At present, Gao Qinghua is a development trend of the security monitoring industry, video optical transceiver terminal equipment as the transmission medium, is particularly important in the whole transmission process, but we in the use of video in the process of the optical transceiver, often will encounter image distortion, jitter, poor image quality problem, so if we encounter similar problems, how to solve?
In the security monitoring project, most of the optical cables are laid by the user, generally G652 single-mode optical fiber. Because the system range is not big, generally use the standard optical link loss (20 km or less) devices are very rich, therefore, video optical transceiver optical path loss not too high, but users are often faced with no issue such as difference of image, image jitter, image quality, when most of its problems are on opposite sides of the light path tail fiber, jump line or on the adapter, and rarely related to the main optical path.
Common problems are:
1. The active connector of the optical fiber is improperly inserted.
2, fiber active connector fiber core (ceramic tube) is contaminated.
1. Reinsert the movable connector or replace the fiber jumper;
2. Wipe plug and socket core with 99.9% anhydrous ethanol;
3. Check the video cable of the camera with a multimeter to determine whether there is a video signal.
In order to meet the needs of security monitoring, all kinds of equipment (matrix, hard recording, decoder) of the system provide rS-485 mode of data interface, the advantages of this format of data interface is long transmission distance, strong load capacity, and can form a four-line full-duplex communication bus, any two devices on the line can achieve two-way communication. The four-wire RS-422 bus can only realize the two-way communication between master and slave machines, but not between slave machines. Its disadvantage is that it has an enabling end, which is in the form of three states, bringing instability and even "stuck" phenomenon to communication. If there is no communication (out of control), find the cause from the following aspects:
Video optical end machine common problem solutions
1. Detect whether there is control signal with multimeter AC 10V file test controller (matrix, hard recording, etc.) output RS-485 port, see whether there is control signal output.
2. Check whether the RS-485 port of the optical terminal is normal. If the UA-B voltage is zero, it is considered abnormal.
This phenomenon is caused by two reasons: a)RS-485 ports A+ and B- are inversely connected; B) Serious mismatching of system impedance.
Switching quantity signal is the pulse string of TTL level, which can control the work of alarm lamp, alarm bell, relay and so on. The load capacity of switching quantity interface is measured by the controlled current. For example, the load capacity of EW series optical terminal machine is less than or equal to 1.5A
1. The switch interface of EW series optical terminal machine supports normally open button, but when connected as shown below, both normally open and normally closed modes are supported.
2. The switching interface cannot be directly connected in parallel. If necessary, it can only be connected through the distribution circuit.
3. Some customers use RS-485 bus transmission switch, according to our practical experience to prove that this way is not desirable, often work for a period of time (such as 3~4 days) that the crash phenomenon. A defective switch to RS-485 converter may be the problem.
1. Generation of transient interference: Transient interference is generated in large inductive load, such as the switch conversion of motor, transformer, relay and other equipment, as well as the occurrence of lightning, it often intrudes into optical terminal machine in the way of electrostatic induction.
2. The harm of transient interference, interference due to its high frequency, short duration, large disturbance amplitude (kv) on hundreds, it can burn out the RS - 485 interface chip optical transceiver, main chip and other key parts, but a trace, especially the summer thunderstorm season, the destructive effect is very big, the user is very nerve-racking, merchants and manufacturers.
3. Response: although optical transceiver manufacturer adopted various means of protection, such as the bypass method (since the recovery diode), absorption method (bidirectional diode inhibition, etc.), isolation method (optical coupling isolation), but still can not completely eliminate the damage caused by transient interference, RS - 485 interface damage frequently, to users and manufacturers are causing a lot of pressure.