Electromagnetic flow meters are sensitive to electrical noise which is present in most of the piping systems. The fluid carries significant electric charge of static electricity in plastic piping systems. This is the reason why the electromagnetic flow meters must be grounded. The grounding rings or the grounding electrode are used for this purpose.
The grounding of the flow meter has to be made of the same material as measuring electrodes because of the same chemical resistance. The high-priced material (tantalum, platinum) is used for grounding of flow meter installed in piping system with aggressive fluids (acid e.g.).
The grounding rings are usually used for small flow meters up to DN25 because there is no possibility to place the grounding electrode into the area of sensor. Both technical solutions can be used for bigger dimensions of flow meters up to DN1200 but grounding rings require more consumption of expensive material. For this reason, it is preferable to use the grounding electrode, which has the same size in all dimensions. The smart solution can save you money.