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 C_n² 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 C_n² 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 C_n² 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 C_n² 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, C_n², using an optical transmitter and receiver.

        In certain cases of relatively high C_n² values the signal can become saturated depending on the diameter of the lens, wavelength and path length.

        The so called saturation limit for C_n² can be derived using the following formula (Ochs and Hill 1982)

        C_n² < 0.18^.D^5/3.L^-8/3.λ^2/6

        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]
        	Calculate
        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]
        	Calculate
        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 C_n² 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 (C_n²), 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 C_n² 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 C_n² (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 C_n² signal and Demod signal. Both signals are measured at the receiver unit. The first signal, re-scaled C_n², 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 C_n² signal. In some cases the C_n² 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, C_n². 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 C_n² to C_T² requires data of:

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

        Step 2: from C_T² 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.

        C_n² data: During clear sunny days the C_n²-signal shows a very distinctive behaviour. Every time the atmosphere changes transition, the C_n²-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 C_T² from C_n² 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 C_T², 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 C_T², C_q², and the co-variant term, C_Tq, 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+

    • What is included with the RaZON+ system?

      • • RaZON+ base unit, including logger
        • 2 year warranty, 5 years on the sensors
        • Smart Pyranometer(PR1) and Pyrheliometer (PH1) plus cables
        • Power connector for 24 VDC

    • Is the RaZON+ system really plug & play?

      • RaZON+ is 100% operational ready. The only thing a customer has to provide is a 24VDC power supply.

    • What is the payload of RaZON+? Is it possible to put other sensor on it?

      • • Only 1 pyrheliometer, the new pyrheliometer PH1 or the SHP1
        • Only 1 pyranometer, the new pyranometer PR1 or any SMP

    • Is RaZON+ easy to install?

      • • Yes, the RaZON+ will guide you, the installation procedure can be done via Ethernet or Wi-Fi on any Smart device. You only need to mount the system on a pole or its tripod and level it. The PH1 and PR1 come pre-installed.
        • On a sunny day, point the system to roughly East and start. The softwaretakes care of fine adjustment and via two small holes in the pyrheliometers you simplycan check the final position
        • If any azimuth adjusting is needed RaZON+ can be rotated on its tripod collar or fine adjustments can be made via WiFi and your Smart device

    • How does the software work?

      • There is a website hosted on RaZON+ that can be accessed on any device with Ethernet and Wi-Fi that has a web browser (pc, tablet or Smart phone)

    • Can you do everything with your smart phone? Or do I need a computer too?

      • The complete set-up and local check can be done on your smartphone or tablet.

        Data logging is done via the Ethernet or RS-485 port.

    • Does the whole RaZON+ system need calibration?

      • No, only the sensors need calibration every 2 years. Because the sensors are smart you can easily exchange them with another sensor to prevent data gaps.

    • Does it include security to prevent data loss?

      • • RaZON+ is a system and a data logger has been integrated.All data is placed in a database.
        • All data over the last year is available.
        • When power fails all data until that moment is secured

    • How can you get access to the data of RaZON+?

      • There are four ways:

        • Through Modbus (pull)
        • Through ASCII string (push)
        • Through Ethernet (database query)
        • Through WiFi (database query)

    • How many data points can be stored on the logger?

      • 1 minute averages for 365 days

         

    • How and when to calibrate the RaZON+?

      • Every two years, the RaZON+ sensors need calibration. They can be sent to Kipp & Zonen for recalibration

    • Can I connect other devices to the RaZON+?

      • A firmware upgrade is planned to accept extra Modbus sensors (pyranometer, temperature sensors) and Modbus weather stations to expand the RaZON+.

    • How can I find the IP / MAC address of your RaZON+?

      • • Connect the RaZON+ with an Ethernet cable to your network
        • Use a Windows PC connected to the same network
        • Go to START and enter CMD in the search program window

           

        • Ping the RaZON+ with its serial number (ping razon150002)
        • This will show it’s IP address
        • Then enter the command  “ arp  –a “
        • All local IP Addresses with their (Physical) MAC Addresses are shown
        • In this example  IP = 172.16.32.110
        • This IP (= RaZON+) has MAC Address:  b8-27-eb-59-dc-7d 
        

    • What is the warranty on the RaZON+ ?

