The sensitivity of any solar sensor deviates over time when exposed to solar radiation. Most sensors have a recommended 2-year recalibration interval.

However, thanks to superior design, build quality and stability, many of our class and industry-leading sensors, including the Class A MS-80 and MS-80S Pyranometers, and MS-57 Phyrheliometer, have a 5-year recommended recalibration interval.

Your sensor should have come boxed with a calibration certificate showing the date of the original calibration and recommended recalibration interval. But, if your sensor has been stored correctly, you can calculate the actual recalibration date, based on the recommendation, from the date of installation or first use.

The calibration is not altered when the product is not used.

EKO Instruments offers Pyranometer, Pyrheliometer & Viscometer recalibration from our accredited global calibration laboratory in Tokyo, Japan. Pyranometer recalibration is also available at our laboratory in the Netherlands.

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All EKO products come with a minimum 2-year warranty.

Some products, including the IS0 9060:2018 Class A MS-80, MS-80S Pyranometer and MS-57 Pyrheliomter come with a 5-year warranty.

Check the product manual and documentation you received with your sensor to confirm the warranty conditions or contact your local EKO sales representative.

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'Soiling' is when the dome or window on your sensor becomes dirty or otherwise blocked with dust or frost, for example.

When measuring solar radiation with pyranometers, pyrheliometers or spectroradiometers, soiling can affect the radiometer output or measured irradiance (re. accuracy) of your data.

EKO sensors are designed to reduce the impact of soiling, and our range of S-Series sensors with in-built diagnostics, and digital outputs, can help to manage and further mitigate the effects of soiling with easy access to sensor status and measured data.

Even so, soiling can occur and should be analysed case-by-case. Regular rain, for example, can have a positive effect, minimising the impact of soiling. On the other hand, dry weather can lead to more dust deposition on the dome over time. Local conditions and changing weather make it difficult to predict when your sensor may need cleaning; however, rain, snow, ice, dust, sand, and salt are the most common causes of soiling, so keep an eye on these conditions and the data from your sensor.

If you do notice that your sensor's dome or window is affected by sand or salt residue, please clean the quartz window with a soft cotton cloth and alcohol or demineralised water.

Outdoor PV modules are even more prone to soiling. Small particles on the transparent surface of the modules cause light to diffract, reducing the amount of solar energy reaching the sensitive surface of the cell. As a consequence, the modules' power output will drop proportionally. Monitoring and maintaining your sensors will help you catch and mitigate the impact of PV module soiling considerably.

EKO sensors are designed to reduce the impact of soiling, and our range of S-Series sensors with in-built diagnostics, and digital outputs, can help to manage and further mitigate the effects of soiling with easy access to sensor status and measured data.

Even so, soiling can occur and should be analysed case-by-case. Regular rain, for example, can have a positive effect, minimising the impact of soiling. On the other hand, dry weather can lead to more dust deposition on the dome over time. Local conditions and changing weather make it difficult to predict when your sensor may need cleaning; however, rain, snow, ice, dust, sand, and salt are the most common causes of soiling, so keep an eye on these conditions and the data from your sensor.

In general, it is recommended to check and clean the dome every week. However, that may not always be possible, and many large PV sites or remote applications may have longer maintenance intervals. Data redundancy, that is, multiple instruments used together to analyse and compare irradiance data, will help you to understand the effect of soiling, identify trends, and customise your maintenance plans.

Though we do offer a range of spare parts and supplies our advice to customers, whenever they have an issue or question about their sensor, is to get in touch. Our service team will work with them to assess their needs and the best solution.

You can also find compatible accessories on individual product pages.

Whether your product is under warranty or not, contact your local EKO office using our online contact form, to discuss your situation and find out how we can help.

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All EKO products are built to the highest quality standards and are thoroughly tested and calibrated during production.

