US 5,088,325 AGranted

System for indicating a condition of material

AssigneeBindicator Company

InventorsRobert T. Eichberger, Scott M. Hewelt

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Abstract

A system for indicating level of material in a vessel as a function of material capacitance includes a capacitance probe adapted to be positioned so as to be responsive to variations in capacitance as a function of material level in the vessel. Detection circuitry is responsive to capacitance at the probe and to a reference signal for indicating material level, and includes facility for selectively adjusting sensitivity of the detection circuitry to material capacitance so as to adapt the system for materials of differing capacitance characteristics. Calibration circuitry for establishing the reference signal includes facility for varying operating characteristics of the detection circuitry during a calibration mode of operation independent of material level so as to calibrate the detection circuitry to capacitance at the probe. The detection circuitry is responsive to a comparison between the reference signal and capacitance at the probe for indicating when the circuitry is out of calibration, and is coupled to the sensitivity adjustment for varying such comparison as a function of the differing material capacitance characteristics.

Claims5

Dependent claims

A system for indicating a condition of material comprising:

probe means adapted to be positioned with respect to the material such that an electrical property of said probe means varies as a function of material condition,
circuit means coupled to said probe means and responsive to said electrical property of said probe means for indicating said material characteristic, said circuit means including:
means coupled to said probe means for providing a first electrical signal that varies as a function of said electrical property at said probe means,
means for calibrating said circuit means such that said first electrical signal is at a first predetermined level independent of material at said probe means,
means responsive to variation of said first signal from said first predetermined level to a second predetermined level for indicating said material characteristic, including sensitivity adjustment means for selectively varying said second predetermined level so as to vary sensitivity of said circuit means, and
means responsive to said first signal and coupled to said sensitivity adjustment means for indicating loss of calibration at said circuit means when said first signal reaches a third level, including means for varying said third level as a function of sensitivity of said circuit means such that departure of said first signal from said first level to indicate loss of calibration at said circuit means increases with decreasing sensitivity at said circuit means.

3 more elements

Dependencies are inferred from the claim text.