Ultraviolet (UV) sensors, also known as UV phototubes, are phototubes that utilize the photoelectron emission effect. They are characterized by responding only to UV radiation below 300nm, exhibiting high sensitivity, high output, and high response speed. Furthermore, they possess strong anti-interference capabilities, stability, reliability, long lifespan, and low power consumption, making them widely applicable in current safety protection and automation control applications. With the widespread use of computers, various sensing technologies serving computers are receiving increasing attention. UV sensors can detect ultraviolet radiation imperceptible to the human senses and avoid interference from sunlight, artificial light, and other common light sources. They are highly useful for fire trap detection and flameout protection, as well as photoelectric control in special locations.
Structural classification of ultraviolet sensors:
Currently, ultraviolet tubes with practical value both domestically and internationally can be classified into spherical, wire, and flat structures according to the cathode shape. These are all electrode structures of diodes, and the shape and material of their outer shells are designed for application requirements. From the perspective of working conditions, it is more appropriate to analyze them by classifying them according to electrode shape.
1. Spherical cathode structure:
To fully avoid the tip effect and make photoelectron emission more stable and uniform, the working area needs to be fixed on the cathode. This is because the ultraviolet tube relies on photoelectron emission and gas multiplication to convert light signals into electrical signals and amplify them. Generally, the light emission utilization rate is highest in the area closer to the electrodes.
Regardless of the angle from which photons radiate onto the hemispherical cathode, the discharge region is always located at the apex of the hemisphere closest to the anode. Because the effective area of the cathode is small, the operating current of the tube is generally less than 0.3mA, but it has a wide viewing angle and relatively uniform spectral sensitivity, making it particularly suitable for fire prediction applications. Focusing techniques can also be used to further enhance sensitivity.
The anode inside the tube is made into a hemispherical reflective surface, such as the ultraviolet phototube in the United States that can withstand temperatures up to 540°C. This causes the received ultraviolet radiation to be reflected back to the central cathode, increasing the tube's sensitivity, because far-ultraviolet radiation has the same rectilinear propagation and reflection effect as visible light.
2. Filament electrode structure:
The electrodes of this type of tube are generally composed of two or more symmetrical metal wires. This was an early structural form of ultraviolet (UV) tubes, often using high-purity tungsten or platinum wires. The closely spaced parallel lines form the working region. Since UV tubes rely entirely on the photoelectron emission effect of the electrode surface and then utilize gas multiplication to obtain a strong signal, their spectral response range depends on the work function of the cathode material.
In photoelectron emission, the shorter the wavelength of a photon, the higher its energy. Even a small number of photons can excite electrons to overcome the work function and escape from the cathode surface. Conversely, a large number of low-energy photons cannot excite electrons from the cathode surface. Ultraviolet tubes require extremely high purity of the cathode material surface; otherwise, the spectral range will be affected, rendering the tube unusable. A symmetrical filamentary structure is used for ease of processing and to minimize contamination of the electrode by other substances.
These types of tubes are characterized by being able to operate under AC conditions, having a relatively large operating current, and using simple circuitry. Impurities on the electrode surface can be removed using appropriate processing techniques. However, their viewing angle sensitivity fluctuates significantly, and uneven emission is prone to occur in the operating area.
3. Flat plate cathode structure
The sensitivity of an ultraviolet (UV) tube depends on the number of far-ultraviolet photons received at the cathode. A larger cathode area results in a higher reception probability, leading to more electrons escaping from the cathode. These electrons are accelerated under a high-voltage electric field and collide with gas molecules inside the tube, ionizing them. The resulting electrons then collide with more gas molecules, and this cyclical process eventually causes the gas inside the tube to discharge. The probability of this avalanche discharge depends on the photoelectron emission effect at the cathode. To improve sensitivity, a flat-plate cathode structure has been developed and researched in recent years for UV tubes.
Finally, we recommend two high-quality UV sensors imported from abroad by ICbuy.com. First is the GUVA-S12SD UV sensor. The GUVA-S12SD uses a surface-mount package (SMD3528), making it particularly suitable for small-sized devices. The sensor's output current is directly proportional to the light intensity, and the output exhibits very high consistency. All sensors have specific spectral responses, and this product is primarily designed for measuring ultraviolet radiation in sunlight and UVA lamp intensity, making it particularly suitable for UVI detection. It is widely used in smart wearable devices, UV-A lamp monitoring, UV LED monitoring, UV curing, and portable devices for detecting UV indexes.
Finally, there's the ultraviolet sensor – GUVB-T11GD-L. This UVB sensor features high sensitivity and good solar blindness, a peak response at 300nm, a TO-46 metal housing, and a large-area photosensitive chip. UV sensors are widely used in: ultraviolet intensity detection and control, UV index detection, outdoor UV index monitoring equipment, and can also be used for ultraviolet disinfection and UV curing, monitoring ultraviolet intensity, UV flame detectors, UV index monitoring, UV-B lamp monitoring, and medical applications.
