Measuring Principles, Types, and Calibrating Illuminance Meters
Measurement principle of illuminance meter:
A photovoltaic cell is a photoelectric component that directly converts light energy into electrical energy. When light is incident on the surface of the selenium solar cell, the incident light passes through the metal thin film 4 and reaches the interface between the semiconductor selenium layer 2 and the metal thin film 4, generating a photoelectric effect at the interface. The magnitude of the potential difference generated is proportional to the illuminance on the surface of the photovoltaic cell receiving light. At this point, if an external circuit is connected, a current will flow through, and the current value will be indicated on a microampere meter with lux (Lx) as the scale. The magnitude of photocurrent depends on the strength of the incident light and the resistance in the circuit. The illuminance meter has a gear shift device, so it can measure both high and low illuminance. Types of illuminance meters: 1. Visual illuminance meter: inconvenient to use, low accuracy, rarely used 2. Optoelectronic illuminance meter: commonly used selenium solar cell illuminance meter and silicon solar cell illuminance meter
Types of illuminance meters:
1. Visual lux meter: inconvenient to use, low accuracy, rarely used
2. Optoelectronic lux meter: commonly used selenium photovoltaic cell lux meter and silicon photovoltaic cell lux meter
Composition and usage requirements of photovoltaic cell illuminance meter:
1. Composition: microampere meter, shift knob, zero adjustment, terminal block, photovoltaic cell, V (λ) correction filter, etc.
Commonly used selenium (Se) or silicon (Si) photovoltaic cell illuminance meter, also known as lux meter
2. Usage requirements:
① Selenium (Se) or silicon (Si) photovoltaic cells with good linearity should be used for photovoltaic applications; Long term work can still maintain good stability and high sensitivity; When using high E, choose photovoltaic cells with high internal resistance, which have low sensitivity and good linearity, and are not easily damaged by strong light irradiation
② Equipped with a V (λ) correction filter, suitable for illumination with different color temperature light sources, with small errors
③ The reason for adding a cosine angle compensator (milky white glass or white plastic) in front of the photovoltaic cell is that when the incident angle is large, the photovoltaic cell deviates from the cosine rule
④ The illuminance meter should operate at or near room temperature (the drift of the photovoltaic cell changes with temperature)
Calibration 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 to select a small range ammeter.
