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Multiplexers can be used to connect PBX, Hot line and other devices of network from central site to user site through fiber optical cable.Multiplexer Application

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Multiplexer Knowledge

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1-64 Channels Video Multiplexer and ST Patch Cord


RS422 Fiber Modem and 10G X2 Module

PDH Multiplexer Common Problems and Solutions

 

The common problems of PDH multiplexers are shown as below:

 
1. Optical Link Problem
 
In the project of security monitoring, most cable is laid by users, typically G652 single-mode fiber. Because the scope of the system is not large generally, the link loss is enough even to use the standard equipment (≤20km). Therefore, the PDH multiplexer do not ask too much of optical link loss. But, users often encounter problems with not image, image jitter, poor image quality and others. In these cases, the problems usually occur at the pigtails of two ends of the optical link, fiber patch cord or fiber optic adapter.
 
And the common problem includes:
 
  1. The optical fiber connector is inserted incorrectly.
  2. The optical fiber connector core (Ceramic tube) is polluted.
 
The solution is:
  1. Re-inserting the connector or replace the fiber optical patch cord.
  2. Wiping the plug and socket core by using 99.9% alcohol.
  3. Using a multi-meter to check camera video cable and determine whether there is video signal.
 
2. Data Interface
 
In order to meet the need of security monitoring, all kinds of equipment system (matrix, hard recorder and decoder) provide RS485 data interface, whose advantages are long transmission distance, strong load capacity and can be composed of four lines of full duplex communication bus.
 
The disadvantage of the RS485 data interface is that it has an end which is Tri-state form and can bring unstable or even “stuck” phenomenon. If there is no communication, we should take the following measures to find out the reasons:
 
 
Testing whether there is control signal. Using a multi-meter to measure the RS485 output port of controller (matrix, hard recorder) by AC 10V.
 
 
Determining the RS485 interface of PDH multiplexer is normal or nor. If the UA-B voltage is zero, the PDH multiplexer is abnormal.
 
 
PTZ can’t be controlled. This phenomenon is caused by two reasons:
 
A) The RS485 port A+ and B+ are connected reversely.
B) The system impedance is mismatch seriously.
 
E1 Fiber Modem
 
E1 Fiber Modem
 

3. Switch Quantity

The switch quantity signal is the pulse string of TTL level. The switch quantity controls the warn lights, alarms, relays and others. The load capacity of the switch quantity interface is measured by the current size of the control. For example, the switch quantity load capacity of EW series of PDH multiplexer is less than 1.5A.

 

4. Transient Interference 

The transient interference is generated in larger inductive load, such as switch motor, transformer, relays and other devices’ switch change. It is also generated in the thunder. The transient interference tends to invade the PDH multiplexer by the way of electrostatic.

 

Because of its high disturbance frequency, short duration and large disturbance amplitude, the transient interference can burn the RS485 interface chip, main chip and other key parts of PDH multiplexer without leaving traces. The impact of this destructive force is very large, that users, merchants and manufacturers are very vexing.

 

Although manufacturers use various means of protection, such as bypass method (self-recovery diode), absorption (bidirectional suppression diode) and isolation method, it still can’t completely eliminate the damage caused by the transient interference. The RS485 interface is damaged frequently that cause great pressure to users and manufacturers.

 

 

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