      • The standard warranty of 2 years applies. However, you can register the PR1 pyranometer and PH1 pyrheliometer and extend the warranty on those instruments to 5 years.

        To register go to www.kippzonen.com/register 

  • 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.

        

    • 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	Spectrally Flat Class C	Spectrally Flat Class B	Spectrally Flat Class A	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

         

         

    • 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.

        

    • 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.

  • 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

    • Can I order a new filter for my CVF 4 ventilation unit?

      • Filters can be ordered in sets of 5.

    • What is the accuracy calculation from a radiometer to the input of the AMPBOX? And the accuracy calculation out of the AMPBOX?

      • The AMPBOX can be delivered in two versions:

        • standard, then the gain is 1 mV = 1 mA
        • adjusted, then the gain is set to 0 – 1600 W/m² = 4 – 20 mA

        The AMPBOX has a 20 bits A/D on the input and a 16 bits A/D on the output.

        The maximum error from the AMPBOX is ±0.05% of span or ±10 µV (over the full temp range)

        This means in daily use that the additional error of the AMPBOX is far below 1 W/m² for all radiometers.

    • What does “gain range” mean in the AMPBOX specification? And how is this value useful?

      • The gain range is the ability to adjust the amplification to the sensitivity of the radiometer:
        

        • Gain adjust --> 0.1 to 4 mA/mV
        • Input voltage range --> -12 to 50 mV

        As mentioned above the amplification can be adjusted to 0- 1600 W/m² = 4 – 20 mA.
        In this case 100 W/m² change on the input gives 1 mA change on the output.
        The benefit is that two different sensors with different sensitivities have an identical output from the AMPBOX.

    • In the AMPBOX specification what does “Zero adjust” mean? And how is this value useful?

      • The zero adjust is used for the pyrgeometer to allow negative inputs.
        The pyrgeometers are adjusted for -300 to +100 W/m² = 4 to 20 mA.
        So 100 W/m² change on the input gives 4 mA change on the output. The zero point for the pyrgeometer is set to 16 mA. This is because a pyrgeometer can be more negative than positive.

    • What is the benefit of using a ventilation unit?

      • To keep the outer dome at the same temperature as the surrounding air temperature. This will keep the zero (a) offset as low as possible. But also to keep the dome as dry and clean as possible (from rain snow, ice and dirt).

    • The ventilation unit has a 5 W and 10 W heater. When do I need 5 W and when do I need 10 W?

      • Advised is to use the 5 Watt heater to keep the offset (a) as low as possible. This can be used during the whole day. If the surrounding temperature is above zero this could be sufficient. Below zero degree Celsius the extra 5 Watt (10 Watt total) can be used. We recommend to use the 10 Watt heater only during the morning (few hours around (preferable before) sunrise) to get the dome clean when measurement starts. After that the heater can be set back to 5 Watt.

    • Can I convert the current output (mA) of an AMPBOX to Volt?

      • Yes you can, by using a shunt resistor and a suitable power supply unit (PSU). You will need a shunt resistor of 500 Ω to convert the output current (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.

        

    • The AMPBOX has a range of range 0 - 1600 W/m2 for 4-20mA. The CMP 3 pyranometer has a sensitivity of 16,51 μV/W/m². And the PQS 1 PAR quantum sensor has a sensitivity of 5,59 μV/μmol/m²s. How can we calculate the output signal?

      • The AMPBOX is set for 0 - 1600 W/m²  for 4 – 20 mA
        For CMP 3 with 16.51 μV sensitivity, this is 0 - 16.51 * 1600 μV =0 - 26.416 mV for 4 - 20mA  (delta = 16 mA)
        Sensitivity AMPBOX = 26.416 mV per 16 mA  =  1.651 mV per 1 mA or 1651 μV per 1 mA

        Now connected PAR with 5.59 μV/μmol.     1651 / 5.59 = 295.35 μmol per mA

        Therefore:
        0 μmol = 4 mA 
        295.35 μmol = 5 mA etc.
        4725.6 μmol = 20mA as maximum input

    • Can we measure low level photosynthesis radiation (0,1 μmol/m²s) with the PQS 1 and the AMPBOX?

      • No, 0,1 μmol/m²s input will result in a very small change on the output of the AMPBOX (around 4,00033 mA). This is outside the accuracy of the AMPBOX and the accuracy of the PAR Lite.

