SOLAR RADIATION MEASUREMENT INSTRUMENTATION

Has been committed to developing the finest scientific instrumentation for precision measurements since 1917. The Meteorology Department produces radiometer, pyranometers, pyrheliometers and pyrgeometers that measure solar and terrestrial radiation. Many National Meteorological Authorities are using our Instrumentation as their standards for radiometric measurements.

In addition to Atmospheric Radiation Measuring Equipment, we manufactures and calibrates:

bulletStandard Lamps
bulletBlackbodies
bulletLaboratory Thermopiles

 

INTRODUCTION TO SOLAR RADIATION

DIRECT, DIFFUSE AND GLOBAL SOLAR RADIATION

RADIATION STANDARDS

CATALOGUE

  PRECISION SPECTRAL PYRANOMETER

  PRECISION INFRARED RADIOMETER-Model PIR

  TOTAL ULTRAVIOLET RADIOMETER-Model TUVR

  NORMAL INCIDENCE PYRHELIOMETER-Model NIP

  SOLAR TRACKERS-Models SMT-3, ST-1, ST-3

  SHADING DEVICES-Models SBS, SDK

  HF ABSOLUTE CAVITY RADIOMETER-Model HF, AHF

  STANDARD LAMPS

  INFRARED CALIBRATION SOURCE

  LABORATORY THERMOPILES

 

INTRODUCTION TO SOLAR RADIATION

Solar radiation is a term used to describe visible and near-visible (ultraviolet and near-infrared) radiation emitted from the sun. The different regions are described by their wavelength range within the broad band range of 0.20 to 4.0 µm (microns). Terrestrial radiation is a term used to describe infrared radiation emitted from the atmosphere. The following is a list of the components of solar and terrestrial radiation and their approximate wavelength ranges:

bulletUltraviolet: 0.20 - 0.39 µm
 
bulletVisible: 0.39 - 0.78 µm
 
bulletNear-Infrared: 0.78 - 4.00 µm
 
bulletInfrared: 4.00 - 100.00 µm

Approximately 99% of solar, or short-wave, radiation at the earth's surface is contained in the region from 0.3 to 3.0 µm while most of terrestrial, or long-wave, radiation is contained in the region from 3.5 to 50 µm.

Outside the earth's atmosphere, solar radiation has an intensity of approximately 1370 watts/meter2. This is the value at mean earth-sun distance at the top of the atmosphere and is referred to as the Solar Constant. On the surface of the earth on a clear day, at noon, the direct beam radiation will be approximately 1000 watts/meter2 for many locations.

The availability of energy is affected by location (including latitude and elevation), season, and time of day. All of which can be readily determined. However, the biggest factors affecting the available energy are cloud cover and other meteorological conditions which vary with location and time.

Historically, solar measurements have been taken with horizontal instruments over the complete day. In the Northern US, this results in early summer values 4-6 times greater than early winter values. In the South, differences would be 2-3 times greater. This is due, in part, to the weather and, to a larger degree, the sun angle and the length of daylight.

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DIRECT, DIFFUSE AND GLOBAL SOLAR RADIATION

As solar radiation passes through the earth's atmosphere, some of it is absorbed or scattered by air molecules, water vapor, aerosols, and clouds. The solar radiation that passes through directly to the earth's surface is called Direct Solar Radiation. The radiation that has been scattered out of the direct beam is called Diffuse Solar Radiation. The direct component of sunlight and the diffuse component of skylight falling together on a horizontal surface make up Global Solar Radiation.

Global radiation is measured by a pyranometer. The modern pyranometer manufactured by us, using wire wound plated thermopiles, can be one of two types: the Precision Spectral Pyranometer (Model PSP) and the Black & White Pyranometer (Model 8-48). The PSP has a black sensor protected by two precision ground, polished hemispheres. The 8-48 has a black and white "star" sensor that is protected by a single polished hemisphere.

