Requirements for the use of illuminance meters
① Photovoltaic cells use selenium (Se) photocells or silicon (Si) photocells with good linearity; they can maintain good stability after long-term work and have high sensitivity; when E is high, choose high internal resistance photocells, which have low sensitivity and good linearity , 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
③Add 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 room temperature or close to room temperature (photocell drift changes with temperature)
Calibration of the lux meter:
Calibration principle:
Make Ls vertically irradiate the photocell → E=I/r2, change r to get the photocurrent value under different illuminance, convert the current scale into the illuminance scale according to 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, which is the calibration curve of the illuminance meter. From this, the calibration of the illuminance meter can be done by dividing the dial of the illuminance meter.
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.
