What are the photoelectric sensors? Detailed explanation of its working principle wiring diagram The photoelectric sensor is a key element to realize photoelectric conversion in various photoelectric detection systems. It is a device that converts light signals (infrared, visible and ultraviolet radiation) into electrical signals. So what are the classifications of photoelectric sensors?

1. Standard photoelectric sensor

1. Diffuse reflection type: general type or energy type (-8), focus type (-8-H), background suppression type (-8-H) photoelectric sensor, background analysis type (-8-HW)

2. Reflector type: general type (-6), type with polarization filter function (-54, -55), type with transparent body detection function (-54-G), type with foreground suppression function (-54-V)

3. Opposite shot type

4. Groove

5. Optical fiber sensor: plastic optical fiber type, glass optical fiber type

6. Color mark sensor, color sensor, fluorescence sensor

2. Safety photoelectric sensor

1. Safety on the radio

2. Safety grating

3. Safety light curtain

4. Safety controller

3. Gated photoelectric sensor

1. Radar sensor: area detection type

2. Active sensor: single beam type, multiple beam type, area detection type

3. Passive sensor: area detection type

4. Elevator light curtain

5. General optoelectronics: slot shape, through-beam type, etc.

Photoelectric sensor is a kind of small electronic equipment, a key element for photoelectric conversion in various photoelectric detection systems. It is mainly a sensor that uses various properties of light to detect the presence or absence of objects and changes in surface conditions. Photoelectric sensors have the characteristics of non-contact, fast response and reliable performance, so they are widely used in industrial automation devices and robots.

The photoelectric sensor is generally composed of three parts: light source, optical path and photoelectric element. The measured change is converted into a change in an optical signal, and then the optical signal is further converted into an electrical signal with the help of photoelectric elements.

The working principle of photoelectric effect: photoelectric element is the most important part of photoelectric sensor, and its core working principle is different types of photoelectric effect. According to the wave-particle duality, light is composed of photons moving at the speed of light. When an object is illuminated by light, its internal electrons absorb the energy of the photon and change state, and its own electrical properties will also change. This phenomenon is called For the photoelectric effect.

According to the different changes of electrical properties, the photoelectric effect is divided into the following three types:

1. External photoelectric effect

The phenomenon that electrons escape from the surface of an object under the action of light is called the external photoelectric effect. The photoelectric elements based on the external photoelectric effect include phototubes, photomultiplier tubes and so on.

2. Photoconductive effect

The phenomenon that the electrons in the semiconductor cannot jump out of the semiconductor after absorbing the photon, changes the conductivity of the object, or generates photoelectromotive force, is called the internal photoelectric effect. The internal photoelectric effect can be divided into photoconductive effect and photovoltaic effect according to its working principle. Photoelectric components based on the photoconductive effect include photoresistors and phototransistors.

3. Photovoltaic effect

Under the action of light, the phenomenon that an object produces a certain directional electromotive force is called the photovoltaic effect. Photoelectric components based on the photovoltaic effect include photovoltaic cells, photodiodes, and triodes.

The working principle of photoelectric components: Based on different photoelectric effects, let's take a look at how they work.

1. External photoelectric effect device

Photoelectric devices made by using the external photoelectric effect of substances emitting electrons under the irradiation of light are generally vacuum or gas-filled photoelectric devices, such as photoelectric tubes and photomultiplier tubes.

Taking a phototube as an example, when incident light illuminates the cathode, a single photon transfers all its energy to a free electron in the cathode material, thereby increasing the energy of the free electron. When the energy obtained by the electron is greater than the work function of the cathode material, it can overcome the bondage of the metal surface and escape, forming electron emission, which is called photoelectron. Only when the frequency of the incident light is higher than the limit frequency, photoelectrons will be produced.

After the photoelectrons are generated, they are absorbed by the anode in the vacuum tube to generate current. If the light intensity is increased at this time, more photons will illuminate the cathode material, thereby generating more photoelectrons, and the photocurrent will increase accordingly. When the resistance R value is determined, the photocurrent in the loop is a function of the intensity of the incident light, so as to achieve photoelectric conversion. The light intensity can be calculated by reading the current through the measuring circuit.

2. Internal photoelectric effect device

Photoelectric devices that use materials to change electrical conductivity or generate electromotive force under light irradiation are called internal photoelectric effect devices. Commonly used are photoresistors, photocells, and phototransistors.

According to energy band theory, the energy state of electrons in free atoms is not arbitrary, and electrons can only exist at a certain energy level. The energy band is divided into valence band, forbidden band and conduction band. Electrons can flow in the conduction band, but cannot flow in the valence band. Under external influence, electrons can enter the conduction band by crossing the band gap from the valence band, thereby changing the resistance of the conductor.

The band gap thickness of different conductors is different. As shown in the figure below, the band gap of the insulator is wide, which makes it difficult for electrons to transition from the valence band to the conduction band, so its resistance is very large; the metal conductor has no band gap, and its valence band and conduction The belts are connected, so the conductivity is good.

After the electron absorbs the energy of the photon, the phenomenon of changing the conductor resistance from the valence band to the conduction band is called the internal photoelectric effect. This effect can be used to make photoresistors, and the amount of light to be measured can be determined by observing the changes in resistance.

Photovoltaic effect device: The photovoltaic effect is abbreviated as photovoltaic effect, which refers to the phenomenon that an object generates electromotive force after being illuminated. Photocell is a kind of self-generating photoelectric element. It can generate electromotive force in a certain direction when it is exposed to light. Without power supply, as long as the external circuit is connected, current will flow. The specific working principle is as follows:

Photovoltaic cells use a diffusion method to dope some P-type impurities on a piece of N-type silicon wafer to form a large-area PN junction. The P area has a large number of holes and the N area has a large number of electrons.

When light irradiates the surface of the P zone, if the photon energy is greater than the band gap of silicon, each photon absorbed in the P-type zone produces an electron-hole pair. The more photons absorbed on the surface of the P zone, the excited electrons are empty. The more holes there are, the less the PN junction area is.

Since the direction of the electric field in the PN junction is directed from the N zone to the P zone, it separates the electron-hole pairs that diffuse to the vicinity of the PN junction, the photogenerated electrons are pushed to the N zone, and the photogenerated holes are left in the P zone. So that the N zone is negatively charged and the P zone is positively charged, forming a photoelectromotive force. If a wire is used to connect the P area and the N area, a photocurrent will flow in the circuit.