12-14 Main Instrument Introduction
Author: Source: Datetime: 2016-12-26 09:48:27
A direct solar meter is a device that measures direct solar radiation. Since the range of measurements is limited to solar radiation from a narrow annular sky at and around the sun, each direct sunset has a collimating tube with an open angle of approximately 5 ° to ensure its intended purpose. The role of collimator: ① aim at the sun ② limited viewing angle .
There are two types of direct and indirect solar radiation tables: absolute and relative. The so-called absolute, refers to the source or without reference to the radiator will be able to measure the direct solar irradiance; relative instruments need to be compared with the absolute instrument to get their own sensitivity.
Modern absolute direct sunlight tables use cavities as radiation receivers. The advantage of the cavity receiver is that it is more fully received. The cavity wall coated with high absorption ratio of black paint, the outer wall is wrapped with heating wire. The measurement process is actually the power instead of y power. Figure 1-9 shows the internal structure of an absolute cavity-type direct solar table. The instrument has two cavities, one for receiving radiation from the sun and the other for compensating for the effects of changes in the environment.
Absolute direct sunlight table according to their work can be divided into active and passive two. The passive instrument measures the time-divided irradiation phase and the compensation phase. The irradiation stage continuously measures the output value of the instrument. The compensation stage cuts off the radiation and energizes and adjusts to the same output as the irradiation phase. The electric power at this time is the radiation power of the irradiation phase. Active instruments rely on electronic circuits for automatic control of electrical power in order to achieve both in the irradiation phase or in the compensation phase to maintain a constant temperature difference purposes. This means that the difference in electrical power between the irradiation phase and the compensation stage is the radiated power received by the cavity.
Absolute direct solar radiation table is the highest accuracy in the measurement of the instrument, but the measurement process is more complex, not suitable for daily measurement work, it is mainly used for calibration of solar instruments.
The induction element of a relatively direct solar table is a thermopile. There are many types of thermopiles used in solar instruments (see Figure 1-10). The most common type of thermopile is a wire-wound thermopile. The thermopile is an anodic oxidation treatment of aluminum skeleton, a certain number of turns around the copper wire, and then half of its protective coating with petroleum jelly or other insulating material, the other half of copper. Thermopiles produced in this way, not only good linearity, and the temperature coefficient is also small.
2. Total radiation table
The total radiation table is the instrument that measures the total solar radiation: the instrument can be carefully placed to measure the irradiance on the slope; or flip over to measure the reflection of the sun: or in the absence of direct sunlight to measure the scattering Daylight, so it is the most widely used solar instruments: the total incidence table according to the sensing surface is divided into all-black and black-and-white two types, the performance of all-black type is usually better than black and white type. However, the latest study found that all-black type instrument has a zero point is too large, the negative impact of the night Rui is still in the improvement of all types of total radiation table is the relative instrument must be directly or indirectly with the standard instrument To obtain a specific comparison spirits shown in Figure 1-11 for the total black-type table structure.
3. Earth radiation table
4. Net total radiation table
Net radiation table is mainly used to measure the net total radiation. It has two sensing surface, that is, hot spots on the upper and lower sides, each forming a sensing surface. In order to prevent the influence of the wind, the upper and lower sensing surfaces are each covered with a hemispherical cover made of polystyrene film. As the polystyrene film can be through short-wave radiation, but also through long-wave radiation, and the instrument is actually sensing the full-band radiation, and the instrument has two sensing surface, can receive the down, can also receive To the upward radiation, so in fact received the instrument is located on the plane up and down the difference between the total radiation flux. Figure 1-13 shows the decomposition and assembly of a net radiation table.
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