Fluent material level control system

Claim 2

Apparatus for controlling the level of a fluent material in a container, said apparatus comprising: means adapted for applying alternating electrical power to said apparatus; an electrical transformer having its input winding connected across said power applying means and having centertapped output windings; a bridge circuit including the output windingS of said transformer, said fluent material and said container, the electrical output of said bridge circuit being uniquely dependent upon the level of the fluent material in said container; a detector circuit adapted to produce first and second operating signals in response to the output of said bridge circuit, said operating signals being nonuniquely dependent upon the level of the fluent material in said container; power control means adapted to produce control signals in response to the output of said detector circuit; and means operative in response to said control signals for adjusting the level of the fluent material in said container; said power control means and said level adjusting means being connected to said power applying means.

Claim 3

The apparatus recited in claim 1, wherein: said detector circuit produces said first operating signal when the fluent material is below a first predetermined level and produces said second operating signal when the fluent material is above a second predetermined level higher than said first predetermined level; said detector circuit produces one of said first and second operating signals when said fluent material is between said first and second predetermined levels, the determination of the operating signal to be produced being dependent upon the immediate past history of the level of the fluent material.

Claim 4

The apparatus recited in claim 2, wherein: said bridge circuit further includes a high level electrode and a low level electrode in said container, said electrodes being electrically insulated from said container walls and being adapted to make contact with the fluent material within said container; said first predetermined level being below said low electrode so that neither electrode makes contact with said fluent material, said second predetermined level being at least as high as said high electrode so that both electrodes make contact with said fluent material.

Claim 5

The apparatus recited in claim 3, wherein: said bridge circuit is balanced and has substantially no output voltage when said low electrode is immersed in the fluent material and said high electrode is above the level of the fluent material; said bridge circuit is unbalanced and produces a first output voltage of such polarity as to cause said detector circuit to produce said first operating signal when the level of the fluent material is below both of said high and low level electrodes; said bridge circuit is unbalanced and produces a second output voltage opposite in polarity to said first output voltage so as to cause said detector circuit to produce said second operating signal when both of said electrodes are in contact with the fluent material.

Claim 6

The apparatus recited in claim 4, and further comprising: a relay, the coil of which is included in said detector circuit and the contacts of which are included in said power control means; said detector circuit and bridge circuit including said container being effectively electrically isolated from said power applying means, said power control means and said level adjusting means by said transformer and said relay.

Claim 7

The apparatus recited in claim 5, wherein: said detector circuit includes a silicon controlled rectifier having its gate connected to one output terminal of said bridge circuit; said relay coil being connected between said centertap on said transformer output windings and the cathode of said silicon controlled rectifier; said detector circuit further including a feedback circuit connected between said transformer centertap and said gate of said silicon controlled rectifier; whereby said first output voltage of said bridge circuit applied to said gate triggers said silicon controlled rectifier into a conducting state energizing said relay coil and producing said first operating signal, said feedback circuit maintaining said silicon controlled rectifier in a conducting state when said bridge circuit becomeS balanced after producing said output voltage; and whereby said second output voltage of said bridge circuit applied to said silicon controlled rectifier gate overrides the feedback circuit signal applied to said gate and causes said silicon controlled rectifier to cease conducting, thereby deenergizing said relay coil and producing said second operating signal.

Claim 8

The apparatus recited in claim 6, wherein: said power control means and said level adjusting means are connected in series across said input windings of said transformer.

Claim 9

The apparatus recited in claim 7, wherein: said relay contacts open in response to one of said detecting circuit operating signals and close in response to the other of said operating signals.

Claim 10

The apparatus recited in claim 8, wherein: said power control means comprises a bidirectional alternating current switch connected in parallel with a series combination of a triggering resistor and a capacitor, the gate of said switch being connected through said relay contacts to the junction of said triggering resistor and said capacitor; whereby said switch is triggered into a conducting state when said relay contacts are closed and power is thereby supplied to said level adjusting means to cause the fluent material level in said container to change; said switch being in a nonconducting state when said relay contacts are open, power thereby being prevented from operating said level adjusting means.

Claim 11

The apparatus recited in claim 6, wherein: the anode of said silicon controlled rectifier is connected to the output winding of said transformer, said silicon controlled rectifier being conductive during one-half of each cycle of the alternating current applied to said anode when a voltage sufficient to trigger said silicon controlled rectifier is applied to said gate; said detector circuit includes a first capacitor in parallel with said relay coil, said first capacitor being adapted to be charged during each conductive half-cycle and to maintain said relay coil continuously energized during each nonconductive half-cycle of said silicon controlled rectifier.

Claim 12

The apparatus recited in claim 10, wherein: said feedback circuit includes a second capacitor, the time constant of said feedback circuit being longer than the time constant of the relay coil circuit; whereby said relay coil is energized upon the production of said first output voltage by said bridge circuit and continues to be energized until said second output voltage is produced by said bridge circuit.