    • Can I use a METEON data logger in combination with the AMPBOX?

      • No, the METEON will not work together with an AMPBOX.

        With a 10 Ohm resistor the 20 mA output from the AMPBOX can be converted to 0.2 V max signal (max for the METEON). But the METEON cannot deal with the zero offset from the AMPBOX (4 mA).

    • Each AMPBOX corresponds to a specific pyranometer, could you please specify this?

      • If the AMPBOX is purchased together with a new pyranometer, or for use with an existing pyranometer, it has the sensitivity of that pyranometer programmed internally.  In this case 0-1600 W/m2 of irradiance on the pyranometer produces 4-20mA from the AMPBOX. The serial number of the pyranometer matching the AMPBOX should be present on a label on the AMPBOX.

  • UV Radiometers

    • Can I measure specific parts of the UV spectrum with the CUV 5?

      • No, it cannot separate UV-A from UV-B, it measures both together, for measurement of these parameters individually we recommend our UVS Series of radiometers.

    • What is the calibration frequency of UV radiometers?

      • We advise to re-calibrate the UV radiometers every two years.

    • Can a METEON data logger be connected to UVS-A-T and UVS-B-T?

      • No, the input range of the METEON is limited to 200 mV (the output from the UVS-X goes up to 3V)

    • What does ‘Mean Adjustment Factor’ mean on the calibration certificate of a UV radiometer?

      • The ‘Mean Adjustment Factor’ on the calibration certificate is equivalent to the sensitivity of a pyranometer. It applies to specific Ozone column and Air-mass (solar elevation) values used as the standard test conditions. Data files are provided to correct the measured values for other Ozone and Air-mass conditions (see Radiation Amplification Factor).

    • Is there an UV-C sensor available?

      • No, we do not have a UV-C sensor. UV-C from the sun is almost completely absorbed by Ozone in the atmosphere and virtually none reaches the ground. 

    • I noticed that the UVS series has a temperature controller, which make it constant 25 ˚C. Do you think this controller can cover ‘automatic temperature compensation’?

      • Actually our thermostat is better than a temperature compensation. We used to have UVS-X-C versions of our instrument (these were temperature compensated). We stopped that line because the UVS-X-T version performed much better. Temperature compensation means correcting the output for changes in sensor temperature. Because our sensor is always the same temperature there is no compensation required. The internal Peltier element heats or cools the actual complete detection system that measures the UV light.

    • What is the bandwidth of the CUV 5 and why does this not match the UV spectrum?

      • The bandwidth of the CUV 4 is 280 - 400nm. The 50 % points are defined to be 290 - 385 nm. 

        

    • What does ‘Radiation Amplification Factor’ mean?

      • The radiation amplification factor is a correction for solar zenith angle and Ozone column. This is required because these two factors strongly influence the UV measurement.

    • Can the UVIATOR software operate with a Campbell logger and its software? Or, do I have to use LOGBOX-SD for compatibility with UVIATOR?

      • The UVIATOR can work with any data logger that is capable of storing UVS measurements. The UV-data must to be stored in the correct format, and Campbell loggers can do this. More details can be found in the UVIATOR manual.

    • Why do I need the UVIATOR software?

      • For easy correction for solar zenith angle and Ozone column.

        This is required because these two factor strongly influence the UV measurement. With the UVIATOR software you can collect the Ozone column data from the OMI satellite data per date, time and location. With this Ozone data and the solar zenith angle the UVIATOR will calculate the optimal correction for every data point.

    • What is the output range of the UVS radiometers?

      • The UVS series of UV radiometers have an output in the range from 0 - 3 V.

    • Can the data from the CUV4 be used as input to calculate UV index?

      • No. According to the WMO / WHO guidelines for the Global UV Index, UV-I should only be derived from UV-E measurements (or from a spectral instrument such as our Brewer Spectrophotometer).

    • Does the UVS-AB measure UV-A and UV-B at the same time?

      • Yes, the UVS-AB has two independent detection systems.

        The UVS-AB has two continuous, simultaneous, analog outputs; one for UV-A and one for UV-B.
        See below drawing of the UVS-AB for details.

        Beneath the dome and diffuser two sets of filters and detectors are positioned. Detector 1 is 4 times bigger than detector 2. Detector 2 is located exactly in the middle, on top of detector 1. Filter 1 has an opening in the middle for filter 2 plus detector 2. In this way we can make sure both detectors have a 180 degree field of view.

