Calibration principle:
Let Ls irradiate the photocell vertically → E=I/r2, change r to obtain the photocurrent value under different illuminance, and convert the current scale to the illuminance scale according to the corresponding relationship between E and i.
Calibration method:
Using the light intensity standard lamp, at a working distance similar to a point light source, change the distance l between the photocell and the standard lamp, record the readings of the galvanometer at each distance, and calculate the illuminance E by the inverse square law of distance E=I/r2, by A series of photocurrent values i with different illuminance can be obtained, which can be used as the change curve of photocurrent i and illuminance E, which is the calibration curve of the illuminometer.
Factors that affect the calibration curve:
The photocell and galvanometer need to be re-calibrated when they are replaced; the illuminometer should be re-calibrated after a period of use (generally 1-2 times within a year); high-precision illuminometers can be calibrated with light intensity standard lamps; The calibration range of the illuminance meter can change the distance r, and different standard lamps can also be used, and a small-range ammeter can be selected.
