                  It is advisable not to keep the Pyranometer of the CMP series under water for longer than 30 minutes.

                  The SP Lite2 pyranometer and the PQS 1 PAR Quantum Sensor can be used for a longer period under water, the depth is limited to 2 meters. Please also take  “breaking of light on the water surface” in consideration.

              • If I use a pyranometer under water, can I connect a data logger to it ?
                • Yes, however the data logger needs to be placed on the surface (it is weather resistant, but cannot be lowered into the water).

                   

              • What is the calibration frequency of a pyranometer?
                • We advise to re-calibrate the Pyranometer every two years. 

              • What does spectral range of 310 – 2800 nm (50% points) mean?
                • The 50 % points are the wavelengths where the output of the instrument is 50 % reduced with 100 % input.

                  spectral range

              • What is the WMO standard for the pyranometers?
                •  

                   

                  CMP 3

                  CMP 6

                  CMP 11

                  CMP 21

                  CMP 22

                  WMO

                  Moderate quality

                  Good quality

                  High quality

                  High quality

                  High quality

                  ISO

                  Second Class

                  First Class

                  Secondary Standard

                  Secondary Standard

                  Secondary Standard

              • What is the resolution of a pyranometer?
                • The instrument has an analog output, therefore the resolution is infinite. Every change is noticed, no matter how small it is.

              • What is the bandwidth of a pyranometer?
                • The bandwidth of most pyranometers is 285 to 2800 nm. This covers the full solar spectrum as shown below.

                  There are some exceptions:

                  • CMP22 has a bandwidth of 200-3600nm (Quartz glass )
                  • SP Lite  has a bandwidth of 400-1100nm (silicon photo diode)
                  • CMP3 has a bandwidth of 300-2800nm

                  Solar Irradiance Spectrum 

                   

              • In our PV application the cable from the CMP 11 (50 meters) will go along other cables that come from the PV panels in which there is a DC voltage and around 100 Amps. Will these cables affect the measurement?
                • The disturbance on the cables on the CMP 11 is difficult to judge from a distance. A test would give the best criteria in this case.

                  Simply cover the CMP 11 so it is fully dark (in box with cloth etc.) Log the data over a period that disturbance is expected, at least one day.

                  If the data is zero no problem is to be expected.

                   

                   

              • Do you have filters that can be used to verify spectral distribution over the following wave lengths? Ultraviolet - B 280-320 Ultraviolet - A 320-360 and 360-400 Visible 400-520, 520-640 and 640-800 Infrared 800-3000nm.
                • No, we do not have filters for any of our pyranometers. The only way to do this in a correct way is to use a filter dome. Otherwise the directional response would be affected.

              • Is there a standard product that converts the pyranometer output signal to 0-5V or 0-2V?
                • The AMPBOX is the best solution.

                  You will need a suitable PSU and a shunt resistor of 500 Ω to convert the current output (4..20mA) to a voltage output of 2-10V , or you will need a shunt resistor of 50 Ω to convert the current to a voltage output of 0.2-1V.

                  Output signal pyranometer

              • What kind of pyranometer do you suggest for usage inside a greenhouse?
                • CMP 6 in combination with PQS1 PAR Quantum Sensor is advised.  CMP 6 for outside usage to measure Global solar radiation. PQS1 to measure  PAR radiation inside which is most sensitive for plants and crops.

              • What type of pyranometer can I use for my fixed PV panels farm?
                • For this application the CMP10 and SMP10 are advised as they have an internal drying cartridge that will last for at least 10 years.

                  Please note that the pyranometer needs to be mounted in the same angle (POA) as the PV panel. 

                   

                  For users that prefer the desiccant visible Kipp & Zonen offers the CMP11 and SMP11 with visible and user changeable desiccant.

              • What type of pyranometer can I use for my solar concentrators farm?
                • None, solar concentrators are reflecting the direct solar radiation  to a concentrator and are tracking the sun. You will need a pyrheliometer on a sun tracker to measure direct solar radiation.