Even so, regular inspection of your sensor and data is advised to ensure consistent performance. Instant changes to the regular data pattern or collocated measurements, for example, may indicate a performance change or issue that necessitates servicing or recalibration.

Data redundancy, that is, multiple instruments used together to analyse and compare irradiance data, can also help you catch any issues.

The internal diagnostics systems of our S-Series range of sensors are another big help, giving users visibility over internal temperature, humidity, tilt and roll angle, helping to ensure optimum performance without the need for regular physical checks.

If you have any doubts or questions about the performance of your sensor, please contact your local EKO office using our online contact form.

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Our STR-21G and STR-22G sun trackers do not require recalibration or re-adjustment. They are built to automatically track the sun's position through calculation and active measurement of the sunspot.

Time information used for the solar position algorithm is retrieved by the GPS receiver and is frequently updated. The sun sensor actively measures the actual position of the sunspot and compensates for misalignments.

Find out more and explore available downloads for the STR-21G by visiting the product page.

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We recommend a monthly check to ensure that the sun tracker cables and cables for all associated solar sensors are still in place, that the sun tracker is still at a horizontal level and that the sun sensor front window is not dirty.

Other than that, no specific maintenance is required.

EKO Instruments Co., Ltd. (EKO) calibration laboratory is accredited and certified by PJLA (Ref: #74158) to perform pyranometer and pyrheliometer calibrations per the requirements of ISO/IEC 17025:2017, which are relevant to calibration and testing.

EKO was the first manufacturer in the world to offer an in-house calibration service for pyranometers and pyrheliometers, and we provide a calibration certificate with all new and recalibrated pyranometers and pyrheliometers.

Customers can have the highest level of confidence when purchasing an ISO/IEC 17025:2017 calibrated sensor, or when sending an existing sensor to us for recalibration. EKO's accredited laboratory status is regularly re-examined to ensure that we maintain the required standards of technical expertise.

EKO Instruments offers Pyranometer, Pyrheliometer & Viscometer recalibration from our accredited global calibration laboratory in Tokyo, Japan.

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EKO offers pyranometer recalibration at our laboratories in Japan and the Netherlands. We also work with a network of partner organisations, including specialised laboratories, meteorological institutes, and universities, to offer recalibration services worldwide.

You can book a recalibration via our services page. For more details or questions about available recalibration services in your region, please contact your local EKO office via the contact page.

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The sun sensor is a crucial component of our STR sun trackers, helping to ensure accurate tracking.

STR sun trackers follow the sun by calculating its position. The position of origin is determined by the orientation and levelling of the tracker. However, it can be difficult to find the perfect position of origin in practice. Consequently, misalignment of the tracker and all the solar sensors attached can occur despite the precise solar position calculation.

With STR sun trackers, the sun sensor is part of an active feedback system, compensating for any deviation from the ideal position of origin.

All STR sun-trackers are equipped with a standard sun sensor to guarantee high precision sun tracking without manual adjustment.

Check out our How To 'Set-up your MS-57 Pyrheliometer' video on YouTube or visit the STR sun tracker product pages to find out more.

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Failure to properly affix a heat flux sensor with the material you wish to measure can lead to local hot spots; or cold spots in cases of negative heat flux. 

Hot spots will alter your thermal gradients and change the convective and conductive heat transfer coefficients. Simply putting a sensor against a surface may still result in a heat flux reading, but the contact resistance will keep the reading from being particularly meaningful.

To improve the thermal contact of flat layered sensors, use a thermally conductive adhesive to help minimize contact resistance.

Software, manuals, specification sheets and more are all accessible via product pages and our dedicated 'Downloads' page.

Search by product type and specific product. Older and obsolete products are also included. 

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The MC-11 is a 4-20mA digital signal converter designed to convert the voltage output of a solar radiation sensor into a 4-20mA current output. 

To convert the mA output into voltage, you will need to connect a voltmeter.

