Introduction to the Precautions of Illuminance Meter
Light Meter Precautions
1. Photovoltaic cells use selenium (Se) photocells or silicon (Si) photocells with good linearity; they can still maintain good stability and high sensitivity after working for a long time; when E is high, choose high internal resistance photocells, and their sensitivity is low and linear Good, not easily damaged by strong light
2. There is a V(λ) correction filter inside, which is suitable for the illumination of light sources with different color temperatures, and the error is small
3. Add a cosine angle compensator (opalescent glass or white plastic) in front of the photocell because when the incident angle is large, the photocell deviates from the cosine rule
4. The illuminance meter should work at or near room temperature (photocell drift changes with temperature)
Calibration of the lux meter:
Calibration principle:
Let Ls illuminate the photocell vertically → E=I/r2, change r to get the photocurrent value under different illuminance, convert the current scale into the illuminance scale by the corresponding relationship between E and i.
Calibration method:
Using the light intensity standard lamp, under the working distance of the approximate point light source, change the distance l between the photocell and the standard lamp, record the readings of the ammeter at each distance, calculate the illuminance E by the inverse square law of distance E=I/r2, and calculate the illuminance E by This can get a series of photocurrent values i with different illuminance, and make the change curve of photocurrent i and illuminance E, that is, the calibration curve of the illuminance meter. From this, the dial of the illuminance meter can be divided into
Calibration of lux meters
Factors affecting the calibration curve:
The photocell and galvanometer need to be re-calibrated when the photocell and galvanometer are replaced; the illuminance meter should be re-calibrated after a period of use (generally 1-2 times within a year); the high-precision illuminance meter can be calibrated with a light intensity standard lamp; The calibration range of the illuminance meter can be changed from the distance r, and different standard lamps can also be selected, and a small-range ammeter can be selected.
