Apparatus for adding material to liquids

Claim 1

Apparatus for adding filter material and the like to a liquid flowing in a system, comprising: a. first means positioned at a first location in said system for sensing the turbidity of said liquid at said first location and producing a first electrical signal having a voltage magnitude that varies as a function of the turbidity sensed; b. second means positioned at a second location in said system downstream from said first location for sensing the turbidity of said liquid at said second location and producing a second electrical signal having a voltage magnitude that varies as a function of the turbidity sensed; c. a source of filter material having an outlet coupled into said system between said first location and said second location, and having a liquid inlet coupled to said system upstream from said filter material outlet, said source including solenoid means for controlling the amount of filter material supplied to said outlet and to said system; d. utilization means for said liquid coupled to said system downstream from said second location; e. an electrical comparison circuit having first and second input circuits and an output circuit for comparing said first and second signals applied to said first and second input circuits and producing an electrical output signal at said output circuit that varies in voltage and polarity as a function of the relative characteristics of said first and second signals applied to said first and second input circuits; f. means respectively coupling said first and second input circuits to said first and second sensing means including ratio means in circuit with said second input circuit and said second sensing means to supply a selectable fraction of said second electrical signal to said second input circuit; g. and means coupling said output circuit to said control means of said source.