PCM Equipment Maintenance: PCM Equipment Fault Analysis and Solutions

In optical fiber communication systems, the optical fiber transmits binary optical pulses "0" and "1", which are generated by on-off modulation of the light source by binary digital signals. Digital signals are produced by sampling, quantizing, and encoding continuously varying analog signals, known as [PCM]( code modulation), i.e., pulse code modulation. This electrical digital signal is called a digital baseband signal and is generated by the PCM electrical terminal.

The PCM terminal multiplexing equipment is a device that completes the multiplexing and demultiplexing of single-channel signals and multi-channel signals (here referring to 2Mbit/s signals), and is also an indispensable device for implementing A/D conversion. Due to its standardized and flexible interfaces and high intelligence, it has become an important component of the electric power communication network. Currently, PCM equipment carries a large number of critical users, such as relay protection information, dispatch telephones, automation information, and conference telephones. Therefore, equipment maintenance is of great importance to ensuring the safe operation of the power system.

I. Classification of PCM Equipment Maintenance

PCM equipment maintenance can be divided into two parts: routine maintenance and fault handling. Routine maintenance mainly ensures the safe operating environment of the equipment, with the primary tasks being to monitor the equipment operating status and inspect key parameters.

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1. Central Station Network Maintenance

Central network maintenance refers to the maintenance personnel at the central station of the network management center querying detailed data of equipment at each station through the network management computer. When a fault occurs, they can locate the fault by analyzing alarm information, thereby effectively handling the fault. Therefore, it features fast and relatively accurate fault location and timely handling, providing certain technical support capability to subordinate stations.

2. Sub-station Network Element Maintenance

Network element maintenance refers to the equipment operation and maintenance personnel analyzing, locating, and handling faults based on the status of equipment indicator lights, combined with user feedback and instrument measurement values.

II. Fault Analysis Methods for Equipment Maintenance

Given that the above two maintenance methods have different focuses in analyzing and handling faults, they are elaborated from two corresponding aspects.

1. Fault Analysis Methods for Network Element Maintenance Personnel

Analysis method: The basis for fault analysis by network element maintenance personnel is the alarm information fed back by the operating status of equipment indicator lights. Due to the limited amount of information, analyzing and locating the fault point is relatively more difficult. Therefore, it is essential to memorize the meanings of various states of each indicator light on the equipment, and to pay close attention to the indicator light conditions during routine maintenance, such as whether they are constantly lit and what color they display.

When a fault occurs in the equipment, multiple boards often alarm simultaneously. In this case, the general analysis principle is to first check the CU (Center Unit), then analyze the TU (Tributary Unit); start by analyzing high-level alarms, then analyze boards with low-level alarms. The main CU types of PCM equipment to check (limited to SIEMENS) include: CUDI, CUD (Center Unit Drop/Insert Multiplexer), CUA (Center Unit Terminal Multiplexer), CUCC (Center Unit Crossconnect), etc. The TU types include SUB (Subscriber Converter-Subscriber Side), SLX (Subscriber Converter on Exchange Side), SEM (Signaling Converter Earth and Minus, also called 4WE&M), DSC (Digital Signal Channel), and other types. During maintenance, first observe from an overall perspective whether the equipment has high-level (critical and major) alarms, i.e., the operating status of the red and green lights on the CU board. Then observe the alarm status of the indicator lights on the tributary boards of the equipment (such as UMUX1300, BMX264, etc.), and combined with user feedback, the fault point can generally be preliminarily determined.

2. Fault Analysis Methods for Network Maintenance Personnel

Analysis method: By monitoring the equipment through the network management computer, a great deal of detailed information can be observed, including alarm information and performance parameters, thus providing an overall view of the entire network. This is extremely advantageous for fault analysis and location. Sometimes there may be too much alarm information; in this case, the analysis principle mentioned above should be followed, focusing on a few basic alarms, through which the fault point can be directly located. This is because some alarms are derived from these basic alarms and cannot be used to locate the fault point. For example, if an AIS (Alarm Indicate Signal) alarm appears at the receiving end of a certain station, it does not indicate a fault at the local receiving end; on the contrary, it indicates a fault at the transmitting end or the transmission link, which is transmitting the alarm indication to the local station.