What are the various grades of night vision image tubes?
The Night Vision Tube is a unique device with which the night vision device can work. Just like many other elements, they are divided into generationsand types. In this article, we will tell you the basic theoretical information about generations of night vision image tubes.
A ray tube or image intensifier tube(IIT), in its essence, is a vacuum photo-electronic device that converts an object invisible to the eye (in infrared, ultraviolet and X-rays) into visible image or to increase (amplify) the brightness of the visible image.
They are used in night vision devices, which is the main feature by which NV generations differ.
The action is based on the conversion of an optical or X-ray image into an electronic image using a photocathode and then an electronic image into a light (visible) image obtained on a cathodoluminescence screen. The image of the object is projected onto the photocathode with the help of the IIT EOS lens.
Single-camera and multi-camera (cascade)IIT are distinguished; the latter are such a sequential connection of two or more single-camera ITT EOS, in which the light flux from the screen of the first IIT (cascade) is directed to the second cathode, etc.
According to the world accepted terminology EOS IIT are classified into five generations - I, II, III, (with some intermediate stages I+,II+).
The distinctive feature of these devices is that the image in the center is clearer and has less distortion than the edges. In addition, if bright light sources such as flashlights, luminous house windows, etc. are in sight, they can illuminate the entire image, preventing you from observing. At lower light levels, additional infrared (IR) illumination is most commonly required.
Structurally, 2nd generation IIT differs from I+ by the presence of a special amplifier of electrons - a microchannel plate. There are two sizes of IIT - with MCP: 25 and 18 mm. From the observer's point of view, the larger size provides quite comfortable observation, but also leads to an increase in the size of the device. All Gen II devices have a useful feature for the observer - manual brightness adjustment, which allows you to choose the optimal ratio of brightness gain and the level of the device's own noise for each specific observation situation and adaptation of the eye.
Thanks to the implemented improvements, night vision devices have a resolution from 55 to 72 lp/mm and a signal-to-noise ratio of 16/24;
The third generation uses a photo cathode based on gallium arsenide, which increased the sensitivity of IIT by an order of magnitude. The working distance is 300 yards (275 meters), and image intensification is from 30000 to 50000 times. Service life is 10 thousand hours. Gen 3 is the "gold" standard used by NATO troops. The image intensifier consists of a high-performance GaAs-based photocathode attached to a glass input window, a current amplifier with a microchannel plate (MCP) and a P-43 fluorescent screen applied to a non inverting fiber optic output window. The Gen 3 photocathode is very sensitive to low levels of visible and especially near infrared light. The tube has an average lifetime of 12,000 hours of continuous operation.
September 30, 2020