What is a projector?

What is a projector?

  • 2021-08-26

A projector, also known as a projector, is a device that can project images or videos onto the screen. It can be connected to computers, VCDs, DVDs, BDs, game consoles, DVs, etc. through different interfaces to play corresponding video signals.
Projectors are widely used in homes, offices, schools, and entertainment venues. According to different working methods, there are different types such as CRT, LCD, and DLP.

Application Classification:

1. Classification according to the application environment

1. Home theater type: Its characteristic is that the brightness is around 2000 lumens (with the development of projection, the number is increasing, and the contrast is higher), the aspect ratio of the projection screen is mostly 16:9, and various video ports Complete, suitable for playing movies and high-definition TV, suitable for home users.

2. Portable business projector: Generally, a projector weighing less than 2 kilograms is defined as a business portable projector. This weight is comparable to a thin and light notebook computer. The advantages of business portable projectors are small size, light weight, and strong mobility. It is a substitute for traditional slide projectors and large and medium-sized projectors. The combination of thin and light notebook computers with business portable projectors is what mobile business users are doing. The first choice for mobile business presentations.

3. Educational conference projector: generally positioned in schools and corporate applications, with mainstream resolution, brightness of about 2000-3000 lumens, moderate weight, good heat dissipation and dust resistance, suitable for installation and short-distance movement, functions The interface is relatively rich, easy to maintain, and the performance-price ratio is relatively high. It is suitable for mass purchase and popular use.

4. Mainstream engineering projectors: Compared with mainstream ordinary projectors, engineering projectors have larger projection areas, longer distances, and high brightness. They also generally support multi-bulb mode, which can better cope with large scales. The changeable installation environment is very suitable for education, media, government and other fields.

5. Professional theater-type projectors: This type of projector pays more attention to stability, emphasizes low failure rate, and has a strong performance in heat dissipation, network functions, and ease of use. Of course, in order to adapt to various professional applications, the main feature of the projector is its high brightness. Its brightness can generally reach more than 5000 lumens, and the higher one can exceed 10,000 lumens. Due to its large size and heavy weight, it is usually used for special purposes, such as theaters, museums, halls, public areas, and can also be used in environments such as traffic monitoring, public security command centers, fire control centers, and air traffic control centers.

6. Measuring projector: This type of projector is different from the above several types of projectors. In the early days, it was called contour projector. With the popularity of grating rulers, projectors are equipped with high-precision grating rulers, and people are also called measuring projectors ( Or projectors, such as the more famous domestic measuring projector CPJ-3015 produced by Gaocheng Company). In order to distinguish it from traditional projectors, this type of projector is called a measuring projector. Its function is mainly to form an enlarged projector through the transmission of light from product parts, and then use standard film or grating ruler to determine the size of the product. Due to the development of industrialization, this measuring projector has become one of the most commonly used measuring instruments in the manufacturing industry. Scheduled projection methods are divided into vertical projectors and horizontal projectors. According to different comparison standards, it is divided into contour projector and digital projector.

2. Classification according to usage
1. Desktop projector
2. Portable projector
3. Floor projector
4. Reflective projector
5. Transmissive projector
6. Single function projector
7. Multifunctional projector
8. Smart projector
9. Touch interactive projector