First, apply a shunt resistance to the 4-20mA current loop circuit and measure the voltage at both ends of the resistor. When a 250Ω shunt resistor is applied, the 4-20mA is converted into 1-5V.

Prepare the shunt resistor according to the measurement range of the voltmeter you are using.

When selecting power supply voltage, keep in mind that the voltage decreases when using a shunt resistor; that minimum supply voltage and the voltage drop across the shunt resistor.

EKO offers a range of converters to change sensor outputs. 

The MC-11 digital signal conditioner converts the voltage output of a solar radiation sensor into a 4-20mA current output. The converter can be used with all passive EKO radiometers or any other mV sensor and can be connected to dataloggers or inverters with a 4-20mA input channel.

The sensor cable can be extended over long distances using the signal conditioner without any signal loss or potential electromagnetic interference in noisy industrial environments.

The MC-20 MODBUS 485 RTU converter is a digital signal conditioner that converts the voltage output of a solar radiation sensor, PT-100 or 10kΩ NTC temperature sensor into a MODBUS 485 RTU output.

The converter can be used with all passive EKO radiometers or other mV sensors connected to data loggers or inverters with a MODBUS 485 RTU input channel.

By using the signal conditioner, the sensor cable can be extended over long distances without any signal loss or potential electromagnetic interference in noisy industrial environments.

With MODBUS up to 100 different sensors and converter units can be addressed and connected in parallel.

ISO 9060:2018, introduced in 2018, is an international standard for solar sensors. It determines how sensors are ranked and categorised; re-defining and providing simpler, clearer, and more consistent standards across all kinds of sensor technologies compared to earlier standards.

Today, all EKO solar radiation sensors correspond to ISO 9060:2018.

Find out more with our quick guide to ISO 9060:2018 Pyranometer Classifications.

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ISO 9060:2018 defines x3 classes of sensors, A, B, and C, based on a series of parameters. Each of these parameters can impact the accuracy, speed and quality of the data produced by the sensor.

Class A is the highest rank, and to ensure the standard, Class A sensors must be individually tested to guarantee that the temperature and directional responses comply with the classification requirements.

The requirements for Class B and Class C sensors are broader or less stringent than Class A but still provide a clear and consistent set of parameters by which to assess and compare different sensors.  

Sensors in the same class, even when made by the same manufacturer, won’t necessarily have matching or equal ratings across each parameter so it is important to understand your specific needs and to research each model of pyranometer available carefully.

Please find out more with our quick guide to ISO 9060:2018 Pyranometer Classifications.

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• Direct irradiance is the part of the solar irradiance that directly reaches a surface.
• Diffuse irradiance is the part that is scattered by the atmosphere.
• Global irradiance is the sum of diffuse and direct components reaching the same surface.

Direct solar radiation measurements are typically conducted using a precision solar tracker and DNI sensor. However, this set-up ignores diffuse irradiance. Filling that gap, measuring diffuse irradiance with a shaded pyranometer allows users to calculate global irradiance accurately.

Understanding global irradiance can help with siting a prospective PV plant and optimising an existing application, improving both output and ROI.

Reference cells are widely used in monitoring applications at PV sites to measure irradiance in absolute units (W/m²).

To understand the advantage of a pyranometer over a reference cell, some elementary principles and the application need to be understood.