         

  • 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.

        

  • Horticultural Sensors

    • Is there a table with the amount of water that we need to irrigate in one hectare, according the readings of the PQS 1 PAR quantum sensor (PAR Lite) daily?

      • We do not have charts or tables indicating irrigation requirements for various plots of land (i.e. based on differing vegetation and climatic factors). There are many scientific publications that refer to evaporation rates from crops, but none, to our knowledge, that specifically link PAR readings from our sensor to irrigation.
        

    • With the PQS 1 (PAR Lite), can I derive the crop evaporation from the net radiation?

      • 
        There is something as a "reference crop evaporation" or "actual evaporation" that can be derived from net radiation (solar plus thermal) together with surface temperature, soil and vegetation data. Unfortunately we don't have the information how to do it. There is a simpler approach in which the expected evaporation is coupled to the total dose of global radiation as measured by a horizontal pyranometer.
        
        If the metoffice gives such figures for your area it should be of importance to know the relation between PAR intensity and total global irradiance for at least a solar spectrum at air mass 1.5 (solar elevation 53°).
        
        This relation is for:
        Clear sky: 681 W/m² total, 308 W/m² in the 400 to700 nm band 1408 µmol/s.m² PAR
        Light cloud cover: 200 W/m² total, 109 W/m² in the 400 to 700 nm band 493 µmol/s.m² PAR
        
        Be aware that many green leaves are highly reflective for near IR but absorb strongly in the 400 to 700 nm band (PAR region). For evaporation only W/m² counts and for photosynthesis only photons counts.
        

    • How many PQS 1 PAR quantum sensors (PAR Lite radiometers_ do you advise to use in a greenhouse?

      • Normally 1 should be enough. If in the greenhouse the conditions differ, like different glass type, shielding or glass cover, it is advised to use more than one PQS 1 PAR quantum sensor per typical condition.

    • Can I use a PQS 1 (PAR Lite) meter under water?

      • Yes, however the depth is limited to 2 meters. Please also take the “breaking of light on the water surface” in consideration. This affects the calibration factor.

        

    • If I use a PQS 1 PAR quantum sensor (PAR Lite radiometer) 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 advised calibration frequency for a PQS 1 (PAR Lite)?

      • We advise to re-calibrate the PQS 1 (PAR Lite) radiometer every two years.

    • PAR readings at noon increase by the order of 0.001 umol/m²s. Can you tell me whether small readings like this are likely to be accurate? If not, what is the effective lower irradiance limit detectable by this sensor?

      • 0,001 µmol represents a voltage of 5nV (nano Volt). As you can understand this very low voltage cannot be measured with a data logger. Besides the absolute error from the data logger, the PQS 1 PAR quantum sensor (PAR Lite) also has some specifications to consider.
        There is the non- stability, non linearity, temperature dependence and the quantum response. Measurements under 1 µmol/m²s are not to be trusted as accurate. (effective limit)

  • Data Loggers

    • What is the extension of the log file of the LOGBOX SD?

      • The extension is .TXT or .XLS. Using the software interface you can select to save this as a text -or Excel file.

    • What is the format of the log file of the LOGBOX SD data logger?

      • The format uses columns,  for example:

        Date	Time	A1	A2	A3
        5-2-2009	10:59:03	3,079	38,763	0,693
        5-2-2009	11:00:03	3,108	38,763	0,697

         

    • How do I connect a Pyranometer with PT100 to the LOGBOX SD Data logger?

      • The picture shows how a PT100 is connected.  PT100 uses four input channels nr 1,2 ,3 and 4. Leaving 4 channels left, nr 5,6,7, and 8, to connect other sensors.

        Please note that the picture uses 2 analogue inputs for the instrument (differential). Of course you can decide to use it single ended, by connecting the – from the instrument to the GND.

        

    • Does the internal battery stop working when you power the Logbox SD with an external power supply? In this case, will you still have power available for excitation on the Power Out connection?

      • The LOGBOX SD has one input for power. You either connect the internal battery or an external power source. So external power will not switch of the battery.

        PWR OUT will provide whatever power is connected as power source for the LOGBOX SD.

    • How does a data logger work?

