Solar Radiation Instruments

Solar radiation instruments are used to measure the spectral range of radiation from the sun. Product categories include radiometers, and quantum sensors. Pyranometers measure broadband solar irradiance incident on a planar surface and calibrate temperature response in units of radiation flux. Radiometers measure the net radiation level by subtracting the reflected solar radiation from the sum of the incoming direct beam and the diffuse solar radiation. Quantum sensors measure the photosynthetic light spectrum or photosynthetic photon flux density (PPFD) as the number of photons incident per unit type on a unit surface. These solar radiation instruments use either thermopile arrays or photovoltaic detectors. Thermopile arrays provide an electrical output proportional to the absorbed radiation. Thermocouples may be connected in series for a higher voltage output, or in parallel for a higher current output. Photovoltaic (PV) detectors consist of photovoltaic cells which measure radiation by generating a potential at a junction between two materials. 

Measured wavelength, accuracy, spectral sensitivity, and operating temperature are important parameters to consider when selecting solar radiation instruments. Wavelength is usually measured in nanometers (nm). Accuracy is expressed as plus/minus percentage ( %). Physical dimensions and mounting styles are also important considerations when selecting solar radiation instruments.  Suppliers specify dimensions such as height and weight in English units such as inches (in) or feet (ft), or metric units such as meters (m) and centimeters (cm). There are two basic mounting styles for solar radiation instruments: base-mounted and pole-mounted. Base-mounted devices are designed for use on a flat surface such as a roof or stand. Pole-mounted devices attach with clips to an elevated pole. They are often used at weather stations and other facilities where multiple variables are monitored over extended periods of time.  

Solar radiation instruments differ in terms of output, interface, front panel type, display, and special features. There are four choices for output: analog voltage, analog current, pulse signal, and switch or relay. Serial, parallel, phone/modem, and other computer interfaces are commonly available. Solar radiation instruments with an analog front panel provide user inputs such as potentiometers, dials, and switches. Products with a digital front panel can be controlled and calibrated with digital keypads or menus. Analog displays have an analog meter or simple visual indicator. Digital displays show numerical values. Video displays use a cathode ray tube (CRT), liquid crystal display (LCD), or other multi-line technology.  In terms of features, some solar radiation instruments are programmable, battery-powered, and include a leveling fixture. Others provide a chart recorder or internal memory for tracking over extended periods of time. 

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