Monday, May 28, 2012

Photoelectric Devices

Light Sensitive Devices :

The light-sensitive elements to respond to changes that occur on light intensity and by changing the internal resistance (ie, less than the value of its resistance to increase the intensity of light), and is called light-resistance (photosensitive resistance) .

Or generate electricity and increase the intensity of power to increase light intensity of photosensitive cells abd also called solar cells.

Photosensitive Resistance :

The value of this resistance decreases by the intensity of light falling on it's made of the photoelectric light-sensitive materials (such as cadmium sulfide) (Cds) or (Slitid cadmium) (Cdse), Although other materials such as (lead sulfide) has been used. They can also improved with other materials such as copper or chlorine, in order to improve the work of the resistance in order to adjust the correct way that they change the value of the resistance according to light intensity.

Most of the Photosensitive Resistors can afford voltage range between 100v and 200v and 300v but consumption (watt) the great ability of these elements varies between 30 million and 300 million Melli Watts.

Photosensitive Resistance has many applications in electronics, for example often used in Alert devices and automatic door mechanism where a sense of the presence or absence of light is required and the following figure shows one of the simplest applications of this element.

With the development of science electronic photoelectric element has been manufactured of silicon which is similar in terms to the transistor structure.

It's the phototransistor however it's different that transistors base is light-sensitive material controls the amount of power that passes from E to C.

It can be used in : Alarms, Automatic doors  mechanism, close the blinds in the absence of the sun or vice versa, and other devices that requires a sense of light. It is also used in television sets as a receiver for the remote control.

Transistors are characterized by the possibility of working with the invisible light such as infrared, where it can be used in alarms against thieves.



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