According to the elevator industry development, the sales volume of elevators is growing rapidly. This also means that the elevator safety becomes more and more important. So elevator manufactures begin to look for stable and safe video surveillance solution in elevator.
The key functions of video surveillance in elevator are to get the elevator car inside situation and enhance passengers’ safety in elevator. And video surveillance becomes particularly important for safe checking and special circumstances. Moreover, the elevators are the building portals and channels. Video surveillance in elevator plays an important role in the whole region security, which becomes an important and indispensable part.
The main form of video surveillance in elevator is to install the camera in the elevator car. Camera transmits the video signal to control room. And all video signals are centralized in the control room. Then you can display, storage and check video information. In order to achieve these basic functions, you may adopt different system structures and solutions.
In fact, the elevator video surveillance faces more difficulties. The cores of the difficulties are interferences and high cost. Therefore, the owners and installers urgently need to cooperate with elevator manufacturers to provide nice video surveillance solution.
Application:
Analog Camera + Twisted Pair Transmitter + UTP Cables + Twisted Pair Receiver + DVR
Difficulties of Video Surveillance in Elevator:
Interferences: There are large numbers of devices installed in elevator hoistway such as mobile communication signal generator, inverter air-conditioning, and lighting equipment. Besides, elevator own frequency pulled cited elevator motor itself will have a relatively large radiation interference, so that the video cable through the these electromagnetic contaminated in the process, will be coupled into a lot of noise interference, causing the image a lot of problems.
The above two pictures are real video caused by interference in elevator car. The left picture interference appears in the elevator running process. There are a lot of pitting in the screen appears. The characteristic of passengers are totally not clear. The right picture interference is caused by power lines. Wave pattern exists throughout the screen, which affect the image.
Cost-effective: The old analog video surveillance in elevator is analog camera + video cable+ DVR. The users buy cameras and DVR by themselves. Elevator manufacturers provide cables of signal transmission. In generally, video cables are embedded in the travelling cables. However, technology requirements are very high such as flexibility of the cables. So the costs are very high. From our survey, we know the elevator video cable price is above 1.56USD / m. Moreover, video cables can not solve all the coupling interference.
Twisted pair transmission can solve below problems:
Anti-Interferences (external interference suppression):
Interference on un-twisted pair:
Please look at below diagram. Us is the interference signal source. Interference current are I1 and I2 on the two conductors L1, L2. L1 is close to interference source. Therefore, I1> I2, I= I1-I2 ≠ 0, it exists interference current.
Interference on twisted pair loop:
Please look at right diagram. It is different from left diagram. Two-loop has a twist at the midpoint position. It exists interference current I11 and I12 on the L1 and interference current I21 and I22 on the on L2. Interference current I = I21 + I22 - I11 - I12. Two lines have the same conditions, so the total interference current I = 0. So long as twisted away are set reasonable, we can achieve the purpose of eliminating the interference.
Differential signals suppress common mode interference:
The common mode interference mainly refers to the loop interference between cables and the earth (ground system). As we all know, the video cables are parallel cables. Twisted pair is each twisted cables, which are suitable for transmitting differential signal. The transmission method of differential signal is 'virtual ground' concept. There is no real association from signal transmission to reception, eliminating the influence of the ground for the cable and also the coupling interference between the earth and cable.
Cost-effective:
Above-mentioned elevators video cable applications, twisted pair transmission require using Twisted Pair + Video Transmission Devices. You can use the variety of twisted pair such as network cable, RVS cables. In elevator hoistway, there is only travelling cable as one media channels connecting the elevator car and control room. The cable kink and flexibility are very important. So RVS cables are very practical (similar free cables in travelling cables can be used). The image transmission quality is very high and relatively low cost.
In summary, if we use twisted pair + UTP Balun, the elevator video surveillance transmission has advantages as follows:
(1) Very cost effective
(2) Surper anti-interferences ability
(3) Easy for obtaining RVS cables
(4) Easy for system upgrading and expansion
Cases in Elevator：