      • Every logger has an A/D converter with a certain resolution (number of bits) - often 10, 12, 16 or 24 bits resolution.  A logger also has a fixed number of analog input ranges - often 20 mV, 100 mV, 1 V, 5 V and 10 Volt ranges.

        For example we use a logger with 12 bits resolution and 5 Volt  input range.
        This means that the 5 Volt is divided in 2¹²  steps. This is 5/4096 = 0.00122 Volt per step. So the smallest detectable change on the input is 1.22 mV.

        If we connect an SP Lite(2) with a sensitivity of 75 microVolt/W/m^2, one Watt (change) will give 0.075 mV (change) on the output. So we need a change of 1.22 / 0.075 = 16.2 Watt/m² before we see a change in the Logger output.

        As you can understand this is not acceptable. A minimum of 1 W/m² should be detected (preferably a factor 10 times better). This can be achieved by lowering the input range to 100 mV (50 times better). Or by selecting a higher resolution e.g. 16 bits (in stead of 12 bits) this is 16 times better ( 2¹⁶- 2¹² = 2⁴ = 16 ).

    • Can I use the METEON in combination with the AMPBOX?

      • No, the METEON will not work together with the AMPBOX. With a 10 Ohm resistor the 20 mA output from the AMPBOX can be converted to 0.2 V max signal (max for the METEON). But the METEON cannot deal with the zero offset of the AMPBOX (4 mA).

    • Can the data from the METEON be downloaded into Excel?

      • Yes, inside the software, at the graphical chart, there is an export button. You can select the default .txt option or customize the extension into .xls.

    • Can a METEON data logger be connected to UVS-A-T and UVS-B-T?

      • No, the output of the UVS is 0-3V and this is too high for the METEON.

    • What is the logging interval for the METEON?

      • The logging interval can be selected from 2 to 65.535 seconds.

    • What is the operating life of the batteries of the METEON?

      • Two AA size internal Alkaline batteries will operate for approximately 1200 hours / 50 days.

    • How is the METEON powered?

      • With two AA size internal Alkaline batteries.

    • Can we use the METEON outside?

      • The METEON is not suitable for unprotected outdoor use. However, the operating temperature range is – 10 ºC to + 40 ºC. When it is placed in an enclosure protected from dust and rain, it would be possible in practice.

    • What is the difference between the SOLRAD and the METEON?

      • The SOLRAD can be used as a very cost-effective and well performing real-time interface to a PC serial port, logging the data on the PC with the supplied software.

        The METEON however, cannot do this. You need to download the data periodically using the supplied software. The METEON interface is USB.

    • I have an outdoor reading of 2000 to 4000 W/m² with my METEON. This does not make sense since theoretically, readings should be less than the solar constant (1360 W/m²).

      • Please check the calibration factor of the pyranometer which is set in the METEON. A wrong calibration factor of the instrument will result in wrong measurements. Also check if the correct instrument is selected.

        

    • If we take an interval of 1 minute then the sum of all the averages for 1 day it says 394838 W/m². If we set it for 30 minutes, then we will get 1 average per 30 minutes so the sum of all these averages for 1 day would be 13161 W/m². What are we doing wrong?

      • Adding the intervals without dividing this by the (interval) time.

        For example:
         
        Radiation in the morning 4 hours 400 W/m².
        Radiation in the afternoon 4 hours 600 W/m².
         
        If you would take a 60 minute interval on the same day:
        Morning = 4 intervals of 400 W/m²
        Afternoon = 4 intervals of 600 W/m²
        Total over the day 4 x 400 + 4 x 600 = 1600 + 2400 = 4000 W/m² (over hourly interval)
        This is 4000 W/m² per hour or 4000 Wh

        The stored interval in METEON is 30 minutes.
        During the morning you will get 8 intervals of 400 W/m²
        During the afternoon you will get 8 intervals of 600 W/m²
        16 intervals (of 30 minutes) with a total of 8 x 400 + 8 x 600 = 8000 W/m² (over 30 min interval)
        This is 8000/2 = 4000 W/m² per hour or 4000 Wh

    • Can a SOLRAD data logger be connected to UVS-A-T and UVS-B-T?

      • Yes, the SOLRAD is perfect because it has a 0-10V input range available (the output of the UVS meter is 0-3V ).

        Please consider that the SOLRAD is intended to display real-time values and/or to store the integrated values for a day. If you fully want to use data logger options it is better to use a LOGBOX SD.