• Different Reference cell types are available. The most common cell materials are crystalline or monocrystalline silicon, but other semi-conductor materials are available. In general, conventional crystalline Silicon cells are sensitive in the spectral range between 300nm - 1100 nm and cover only a part of the solar spectrum. In contrast, true thermopile detectors, which are used in pyranometers, have a flat spectral response and are sensitive to solar radiation within the range approx. 300 nm - 2800 nm, 99% of the full solar spectrum.
• Since the solar spectrum is not a constant but will gradually change with the elevating path through the atmosphere, the Si reference cell has a significant disadvantage. Due to the non-uniform spectral response function of the Si-cell, the output won't respond proportionally. Si reference cells are calibrated for a particular spectrum. Consequently, the sensor sensitivity will change when the ratio of the detector response with the solar spectrum changing accordingly. So-called "spectral error" can only be corrected if the solar spectral distribution is considered. As a consequence of the spectral error, the measurement error can typically be 5% for lower solar elevation angles compared to pyranometers.
• Pyranometers are built to global ISO standards. ISO 9060:2018 specifies three different categories of solar sensors with varying characteristics and degrees of accuracy. There are no consistent standards for reference cells.
• Pyranometer calibrations are traceable to the World Radiometer Reference (WRR), a reference group of sensors that determines the radiation scale. Calibration methods for pyranometers are harmonized and applied worldwide.

STR sun trackers can be used for sun tracking or positioning applications.

The STR can be used for precision positioning applications through the control command protocol. The position control function will be 'open loop', which means no active feedback is given about the absolute position.

For solar applications, precise sun tracking is supported by the 'closed loop' sun detection function. The standard four-quadrant sun sensor automatically corrects for alignment offsets.

The tracker position can be actively monitored when operating in sun tracker mode. The available GPS time information, longitude, and latitude can be used to synchronise dataloggers or PCs. 

STR sun trackers are controlled via two sun tracking modes that can work simultaneously; Sun-sensor mode and Calculation mode.

In the Sun-sensor mode, a quadrant Si-photodiode detector with a 30° degree field will detect the sun and will compensate for any misalignment of the sun tracker.

Since the offset in most cases is static, the misalignment can be easily corrected within the sensor field of view. When clouds obscure the sun, the STR follows the solar path by calculation and open loop positioning. The tracking mode will automatically be switched depending on the solar radiation conditions to maintain the highest tracking accuracy possible.

The STR-series has a built in GPS (Global Positioning System), which acquires all necessary parameters (latitude, longitude, date and time) to operate in Calculation mode and automatic initialisation and sun tracking.

Tracking starts when the solar elevation-angle is -5° in Calculation mode. The mode changes to Sun-sensor mode when the direct solar irradiance is more than the threshold value of the Sun-sensor.

The tracking mode changes into Calculation mode when the direct solar irradiance is less than the threshold value of the Sun-sensor. When the sun goes down to -5°, the tracker waits at an elevation-angle of -15°, azimuth-angle of 0° (South).

In summary, our STR sun trackers guarantee accurate sun tracking and pointing of the attached solar sensors, automatically adjusting to the sun's position and automatically correcting or compensating for misalignment.

'STC' is the acronym for Standard Test Conditions. 

STCs are harmonised test conditions described in the IEC 60891 procedures for temperature correction and irradiance correction of solar cells and modules.

Cell and module manufacturers specify various cell parameters (e.g. Voc, Isc, Pmax, Efficiency, FF). Those values are generally recorded on the rear of the module and are used as typical performance indicators.

According to the IEC 60891, all parameters are measured in a lab using a high class 1000 W/m2 sun simulator or flasher, I-V tracer and calibrated reference cell. During the characterisation process, the temperature of the test cell or module will be controlled at 25°C.  

The test conditions are:

• Global Irradiance: 1000W/m2  / AM1.5 / 37° Tilt angle
• Module temperature: 25°C

STCs are used to rate solar modules. To understand the correlation of PV modules during non-standard conditions a conversion can be made (T ≠ 25°C, I ≠ 1000W/m2).

All EKO I-V tracers apply an STC conversion method according to the specifications in ISO 60981.

A thermopile is a thermal sensor composed of multiple thermocouples in series.

A thermocouple is a sensor that measures temperature. It consists of two different metals, joined together at one end. When the junction of the two metals is heated or cooled, a voltage is created. If both junctions are at the same temperature, the voltage will be zero. However, if one side is warmer than the other, the thermal difference will give a proportional voltage.

Many pyranometers use a thermopile detector with a black surface that absorbs solar radiation within the full spectral range.

