Classes of illuminance meters and measurement principles
Illuminance meter is a special instrument for measuring luminosity and brightness. It is the measurement of light intensity (illuminance) is the degree of the object is illuminated, that is, the surface of the object to get the ratio of luminous flux and the illuminated area. Illuminance meter is usually composed of selenium photocell or silicon photocell and microampere meter.
Classes 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 photoelectric cell illuminance meter requirements:
1. Composition: microampere meter, shift knob, zero adjustment, terminal, photocells, V (λ) correction filter and other components.
2. Use requirements:
① photocell application of good linearity of selenium (Se) photocells or silicon (Si) photocells; long working hours can still maintain good stability, and high sensitivity; high E when the choice of high-resistance photocells, its sensitivity is low and good linearity, not easily damaged by bright light irradiation
② paid within the V (λ) correction filter, suitable for the illumination of the light source with a different colour temperature, 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)
Measuring principle of illuminance meter
Photocells are photoelectric elements that convert light energy directly into electrical energy. When light is directed onto the surface of a selenium photocell, the incident light passes through the metal film 4 to reach the dividing surface of the semiconductor selenium layer 2 and the metal film 4, generating a photovoltaic effect at the interface.
The magnitude of the generated photogenerated current has a certain proportionality to the illumination 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 graduated 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. Cite the type of illuminance meter:
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
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 calibrated 1-2 times); high-precision illuminance meter can be used to check the light intensity of the standard lamp; expanding illuminance meter calibrated range can be changed to the distance r, you can also choose a different standard lamp, the choice of a small range of the ammeter.