              • Is there a Pyranometer available that has the same spectral characteristics as a PV panel?
                • Yes, we do have a Pyranometer with the same spectral characteristics as a PV panel. This is the SP Lite(2) Pyranometer.

                  Our SP-Lite is based on a silicon diode which has a response from 400 – 1100 nm.
                  The advantage is the response time, which is as fast as any PV panel ( milli seconds).
                  The disadvantage is that not all PV panels have the same spectral range. 
                  A thermopile pyranometer covers the full spectral range of the sun and will give a more accurate measurement of the total (global) solar radiation.

              • Is it possible to connect the Pyranometers to a computer? That way, I could, using software (if there is any available), measures solar radiation all the time, non-stop.
                • The output from thermopile Pyranometers, such as our CMP Series, is very low – typically around 10 milli-volts on a clear sunny day. To resolve changes of 1 W/m2 requires an ADC with an accuracy and resolution of around 5 micro-volts. These PC interfaces are very expensive and difficult to find in a form that is easily interfaced to the PC. This is why meteorological data loggers are normally used that can cope with the low signal levels.

                  Kipp & Zonen has solutions like handheld- or fixed location data loggers.

              • I would like to know what kind of output the CMP 6 Pyranometer has (analog or digital)? What voltage range do you have?
                • The CMP 6, as with all our solar radiometers based on thermopiles has a continuous small analoge voltage output. For CMP 6 an irradiance of 1 W/m2 generates an output signal in the region of 5 to 15 micro-volts. We have additional solutions to increase this voltage.

              • Do the pyranometers come with a calibration certificate, NIST traceable?
                • NIST in the USA supplies calibration services to industry – in case of light they characterise sensors, detectors and lamps for use in manufacturing and for luminance measurement (LUX).

                  They are not set up for the calibration of sensors for solar radiation and they are not a traceable reference. 

                  The only accepted world standards for the calibration of radiometers for the measurement of global or direct broadband solar radiation are as below:

                  • ISO 9059 Calibration of Field Pyrheliometers by Comparison to a Reference Pyrheliometer
                  • ISO 9060 Specification and Classification of Instruments for Measuring Hemispherical Solar and Direct Solar Radiation

                  • ISO 9846 Calibration of a Pyranometer Using a Pyrheliometer Guide to Meteorological Instruments and Methods of Observation, Fifth ed., WMO-No. 8

                   

              • What does Zero Offset A mean?
                • By physical laws any object having a certain temperature will exchange radiation with its surroundings. The domes of upward facing radiometers will exchange radiation primarily with the relatively cold atmosphere. In general, the atmosphere will be cooler than the ambient temperature at the Earth’s surface. For example, a clear sky can have an effective temperature up to 50°C cooler, whereas an overcast sky will have roughly the same temperature as the Earth’s surface. Due to this the Pyranometer domes will ‘lose’ energy to the colder atmosphere. This causes the dome to become cooler than the rest of the instrument. This temperature difference between the detector and the instrument housing will generate a small negative output signal which is commonly called Zero Offset type A. This effect is minimized by using an inner dome. This inner dome acts as a ‘radiation buffer’.

                  The Zero Offset A can also be reduced by using a Ventilation Unit CVF 3.

              • Are there any accessories needed with the Pyranometer to avoid reflected radiation from the surface?
                • No, all the Pyranometers have a 180 degree field of view. When mounted horizontally, they cannot see light reflected from the ground due to its design.

              • What is the big difference between CMP 11 and CMP 21?
                • The CMP 11 uses a default temperature compensation setting and the dependency is ±1% from -10 to +40°C.

                  The CMP 21 is individually tested and the temperature compensation is optimised.  It is ±1% from -20 to +50°C. However, from -10 to +40°C it is within ± 0.5%, typically ± 0.3%. In addition a temperature sensor is fitted and the temperature response curve is supplied. Each CMP 21 has the directional (cosine) response tested, and this is also supplied. This means that for the serious scientist the irradiance values can be corrected for temperature and solar elevation – increasing the accuracy. This is not possible with the CMP 11.

