What is a photocell sensor?

There are many kinds of photovoltaic cells, such as selenium, cuprous oxide, thallium sulfide, cadmium sulfide, germanium, silicon, and gallium arsenide photocell. Among them, the most important thing is silicon photocell, because of its stable performance, wide spectrum range, good frequency characteristics, high transmission efficiency and high temperature resistance. Therefore, the following is only an introduction to silicon photovoltaic cells.

 The silicon photocell is a N type silicon chip, which uses the diffusion method to mix some P-type impurities to form a large surface PN junction. When the light is illuminated to the PN junction, the electromotive force appears at both ends of the PN junction ( P region is positive potential, and N region is negative potential ), which is called the photovoltaic effect.

The short circuit current of photocell is linearly related to the light intensity in a large range ; the open-circuit voltage and the light source are nonlinear, and tend to be saturated under the illumination of 2000 lux.

Therefore, when the photocell is used as the measuring element, it should be used as the form of current source, that is, the short circuit current is linear with the light intensity, this is one of the main advantages of photovoltaic cells, and can not be used as a voltage source for measurement.

The so-called short circuit current of a photovoltaic cell is the current value of an external load resistor ( as opposed to its internal resistance ). The internal resistance of the photocell decreases with the increase of illumination, so in different illuminance, the load resistance of different sizes can be used to approximately meet the " short circuit " condition.

The smaller the load resistance, the better the linear relationship between the photocurrent and the illuminance is, and the linear range is wide. When the photocurrent is used as the measuring element, the magnitude of the load resistance used should be determined according to the specific situation of the light intensity. The biggest advantage of a photovoltaic cell is that it is energy itself, so it can be directly connected with the indicating instrument without external power supply.

In practical application, we also need to consider the spectral characteristics of the photocell, and at the same time, we should select the photocell according to the nature of the light source, and vice versa, the light source can be selected according to the characteristics of the photocell.

In addition, we also need to consider the frequency characteristics and temperature characteristics of the photocell.

This article is from Allicdata Electronics.