Three, according to the interface category classification

1. VGA interface projector
2. HDMI interface projector
3. Projector with network port

light source

The technical solutions adopted by mainstream projectors on the market are basically divided into digital light processing (DLP) technology and 3LCD technology.
The light sources used in the projector include traditional high-intensity gas discharge light sources (such as ultra-high pressure mercury lamps, short arc xenon lamps, metal halide lamps) and new light sources represented by LED light sources and laser light sources. Traditional light source projectors usually make the projected image darker and yellowish (such as brightness attenuation, color saturation reduction, etc.) with the attenuation of the light emitted from the light source after a period of use. In use occasions that require high image quality , Even if the light bulb is still glowing, the light bulb has to be replaced because of this. Therefore, light decay has become a major obstacle that cannot be surpassed by projectors using traditional light sources. With the development of semiconductor lighting technology and laser technology, LED light sources and laser light sources have not only developed rapidly in the field of lighting, but also have been widely used in the field of display. LED is the earliest product used in projectors among new light sources. Because LEDs can make the imaging structure of projectors simpler, projector products with smaller size, easy to carry, and simple to use have brought to teaching, business and personal entertainment. Great convenience. At the same time, as a brand-new projection light source, the emergence of laser solves the defects of projectors that use traditional light sources in brightness attenuation, color, power consumption, etc. At the same time, because it is a cold light source, it has the ability to turn on and turn on immediately. Features, fundamentally eliminate the need to wait for power on and stable light emission when using traditional light sources.

main indicators

The performance index of the projector is a sign that distinguishes the grade of the projector. There are mainly the following indexes:
Light output
Refers to the light energy output by the projector, the unit is "lumens" (lm). A physical quantity related to light output is brightness, which refers to the ratio of the light energy emitted by the surface of the screen to the area of the screen. The common unit of brightness is "lux" (lx, 1lx=1lm/m2). When the light output by the projector passes a certain amount, the larger the projected area, the lower the brightness, and vice versa, the higher the brightness. The factors that determine the light output of the projector are the projection and phosphor screen area, performance and lens performance. Generally, the phosphor screen area is large and the light output is large. The performance of the projector lens with the liquid coupling lens is good, and the light output of the projector can be improved accordingly.
Horizontal scanning frequency
The movement of electrons from left to right on the screen is called horizontal scanning, or line scanning. The number of scans per second is called the horizontal scan frequency. The horizontal scan frequency of the video projector is fixed, 15.625KHz (PAL system) or 15.725KHz (NTSC system). The scanning frequency of data and graphic projectors is not a different frequency band; In this frequency band, the projector can automatically track the horizontal frequency of the input signal, and the phase-lock circuit realizes complete synchronization with the horizontal frequency of the input signal. The horizontal scanning frequency is an important projector index that distinguishes the grade of the projector. A projector with a frequency range of 15kHz-60kHz is usually called a data projector. The upper limit frequency exceeds 60kHz is usually called a graphic projector.
Vertical scan frequency
The electron beam moves from top to bottom while scanning horizontally. This process is called vertical scanning. Each scan forms an image. The number of scans per second is called the vertical scan frequency, and the vertical scan frequency is also called the refresh frequency, which represents the number of times the image is refreshed per second. The vertical scanning frequency is generally not less than 50Hz, otherwise the image will have a sense of flicker.
Video bandwidth
The total bandwidth of the video channel of the projector is defined as the upper limit frequency of the corresponding signal when the video signal amplitude drops to 0.707 times. The increment corresponding to 0.707 times is -3db, so it is also called -3db bandwidth.
There are three resolutions: addressable resolution, RGB resolution, and video resolution.
For CRT projectors, the addressable resolution refers to the highest pixel that the projection tube can distinguish. It is mainly determined by the focusing performance of the projection tube and is an important parameter of the quality index of the projection tube. The addressable resolution should be higher than the RGB resolution.
RGB resolution refers to the highest pixel that the projector can pass through when the RGB resolution video signal is connected, such as a resolution of 1024×768, which means that the horizontal resolution is 1024, the vertical resolution is 768, the RGB resolution and the horizontal scanning frequency , Vertical scanning frequency and video bandwidth are all related.
Video resolution refers to the highest resolution of the projector when displaying composite video. Here, it is necessary to analyze the relationship between the video band, horizontal scanning frequency, vertical scanning frequency and RGB resolution: First, look at the relationship between horizontal scanning frequency and vertical scanning frequency.
Focusing performance of CRT tube
The smallest unit of graphics is the pixel. The smaller the pixels, the higher the graphics resolution. In the CRT tube, the smallest pixel is determined by the focusing performance. The so-called addressable resolution refers to the number of smallest pixels. The projector focusing mechanism of CRT tube includes electrostatic focusing, magnetic focusing and electromagnetic composite focusing. Among them, electromagnetic composite focusing is more advanced. Its advantage is good focusing performance, especially defocusing under high brightness conditions, and high focusing accuracy. It can focus on sub-regions, edges, and four corners, so that every point on the screen is very clear.
Convergence means that the three colors of RGB are overlapped on the screen. For CRT projectors, convergence control is particularly important, because it has three RGB CRT tubes, which are installed in parallel on the ground bracket. If you want to achieve complete convergence of the image, It is necessary to correct various distortions of the image. As the position of the machine changes, the convergence must be re-adjusted. Therefore, the requirements for convergence are one of full functions, and the other is convenient and fast. Convergence has static convergence and dynamic convergence. Dynamic convergence has functions such as tilt, bow, amplitude, linear, trapezoid, and pincushion. Each function can be adjusted in both horizontal and vertical directions. In addition, non-linear balance, trapezoidal balance, and pincushion balance can also be adjusted. Some projectors have a point convergence function, which divides the full screen into 208 points, and adjusts the 208 points point by point, so every point on the screen is accurately converged.

