仪器接地问题的若干考虑.pdfVIP

Agilent Technologies Considerations for Instrument Grounding Application Note Kuo Yen-Lung Agilent Technologies Taiwan Many people have heard of the term “grounding”, but few fully understand its meaning and importance. Sometimes, even experienced electricians do not treat grounding as a serious issue. The impact of an incorrect or absent grounding ranges from noise interference, resonance or humming during the use of electrical equipment to the worst case where electricity leakage through the chassis causes personal injury or damage to instrument components. Grounding, therefore, is a very practical issue that should be dealt with properly. For those who operate electrical equipment frequently, a complete understanding of grounding theories and applications is necessary in order to become a best-in-class technician. In the eighteenth century, Benjamin Franklin performed the famous kite experiment to observe how lightning in the sky was conducted to the earth. This experiment led to the invention of lightning rods to avoid lightning strikes. From then on, people began to realize that the vast ground under our feet is a huge electrical conductor. It may not be the best conductor, but it is certainly a good one. It is so enormous in size that it can sustain a tremendous amount of current. That is why the voltage level of the ground is set to be zero. Safety regulations require that all metal parts which do not carry electricity should be kept at zero or the earth voltage level. There are several reasons for grounding. Some are for safety purposes, and some are for maintaining circuit stability. The following are some examples: 1. Power system grounding: As you can see in Figure 1, this design is to prevent the secondary side from being damaged by the high voltage on the primary side, as the current will be conducted to the ground through the Grounding Wire to protect human lives.