When using a twisted pair transmitter, sometimes due to environmental factors, the phenomenon of moire on the monitor may occur. For this reason, Utech has performed the following simulation experiments to analyze and propose solutions.
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First, the experimental equipment:
Front-end equipment camera, rear-end equipment monitor, twisted pair transmission UTP101P-II pair, 300 meters super 5 twisted pair.
Second, the experimental method:
1. Connect the camera and monitor to two different ground networks, using different power supplies;
2. Both ends are connected normally through a passive twisted pair transmitter;
3. Use a multimeter to measure the voltage between the two power supply ground grids to 110V;
4. Observe the monitor display effect;
5. Add a signal isolator to the camera or monitor, and observe the monitor again.
The connection method is as shown:
Third, the phenomenon description:
1. A parallel, translucent horizontal line interference appears on the monitor screen and slowly moves up or down as shown:
2. When adding a signal isolator to any camera or monitor, the horizontal interference disappears and the video image is very clear, as shown:
Fourth, the cause of the phenomenon:
To make the signal transmission intact and without distortion, the ideal situation is that the signals in all devices have a common reference point, that is, have a common "ground", or simply isolate the ground at both ends of the device. Only then can the potential difference between the signal reference points of all devices be "zero". Obviously, it is difficult to ensure that the grounding resistance of different devices is equal, and if there is interference from a large device at one end, the level of the reference ground of the front-end device and the back-end device will be very different, sometimes even generating a potential of up to 200V. difference. It can be seen from the above figure that there is an AC voltage difference of 110V between the grounding ground of the camera and the grounding ground of the monitor, thus forming common mode interference to the video signal. The environment simulated by this test is the engineering site. Because the on-site monitoring area is relatively wide, the front-end equipment and the back-end equipment are far away, and it is inevitable that there will be different power supply bodies. The grounds they refer to are different. When the local network is different, It is easy to form a voltage difference and cause strong interference to the video signal.
Fifth, the solution:
There are currently three ways to solve this type of problem:
The first option is to monitor the device not to be grounded (whether it is a front-end device or a back-end device), so that there is only one ground point in the process loop. However, in practical applications, such a solution is often difficult to implement because most monitoring equipment must be grounded to ensure stable work and personal safety. It is also possible that the equipment will form a new grounding point due to long-term corrosion and wear or weather.
The second solution is to make the relative potential of each point of the device on the monitoring transmission the same. One method is to connect the front end device to the ground of the back end device with a wire, but the wire itself also has a resistance, and the effect is not Very good, and need additional wiring, increasing the complexity of the project; the second method is to use shielded twisted pair, but it will inevitably have loss of video signal, thus shortening the transmission distance.
The third option is to add a signal isolator to the front-end or back-end equipment and a signal isolator in the process loop. The signal isolators use isolation technology to break the DC path in the process loop without affecting the normal transmission of the process signal, thus completely solving the above problems.
The following picture shows the UTP1201XP coaxial loop signal isolator developed by Youpupu:
Sixth, the role of signal isolators
The signal isolator has the feature of electrically isolating the DC signal in the input/output process loop. In other words, if there is no "ground" between the video signal input device and the video signal receiving device, then even if there is a pressure difference of hundreds of volts between the two places, the signal received by the back end after passing through the isolator Both become standard signals for the original video input.
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