Over the years, there have been efforts to increase the linearity of response, durability, the adherence to the Lambert cosine response law and independence from ambient temperature effects. The precision pyranometer operates without deviations at various inclinations and is, therefore, often used to test solar panels, where it is mounted in the plane of the collector.

Direct radiation is best measured by use of a pyrheliometer, which measures radiation at normal incidence. The Normal Incidence Pyrheliometer (Model NIP) consists of a wire wound thermopile at the base of a tube, the aperture of which bears a ratio to its length of 1 to 10, subtending an angle of 5°43'30". This limits the radiation that the thermopile receives to direct solar radiation only.

The pyrheliometer is mounted on a Solar Tracker (Models ST-1 and ST-3) or an Automatic Solar Tracker (Model SMT-3) for continuous readings.

Diffuse radiation can either be derived from the direct radiation and the global radiation or measured by shading a pyranometer from the direct radiation so that the thermopile is only receiving the diffuse radiation. We has developed Shade Disk Adaption Kit (Model SDK) that mounts on the SMT-3 which allows you to measure the diffuse and direct at the same time. We also manufacture the Shadow Band Stand (Model SBS).

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RADIATION STANDARDS

Self calibrating cavity pyrheliometers are used to define the scale of solar radiation. This type of instrument can be constructed and characterized to yield absolute radiation values in Standard International (SI) units by employing the electrical substitution method. A selected group of these instruments is know as the World Standard Group (WSG) which is maintained at the World Radiation Center (WRC) in Davos, Switzerland. Using this group of instruments, the World Radiation Reference (WRR) is periodically determined. All other cavity instruments are referenced to the WRR by intercomparison.

The self-calibrating cavity pyrheliometer is the Absolute Cavity Pyrheliometer (Model HF). This device has a cavity receiver configured as an inverted cone within a cylinder. A precision aperture defines the area of the direct solar beam for the measurement. One model HF instrument is included in the WSG.

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CATALOGUE

This is a list of our currently available instruments. By clicking each individually you get a data sheet for that instrument.

Note that in addition to Atmospheric Radiation Measuring equipment there are three other product lines added to the bottom of the list.

Please contact us if you have any special requirements

 

PRECISION SPECTRAL PYRANOMETER-Model PSP

The Precision Spectral Pyranometer is a World Meteorological Organization First Class Radiometer designed for the measurement of sun and sky radiation, totally or in defined broad wavelength bands. It comprises a circular multi-junction wire-wound  thermopile which has the ability to withstand severe mechanical vibration and shock. Its receiver is coated with Parson's black lacquer (non-wavelength selective absorption). This instrument is supplied with a pair of removable precision ground and polished hemispheres of Schott optical glass. Both hemispheres are made of clear WG295 glass which is uniformly transparent to energy between 0.285 to 2.8µm. For special applications, other Schott glasses and Infrasil II quartz hemispheres are available. Included is a spirit level, adjustable leveling screws and a desiccator which can be readily inspected. The instrument has a cast bronze body with a white enameled guard disk (shield) and comes with a transit/storage case. A calibration certificate traceable to the World Radiation Reference and a temperature compensation curve is included.

SPECIFICATIONS

bulletSensitivity: approx. 9 µV/Wm-2.
bulletImpedance: approx. 650 Ohms.
bulletTemperature Dependence: ±1% over ambient temperature range -20 to +40°C
bullet(temperature compensation of sensitivity can be supplied over other ranges at additional charge).
bulletLinearity: ±0.5% from 0 to 2800 Wm-2.
bulletResponse time: 1 second (1/e signal).
bulletCosine:
bullet±1% from normalization 0-70° zenith angle;
bullet±3% 70-80° zenith angle.
bulletMechanical Vibration: tested up to 20 g's without damage.
bulletCalibration: integrating hemisphere.
bulletSize: 5.75 inch diameter, 3.75 inches high.
bulletWeight: 7 pounds.
bulletOrientation: Performance is not affected by orientation or tilt.

