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Photoelectric sensors you don't know

by:Rika Sensors     2021-12-11
Photoelectric sensors you don't know
A variety of sensors are important sensing devices that construct the perception layer of the Internet of Things, and are the initial link for the Internet of Things to obtain information and realize object control. It can be said that sensors have a very important impact on the Internet of Things.

The photoelectric sensor is a sensor that uses a photoelectric element as the detection element. It has the advantages of fast response, high precision, non-contact, etc., and has many measurable parameters, simple structure, and flexible and diverse forms. Therefore, photoelectric sensors are widely used in the field of monitoring and control.

1. The principle of the photoelectric sensor

The photosensitive element of the photoelectric sensor adopts the photoelectric effect, and the photoelectric effect is divided into the external photoelectric effect and the internal photoelectric effect.

1. Internal photoelectric effect:

(1) Photoconductivity: When an incident photon hits the surface of a semiconductor, the semiconductor absorbs the incident photon to generate electron-hole pairs, which increases its own conductance.

(2) Photovoltaic: When a certain wavelength of light irradiates a non-uniform semiconductor (such as a PN junction), under the action of a self-built field, a photovoltage is generated inside the semiconductor.

When light irradiates the surface of a semiconductor or an insulator, the bound electrons inside the object are excited, thereby changing the electrical conductivity of the object. This is called the internal photoelectric effect. Obviously, the larger the radiant flux, the more electrons are excited, and the smaller the resistance value of the object becomes.

Light pipe (also known as photoresistor) is a semiconductor device made of internal photoelectric effect. The ones like cadmium sulfide, lead sulfide, indium sulfide, cadmium selenide, lead selenide are all semiconductor light pipes. The advantages of light pipes are small size, strong and durable. It is mainly used for optical receivers, photoelectric control, laser receiving and long-distance detection of spectroscopic instruments.

2. External photoelectric effect:

Photoelectron emission caused by photoelectric effect or photoionization. Under the action of light, electrons can escape from the surface of an object, which is called 'external photoelectric effect' or photoemission.

When a substance is irradiated by light, electrons are emitted from the surface of the substance after receiving enough light energy, which is called the photoelectron emission effect. The emitted electrons are called photoelectrons, and the objects that can emit photoelectrons are called photoemitters. The current formed by photoelectrons is the photocurrent.

Second, photoelectric product application

1. Total solar radiation sensor

The total solar radiation sensor adopts the photoelectric principle and can be used to measure the total radiation value under sunlight. The radiation sensor uses high-precision photosensitive elements, wide spectrum absorption, high absorption in the full spectrum range, and good stability; at the same time, a dust cover with a light transmittance of up to 95% is installed outside the sensing element, and the dust cover is specially treated to reduce dust Adsorption can effectively prevent the interference of environmental factors to internal components, and can measure the amount of solar radiation. The product adopts the standard Mod-bus communication protocol, which can directly read the current solar radiation value, and the wiring method is simple. The appearance is small and beautiful, and it takes up little installation space. Products are widely used in solar energy utilization, meteorology, agriculture, building materials aging, and air pollution departments to measure total solar radiation.

2, photoelectric smoke sensor

The photoelectric smoke fire detection sensor (hereinafter referred to as the sensor) can detect the smoke produced during a fire. Using photoelectric cigarette devices and excellent production technology, stable work, beautiful appearance, simple installation, no debugging, can be widely used in shopping malls, hotels, shops, warehouses, computer rooms, residential and other places for fire safety detection. Built-in buzzer, can make a strong sound after alarming.

3. Photosynthetically active radiation sensor

The photosynthetically active radiation sensor adopts the photoelectric sensing principle and can be used to measure the photosynthetically active radiation in the spectral range of 400~700nm. The sensor uses high-precision photoelectric sensing elements, wide-spectrum absorption, high absorption in the 400-700nm range, and good stability; when there is light, it generates a voltage signal proportional to the intensity of the incident radiation, and its sensitivity is lower than that of the incident light. The cosine of the direct angle is proportional. The dust cover adopts special treatment to reduce dust absorption, effectively prevent environmental factors from interfering with internal components, and can measure photosynthetic effective radiation.

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