                  BSRN requirements state that the solar radiometers must be fitted with an internal temperature sensor and the data recorded, so CMP 21 is compliant to this, but CMP 11 is not. 

              • Does a Pyranometer require any power?
                • Our thermopile-based instruments, including the CMP range of pyranometers and the CH(P) 1 pyrheliometer, do not require power to operate. They generate a small voltage output in response to the solar radiation.

              • The colour of the desiccant in the pyranometer was nearly transparent and not orange.
                • Kipp & Zonen states that the replacement of the (external replaceable) desiccant for their radiometers can be done at 6 months intervals. Even in humid environments the desiccant is guaranteed for at least 6 months, so no condensation takes place inside the instrument. A good practice is to combine checking the desiccant and the leveling of the instrument and cleaning the dome.

                  The color change of the desiccant beads takes place from orange to transparent at 6% weight absorption at 40% relative humidity. The maximum weight absorption is 23% at 40% rH. This means that even after the desiccant color has changed to transparent the beads are still active.

                  Desiccant beads can be easily exchanged by using refill packs. To compensate for a long storage interval before installation, extra desiccant packs are provided. Alternatively the beads (not the cartridge) could be regenerated by drying in an oven at 120°C (several hours) until the color has changed back to orange.

                  Kipp & Zonen introduced the CMP/SMP10 with CMP/SMP11 specifications but with enough internal desiccant(molecular sieve) for 10 years to solve the issue of the external desiccant.

                  http://www.kippzonen.com/Download/902/Technical-Advise-Desiccant-replacement-interval

              • Pyrgeometers

                • Why is the Pyrgeometer from Kipp & Zonen so much better than those from the competition?
                  • The CGR 4 differs from all other Pyrgeometers in that it allows accurate daytime measurements on sunny days without the need for a shading device. Due to the unique construction of the CGR 4, solar radiation of up to 1000 W/m² induces window heating of less than 4 W/m² in the overall calculated downward radiation. In the Baseline Surface Radiation Network (BSRN) manual (WMO/TD-No.897) an extended formula is described. This formula corrects for window heating and so called “solar radiation leakage”. Due to the very low window heating offset and optimal spectral cut-on wavelength, these corrections are not necessaire for the CGR 4.

                • What is the calibration interval of a pyrgeometer?
                  • We advise to re-calibrate the Pyrgeometer every two years.

                    More information about our calibration service can be found here.

                • I am using a Ventilation unit on the Pyrgeometer. Do I need to put this on 5W or 10W?
                  • If the CVF 3 is used for a Pyrgeometer the effect of sunrise is not valid and continuous 5 Watt is preferred. In extreme cold climates , polar / mountain tops, the 10 Watt heater can be used continuously.

                • Sun Tracker

                  • Is it possible to mount 4 pyreliometers plus an extra sun sensor?
                    • Yes. Normally 4 of these side-mounted sensors is the maximum, however we are able to make an extension on one pyrheliometer mount for the extra sun-sensor.

                  • How much power is needed for the 2AP?
                    • The power use of the 2AP itself is about 1.5 A to 2 Amps. (internal fuse is 3 Amps slow)

                  • What power supply is needed when heaters are used?
                    • The power use of the 2AP itself is about 1.5 A to 2 Amps. (Internal fuse is 3 Amps slow)

                      Part number for the 24V heater kit is: 12136346.
                      This kit contains two 50 Watt heaters.
                      So the current for these heaters is 4.2 A (at 24V), fuse is 5 A slow blow.

                      If we add up the total power we have:
                      5A (heaters) + 3.15 (2AP)= 8.15 A

                      Normal conditions:
                      4.2 A (heaters) + 1.25A (2AP) = 5.5 A normal

                      Therefore a 5 Amp power supply will not survive very long.
                      We recommend to take a power supply that can deliver the 8.15 A. (when heaters are used)

                  • Does the 2AP work autonomously?
                    • The 2AP works fully autonomously, after the setup. Setup is done in combination with a PC. (Entering Longitude, Latitude etc.) Indeed a data logger is needed to collect data from the sensors, but this logger has no (hardware) connection with the 2AP.

