Method & apparatus for liquid level conductance probe control unit with increased sensitivity
First Claim
1. An electrically conductive liquid level detection apparatus for a container having a conductive member in contact with the conductive liquid in the container and having a probe assembly mounted in said container to contact the liquid at least reaching a predetermined level in the container, and said probe assembly having a liquid level sensing probe member insulated electrically from said conductive member positioned to be contacted by the liquid in the container reaching said predetermined level, the apparatus being able to differentiate between liquid between said probe and container and foam or scale deposits there between comprising in combination:
- a voltage divider including in said divider the resistance of the liquid between the container conductive member and the probe member;
a source of alternating current across said divider to produce a probe signal having positive voltage peaks;
said positive voltage peaks being coupled to one input of a comparator and to a peak detector for detecting said positive voltage peaks;
an A/D- D/A converter and digital latch circuit being coupled to said peak detector and having an analog voltage output representing a previously stored probe signal which is coupled to the other input of said comparator;
timing means being connected to the output of said comparator to control after a predetermined time a following coupled relay means which depending on the output of said comparator remains activated or is deactivated representing the presence or absence of the liquid between the conductive member and the probe member;
reference and recalibration means being connected between said timing means and a calibrate control means for automatically and periodically recalibrating; and
said calibrate control means being connected to said A/D-D/A converter and latch circuit to control calibration thereof and prevent the automatic and periodic recalibration when the liquid between the conductive member and the probe member are not present for a given time such that if the voltage at said one input of said comparator is higher than said other input, the output of said comparator is low and the output on said timer means is high resulting in the relay of said relay means remaining activated, and if the voltage at said one input is lower than said other input, said comparator output is high and the timing means charges for a period of time after which if the input comparator output goes low turning off the relay of said relay means.
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Abstract
An apparatus and method employing a liquid level detection conductance probe mounted in a container to sense resistive differences between the probe and container depending upon the presence or absence of liquid therebetween. A sensing circuit senses probe signal variations and stores a probe signal. A comparator compares the stored probe signal to current probe signals and switches means connected to the comparator depending upon the presence or absence of liquid between the probe and container. The sensing circuit has sufficient sensitivity to differentiate between liquid between the probe and container and foam or scale deposits therebetween.
50 Citations
3 Claims
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1. An electrically conductive liquid level detection apparatus for a container having a conductive member in contact with the conductive liquid in the container and having a probe assembly mounted in said container to contact the liquid at least reaching a predetermined level in the container, and said probe assembly having a liquid level sensing probe member insulated electrically from said conductive member positioned to be contacted by the liquid in the container reaching said predetermined level, the apparatus being able to differentiate between liquid between said probe and container and foam or scale deposits there between comprising in combination:
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a voltage divider including in said divider the resistance of the liquid between the container conductive member and the probe member; a source of alternating current across said divider to produce a probe signal having positive voltage peaks; said positive voltage peaks being coupled to one input of a comparator and to a peak detector for detecting said positive voltage peaks; an A/D- D/A converter and digital latch circuit being coupled to said peak detector and having an analog voltage output representing a previously stored probe signal which is coupled to the other input of said comparator; timing means being connected to the output of said comparator to control after a predetermined time a following coupled relay means which depending on the output of said comparator remains activated or is deactivated representing the presence or absence of the liquid between the conductive member and the probe member; reference and recalibration means being connected between said timing means and a calibrate control means for automatically and periodically recalibrating; and said calibrate control means being connected to said A/D-D/A converter and latch circuit to control calibration thereof and prevent the automatic and periodic recalibration when the liquid between the conductive member and the probe member are not present for a given time such that if the voltage at said one input of said comparator is higher than said other input, the output of said comparator is low and the output on said timer means is high resulting in the relay of said relay means remaining activated, and if the voltage at said one input is lower than said other input, said comparator output is high and the timing means charges for a period of time after which if the input comparator output goes low turning off the relay of said relay means. - View Dependent Claims (2, 3)
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Specification