Level gauge system for urea solution used in selective catalytic reduction of exhaust pollutants, includes sensors for interdependent magnitudes, to establish filling level reliably

摘要

A reference sensor (20) determines a second value of a measured magnitude (C, L). It is arranged in the liquid (F) such that the second value is a function of other liquid parameter(s) (T, c, Fl). With the level (H) above a minimum (Hmin), this measurement is independent of the level. An Independent claim is included for the corresponding method of level measurement. Preferred Features: The parameter is a liquid: temperature (T) and/or composition (Fl) and/or concentration (c). The measured magnitude is electrical conductivity (L) and/or capacity (C). Main electrodes (12, 14) and a reference electrode (22) are included. The first electrode is common to the second- and reference electrodes. In a variant, the reference sensor element (20) is introduced through a base wall of the vessel. Reference sensor (20) and sensor element (10) are immediately adjacent, they may be included in a common measurement head or carrier body which includes a temperature sensor (60). The measurement head includes heating and cooling arrangements. Reference sensor element and sensor element are fastened at or form, an inlet or outlet unit for the fluid, e.g. they are formed by the corresponding pipes.