Ac solenoid control circuit

Claim 1

In a control system for regulating the supply of a detergent in a washing bath of a dishwashing apparatus having a tank for containing said bath and a plurality of water jets, wherein an AC solenoid is utilized to control the dispensing of said detergent into said tank, an AC solenoid control circuit comprising: a. a voltage reducing transformer means having a primary side and a secondary side, said primary side being electrically coupled to a conventional source of AC power, and said secondary side providing a first AC power signal, said first AC power signal being substantially in phase with said conventional source; b. a first low impedance probe having an insulated inner conductor approximately one-sixteenth inch in diameter and approximately three-fourths inch in length with first and second ends, said first probe being sealedly secured through a hole in a wall of said tank at a position in which water fRom said water jets will at least intermittently bathe said first end of said first probe when said dishwashing apparatus is activated, said second end of said first probe being disposed exterior to said tank, said tank being connected to circuit ground; c. switching means energized by said first AC power signal and electrically coupled to said second end of said first probe, said switching means being adapted to provide a second AC power signal when water from said water jets intermittently bathes said first end of said probe, said second AC power signal being a half-wave rectified derivative of said first AC power signal and substantially in phase therewith; d. a second low impedance probe having an insulated inner conductor approximately one-sixteenth inch in diameter and approximately three-fourths inch in length with first and second ends, said second probe being sealedly secured through a hole in a wall of said tank at a position below the water line, said first end thereof being disposed within said washing bath and said second end thereof being disposed exterior to said tank; e. voltage dividing means having an input electrically coupled to said second end of said second probe, said voltage dividing means providing at its output an analog signal whose amplitude is a function of the concentration of said detergent in said bath, said voltage dividing means being energized by said first AC power signal; f. means for generating a trigger signal when the amplitude of said analog signal exceeds a predetermined trigger level, said trigger generating means being electrically coupled to said output of said voltage dividing means, said trigger generating means being energized by said second AC power signal; g. first and second silicon controlled rectifiers (SCR''S) electrically coupled to conduct in opposite directions between said solenoid and said conventional power source, each of said SCR''S having a control leg; h. a diode electrically coupled in series with said first SCR; i. a first capacitor electrically coupled to said trigger generating means and to said control leg of said first SCR, said first capacitor being adapted to charge when said trigger voltage appears; and j. a second capacitor electrically coupled in parallel across said diode and to said control leg of said second SCR, said second capacitor being adapted to charge when said first SCR conducts, whereby, when said dishwashing apparatus is activated, said trigger generating means is energized by said second AC power signal, and following the appearance of said trigger signal, the voltage stored on said first capacitor causes said first SCR to fire when the latter is forward biased during a first half-wave of said conventional power source, and the voltage stored on said second capacitor causes said second SCR to fire when the latter is forward biased during a second half-wave of said conventional power source, said sequential firing of said SCR''S causing said conventional power source to be switched across said solenoid until the concentration of said detergent in said bath reaches a desired level, said desired level causing said amplitude of said analog signal to fall below said predetermined trigger level.