Explanation of the illuminance calibration principle and method of illuminance meter
Calibration principle:
Illuminate the photovoltaic cell vertically with Ls → E=I/r2, and change r to obtain the photocurrent values under different illuminance. Convert the current scale to the illuminance scale based on the correspondence between E and i.
Calibration method:
Using a light intensity standard lamp, at an approximate working distance of a point light source, change the distance l between the photovoltaic cell and the standard lamp, record the readings of the ammeter at each distance, and calculate the illuminance E using the inverse distance square law E=I/r2. From this, a series of different illuminance photocurrent values i can be obtained, and the variation curve of photocurrent i and illuminance E can be made, which is the calibration curve of the illuminance meter. The calibration curve of the illuminance meter can be divided by the dial of the illuminance meter, which is the calibration curve of the illuminance meter
Factors affecting the calibration curve:
When replacing photovoltaic cells and ammeters, recalibration is required; After using the illuminance meter for a period of time, it should be recalibrated (usually 1-2 times a year); High precision illuminance meters can be calibrated using standard light intensity lamps; Expanding the fixed range of the illuminance meter can change the distance r, and different standard lamps can also be used. A small range ammeter can be selected
An ideal illuminance meter should have the following conditions:
● Small size and light weight (Compact Size, Light Weight)
The opportunities for using an illuminance meter are very wide, and the timing of application is often in different places, so a portable body with small size and light weight is the first prerequisite for an illuminance meter.
● Accuracy
The quality of an illuminance meter is absolutely related to its accuracy. Of course, it is also closely related to its price, so it is necessary to buy an illuminance meter with high accuracy at a reasonable price, generally with an error of no more than ± 15%.
Color Compensation
There are various types of light sources, some of which focus on longer wavelength red high-pressure lamps, or shorter wavelength blue purple lamps such as Daylight fluorescent lamps; There are also relatively evenly distributed series such as incandescent bulbs, where the sensitivity of the same illuminance meter may vary slightly for different wavelengths, so moderate compensation is necessary.
● Cosine Compensation
As we all know, the brightness of the illuminated surface is related to the incident angle of the light source. By the same token, when using an illuminance meter for measurement, the angle of incidence between the sensor and the light source will naturally affect the reading of the illuminance meter. So whether a good illuminance meter has cosine compensation function cannot be ignored.
