Weak current College】 【projection display system interference and elimination --- Power By】 【China power house network.

In projection display systems engineering, often image interference problems. Especially in recent years, the size of the projection display system there is a growing trend. Large display system connection between the more complex, the probability of interference has increased significantly, and it is difficult to exclude it. Therefore, the system interference has become disturbed system integrators.
According to different sources of interference, can interfere into electromagnetic radiation interference and ground disturbance. This article will result from interference, analysis of the principles set out to cause interference, the Elimination of interfere.

1. electromagnetic interference causes and elimination of method
1.1 transmission lines to eliminate external electromagnetic interference principle
Display system for the transmission line is coaxial cable, there is also some use twisted pair. Both coaxial cable or twisted-pair, they both have the ability to electromagnetic interference.
Coaxial cable is a shielded method against electromagnetic interference. The coaxial cable from the outer conductor and inner conductor, both the center point of a cable as the Centre of concentric circles, therefore it is called the coaxial cable. In the inner and outer conductors between the insulating materials as fillers. Outer conductor are often woven into a network, it to external electromagnetic interference shielding effect with good. Inner conductor in outer conductor of strict protection, therefore, coaxial cable with good anti-interference ability.
Twisted pair is taking a balanced approach to eliminate external electromagnetic interference. A pair of the twisted pair cable, the two conductors of physics characteristics (material, wire diameter) exactly the same, and in accordance with certain rules for new twist. In this way, outside interference sources and each line of electromagnetic coupling parameters exactly equal, interference currents are exactly equal, which flows through the Terminal load direction contrary to offset each other to achieve the purpose of elimination of interfere.
1.2 strong electromagnetic interference on line and elimination
To sum up, the transmission line is protected from external electromagnetic interference capability, enabling effective transmission signal. The transmission line is protected from external electromagnetic interference capability is often used to express the degree of interference with the defence, its definition is: interference signal strength and in transmission interference signal strength ratio, then take the logarithm. The greater the degree of interference with the defence that stronger anti-interference ability. Transmission line interference directivity enough to withstand normal circumstances of various interference. However, when the interference source too strong, over the transmission lines of Defense, the image signal interference. These strong electromagnetic interference in the following two ways: first, there is a strong electromagnetic radiation source in the vicinity. Second, improper wiring design, strong power line transmission interference.
Strong electromagnetic radiation sources typically have high power stations or electromagnetic radiation of electrical equipment. Strong electromagnetic interference in the image on the mesh ripple noise. For such interference, you can do to eliminate interference. First, as far as possible, avoid interference sources, to display the system equipment and lines to and radiation source at arm's length. Second, the choice of shielding performance of cables. Coaxial cable outer shielding network weaving density directly affect cable interference directivity, braided density, the higher the directivity. Therefore, you should select the braided density larger cable. Cable brand on the market, quality is different. Therefore, it is necessary to pay attention to selection of high quality cable.
By wiring interference, mainly because of the transmission line and strong electricity line and long distance close parallel wiring, produce electromagnetic coupling. Coaxial cables jamming directivity in low frequency is low, and the strong electric interference components mainly 50 Hertz AC and harmonic, therefore a threat to the coaxial cable. Therefore, to avoid signal lines and strong electricity line and long distance close parallel wiring. The strong power lines and signal transmission lines share trunking arrangement and trunking between maintaining a certain distance. Of course, nor with dread, transmission lines and strong electric line distance parallel wiring is interference will not occur. Both ends of the display system and the equipment cabinet, inevitable the strong power lines and signal cable distance between parallel wiring, this is the interference will not occur.

2. ground disturbance causes and elimination of method
2.1 ground disturbance generated by the principle
Ground jamming is display system frequently occurring interference, works in interference most such interference. Generated ground disturbance as a result of system there are more than two conflicting ground wire. Figure 1 indicates that the two principles of interfering with the ground wire, Figure 2 is the equivalent figure. Figure 1 two ground wire is present in the G1 is the signal source ground, G2 is a display device (projector). The two ground there, resistance Rg. The Earth as the various electrical equipment of public ground current loops, exist. And current to the ground resistance Rg the voltage drop on the Ug. Ug-generated electrical current flows through the cable outer conductor Ig. Because the cable outer conductor resistance also exist, Ig in Rw Rw voltage drop on the Uw, this voltage is interference voltage. Uw and the signal source voltage Uy superposition (see Figure 2), the formation of the image. The main components of ground current is 50 Hertz alternating current and electric equipment interference pulses, the image of the performance is a horizontal black stripes, mixed with levels of clutter, and slow-moving along the vertical direction.
2.2 ground wire interference cancellation method
2.2.1 measures to maintain the system altogether.
According to the above analysis, when the system has two above ground, it will cause interference. Therefore, to eliminate interference, it must ensure the system is only one ground, the so-called total. For that purpose, the following areas.
First, in the system design stage, on the ground wire for stringent system design to eliminate the hazard. System ground including equipment power supply power strip of ground and ground installation equipment cabinet. The ground wire must be from a common ground, absolutely not allowed to have two or more ground exists.
Second, display equipment installation should avoid and architecture or in other conflicts with system ground connection of the ground. Install the screws of the display device and the device is connected to the ground, some devices of the shell is the metal material, which is in itself a ground equipment. In the device setup, easy to connect with other Earth occurs. In order to avoid interference, the device should avoidConnection with other ground wire, especially the building ground connection. When you cannot avoid, insulation measures must be taken.
Third, and displaying system connected to the other system's ground wire must be ground with the display system altogether. The other system, mainly in the central control systems, audio systems, etc. These systems of Earth as and display system does not have to, the interference into the display system.
Fourth, deal with UPS ground, UPS ground wire must be the system Earth total.
2.2.2 using signal isolators, eliminate ground disturbance.
In some occasions, the causes of interference are complex, and influenced by various factors, could not be ruled out. At this point, you must take to correct the interference signal isolator. Isolator is to take the input and output components of ground isolation methods to eliminate interference. Beijing Zhao hengye electronic technology co., Ltd. under exclude system interference in recent years of practice, developed a series of anti-jamming isolator device. These devices have RGB signal isolators, signal isolators, signal isolators, product type and function in the table below.
With the above isolator products, various ground jamming in the system can be eliminated. Zhaoke company series isolator products since 2005, developed and widely used in engineering to solve multiple display system interference problems and achieved great success, becoming indispensable to solve system interference.
2.2.3 using twisted pair transmission system.
Twisted pair transmission system is balanced system, with strong ability to suppress common-mode noise. In Figure 3, ground disturbance currents Ig in twisted-pair of two conductors in size equal to the current I1 and I2. Because of the A2 is differential input amplifier, common-mode signal on such does not have a zoom function. The A1 amplifier output is differential-mode signal is amplified normal output A2. Thus, in a twisted-pair systems, ground disturbance signal is suppressed, the useful signal transmitted by normal zoom.
According to the analysis of the twisted pair transmission system can be effective on the ground, this is twisted pair system one of significant advantages. In engineering design, according to the works of the actual situation in a timely manner using twisted, but also avoid ground disturbance. Zhaoke company twisted device has a twisted-pair transceivers, twisted-pair matrix, has formed a series, may constitute a twisted pair transmission switching systems, and engineering meet widely applied, can provide practical solutions.