One of the applications of the optical dome - Pyranometer

The pyranometer, also known as the sky radiation meter, is used to measure the total radiation (short-wave) on a horizontal plane, within a 2π stereo angle, received by the sum of direct solar radiation and scattered solar radiation. It is the most basic item of radiation observation and is mostly used for monitoring total radiation data on solar radiation stations.

Measuring principle

1. The pyranometer consists of a double-layer quartz glass cover, a sensing element, a sunshade, a body, a desiccant, etc. The sensing element is the pyranometer's core, consisting of a fast-response winding electroplating thermopile. The sensing surface is a hot junction, and when there is sunlight, the temperature rises, forming a temperature difference electromotive force with the cold junction on the other side, which is proportional to the intensity of solar radiation.

2. The double-layer glass cover of the pyranometer is designed to reduce the impact of air convection on the pyranometer. The inner cover is designed to cut off the infrared radiation of the outer cover itself.

3. The output radiation of the pyranometer (W/m) = the measured output voltage signal value (μV) ÷ the sensitivity coefficient (μV/W·m). Each sensor is given a calibrated sensitivity coefficient.

Working principle

This pyranometer is based on the principle of thermoelectric effect. The sensing element adopts a winding electroplated multi-junction thermopile, and its surface is coated with a black coating with a high absorption rate. The hot junction is on the sensing surface, while the cold junction is located in the body. The hot and cold junctions generate a temperature difference potential. Within the linear range, the output signal is proportional to the solar irradiance. To reduce the influence of temperature, it is equipped with a temperature compensation circuit. To prevent the influence of the environment on its performance, it uses two layers of quartz glass covers, which are made by precision optical cold processing.

Resettlement conditions

The pyranometer should be placed in an open area with no obstacles on the sensing surface. If this condition cannot be met, it should be placed as far away from obstacles (man-made or natural) as possible, and the shadow of obstacles should not be cast on the sensing surface at any time. The obstacles should not exceed 5° in the direction of sunrise and sunset at any time of the year. At the same time, do not place them near light-colored walls or other objects that reflect sunlight. Also, try to avoid places with serious air pollution such as local fog, smoke, etc.

Use and Maintenance

When observing global radiation at a meteorological station, the metal cover should be opened before sunrise. The radiometer will start sensing and the recorder will automatically display the instantaneous value and cumulative total of global radiation. The cover should be put on after observation stops at sunset. If there is no precipitation at night or no other phenomenon that may damage the instrument, the global radiometer can also be left uncovered.

CLZ Optical Co., Ltd. is an optical components manufacturer, mainly products are spherical lenses, optical domes, optical windows, etc. Optical glass domes are available for use with pyranometers. In addition, we can also provide customization, if you have customization needs please feel free to contact us!