What is the photocell, working principle and application

In electrical engineering, used a lot of different elements, and not the least among them is the resistance of a particular kind - LDR. In this article, I'll tell you what it is and where it is still widely used these elements. So, let's begin.

Content

Determining performance and image of the schemes

Operating principle

How to check the serviceability of the element

The main characteristics of photoresists

Where such elements are used

conclusion

Determining performance and image of the schemes

So, first let's define. Photoresistor - a semiconductor device, the resistance (conductance) which changes depending on the light-sensitive layer of the article.

In the above presented photo shows the most common embodiment, but there are models in special protective casings with a transparent upper part.

That's how an element is indicated in the diagrams:

Operating principle

Now let's find out what is the principle of action in a given radioelement.

Between two conductive electrodes semiconductor located. In that case, if the light misses a semiconductor, its ohmic resistance is high (up to several megohms). Once the light enters a semiconductor, the resistance begins to decrease, i.e. the conductivity increases.

The following materials can be used for the production of the semiconductive layer: cadmium sulfide, lead sulfide, selenium Cadmium and the like On what kind of material was used for the production of semiconductor will depend on its spectral characteristic.

In other words the range of wavelengths when illuminated which will be the correct change in resistance.

It is for this reason that when choosing the resistor is important to understand, for what spectrum it is intended.

The spectral characteristics of the materials are as follows:

Very often the question arises: what is the polarity of the photoresist? So this item has no P-N junction, which means that a certain direction of current flow is not the same. That is absolutely no difference how to connect the photocell, as it non-polar element.

How to check the serviceability of the element

Check photoresist is actually very simple. For this we need the meter, for example, a folder for papers.

Testing is performed as follows: place the handle in position multimeter resistance measurement, crocodiles connect the probes (polarity is not important) and place the item in the folder to exclude exposure to light element.

Thus you get the resistance of the cell in a dark state. Pulling the photocell from the folder, you will see that the resistance element has changed. Moreover, the more intense will be the luminous flux, the smaller the resistance element will have.

And the dependence of the resistance on the light will be as follows:

The main characteristics of photoresists

In data elements have several key characteristics, which should pay attention when choosing a product:

1. Dark resistance. This cell resistance, when it does not affect the light output.

2. Integral photosensitivity. This parameter describes the reaction element, the change of current flow to change the luminous flux. This parameter is measured at a constant voltage. It denoted as S. (A / lm).

It is also important to know that all photoresists possess inertia in one degree or another. The resistance does not change instantly, and within a certain period of time (tens of microseconds). This factor limits the use of photoresists in fast circuits.

Where such elements are used

So, despite some limitations, these elements are widely used in the following devices:

1. Photorelay. The devices are designed to automatically turn off lighting systems without active human intervention.

2. ambient light sensors. In such devices, photoconductive perform the function of light flux registrar.

3. Signaling. The signaling systems used photoresists sensitive to ultraviolet waves. The principle is constantly illuminated LDR source of ultraviolet radiation and once between the source and the receiver there is an obstacle - the alarm is triggered.

4. Sensors that detect the presence of something.

conclusion

Here is a summary of the photoresists his device and application. If the article was useful to you, or are interested in, you will appreciate it Like. Thank you for your attention.