Photosensitive resistance without polarity, is purely a resistance device, can be added when using dc voltage, also can add ac voltage. Photosensitive resistor is made of semiconductor material used in photoelectric effect of optoelectronic devices. Under the action of light, its resistance is often smaller, this phenomenon is called optical effect, therefore, the photosensitive resistance is also called light pipe. On opposite sides of the photosensitive resistance and voltage between the metal electrode, which has an electric current passes through, by appropriate wavelength of light, the current will be along with the increase of light intensity, so as to realize the photoelectric conversion.

Used in the manufacture of photosensitive resistance of the material is mainly metal sulphide selenide and telluride semiconductor, etc. Usually the methods of coating, spraying, sintering on the insulating substrate made very thin photosensitive resistance body and comb ohmic electrodes, and then pick out lead, encapsulated in a transparent lens of the seal housing, so as not to affect the sensitivity of be affected with damp be affected with damp.

In dark environment, its resistance value is very high, when when exposed to light, as long as the photon energy is greater than the semiconductor materials forbidden band width, the valence band of electron absorbs a photon energy after the transition to the conduction band, and produced a positively charged in the valence band hole, the electrons produced by light - hole to increase the number of carriers in semiconductor material, make its resistivity decreases, thus causing the deterioration of photosensitive resistance tolerance. The more light is strong, the low resistance. Disappear into the shoot the light, the photons produce electronic - hole for complex, will gradually photosensitive resistance value is gradually restore original value.

Main parameters of photosensitive resistor have bright resistance (RL), dark resistance (RD), the maximum working voltage (VM), light current (IL), dark current (ID) and time constant, the temperature coefficient of sensitivity, etc.

1. The bright light resistance is the point at which the photoresistor by light irradiation resistance.

2. Dark dark resistance refers to the photosensitive resistor in light irradiation (dark) resistance value.

3. The highest operating voltage working voltage is refers to the photosensitive resistor under the rated power is allowed to carry the highest voltage.

4. Light depending on the current refers to the light irradiation, the photosensitive resistor in the regulation of the applied voltage is light through by the current.

5. Dark current dark current refers to the light irradiation, the photosensitive resistor under the provisions of the applied voltage by the current.

6. Time constant time constant is refers to the photoresistor light current from the light jump to the stable of 63% when the time required.

7. The temperature coefficient of resistance temperature coefficient refers to the photosensitive resistor when environment temperature change 1 ℃, the relative change of electrical resistance.

8. Sensitivity refers to the sensitivity of photosensitive resistor when light and light irradiation resistance relative changes.

Photosensitive resistance detection methods are:

A photosensitive resistance with A black paper cover of pervious to light the window, at this time keeping basic of pointer multimeter, resistance close to infinity. The bigger this value shows that the better the performance of photosensitive resistance. If this value is very small or close to zero, the photosensitive resistance has been burning through damaged, can't continue to use.

B will be a light source on the photosensitive resistance of pervious to light window, at this time should have a move of pointer multimeter, resistance significantly reduce some of the smaller this value shows that the better the performance of photosensitive resistance. If this value is very big and infinite, suggesting that the photosensitive resistance internal open circuit is damaged, can no longer continue to use.

C aim the photoresistor pervious to light the window the incoming light, shading the window of the little black paper in photosensitive resistance, punctuated by light, the pointer multimeter should shake with the black pieces of paper and swinging. If the multimeter pointer always stopped at a particular location not shaking with pieces of paper and swing, explain photosensitive resistance photosensitive material has been damaged.

Analysis of the application of photosensitive resistance from you to have a light, no light, and the strength of the light level three scenarios to consider.

Through the special production process can produce a more sensitive to specific wavelength range light resistance, but the natural light, sunlight, wavelength range is too wide, so will affect the application of photosensitive resistance or other photosensitive device.

Here are two improved methods:

1, add light path. Light travels in straight lines, make the light of the specific path and some light barrier (such as charge started using circular tube, holes, mirror, lens, filter, etc.)

2, encoding optical signals. To emit light signal is encoded according to certain rules or debugging. So it is easier for the receiver according to the rules of the selection signals.

The combination of the above two points was used most frequently. Such as TV, VCD filters, with reddish brown added the shell and the optical path of barrier, emitting diode vitreous and quite so lens focusing point is determined.