    • How can we program the SOLRAD for the output to be in W/m² ?

      • The UVS has a ‘Mean Adjustment Factor’ on the calibration certificate.  This is equivalent to the sensitivity of a Pyranometer.  This can be entered into the SOLRAD and the readings will be in W/m².

    • I understand the SOLRAD is not really a data logger. Is this correct?

      • The SOLRAD is not a data logger. It is intended to display real-time values and/or to store the integrated values for a day. 31 records allows a month of daily integrated values to be stored. 

    • How is the SOLRAD powered?

      • The internal battery will only run it for a little more than one day. For longer periods it requires an external DC supply.

    • Can we use the SOLRAD outside?

      • It is not suitable for unprotected outdoor use. However, if it is in an enclosure protected from dust and rain it would be OK in practice.

    • How long can I record data on my COMBILOG data logger

      • This depends on the number of recorded channels and storage interval. A detailed description of the storage capacity can been found in the COMBILOG manual, available on it's product page.

        In case you want to quickly calculate the storage capacity in days for your application, please use the calculation tool below.

        Please enter your desired settings for the data logger:
        Number of Channels:
        Storage interval [seconds]:
        	Calculate
        Total number of days recording time:
        With standard internal memory:
        7MB		Days
        With optional SD-card:
        1024MB / 1 GB:		Days

• DustIQ

  • General

    • What does DustIQ measure?

      • The DustIQ measures the amount of light relected by the dust back into the sensor. This is converted into Transmission Loss and Soiling Ratio. The DustIQ reports 2 independent transmission losses and soiling ratios of its 2 sensors.  (Transmission loss = 100% - soiling ratio)

    • How does soiling loss translate into power/energy loss?

      • How does soiling loss translate into power/energy loss? Transmission loss, according to several publications and reports, directly translates into energy loss because the relationship is almost linear for soiling losses up to 20%.

    • What is the accuracy of dust measurement by the DustIQ?

      • Transmission loss measurement accuracy: ± 10% of reading after local dust calibration (not including zero offset). Zero offset: < ± 1% when clean.

    • What can I do with the zero offset ?

      • The zero offset can be subtracted from the measurements to reach zero again. E.g. a transmission loss of 0.3% for a completely clean DustIQ is within specification and can be compensated by TLcorrected = TL - 0.3 or Soiling Ratiocorrected = Soiling Ratio + 0.3

    • How closely do dust levels on sensor and PV plant panels match?

      • When installed next to or in between the actual PV modules the relationship is between 80 and 100%.

    • Is the Dust IQ soiling loss accurate when compared with a 2-panel system?

      • A 2-panel system with PV modules identical to the ones used in the PV plant and cleaned every day is the most accurate but also most expensive solution. It is also very unlikely that a 2-panel system can be installed right in between the real PV modules and thus the soiling will be different. The DustIQ is the optimum balance between accuracy and being maintenance-free with a low TCO.

    • What is the maximum soiling measurement range of DustIQ?

      • The DustIQ can measure up to 50% soiling loss.

    • How can the soiling be the same as on the panels?

      • The DustIQ is installed next to or in between the actual PV modules and will get the same dust, wind, rain and cleaning. The surface is also very similar to a many PV modules.

    • What is the significance of the solar cell on the DustIQ?

      • The silicon cell is only used once for the local dust calibration to correlate the step change in energy with the optical sensor measurement.

    • What is the impact of the panel temperature on the Dust IQ?

      • The DustIQ uses its own Optical Soiling Measurement. The DustIQ performance is not affected by external factors in the temperature range given in the specifications: from -20 to +60° C

    • What is the purpose of the temperature option when selecting the correct model of DustIQ?

      • The PV module temperature sensor (standard since 2019) can be connected to the second port on the DustIQ to measure the rear temperature of a nearby PV module. The IEC advises to take many temperature measurements to be able to take the PV module temperature into account in the Performance Ratio calculations.

    • How many DustIQs are needed relative to the installed PV plant power? (Number of sensors per 1 MW)

      • "The standard IEC61724-01 on monitoring gives recommendations. Due to copyright we cannot share the document. Table 1 in the document advises as follows:
        
        5MW 1 instrument
        40MW 2 instruments
        100MW 3 instruments
        200MW 4 instruments
        300MW 5 instruments
        500MW 6 instruments
        
        Please see below for a preview and ways to buy the document. https://webstore.ansi.org/Standards/IEC/IEC61724Eden2017

    • Technically speaking, how does the DustIQ measure soiling according to IEC 61724?