                  • Can the tracker be connected to a PC at 30 m distance?
                    • To connect the 2AP with a PC for communication, a 3-wire cable is used (or 2 wires plus shield) as described on page 5 of the manual.
                      Advised is a shielded cable, where the shield can be the ground connection.

                      • On the 2AP side the wires are connected to the communication board.
                      • On the PC side a 9 or 25 pin Sub D connector is used for the serial port.

                      This cable length can be 30 meter. We can supply this cable, but it can be bought "around the corner".

                      The communication software is included with the 2AP.

                  • Why does the COM port of my Pentium not address the 2AP like my old 4.86?
                    • The CMD and sun tracker software will work on COM1 or COM2 only, specified as the first parameter after the program name in the command line. Make sure the 2AP is connected to one of these two ports. Problems can also occur if another program has taken over the COM port and will not give it up. Also, some Compaq computers have non-standard COM ports, which the CMD and sun tracker programs cannot communicate through. The solution for this problem could be found in a simple add-on card with a standard extra serial port, if it can be set as COM 1 or 2.

                  • What is the range of the temperature?
                    • The temperature range for the 2AP tracker is:

                      Standard temp range: 0 - 50 degrees Celsius
                      With cold cover: -20 - 50 degrees Celsius
                      With cold cover and heater -50 - 50 Degrees Celsius

                      Normally the heater is built in, in the factory. However we can supply you with a kit plus instructions to do it yourself.

                  • What is the accuracy of the 2AP tracker in combination with a sun sensor?
                    • The 2AP has the following errors:

                      • Time
                      • Setup (leveling)
                      • Calculation (algorithm according to Michailsky error max. is 0.025 degree)
                      • Mechanical (BD = 0.09 and GD =0.045 degree max.)

                      The first 2 are user controlled and the last 2 are fixed.

                      Assuming that the leveling is done optimal the only error remaining that can be corrected is time. If we assume that the clock is reset every 1,000,000 seconds (11.5 days) there will be an expected error of 5 seconds. If we assume that the sun rotates 360 degrees in 24 hour then RMS 0.72 * 5 seconds = an actual time error of 3.6 seconds. For a period of 11.5 days the total time error contribution is 0.015 degrees (the diameter of the solar disk is 0.25 degrees). Per year this would result in 0.5 degree.

                      If this time correction and the check on leveling are done on a regular interval there is no need for a sun sensor. If however this interval can or will not made, the sun sensor will correct for both (leveling and time).

                      The sun sensor is normally used for first checking the tilt error. Assuming that there is sunshine for at least 2 full days over the full day. This information is stored in an internal log file and used to correct (in combination with PC). Over this period the user has to correct time. (if more than 2 weeks). After this initial run and correction for tilt, the sun sensor is used for time correction. This means that optimal accuracy is maintained without user (time) correction. This means that the 2AP is within specs the whole year without intervention.

                      Please note that the sensors used on the 2AP also need maintenance on a regular base (drying cartridge and dirt on domes).

                      Better than giving an error in percentage we would like to show the benefit of not having to correct to clock. The 2AP error in degrees can be calculated as percentage of 360 degrees, but the error in sensor reading depends on the type of sensor.

                  • Is there a compensation for temperature drift?
                    • The controller board has a temperature compensated oscillator module for the microprocessor. While power is applied the firmware keeps accurate time and updates the real time clock (which is not very accurate) every 8 hours.

                      We enter a room temperature correction, which compensates for initial calibration of the oscillator module. The oscillator module can drift up to ±11 ppm over the 0 °C to 70 °C temperature range. The module can also drift up to ±2 ppm in a year.

                      The temperature drift is different for each oscillator so cannot be compensated for in firmware.

                  • Is compensation for pressure variations needed?
                    • The air pressure that is required should be an average value for the site the instrument is operated. It does not need to be updated over time. The meaning of it is to correct for (a small) optical shift due to atmospheric pressure. A normal value depends of course on the heath of operation. A value of 1000 mBar is typical for sea level.