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PRECISION INFRARED RADIOMETER-Model PIR

The Precision Infrared Radiometer, Pyrgeometer, is intended for unidirectional operation in the measurement, separately, of incoming or outgoing terrestrial radiation as distinct from net long-wave flux. The PIR comprises a circular multi-junction wire-wound  thermopile which has the ability to withstand severe mechanical vibration and shock. Its receiver is coated with Parson's black lacquer (non-wavelength selective absorption). Temperature compensation of detector response is incorporated. Radiation emitted by the detector in its corresponding orientation is automatically compensated, eliminating that portion of the signal. A battery voltage, precisely controlled by a thermistor which senses detector temperature continuously, is introduced into the principle electrical circuit.

Isolation of long-wave radiation from solar short-wave radiation in daytime is accomplished by using a silicone dome. The inner surface of this hemisphere has a vacuum-deposited interference filter with a transmission range of approximately 3.5 to 50 µm.

SPECIFICATIONS

bulletSensitivity: approx. 4 µV/Wm-2.
bulletImpedance: approx. 700 Ohms.
bulletTemperature Dependence: ±1% over ambient temperature range -20 to +40°C.
bulletLinearity: ±1% from 0 to 700 Wm-2.
bulletResponse time: 2 seconds (1/e signal).
bulletCosine: better than 5%.
bulletMechanical Vibration: tested up to 20 g's without damage.
bulletCalibration: blackbody reference.
bulletSize: 5.75 inch diameter, 3.5 inches high.
bulletWeight: 7 pounds.
bulletOrientation: Performance is not affected by orientation or tilt.

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VENTILATOR-Model VEN

The Ventilator is designed to be used with the Precision Spectral Pyranometer, Model PSP or the Precision Infrared Radiometer, Model PIR.

A "muffin" fan in the base continuously blows air over both the instrument case and the instrument dome, keeping the hemispheres cleaner from frost, snow, dew and moisture buildup. The fan provides approximately 30 C FM of ventilation and draws approximately 0.15 amps, or 11 watts, in the 115 volt configuration. The clear plastic upper housing allows the instrument, connector, and desiccator window to be easily viewed. A white enameled guard disk, leveling screws and hold down holes are provided. The 8 inch diameter, 5.75 inch high ventilator weighs 5.5 pounds.

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TOTAL ULTRAVIOLET RADIOMETER-Model TUVR

The Total Ultraviolet Radiometer is a rugged, relatively simple detector for the measurement of solar UV radiation. Ease of operation combined with performance accuracy comparable with pyranometers intended for the recording of the total short-wave radiation (0.295 to 0.385 µm) make this instrument an attractive instrument for UV measurement.

This instrument utilizes a hermetically sealed selenium barrier-layer cell which is protected by a quartz window. It is operated at low light levels and under conditions of minimum electrical current drain, in order to ensure a high degree of performance stability over lengthy periods of exposure. A specially designed teflon diffuser not only reduces the radiant flux to acceptable levels but also provides close adherence to the Lambert cosine law. An encapsulated narrow bandpass (interference) filter limits the spectral response of the photocell to the wavelength interval 0.295 to 0.385 µm, with negligible secondary transmission.

The unit is of brass construction and includes adjustable leveling screws and a circular spirit level

A calibration certificate traceable to the National Institute of Standards and Technology (NIST) is included.

SPECIFICATIONS

bulletSensitivity: approx. 150 µV/Wm-2.
bulletImpedance: approx. 1500 Ohms.
bulletTemperature Dependence: ±0.3% / °C over ambient temperature range -40 to +40°C.
bulletLinearity: ±2% from 0 to 70 Wm-2.
bulletResponse time: milliseconds.
bulletCosine: ± 3.5 % from normalization 0-70° zenith angle.
bulletMechanical Vibration: tested up to 20 g's without damage.
bulletCalibration: reference secondary standard group of UV Radiometers.
bulletSize: 5.75 inch diameter, 6.75 inches high.
bulletWeight: 6 pounds.