      • "IEC 61724 specifies two methods to measure soiling that were available at that time:
        
        Method 1: max power and temperature of the soiled device
        
        Method 2: short-circuit current and temperature measurement
        
        The optical measurement that has been introduced with the release of the DustIQis equivalent to the short-circuit current method. Obviously it does not measure short-circuit current but the reflected light, that then is translated into transmission loss. The local dust calibration is done based on the step change of the short-circuit current of the built-in silicon panel."

    • Is the DustIQ useful for Polycrystalline or Thin-film modules?

      • Yes, it is. Although the Thin-film might react a little bit different, the relationship between sunlight lost due to soiling and energy loss remains the same.

    • What is the expected soiling loss percentage with respect to dry cleaning and wet cleaning?

      • This question is best answered by the people supplying the dry cleaning robots. However, we have seen dry cleaning robots to reach 0.5% soiling loss compared to 8% loss before the cleaning. Wet cleaning sometimes is better but only when done very carefully, with very clean water and in absence of wind that brings new dust directly sticking to the wet PV modules.

    • Can we trigger automatic movement of robotic cleaners for cleaning of modules through RS-485?

      • The short answer is no. The data produced needs "clever" robot control software to filter out rain and dew events, to be able to start a cleaning cycle. Humans can see immediately from a graph and the weather report what happened. Computers need machine learning and AI. Thus, in the future this can be possible.

    • Can the soiling data be transmitted to SCADA via Wi-Fi?

      • The DustIQ doesn't have Wi-Fi as customers told us they don't trust the connection to be 100% available all the time. Therefore, we use Modbus RTU over RS-485 wired connection that also supplies the 12-24V power. However, the solution can be made wireless by using an integrator or customer supplied RS-485 to Wi-Fi converter and Modbus over TCP/IP.

    • Can we link in to SCADA system to measure the Performance Ratio (PR)?

      • Absolutely. The DustIQ produces Modbus registers to be read out. Please see the manual.

    • Can the DustIQ resist harsh conditions, for example in locations near the sea?

      • Yes. The DustIQ is made with glass and aluminium with PV standard quality. Thus the same procedures for using and cleaning the PV modules can be used.

    • Is there a way to identify the soiling rate on the glass dome of a pyranometer using the DustIQ?

      • There is no direct relationship between the soiling of the flat DustIQ and the round glass dome of a pyranometer. Also the influence of soiling on a round dome on solar radiation measurement changes from plus to minus over the day and with the angle of the sun. Currently, there is no better solution than regular cleaning of the dome.

    • What is the advantage by using blue LED light?

      • Only blue LEDs are available with manufacturer documents to show long time stability in UV rich environments.

    • Why can the reported soiling ratio differ between the two sensors of the DustIQ?

      • Analyses show that the bottom of PV modules often gets soiled more than the top part and so will the bottom DustIQ sensor. Resulting in higher reported transmission loss.

    • Following IEC 61724-01, would you recommend measuring soiling in heavy rainy areas, e.g. Quebec in Canada?

      • According to IEC 61724-01, soiling monitoring is necessary when energy losses can exceed more than 2%. In areas with a lot of rainfall, this probability is very small and measuring soiling would not be needed.

    • How fast can the DustIQ report data?

      • The DustIQ takes a measurement once per minute. It operates throughout the whole day. The measurements are reliable as long as the device is dry. Storing 24x7 measurements of every minute does not really make sense as soiling grows very slowly. A few measurement points per day are enough.

    • The DustIQ is obviously smaller than a solar panel. By saying "it has PV panel dimensions", what does that mean?

      • Its length (996 mm) is the most common width of PV modules as is its height (35mm). The aluminium frame and glass are PV module equivalent, too.

    • What if the soiling buildup does not look the same on the DustIQ collection area compared to other modules?

      • Theoretically, the DustIQ measurement could be different then. According to the experience our customers made, the results are still close enough.

    • Many PV plants are installed near the ocean or industrial areas. What do you recommend to handle bird droppings and organic material or soot?

