Techniques for ion beam current measurement using a scanning beam current transformer are disclosed. A communication session is initiated between a client and a server. In another example, the at least one RC detection result may be obtained by performing RC detection on at least a portion of the transmitter without individually measuring resistance values of resistors therein and capacitance values of capacitors therein. The clear well chamber is in fluid communication with the second filter chamber section for receiving filtered liquid. If a query is a collection query, indexers may generate summarization information based on event records located on the indexers. In the present invention, a cation exchange membrane excellent in selective permeability to monovalent cations is produced by bringing high molecular cations into contact with a surface of a cation exchange membrane in the presence of anions of an oxyacid or anions of an organic sulfonic acid.