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NORMAL INCIDENCE PYRHELIOMETER-Model NIP

The  Normal Incidence Pyrheliometer is a World Meteorological Organization First Class Pyrheliometer designed, as its name implies, for the measurement of solar radiation at normal incidence.

The NIP incorporates a wire-wound thermopile at the base of a tube, the aperature of which bears a ratio to its length of 1 to 10, subtending an angle of 5°43'30". The inside of this brass tube is blackened and suitably diaphragmed. The tube is filled with dry air at atmospheric pressure and sealed at the viewing end by an insert carrying a 1 mm thick, Infrasil II window. Two flanges, one at each end of the tube, are provided with a sighting arrangement for aiming the pyrheliometer directly at the sun. A manually rotatable wheel (not shown) which can accommodate three filters, while leaving one aperature free, is provided.

The pyrheliometer is mounted on a power-driven equatorial mount for continuous readings. Please see Solar Trackers.

A calibration certificate traceable to the World Radiation Reference and a temperature compensation curve are included.

SPECIFICATIONS:

bulletSensitivity: approx. 8 µV/Wm-2.
bulletImpedance: approx. 200 Ohms.
bulletTemperature Dependence: ±1% over ambient temperature range -20 to +40°C. (temp. compensation can be supplied over other ranges at additional charge.)
bulletLinearity: ±0.5% from 0 to 1400 Wm-2.
bulletResponse time: 1 second (1/e signal).
bulletMechanical Vibration: tested up to 20 g's without damage.
bulletCalibration: reference  primary standard group of pyrheliometers.
bulletSize: 11 inches long.
bulletWeight: 5 pounds.

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SOLAR TRACKERS-Models SMT-3, ST-1, ST-3

The two types of Solar Trackers to be used with the Normal Incidence Pyrheliometer and the Cavity Radiometer.

The Automatic Solar Tracker, Model SMT-3 is a 2 axis, azimuth/elevation device programmed to align direct beam instruments with the normal incidence of the sun from any position on the earth’s surface. Tracking is achieved using a computer program which calculates the solar position for the time and location and transmits pulses to the drives, which then operate the 2 stepping motors. The stepping motors move the elevation and azimuth axes to the correct position. After initial installation, the tracker will continue to track the sun and reset during darkness. Only periodic resetting of the system clock is required.

The Models ST-1 and ST-3, "green tracker" are electrically driven using a clock-based motor which makes one revolution every 24 hours. The ST-1 is designed for use with a single instrument while the ST-3 accommodates up to three. The ST-3 also incorporates worm and gear fine adjustments for declination and equation of time.
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SHADING DEVICES-Models SBS, SDK

Diffuse Solar Radiation can be determined by measuring the Direct Beam Radiation using a Normal Incidence Pyrheliometer on a Solar Tracker and the Total Solar Radiation using a Precision Spectral Pyranometer and computing the difference. However, the Diffuse measurement can be taken by shading the Direct Beam from the pyranometer measuring Total Radiation. The Laboratory manufactures two standard types of Shading Devices to be used to block the Direct Beam Radiation from a receiving sensor, the Shadow Band Stand and the Shade Disk Kit (to be used on the Automatic Solar Tracker).

The Shadow Band Stand, Model SBS, is constructed of anodized aluminum, weighs approximately 24 pounds and uses a 3" band of approximately 25" diameter to shade the pyranometer. The declination setting must be adjusted regularly.


Many National Authorities wished to shade the Precision Infrared Radiometer to reduce the heating effect of the silicon dome. Since they already owned the Automatic Solar Tracker, an adaption kit was designed to shade and ventilate the PIR while the tracker aligned NIP for direct measurement. This Shade Disk Kit, Model SDK also allows for the measuring of Diffuse and Direct Solar Radiation simultaneously. The SDK attaches onto the SMT-3 Tracker and includes a mounting plate with built-in ventilators that allows one or two instruments to be shaded by a shade disks extended over the radiometers on an arm. The standard 1:10 ratio is maintained by using a 6 cm diameter disk at a distance of 60 cm from the receivers of the instruments. This picture shows the SMT-3 Tracker equipped with the SDK and an HF Cavity Radiometer, a Normal Incidence Pyrheliometer, a Precision Spectral Pyranometer and a Precision Infrared Radiometer.

