Problems with the noise meter and grounding
Earth and electricity (signal) are inseparable twins. Grounding usually refers to connecting to the earth with a conductor. But the ground in electronic technology may have nothing to do with the earth. It is just the first equipotential surface in the circuit. For example, the ground in radios and televisions is just a potential reference point in the receiver circuit. Grounding is both simple and complex in power and electronics technology, and it is also essential. According to the role of grounding, it can be divided into working grounding, protective grounding, overvoltage protection grounding, anti-static grounding, shielding grounding, signal grounding, etc. In radio and television technology, the above grounding types will be encountered. Now we will elaborate on some grounding technical issues based on the actual situation.
one. Protective grounding Protective grounding is a protective device set up to prevent insulation damage from causing live equipment to endanger personal life. It has two methods: grounding and zero connection. According to power regulations, for systems that use three-phase four-wire power supply, since the neutral line is grounded, the zero connection method should be used, and the metal shell of the equipment should be connected to the neutral line through a conductor, and the equipment shell is not allowed to be directly grounded. This is especially common in switching equipment in the power distribution room of the radio and television system, power switching equipment such as central air conditioners and transmitters, and large power-consuming equipment. When planning and designing, the grounding bus should be led from the ground grid to each device, and then the machine shell should be connected to the grounding bus with a conductor. It is worth pointing out that the grounding wire should be connected to the dedicated grounding terminal of the equipment, and the other end is preferably welded. Sometimes the equipment shell will feel numb. This is caused by AC leakage and the equipment shell is not connected to zero. Generally, the problem can be solved by unplugging the power plug, changing its position and then plugging it in again. In some frequently moved recording equipment, since the zero line is often ignored, some operators may touch both zero-connected and non-zero-connected equipment at the same time, and the above phenomenon may occur.
two. Overvoltage protection grounding This is a grounding protection device set up to protect against lightning. The most widely used lightning protection devices are lightning rods and arresters. The lightning rod is connected to the ground through the iron tower or building steel bar, and the lightning arrester is connected to the ground through a dedicated ground wire. Lightning arresters must be inspected every year before the thunderstorm season to prevent failure. For example, if the telephone access point of our station was struck by lightning, it was due to the failure of the phone line lightning protector. On the lightning protection down conductor, never connect the ground wire of other equipment. The lightning protection down conductor can only be directly connected to the ground alone, otherwise lightning will damage other equipment through the down conductor. For example, a satellite TV receiver has been struck by lightning several times. The original problem was that the feeder wire rubbed against the metal guardrail on the roof, causing insulation damage. The metal guardrail and the lower body of the lightning rod were welded together, causing lightning to penetrate and damage the receiver.