                  • Is there a way to fix a tracker via remote PC?
                    • You can try the following:
                      If you send the command “CO”, the 2AP will cold start. This means ignore all present settings and start without using any previous (possibly wrong) settings.

                      If you then start the sun tracker program, it will start up with the message “”recovering from cold start””

                      Then longitude and latitude etc. will be recovered from the .ini file, the time and date of course cannot be stored and has to be entered again. If no further error message is given, the 2AP is most likely operational again.

                      This could solve the problem, if not please contact us and we will discuss further options.

                  • Why is the altitude limited to 2000 m?
                    • The 2AP BD altitude specification (2000m) is limited by the CE and CSA (Canadian Standards Association) recommendation for main power board design. CSA recommends that AC boards have certain spacings between the board tracings for various elevation (pressures). As the pressure decreases there is more probability for arcing when the wires are close. Unfortunately there is not enough room internally, in the 2AP BD, to increase the size of this board (to make the spacings bigger).

                      The best solution is to sell/quote a 2AP Gear Drive with 24VDC, as this would eliminate the altitude restrictions associated with high voltage AC.

                  • How many (CHP 1) pyrheliometers can be mounted?
                    • Standard one CHP 1 mount is included. An extra mounting clamp can be added on top of this CHP 1 mounting. The same can be done on the other side. So standard, 4 CHP 1’s is possible.

                      The SOLYS Gear Drive can easily handle more, but for mounting more instruments (e.g. 8 pyrheliometers) a larger mounting plate is required.

                  • What about the pointing accuracy?
                    • Pointing accuracy is better than 0.02°, when active tracking, under all conditions.

                  • Can the PMO-6 be mounted?
                    • Yes, like on the SOLYS 2 a special mounting clamp is available for the PMO-6.

                  • Is there any altitude limit in this as in 2AP?
                    • The power supplies used in the SOLYS have EN60950-1 approvals. This means approved up to 5000m. If higher altitudes are required we can check or test if this is feasible.

                  • How long takes the night time rewinding?
                    • It takes a few minutes for the SOLYS to return to its home position. Then the SOLYS goes to sleep mode (for power reduction).

                  • Are the Zenith/Azimuth Positions of tracker available in log file?
                    • Yes, both the Solar Zenith and Azimuth positions and the SOLYS motor Zenith and Azimuth positions are available in the log file.

                  • What is the power requirement for AC and DC?
                    • The power requirement is for both AC and DC is 25 Watt during operation and 13 Watt at night. For the SOLYS “night” is from ~ 5 minutes after sunset to ~ 5 minutes before sunrise.

                      When used in cold climates, the heater switches on to keep the interior above -20°C

                      This is switched automatically and only used when powered from AC.

                      The cold cover can be used to reduce the required heating power.

                  • Is there any option for Sun sensor, can we remove from tracker?
                    • The Sun Sensor is supplied as standard with the SOLYS Gear Drive. It can be removed (or not mounted) then the SOLYS will follow the sun based on its internal calculation.

                      This is normally accurate enough, but does not correct for any misalignment or unstable mounting.

                  • How well does the SOLYS work in salty air that is close to the ocean?
                    • Like our radiometers, the SOLYS’s are made of anodised aluminium. Until now we did not see any effect on the functioning of the trackers that are mounted on the sea shore.

                      The SOLYS has in addition to the radiometers a paint coating to further protect it.

                  • Do you recommend the SOLYS Gear Drive in polar conditions?
                    • Absolutely! Great care has been put in extending the temperature range and minimising the possible disturbance from dry air (ESD) to make the SOLYS Gear Drive suitable for this climate.

                  • Solar Instruments Accessories

                    • UV Radiometers

                      • 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.V3/4) this refers to the calibration factor. Better is to say the output should be multiplied with a factor (1+x.V3/4).

                        • 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.

                        • Horticultural Sensors

                          • Data Loggers