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HF ABSOLUTE CAVITY RADIOMETER-[Absolute Cavity Radiometer]Model HF, AHF

The self-calibrating Absolute Cavity Pyrheliometer, Model HF, has been a reference standard level device for many years. The sensor consists of a balanced cavity receiver pair attached to a circular wire-wound and plated thermopile. The blackened cavity receivers are fitted with heater windings which allow for absolute operation using the electrical substitution method, which relates radiant power to electrical power in SI units. The forward cavity views the direct beam through a precision aperture. The precision aperture area is nominally 50 mm2 and is measured for each unit. The rear receiver views an ambient temperature blackbody. The HF radiometer element with baffle tube and blackbody are fitted into an outer tube which acts as the enclosure of the instrument. The Model AHF has an automatic shutter attached to the outer tube.

Model HF ControlThe operation of the cavity radiometer, and the measurement of the required parameters is performed using an appropriate control box. The control functions include setting of the calibration heater power level, activation of the calibration heater, selection of the signals to be measured and control of the meter measurement functions and ranges. The measured parameters include the thermopile signal, the heater voltage and the heater current which is measured as the voltage drop across a 10 Ohms precision resistor. The instrument temperature may also be measured using an internally mounted thermistor. The meter resolution of 100 nV allows for a thermopile signal equivalent in radiation of approximately 0.1 Wm-2.

Control boxes for manual or manual/automatic are available. The control box can operate either one radiometer in the measurement mode or two radiometers in the comparison mode. Automatic operation allows for computer control of shuttering, calibration heating and measurement functions. Calculation operations and data storage are also possible under computer control. Programs for independent, automatic measurement and cavity radiometer comparison are supplied with automatic units.

Although these are absolute devices, the radiometers are compared with the reference cavity radiometers which have participated in the International Pyrheliometric Comparison (IPC) and other intercomparisons and are directly traceable to the World Radiation Reference (WRR).

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STANDARD LAMPS

 

The Source Examination Department is equipped to determine the Spectral and Total Radiation characteristics of most laboratory and industrial sources currently in use. Color Temperature and Brightness Temperature measurements can be performed on specific sources.

  Two basic radiometric standards are available with traceability to the National Institute of Standards and Technology (NIST); the Standard of Spectral Irradiance and the Standard of Total Radiation. We supplied, or customer supplied, sources can be calibrated.

  Photometric Standards are also available, calibrated in horizontal candle power.

  Please contact us for all your Standard Lamp needs.

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INFRARED CALIBRATION SOURCE

 Model BB810T
For over thirty years, The Laboratory has concentrated on low temperature sources of extended area. Our impressive customer list includes: NOAA, NASA, SAIC, Honeywell (US, Germany), Spacebell (Belgium), Hughes, Westinghouse, and others. In addition we has served on several Space Satellite Projects, including SIRS, VTPR, VHRR, SCMR, HIRS, ERB, and APEX among others. Source areas have ranged from 10 to over 1000 cm2.

  Often thermoelectric heat pumping is utilized to precisely control a blackened cavity array radiator to produce a source with high stability (0.05o C), uniformity (0.1o C), and emissivity (>0.995) over a temperature range of -20o C to 125o C. Most sources can be obtained with a flat plate radiator that has an emissivity of 0.98. Forced convection is employed to stabilize the thermoelectric heat sink for sources with areas up to 150 cm2. Larger area sources require fluid stabilization. Temperatures down to -50o can be achieved with a refrigerated heat sink fluid. Sources operating below -50oC require liquid nitrogen cooling and resistive heating. Thermoelectrics are not employed.

