What is UV sensor classification of UV sensor

What is UV sensor classification of UV sensor

Ultraviolet sensor is a kind of sensor, which can use photosensitive element to convert ultraviolet signal into measurable electrical signal through photovoltaic mode and light guide mode. The earliest UV sensors were based on pure silicon, but according to the instructions of the National Institute of Standards and Technology, pure silicon diodes also respond to visible light and form unwanted electrical signals, resulting in low accuracy. The accuracy of GaN UV sensors is much higher than that of monocrystalline silicon, making them the most commonly used UV sensor material.

With the widespread application of electronic computers, various sensor technologies serving computers have received more and more attention. The ultraviolet sensor can detect ultraviolet rays that are not detectable by the human senses, and can avoid the interference of sunlight, lights and other common light sources. It is very useful for the detection of fires, flameout protection, and photoelectric control in special places.

Structural classification of ultraviolet sensors

At present, the ultraviolet tubes that are of value at home and abroad can be divided into spherical, filamentary, and flat-shaped structures according to the shape of the cathode. The types of materials are designed for use requirements. From the perspective of working conditions, it is more appropriate to classify and analyze the electrode shape.

1. Wire electrode structure

The electrode of this type of tube is generally composed of two or more symmetrical metal wires. This is an early structural form of ultraviolet tubes, and high-purity tungsten wires are often used. Or platinum wire, the closer parallel line is the working area.

Because the ultraviolet tube completely relies on the photoelectron emission effect on the electrode surface, and then uses gas multiplication to obtain a stronger signal, its spectral response range depends on the work function of the cathode material. In the process of photoelectron emission, the shorter the wavelength of the photon, the higher the energy. Even a small amount can excite electrons to overcome the work function and fly out of the cathode surface. Even a large number of photons with low energy cannot excite electrons on the surface of the cathode. In the ultraviolet tube, the surface purity of the cathode material is very high, otherwise it will affect the range of the spectrum and lose its use value. The symmetrical filament structure is used for the convenience of processing and avoiding other substances to the electrode as much as possible.

The characteristics of this type of tube are that it can work under AC conditions, the working current is large, the use of the circuit is simple, and the impurities on the electrode surface can be removed by appropriate processing, but the viewing angle sensitivity fluctuates relatively large, and the working area is prone to emission Uneven phenomenon.

2. Spherical cathode structure

In order to fully avoid the tip effect and make the photoelectron emission more stable and uniform, the working area needs to be fixed on the cathode, because the ultraviolet tube relies on photoelectron emission and gas multiplication to complete the optical signal Converted into electrical signals and amplified, generally in the area close to the electrode, the light emission utilization rate is the highest, and thus the ultraviolet tube with a dot structure spherical cathode is designed.

No matter from which angle the photons radiate to the hemispherical cathode, the discharge area is always on the hemispherical vertex close to the anode. Because the effective area of u200bu200bthe cathode is small, the working current of the tube is generally less than 0.3mA, but its viewing angle is wider and the viewing angle sensitivity is relatively uniform, which is especially suitable for fire forecasting places. Focusing methods can also be used to improve sensitivity.

In the tube, the anode is made into a hemispherical reflective surface, such as the UV-sensitive tube resistant to high temperature of 540°C in the United States. The received ultraviolet radiation is reflected to the cathode in the center, and the sensitivity of the tube is improved, because far ultraviolet radiation has the same linear propagation and reflection effect as visible light.

3. Flat cathode structure

The sensitivity of the ultraviolet tube depends on the number of photons received by the far ultraviolet radiation on the cathode. The larger the area of u200bu200bthe cathode, the higher the probability of reception, so that there are more photons on the cathode. The electrons escape and are accelerated under the action of the applied high-voltage electric field and collide with gas molecules in the tube to ionize the gas molecules. The electrons generated after ionization collide with the gas molecules. This cyclical motion will eventually discharge the gas in the tube. The chance of this avalanche discharge depends on the photoelectron emission effect on the cathode. In order to improve the sensitivity, a flat-shaped cathode structure ultraviolet tube has been developed and developed in recent years.

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