Types of illuminance meters Calibration of illuminance meters
Illuminance meter (or lux meter) is a specialized instrument for measuring luminosity and brightness. It is the measurement of light intensity (illuminance) is the degree of illumination of an object, that is, the ratio of the luminous flux received by the surface of the object to the area illuminated. The illuminance meter is usually composed of a selenium photocell or silicon photocell and a microammeter.
Types of illuminance meter
1. Visual illuminance meter: inconvenient to use, 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.
Commonly used selenium (Se) photocell or silicon (Si) photocell illuminance meter, also known as lux meter.
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, by the bright light is not easily damaged.
② V (λ) correction filters paid inside, suitable for illuminance with different color temperature light source, small error.
③ photocell before adding 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 illuminance meter
Principle of calibration:
Make Ls perpendicular irradiation photocell → E = I / r2, change r can be obtained under different illumination of the value of the light current, by the corresponding relationship between E and i will be converted to the 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 E curve, that is, for the illuminance of the calibration curve from this illuminance can be made to dial The calibration curve of the illuminometer can be divided into degrees, which is the calibration of the illuminometer.
Factors affecting the calibration curve:
Photocells and ammeter replacement needs to be re-calibrated; illuminance meter use 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 calibration illuminance meter can change the distance r, you can also choose a different standard lamps, the choice of a small range of the ammeter.