  Remote control is an option with the digital controllers through either RS232 or IEEE-488 interface. Remote interrogation of the temperature readout is also available.

  Please contact us outlining your specific requirements and we'll be happy to make specific recommendations and provide pricing and delivery details.

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LABORATORY THERMOPILES

One of the earliest devices employed to measure radiant energy was the thermopile. A circular and linear type of thermopile were introduced by W. W. Coblentz who subsequently arranged with the Laboratory for their commercial manufacture and improvements. In principle, they are have been referred to as “compensated thermopiles”, which applies to their thermal compensation where the total area (mass) of the shielded cold receivers is equal to that of the single hot receiver.

We now manufactures wire-wound thermopile detectors that are essentially sensitivity-independent over wide intensity ranges. Originally designed for installation in rocket, satellite and spacecraft vehicles, these sensors have successfully withstood the mechanical shocks encountered in launching.

We manufactures four models (E6, G3, H6, J3) that are calibrated in accordance with customer requirements. Low intensity calibrations (40-80 µW/cm-2, 3 points) are undertaken by exposure of the thermopile to a NIST furnished carbon-filament secondary standard of total irradiance, in accordance with NIST procedures. High (10-100 mW/cm-2, 3 pts) and Very High (100-250 mW/cm-2, 3 pts) calibrations are undertaken by exposure to a tungsten source; the radiation reference is the World Radiometric Reference Scale with the sun as a source.

Thermopiles can be mounted in three different case designs: air, vacuum, and fluid (e.g. water) cooled. Various window materials to minimize the effects of air convection are available. These windows are normally mounted in metal slides or inserts, each of which is interchangeable.

Air and vacuum cases are limited to exposure to a maximum flux density of 100 mW/cm-2 for lengthy periods and 300 mW/cm-2 for short periods (approx. 30 seconds). Water jacketed cases are limited to a maximum flux density of 2 W/cm-2. Both of these values are for conditions of continuous operation. When using a water-jacketed case, care should be taken to keep the coolant temperature close to +25°C, the approximate temperature used during calibration. One-quarter inch (1/4”) I.D. high-pressure tubing is recommended to connect the coolant to the thermopile case.

All standard cases are constructed of stainless steel and are supplied with copper binding posts and slide holders for easy insertion of a removable window mounted on a slide. The two etched lines on either side of the case indicate the position of the thermopile receiver surface inside the case.

If a special design is required, non-standard thermopiles can be constructed. Please contact the Laboratory with a detailed statement of requirements. The following information should be included: Nature and approximate intensity of the source; Distance between the source and the thermopile; Wavelength range of radiation to be measured; desired shape and size of the receiver; and Desired sensitivity, responses time and resistance.

 

THERMOPILE SPECIFICATIONS
Thermopile Type Aperture Size Sensitivity µV/µW cm-2 Impedance Ohms Response Time (1/e)
E6 3/8" 0.10 200 1.0
G3 1/4" 0.10 800 0.8
H6 9/16" X 1/8" 0.05 300 1.0
J3 1/8" 0.02 300 0.5

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SPECIAL PROJECTS

While the Laboratory does not recommend the "re-inventing of the wheel", we often work with customers to satisfy any non-standard requirements they may have. This may be as simple as extending the temperature dependence range or as extensive as re-building an instrument in a special case.

Recent projects include:

bulletdesign and construction of albedometers and net pyrgeometers.
bulletreplacement of bronze case of the PSP and PIR with aluminum or plastic (Delrin, PVC, PET) for use on aircraft, balloons, ships, and marine bouys.
bulletspecial wiring and extended testing of PSPs, PIRs and NIPs for ARM (Atmospheric Radiation Measurement), BSRN (Baseline Surface Radiation Network), and GAW (Global Atmospheric Watch).


Tierra del Fuego - GAW Site


Albedometer

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