The MS-80, however, our industry-leading Class A pyranometer launched in 2016 and based on a patented design, features an isolated thermopile detector and white quartz diffuser.

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Near the equator, the zenith angle is always close to 0° degrees at noon. Moving closer to the poles, the zenith angle changes, which changes the amount of solar radiation that reaches the Earth's surface.

'Cosine Response' is used to describe the behaviour of a sensor that measures solar irradiance. A device with a good cosine response can estimate direct irradiance by using the measurements at the surface and the zenith angle.

The directional response error or cosine error is the deviation of the actual sensor response as a function of the theoretical value. The error can be specified as a percentage or absolute value (W/m²).

Traditionally the output of a pyranometer is an analog voltage in micro or milli-Volts. The analog output can be converted into a current (4-20mA), or different voltage output ranges with an amplifier.

The output can also be digitized through an AD converter. Different digital interface standards can be applied based on the AD converter and microprocessor. Modbus, SDI-12, Zigbee, I²c are common detector interface standards. 

The Class A MS-80S Pyranometer features a 4-channel smart signal transducer giving users a choice of Modbus 485 RTU and SDI-12 for digital output, alongside 4-20mA and 0-10mA (0-1V) analogue options, for compatibility with 99% of data loggers, DAQ, and SCADA systems.

The MS-80, launched in 2016, was based on a new and patented design concept. The new detector at the core of the pyranometer helped to define superior performance characteristics against sensors in the same class, including:

• Fast response time, x10 times faster thermopile
• Lowest offset A achieved by isolating the detector inside the body
• Offset B inherently improved because the isolated detector adapts better to ambient temperature changes
• Better long term stability because the detector is hermetically sealed, making it immune to humidity changes and UV impact 
• Temperature dependency optimised for each detector
• Non-linearity effect   

Typical Class A or 'Secondary Standard' thermopile pyranometers use a 'double dome' construction to improve the sensor's thermal balance and lower the offset characteristics.

The most 'high-end' pyranometers have domes made of expensive Quartz or Sapphire to reduce the offset uncertainty and are most commonly used for top research specific applications.

The compact MS-80 sensor uses only a single glass dome and, through clever optical design, is immune to thermal offsets; this means that the performance of the MS-80 rivals any traditional 'high-end' sensor at a fraction of the cost.

Without a second dome to get in the way, the optics were designed to provide a true cosine response and flat spectral responsivity in the range 285nm – 3000nm.

Furthermore, the isolated thermopile detector is hermetically sealed and located deep inside the sensor body to keep it thermally balanced. The long-term detector responsivity is enhanced and is no longer affected by long-term exposure to UV irradiance, humidity, and pressure fluctuations.

An additional bonus, the MS-80 contains the drying agent inside the sealed sensor body, so there is no need for a replacement, helping us extend the warranty and recalibration interval from the usual 2 to 5-years.

In summary, superior design, build quality and performance are why the MS-80 is both class and industry-leading.

The MS-80S, meanwhile, launched in 2021, adds a new internal diagnostics system and 4-channel smart interface, building on the revolutionary qualities of the MS-80.

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Yes. Our STR sun trackerS and ISO 9060:2018 Class A MS-80 and MS-80S Pyranometers and MS-57 Pyrheliometer comply with the BSRN criteria.

Find out more about BSRN standards and requirements at 'bsrn.awi.de'.

The data logger can be installed outdoors in an enclosure box.

Depending on the datalogger type, it can be set up to communicate via ethernet or USB. It can also be equipped with a GSM for remote applications.

Our engineers can prepare a solution already set up with the instruments of your choice and a data logger.

For example, a solar monitoring station including a sun tracker, pyranometers, a pyrheliometer and weather sensors can be pre-configured and set up ready to use with a Campbell Scientific data logger.

Please contact your local EKO office using our online contact form to find out more.

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