Principles and Classification of Illuminance Meters and How Illuminance Meters Work
Illuminance meter measuring principle: Photocell is a photoelectric element that converts light energy directly into electrical energy. When the light to the surface of the selenium photovoltaic cell, the incident light through the metal film 4 to the semiconductor selenium layer 2 and the metal film 4 on the dividing surface, the interface photoelectric effect. The magnitude of the potential difference generated is proportional to the illuminance on the light-receiving surface of the photocell. At this point, if an external circuit is connected, a current passes through, and the value of the current is indicated from a microampere meter scaled in lux (Lx). The magnitude of the photocurrent depends on the intensity of the incident light and the resistance in the circuit. The illuminance meter has a variable stopping device, so that it can measure either high or low illuminance. Cited types of illuminance meter: 1. visual illuminance meter: inconvenient to use, high precision, rarely used 2. photoelectric illuminance meter: commonly used selenium photoelectric cell illuminance meter and silicon photoelectric cell illuminance meter
Illuminance meter measurement principle.
Photoelectric cell is a photoelectric element that directly converts light energy into electrical energy. When the light to the surface of the selenium photovoltaic cell, the incident light through the metal film 4 to reach the semiconductor selenium layer 2 and the metal film 4 on the dividing surface, in the interface to produce the photoelectric effect. The magnitude of the potential difference generated is proportional to the illuminance on the light-receiving surface of the photocell. At this point, if an external circuit is connected, a current passes through, and the value of the current is indicated from a microampere meter scaled in lux (Lx). The magnitude of the photocurrent depends on the intensity of the incident light. The illuminance meter has a variable-speed device, so that it can measure high illuminance as well as low illuminance.
Types of illuminance meters:
1. Visual illuminance meter: inconvenient to use, not high precision, rarely used
2. photoelectric illuminance meter: commonly used selenium photocell illuminance meter and silicon photocell illuminance meter
Composition and use of photocell illuminance meter requirements:
1. Composition: microampere meter, shift knob, zero adjustment, terminal, photocells, V (λ) correction filter and other components.
2. Requirements for use
① photocell application of good linearity of selenium (Se) photocells or silicon (Si photocells; long time work can still maintain good stability, and high sensitivity; high E when the choice of high internal resistance photocells, its low sensitivity and good linearity, not easily damaged by bright light irradiation
② paid within the V (λ) correction filter, suitable for the illumination of light sources with different colour temperatures, the error is small
③ photocell before the addition of a cosine angle compensator (opal glass or white plastic) because the incident angle is large, the photocell deviates from the cosine rule
④ illuminance meter should work at room temperature or near room temperature (photocell drift with the temperature change and change)
Calibration of the illuminance meter:
Calibration principle: make Ls perpendicular irradiation photocell → E = I / r2, change r can be obtained under different illumination of the light current value, by the corresponding relationship between E and i will be converted to current scale illuminance scale.
Calibration method:
The use of light intensity standard lamp, in close proximity to the working distance of the point light source, change the photocell and the standard lamp distance l, recorded under the distance of the ammeter readings, by the inverse square law of distance E = I / r2 calculation of light illuminance E, which can be obtained from a series of different illuminance of the light current value of i, for the photocurrent i and the illuminance of the E curve of change, that is, for the illuminance of the calibration curve of the calibration curve of the illuminance of this illuminance can be made to dial This is the calibration curve of the illuminance meter, thus the dial of the illuminance meter can be graded.
Factors affecting the calibration curve:
Photocells and ammeter replacement needs to be re-calibrated; illuminance meter should be used for a period of time should be re-calibrated illuminance meter (generally within a year should be checked 1-2 times); high-precision illuminance meter can be used to check the light intensity of the standard lamp; expanding the range of illuminance meter can be changed to the distance r, you can also choose a different standard lamps, the choice of a small range of ammeter