      • Bird droppings are very local and only a 2-panel system can work accurately. However, preventing bird colonies even when building the PV plant is paramount. Cleaning is very difficult or expensive and once colonized, the birds are difficult to deter.

    • What is the main difference between normal soiling station of other makes and DustIQ?

      • Normal 2-panel systems require daily cleaning of the clean reference cell or panel, they do not fit in between the real PV modules and they only work well on sunny, cloudless days around solar noon. The DustIQ works 24/7 as long as the DustIQ is free from rain or dew. It even works up-side-down for bifacial PV plants.

    • How does the DustIQ compare to the Atonometrics MARS sensor?

      • They both use optical soiling measurement. The MARS uses a camera and only works around sunset and with a clear sky. Thus, one measurement window per day. The DustIQ measures accurately 24x7 as long as the DustIQ itself is dry. Supposedly, the MARS does not need dust calibration, but no prove has been published.

    • Does DustIQ work independently or for all PV technologies, i.e. Bifacial PV?

      • It works for all silicon- based PV modules and also upside down for bifacial.

    • What if there are different types of dust throughout the year?

      • The DustIQ has not been designed for that.

    • Is there a plan to offer a traceable temperature sensor for the DustIQ?

      • This is under investigation.

  • Calibration

    • How often do I need to execute local calibration?

      • Only once. The calibration is valid for the whole lifetime of the device.

    • What is the calibration frequency with respect to the lifetime of the DustIQ?

      • It is needed only once to make sure the effect of your local dust is used to get the best measurements.

    • What is the calibration frequency of the DustIQ (mainly the LED)?

      • The DustIQ does not need recalibration for at least 5-10 years as it has extra internal sensors and compensation for any potential wear or drift.

    • Is it necessary to send to a K&Z facility for calibration?

      • No. All components have been selected in such a way that we do not anticipate factory recalibration. A local dust calibration also measures and corrects for any future deviation from the original factory calibration.

    • Is the DustIQ able to calculate loss when covered with dust different to the calibration dust sample?

      • The DustIQ works with dust it has been calibrated with. For the factory calibration it is Arizona Test Dust. For other dust types, the DustIQ can be calibrated locally, it cannot be calculated or "programmed".

    • Since it is needed to do calibration with natural soiling, is the data still valid before calibration?

      • The data will be less accurate most likely. After local dust calibration the "old" data can be post-processed as described in the manual.

    • What to do in case of a dust storm where the local dust is different?

      • Ideally, perform a local dust calibration soon after and record the mentioned Modbus registers for dust slopes before and after. Going back to factory settings is possible.

    • Can you provide more details about the on-site calibration? How long does this take, how much labor is required, etc.?

      • We have compiled all relevant information on a separate page. Please see: https://www.kippzonen.com/Download/999/DustIQ-Calibration-Procedure-0386910-and-0386915-models

  • Cleaning

    • What is the periodic time to clean the DustIQ?

      • The DustIQ is never cleaned on its own. It is only cleaned when the actual PV modules are cleaned. Then it remains "in sync" with the real PV modules.

    • How should the DustIQ itself be cleaned?

      • The DustIQ is made of PV module material like the glass and aluminium. Thus, the same procedures as for cleaning the PV modules can be used.

    • What data filtering/filters should be applied to raw data measured by the DustIQ to make the measurements useful for soiling analysis and wash decision?

      • Remove all data when the weather station indicates rain (30 minutes before and 1 hr after) and when the dew point is close to or below the PV module temperature (dew). Or install a Modbus dew-rain sensor next to the DustIQ.
        
        

    • We are using self-powered module cleaning robots. If we keep its frequency of say twice a week, will dust measurement sensors be required?

      • Probably not, but the PV plant owner might ask you to show that indeed the PV modules were cleaned (step change in soiling loss) and how good the robots do their job (how close to 0% loss you get)

  • Installation

    • How and where to mount the DustIQ?

      • The DustIQ is installed next to or in between the actual PV modules.
        
        

    • Can the DustIQ be installed on the open end of a row of panels or does it have to be supported on both sides between two panels?

      • For long term installation the DustIQ needs mounting support. Either from two adjacent PV modules or its own support structure.

    • Can the DustIQ be mounted horizontally rather than vertically for single roof panel arrays for commercial rooftop systems?

      • Yes, that is possible.