SYSTEM, APPARATUS, AND METHOD FOR MEASURING AN ION CONCENTRATION OF A MEASURED FLUID

摘要

An apparatus, system and method maximizes efficiency and accuracy of measuring an ion concentration of a measured fluid by varying a flow of ions within a measuring cell (1006) in accordance with an output signal of a sensor cell (1006) (206). The pump current through a pump cell is switched between a constant positive current and a constant negative current when upper and lower thresholds of the output signal are reached. The pulse width ratio of the square wave produced by the varying current is compared to a pulse width ratio function derived from a calibration procedure to determine the ion concentration of the measured fluid. In one embodiment, the functions of the pump cell and sensing cell are performed by a single electrochemical cell (1006). In an embodiment where a concentration of a compound is determined, a primary electrochemical cell system (1404) pumps an ion of an element of the compound into and out from a measuring chamber (1402). A secondary electrochemical cell system (1406) reduces the compound to ions of the same element as pumped by the primary electrochemical cell system (1404) to form a local concentration (1422) of the ion near an electrode (1622) of the secondary electrochemical cell system (1406). The secondary electrochemical cell system (1606) pumps the ions into and out from the measuring chamber (1402) in accordance with the relationship between the general ion concentration (1420) measured by the primary electrochemical cell system (1404) and the local ion concentration (1422) measured by secondary electrochemical cell system (1406). The duty cycle of a secondary pump current flowing through the secondary electrochemical cell system indicates the concentration of the compound.