Daily maintenance

1. The ambient light of the projection should not be strong, preferably weak light
The projection quality of a projector is not only related to the brightness of the projection bulb, but also to the impact of the projection environment. The light intensity of the projector's working environment will directly affect the projection effect. Therefore, before using the projector, you must first arrange the projector's working environment and make the projection bulb work in a dimly lit environment as much as possible. Bright ambient light will make the brightness effect of the projection bulb worse, making it difficult for students to watch. In order to get a better projection effect of the projector, we may as well install dark opaque curtains in the room to block the outdoor light, and the walls of the room use materials that are not suitable for reflection. These details will make the brightness of the projector in the projection bulb the same. Under the circumstances, a better projection effect is produced.
2. Pay attention to the order of power switch
Properly turning on and off the power of the projector has a great influence on the service life of the projection bulb and the internal accessories of the projector. If you turn off the power of the projector indiscriminately, it may turn off the power of the projection lamp and the circuit part of the projector together, causing the cooling fan inside the projector to stop working due to the power failure, resulting in the projection lamp and the projector during the working process. A large amount of heat cannot be discharged through the cooling fan in time. This situation is likely to cause the projection bulb to explode, damage the internal circuit board and cause the projector to fail to work normally. The correct operating sequence for switching the projector's power on and off is: first turn on the power when turning on the projector, and then continue to hold down the indicator button on the projector control panel until it does not flash; you can also use the power button on the remote control to issue a power-on command. The projector starts up according to the preset startup procedure. When shutting down, do not cut off the power supply of the projector directly. You should first press and hold the shutdown indicator button until the light does not flash. (At this time, the cooling fan inside the projector will continue to run to dissipate heat, and stop rotating after about 5 minutes); the shutdown command can also be issued through the shutdown button on the remote control. At this time, the CPU inside the projector will instruct the cooling fan to dissipate heat at full speed. At the same time, the CPU must detect the internal temperature of the projector. If it is above 40°C, it will issue a command to keep the cooling fan running and dissipate heat. Cut off the power, then cut off the power supply of the projector.
3. There should be a certain interval of time after shutting down and turning on again
When the projector is switched from the on state to the off state, there should be at least about 5 minutes of cooling time. Because the projector’s power supply uses a switching power supply method to step down, stabilize, and stabilize the mains power, the high-power switching tubes and transformers used in the projector’s power supply will work when the power is switched on and off frequently. At higher frequencies, the switch tube will produce considerable power consumption during frequent switching, and the lost power will be transferred into heat and emitted, which will increase the temperature inside the projector; in addition, the light bulb itself emits The heat is concentrated in the small space inside the projector, and sudden changes in temperature can easily cause the projection bulb to explode; in addition, frequent switching of the projector power supply will also produce a large current impact on the projection bulb, which can easily cause the projection bulb Damage; it may also damage the components in the circuit.
4. the power supply voltage used should be stable
