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A conductive multilevel liquid sensor uses conventional integrated circuits such as inverters and voltage comparators as signal detectors, and a flat cable having corrosion-resistant probe conductors of different lengths as the sensing probe assembly. The binary encoded outputs of the signal detecto

A conductive multilevel liquid sensor uses conventional integrated circuits such as inverters and voltage comparators as signal detectors, and a flat cable having corrosion-resistant probe conductors of different lengths as the sensing probe assembly. The binary encoded outputs of the signal detectors identify the sensed liquid level. A continuous level control is realized by the addition of timing logic, and sensor operation range is improved by having the voltage at one comparator input be adaptive to the change in liquid conductivity.

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1. a multilevel liquid level sensing system comprising: a flat cable sensing probe assembly having a plurality of probe conductors whose lower ends are at different discrete levels in a container for liquids; resistance bridges each comprised of a pair of said probe conductors connected with thr

1. a multilevel liquid level sensing system comprising: a flat cable sensing probe assembly having a plurality of probe conductors whose lower ends are at different discrete levels in a container for liquids; resistance bridges each comprised of a pair of said probe conductors connected with three fixed value resistors, the third resistor so that the state of the bridge is known with both probe conductors out of the liquid; means for supplying a train of low duty cycle dc interrogation pulses in parallel to said resistance bridges and hence to said probe conductors; integrated circuit voltage comparator signal detectors each of which has a binary output and inverting and noninverting inputs connected across one of said resistance bridges such that the output is in one state when the lower ends of both probe conductors are in or out of the liquid, and is in the other state when the lower end of one probe conductor is in the liquid and the lower end of the other probe conductor is out of the liquid, said binary outputs in combination indicating the different discrete liquid levels; storage means for said binary outputs which are read out between said interrogation pulses to timing logic means to achieve a continuous liquid level control; said timing logic means comprising a timer which measures the time for the liquid to rise or fall between two adjacent discrete levels, and a flow rate calculator which monitors the flow rate of liquid between the two discrete levels. 2. The system of claim 1 wherein said means for supplying dc interrogation pulses includes a transistor which is turned on and off by a pulse source. 3. An adaptive multilevel liquid level sensing system comprising: a flat cable sensing probe assembly having a plurality of probe conductors whose lower ends are at different levels in a container for liquids; a resistor connected to the other end of each probe conductor; means for supplying a train of low duty cycle dc interrogation pulses in parallel through every resistor to said probe conductors; a fluid conductivity sensor for generating a voltage that varies with measured liquid conductivity; integrated circuit voltage comparator signal detectors each having two inputs of which one input is connected to one of said probe conductors, the other input of every voltage comparator being connected to said fluid conductivity sensor such that the threshold voltage at which each voltage comparator changes state is a function of the measured liquid conductivity; said voltage comparators each having a binary output indicating that the lower end of the respective probe conductor is in or out of the liquid and the binary outputs in combination indicating the sensed liquid level; and storage means for said binary outputs for readout to control circuitry at preselected intervals. 4. The system of claim 3 wherein said means for supplying dc interrogation pulses includes a transistor which is turned on and off by a pulse source.