Liquid level sensing system and apparatus

Claim 3

The combination according to claim 1 wherein said first, second, third and fourth electrodes all are made of the same material.

Claim 4

The combination according to claim 2 wherein said first, second, third and fourth electrodes are made of stainless steel.

Claim 5

The combination according to claim 1 wherein said first and second means for connection with the primary source of electrical potential comprise first transformer means having at least one primary winding and first and second secondary windings corresponding to said first and second connection means, respectively, with the primary source of electrical potential being an alternating current potential supplied to said primary Winding, said first secondary winding being connected between said first and second junctions and said second secondary winding being coupled in circuit with said indicating means; and said bridge circuit output means comprises a second transformer having a primary winding coupled between said third junction and said point on said resistance means and having a secondary winding coupled with said indicating means.

Claim 6

The combination according to claim 4 wherein the coupling of said second secondary winding of said first tranformer means with said indicating means is in series circuit through said secondary winding of said second transformer.

Claim 7

The combination according to claim 5 wherein said first transformer means comprises step-down transformer means and said second transformer comprises a step-up transformer.

Claim 8

The combination according to claim 6 wherein the second secondary winding of said first transformer means and the secondary winding of said second transformer are connected together in series circuit with said indicating means, the imbalance of said bridge circuit for the same liquid level at the first and second spaced points causing a signal to be produced in the secondary winding of said second transformer which is in phase opposition to the signal from the second secondary winding of said first transformer means to cause a first output to be obtained from said indicating means, balancing of said bridge removing such phase opposition signal with the signal from the second secondary winding of said first transformer means in the absence of such phase opposition signal being of sufficient magnitude to cause a second output to be obtained from said indicating means.

Claim 9

A liquid level sensing system for sensing differences in the level of a liquid on opposite sides of a screen disposed in a stream channel including in combination: an alternating current power supply circuit; a relay with a winding and having a normal condition of operation and an alarm condition of operation; an electronic control device having an output circuit connected in series with said relay winding to said power supply circuit and having a control electrode; first and second spaced conductive electrodes comprising a first pair of electrodes extending downwardly on one side of the screen for partial immersion into liquid located on said one side of the screen; third and fourth spaced conductive electrodes comprising a second pair of electrodes extending downwardly at the other side of the screen for partial immersion into liquid located at said other side of the screen, the ends of said third and fourth electrodes extending downwardly beyond the ends of said first and second electrodes a predetermined distance; resistance means connected between said first and third electrodes at first and second junctions, respectively; means for interconnecting said second and fourth electrodes at a third junction to complete a bridge circuit comprising said resistance means and said first and second pairs of electrodes; supply transformer means having at least one primary winding and first and second secondary windings, the primary winding of which is coupled with said alternating current power supply circuit, the first secondary winding of which is connected across said first and second junctions; a bridge output tranformer having a primary winding and a secondary winding, with the primary winding connected between said third junction and an intermediate point on said resistance means; means for connecting the secondary winding of said bridge transformer in series circuit with the second secondary winding of said supply transformer means and the control electrode of said electronic control device, said electronic control device causing the relay to be in its normal condition of operation with the secondary winding of said bridge transformer supplying AC signals in phase opposition to the signals applied to the electronic control device from The second secondary winding as a result of a bridge circuit imbalance caused by the differences in deth of immersion of said first and second pairs of electrodes for liquid of the same level on opposite sides of the screen, the signals from the second secondary winding being sufficient to cause said electronic control device to operate said relay to said alarm condition of operation in the absence of phase opposition signals from the secondary winding of said bridge transformer; and means coupled with said relay circuit for responding to said alarm condition of operation thereof.

Claim 10

A liquid level sensing system for sensing differences in the level of a liquid on opposite sides of a screen disposed in a stream channel including in combination: an alternating current power supply circuit; a relay with a winding and having a normal condition of operation and an alarm condition of operation; an electronic control device having an output circuit connected in series with said relay winding to said power supply circuit and having a control electrode; first and second spaced conductive electrodes comprising a first pair of electrodes extending downwardly on one side of the screen for partial immersion into liquid located on said one side of the screen; third and fourth spaced conductive electrodes comprising a second pair of electrodes extending downwardly at the other side of the screen for partial immersion into liquid located at said other side of the screen, the ends of said third and fourth electrodes extending downwardly beyond the ends of said first and second electrodes a predetermined distance; resistance means connected between said first and third electrodes at first and second junctions, respectively; means for interconnecting said second and fourth electrodes at a third junction to complete a bridge circuit comprising said resistance means and said first and second pairs of electrodes; supply transformer means having at least one primary winding and first and second secondary windings, the primary winding of which is coupled with said alternating current power supply circuit, the first secondary winding of which is connected across said first and second junctions; a bridge output tranformer having a primary winding and a secondary winding, with the primary winding connected between said third junction and an intermediate point on said resistance means; means for connecting the secondary winding of said bridge transformer in series circuit with the second secondary winding of said supply transformer means and the control electrode of said electronic control device, said electronic control device causing the relay to be in its normal condition of operation with the secondary winding of said bridge transformer supplying AC signals in phase opposition to the signals applied to the electronic control device from The second secondary winding as a result of a bridge circuit imbalance caused by the differences in deth of immersion of said first and second pairs of electrodes for liquid of the same level on opposite sides of the screen, the signals from the second secondary winding being sufficient to cause said electronic control device to operate said relay to said alarm condition of operation in the absence of phase opposition signals from the secondary winding of said bridge transformer; and means coupled with said relay circuit for responding to said alarm condition of operation thereof.

Claim 11

The combination according to claim 8 wherein said first transformer means comprises first and second transformers having first and second primary windings coupled with said alternating current power supply circuit, said first and second transformers being step-down transformers having the first and second secondary windings, respectively, and said bridge output transformer comprising a step-up transformer.

Claim 12

The combination according to claim 8 wherein said electronic control device comrises a triode tube, with an anode, cathode and grid, having the anode and cathode connected in series circuit with said relay winding to said power supply circuit, with the second secondary winding and the secondary winding of said bridge output transformer being connected in series circuit across the grid and cathode of said triode, the signals induced in said second secondary winding being sufficient to cause said triode to be rendered nonconductive in the absence of signals of opposite phase from the secondary winding of said bridge output transformer.