The grounding of equipment fitted up in laboratory is special, which is different from that of common equipment. Some of the equipment will interfere with the signal acquisition circuit due to harmonic and high frequency factors, thus forming a false value. The usual way is to eliminate harmonics, shield and grounding. Because of the impurity of the power load inside the municipal power supply, it is difficult to prevent interference by using the integrated grounding system. So long, an independent grounding system is needed. The grounding resistance value also depends on the detailed conditions. For example, the request for grounding resistance of common laboratory equipment is_4, but the more stringent EMC laboratory general request is not greater than 1. The maximum requirement for grounding for high multiple electron microscopes is 0.1_.
Practice of General Grounding Electrode
Grounding system can never avoid a job, that is, grounding pole. The common method of hybrid grounding system is to use the reinforced bar of the ground beam of the building as the main grounding electrode. The grounding routine of field equipment is to drill grounding piles around the equipment and use one or more grounding piles in parallel to form a small grounding system for lightning protection grounding. The grounding system of signal shielding is special. Because the annular grounding is good for signal acceptance, this kind of grounding is composed of a C-shaped grounding grid, which uses multiple grounding poles in parallel and retains teeth.
Varieties of Grounding Piles
There are many kinds of grounding piles, including hot-dip galvanized angle steel, copper, copper clad steel and carbon rod. In this way, angle steel can be used to penetrate into open grounding poles, cage-shaped ones, buried open grounding poles, star-shaped structures and open grounding poles. These methods are relatively common, and their characteristics are mainly the application of increasing contact surface to reduce grounding resistance.
In this paper, several special grounding poles are mentioned. One of the grounding methods in Japan is to dig a pit, then mix a certain amount of carbon powder into the excavated soil, add some cement into the pit with bare copper wire, and then fill the average soil back into the pit and compact the water to form the grounding pole. Another is to sink a deep well into a bare copper wire far greater than the depth of the well, so that it bends and enlarges the contact surface with the soil. If the geological conditions are not good, the earth will be replaced to ensure the resistance value of the grounding resistance.
Why Grounding Can't Be Budgeted
Because of the different geological conditions, the conductivity varies greatly, and the standard only gives the reference values of different geological conditions. So no one can tell how much the grounding resistance can reach before grounding is done well.
Different disposal methods under special geological conditions
In many cases, when the establishment is completed, the grounding resistance is often not up to the required value when measuring the grounding resistance. Don't be surprised, as I said before, the conductivity is different under different geological conditions. Then, it is normal to exceed or fail to reach the design value. At this time, the corresponding measures are needed to compensate for it, so that the final result can reach the design target.
The common practice is to add the grounding pole outside the original grounding system and add additional grounding piles into the original grounding system; if the geological conditions are not good, soil change and resistance reducing agents are also needed; if the geological conditions are very poor, the rock strata need to be from a far central place, and do additional grounding poles to bring them into the grounding system; if the environmental conditions are limited, for example, space is not enough. If the surrounding environment is limited, it is advocated to drill deep wells and replace soil for disposal.