When a low-voltage electrical equipment fails, quickly and accurately identifying the cause of the fault, finding the fault location, and properly repairing it is one of the skills necessary to repair the electrician.
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The connection sequence of RJ-45 line in common B standard is orange white, orange, green white, blue, blue white, green, brown white and brown. When connecting different equipment, use standard a. the connection sequence is green white, green, orange white, blue, blue white, orange, brown white and brown. Generally, the pressing method of b-mark is commonly used. If you want to make a cross line, one side is a standard, and the other side is b standard.
Working in the data link layer, the switch has a high bandwidth back bus and internal exchange matrix. All ports of the switch are connected to the back bus. After the control circuit receives the data packet, the processing port will look up the address reference table in memory to determine which port the NIC (network card) of destination MAC (hardware address of network card) is attached to. The data packet is quickly transmitted to the destination port through the internal exchange matrix. If the destination MAC does not exist, it will be broadcast to all terminals After the receiving port responds, the switch will "learn" the new address and add it to the internal MAC address table. The switch can also "segment" the network. By comparing the MAC address table, the switch only allows the necessary network traffic through the switch. Through the filter and forward of switch, the conflict domain can be effectively reduced, but it can not divide network layer broadcast, that is, broadcast domain. The switch can transmit data between multiple port pairs at the same time. Each port can be regarded as an independent network segment, and the network equipment connected to it can enjoy all the bandwidth without competing with other devices. When node a sends data to node D, node B can send data to node C at the same time, and these two transmissions enjoy the full bandwidth of the network and have their own virtual connections. If a 10Mbps Ethernet switch is used here, the total flow flux of the switch is equal to 2 × 10Mbps = 20MBps, and the total flow flux of a hub will not exceed 10Mbps when using 10Mbps shared hub. In a word, switch is a kind of network equipment based on MAC address recognition, which can encapsulate and forward data frames. The switch can "learn" the MAC address and store it in the internal address table. By establishing a temporary exchange path between the originator and the target receiver of the data frame, the data frame can reach the destination address directly from the source address. RJ45 3U Gold,Gold Flash Plated,8P8C with Shield,Shield with EMI ShenZhen Antenk Electronics Co,Ltd , https://www.pcbsocket.com
Low-voltage control equipment faults can be divided into two categories, one is the "dominant" fault, that is, the fault location has obvious appearance characteristics, which is easy to be discovered. Such as relay and contactor winding overheating, smoke, burning smell, contact burning, loose joints, abnormal electrical sound, excessive vibration, inability to move, invigorating rotation. The other type is the "hidden" fault, that is, the fault has no external features and is not easily found. Such as: fuse blown, internal break of insulated wire, improper adjustment of thermal relay setting value, unsynchronized contact opening and closing. “Hidden†faults often require more time and effort to analyze and find out because they have no external features. However, no matter how complicated the fault is and how hidden the fault is, it is sure to be “fast†if the correct method and steps are taken. "And "quasi" to find and troubleshoot.
There are six main methods of troubleshooting: 1. Intuitive method. It is to find out the abnormal situation by "ask, see, listen, touch, smell" to find out the fault circuit and the location of the fault.
(1) Ask. Obtain the situation before and after the fault to the field operator. If the fault occurs before the overload, frequent start and stop; whether there is abnormal sound and vibration, whether there is smoke or fire, etc. when the fault occurs.
(2) Look. Look closely at the changes in the appearance of various electrical components. For example, if the contact is burned or oxidized, whether the fuse indicator jumps out, whether the thermal relay is tripped, whether the wire and the coil are burnt, the setting value of the thermal relay is appropriate, and whether the automatic switching current setting current meets the requirements.
(3) Listen. Mainly listen to whether the electrical appliances have different sounds before and after the fault occurs. If it is heard when the motor starts, it will not turn; if the contactor coil is powered, it is very noisy.
(4) Touch. After the fault occurs, disconnect the power supply, touch or gently push and pull the wire and some parts of the appliance to detect abnormal changes. If you touch the surface of the motor, autotransformer and electromagnetic coil, feel the temperature is too high; lightly pull the wire to see if the connection is loose; push the electrical activity mechanism to see if the movement is flexible.
(5) Smell. After the fault occurs, place your nose near the motor, autotransformer, relay, contactor, insulated wire, etc., and smell if there is burnt smell. If there is a burnt smell, it indicates that the electrical insulation layer has been burnt out, mainly due to overload, short circuit or serious imbalance of three-phase current.
2. Measurement method. That is, the electrical instrument is used to measure the size of certain electrical parameters, and after comparison with the normal values, the fault location and the cause of the fault are determined.
(1) Measuring voltage method. Use a multimeter to exchange 500V files to measure the power supply, the main circuit line voltage, and the voltage across the contactors and relay coils and each control loop. If the measured voltage does not match the rated voltage (more than 10%), it is a suspicious fault.
(2) Measuring current method. Use a clamp ammeter or an AC ammeter to measure the operating current of the main circuit and related control loops. If the measured current value does not match the design current value (more than 10%), the phase circuit is suspicious.
(3) Measuring resistance method. That is, after disconnecting the power supply, measure the resistance value of the relevant part with a multimeter ohmmeter. If the measured resistance value differs greatly from the required resistance value, the part is most likely to be the fault point. Generally speaking, when the contact is turned on, the resistance value approaches “0â€, and when the contact is turned off, the resistance value is “∞â€; when the wire is firmly connected, the contact resistance at the connection also tends to “0â€, when the connection is loose. The resistance value is “∞â€; the DC resistance values ​​of various windings (or coils) are also small, often only a few ohms to several hundred ohms, and the resistance value after disconnection is “∞â€.
(4) Measuring the insulation resistance method. That is, the power is turned off, and the insulation resistance meter is used to measure the electrical component and the line to ground and the phase insulation resistance value. The insulation resistance of the electrical insulation layer shall not be less than 0.5MΩ. The insulation resistance value is too small, which is the main cause of leakage and short circuit between phase line and ground, phase line and phase line, and between phase line and neutral line. If this situation is found, it should be checked.
3. Reproduce the fault method. That is, turn on the power, press the start button, and let the fault phenomenon appear again to find out the fault. When reproducing the fault, it is mainly observed whether the relay and the contactor work in the control sequence. If it is found that the operation of one of the electrical appliances is incorrect, it indicates that the circuit or the related circuit of the electrical appliance is faulty, and then further inspection of the electrical circuit can be found. The cause of the failure and the point of failure.
4. Analysis method. That is, according to the control principle and control circuit of the control device, combined with the fault phenomenon and characteristics, the cause of the fault is analyzed and the fault range is determined. In the analysis, first start from the main circuit, then analyze each control loop in turn, and then analyze the signal circuit and the remaining auxiliary circuits.
5. Replacement method. Replace the suspected appliance with a good one to determine the cause of the fault and the location of the fault. When adopting this method, the electrical appliances used for replacement should be consistent with the specifications and models of the original electrical appliances, and the wire connections should be correct and firm to avoid new faults.
6. Menu method. That is, according to the fault phenomenon and characteristics, the various causes that may cause such a fault are listed in order, and then searched and verified one by one until the true cause of the fault and the fault location are diagnosed. This method is best for beginners.
The above methods can be used alone or in combination, and should be flexibly controlled and applied according to different fault characteristics.