The stability of the power supply means that the projector and its signal source (that is, the computer that is connected to the projector and provides projection signals to the projector) should be connected to the same power outlet with good quality. The projector and its signal source use the same high-quality power socket, which can avoid sparking between sockets caused by plugging and unplugging the power source, damaging the power supply circuit inside the projector, and preventing possible power mismatch Problem, to ensure that the projector is working properly. In order to prevent the explosion of the projection lamp and the mismatch of the working power of the projector, the power supply specification used by the projector has strict regulations. When the user connects the projector to a power outlet. When the user plugs and unplugs the signal line or other circuits with power on, it will cause ignition between the plugs and sockets, damage the signal input circuit, make the projection bulb not work properly, and seriously damage the projector, or even cause a fire accident. Therefore, you must use the power cord that comes with the projector, sometimes because you need an extension cord when you use it, the power extension cord should use good quality copper core wire, and the wire diameter should not be too thin; at the same time, ensure that the power socket connected to the power cord must be reliably grounded .
5. Cannot work continuously for more than four hours
If the projection lamp continues to work for more than four hours, the accumulation of heat emitted by the imaging system inside the projector will cause the temperature inside the projector to rise rapidly, because the quartz on the inner wall of the projection lamp will devitrify at high temperatures. Phenomenon, white spots appear on the shell of the projection bulb, and the devitrification part will block the light emission, which makes the temperature of the local area of the projection bulb shell increase abnormally, promote the further expansion of the devitrification area, and make the brightness of the projection bulb rapidly attenuate, and It is easy to cause the bulb to explode. Therefore, it is necessary for the projector to stop working and cool down in a timely manner to prolong the service life of the projector and the projection bulb. Don't: the duration of the projector should not exceed four hours each time.
6. Abnormal shutdown and sudden power failure are strictly prohibited
Most of the projectors use cold light source systems. The conversion efficiency of the projection bulbs is relatively high. Compared with the original metal halide bulbs, the heat generated is greatly reduced. However, the volume of the projectors is generally small, and it is easy to form accumulated temperature locally. , Need to rely on the exhaust channel to quickly dissipate heat, which requires the cooling fan to continue to be energized for a period of time after shutting down, so that the accumulated temperature inside the projector can be emitted in time. Because of this, when the projector is switched on and off, Must strictly follow the normal turn-on and turn-off sequence. Abnormal shutdown is a kind of wrong operation that seriously violates the opening and closing procedures. This kind of wrong operation can reduce the effective life of the projection lamp by up to 200 hours or even longer at a time. It is costly and must be avoided. Sudden power failure is more harmful to the projector than an abnormal shutdown. Because the sudden power failure makes the internal temperature of the projector too high, it may cause the chipset on the motherboard to work abnormally, causing the image to turn yellow and no signal output. .
7. regular dust removal
When the projector is in use, it is often necessary to install a hanging box to hang it high in the air. This environment is prone to accumulate a large amount of dust, which can easily cause the projector to produce overheating protection for half an hour after it is turned on, and it cannot be turned on. In hot and humid seasons or regions, humidity will cause the dust accumulated on the projection bulb shell to form a cement-like film, which will cause the projection bulb to explode due to excessively high accumulated temperature, thermal expansion and contraction during the working process. Therefore, regular professionals are required to clean up the dust and prolong the service life. Based on the above reasons, the fundamental reason for prolonging the life of the lamp is to firstly shut down the lamp safely and fully dissipate heat. However, in order to improve the utilization rate of the light source, many projector products are equipped with a good heat dissipation design and other means to extend the life of the bulb.

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