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A capacitive system for sensing the level of material includes a conductive member electrically connected to ground potential, a probe including a sensing element arranged to establish a capacitance between the sensing element and conductive member which is determined by the level of the material an

A capacitive system for sensing the level of material includes a conductive member electrically connected to ground potential, a probe including a sensing element arranged to establish a capacitance between the sensing element and conductive member which is determined by the level of the material and a shielding element interposed between the conductive member and the sensing element to form an electrically neutral zone therebetween to thereby reduce the effect of a conductive buildup of the material on the probe on the capacitance between the conductive member and the sensing element, and a first circuit electrically connected to the sensing and shielding elements for applying generally the same electrical potential to both the sensing and shielding elements, the first circuit having an output which varies in response to a change in the capacitance between the conductive member and the sensing element. A device for measuring an electrical characteristic of the shielding element which is related to the conductivity of the buildup of material on the probe is electrically connected to a second circuit which, through a feedback loop connected to the first circuit, automatically adjusts the sensitivity of the first circuit in response to changes in the electrical characteristic to compensate for a highly conductive buildup of material on the probe.

대표청구항 ▼

In a control system for a capacitive level sensor of the type which includes a probe having a sensing element arranged therein to establish a capacitance between the sensing element and a grounded conductive member which changes in response to the presence of a material, a shielding element interpos

In a control system for a capacitive level sensor of the type which includes a probe having a sensing element arranged therein to establish a capacitance between the sensing element and a grounded conductive member which changes in response to the presence of a material, a shielding element interposed between the sensing element and the conductive member, and a first circuit for applying generally the same electrical potential to both the sensing element and the shielding element to establish an electrically neutral field between the sensing element and the conductive member and thereby reduce the effect of a conductive buildup of material on the probe within a limited range of conductivity, the improvement which comprises a means for sensing an electrical characteristic of the shielding element which is related to the conductivity of the buildup of material on the probe and a second circuit electrically connecting the sensing means to the first circuit for automatically adjusting the sensitivity of the first circuit in response to changes in the electrical characteristic to compensate for buildup of the material having a conductivity both within and outside the limited range of conductivity.