AC SOLENOID CONTROL CIRCUIT

• US 3,796,925 A
• Filed: 08/17/1972
• Issued: 03/12/1974
• Est. Priority Date: 08/17/1972
• Status: Expired due to Term

• Current Assignee: William C. Breeding
• Original Assignee: William C. Breeding
• Inventors: Breeding, William C.
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Moose, Jr., Harry E.
• Application Number:
  US05/281,474
• Time in Patent Office: 572 Days
• Field of Search: 307/116,118,252T 222/56,57 137/88,93,268,392 324/65R,65P 134/57D,58D,93 200/61.05 317/DIG.3,148.5B,157
• US Class Current: 361/178
• CPC Class Codes: A47L 15/0055 Metering or indication of used products, e.g. type or quantity of detergent, rinse aid or salt; for measuring or controlling the product concentration
• CPC Class Codes: A47L 15/449 Metering controlling devices A47L15/4229 takes precedence
• CPC Class Codes: A47L 2501/26 Indication or alarm to the controlling device or to the user
• CPC Class Codes: G05D 21/02 characterised by the use of electric means
• CPC Class Codes: H03K 17/723 using transformer coupling
• CPC Class Codes: Y10T 137/2509 By optical or chemical property

Abstract

A solid state low power circuit for controlling an AC solenoid, comprising a power section and a control section. The control section provides a means which responds to the conductivity of a fluid, preferably a low impedance probe, and a means for switching AC power to a solenoid when the conductivity falls below a predetermined level. Typically, the present invention is used to control the concentration of a particular material in a fluid such as, for example, the concentration of a detergent in the water bath of a commercial dishwashing apparatus. The invented circuit monitors the concentration of the material in the fluid and activates an AC solenoid when additional material is required. The solenoid, when activated, causes the controlled material to be dispensed into the fluid. The power section is adapted to receive AC power from a conventional source; it provides low AC power to the control section. A preferred embodiment of the power section has an automatic turn-on capability provided by the use of the low impedance probe which detects the presence of the fluid (typically water) in the vicinity of its supply source. The present invention is adapted to operate with an electronic alarm and an electronic monitor section. The alarm section provides an audio and visual indication when the conductivity of the fluid, i.e., the concentration of the controlled material, reaches a predetermined alarm level. The monitor section provides a meter which, when properly calibrated, indicates the conductivity of the fluid and, therefore, the concentration of the controlled material therein. The present invention is characterized by a high degree of sensitivity to changes in the concentration of the controlled material, very sharp turn-on and turn-off of the solenoid without bounce, great accuracy or resolution of control, and relative insensitivity to temperature changes of the fluid.

Claims

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.

2. In a control system for regulating the supply of a material in a fluid, wherein an AC solenoid is utilized to control the dispensing of said material into said fluid an AC solenoid control circuit comprising:

a. a power section adapted to provide AC power to said solenoid and to said control circuit;

b. means responsive to the concentration of said material in said fluid, said responsive means providing at its output an analog signal whose amplitude is a function of the concentration of said material in said fluid;

c. means for generating a trigger signal when the amplitude of said analog signal exceeds a predetermined trigger level, said means for generating a trigger signal being electrically coupled to said output of said responsive means;

d. first and second silicon controlled rectifiers (SCR'"'"''"'"'S) electrically coupled to conduct in opposite directions between said solenoid and said AC power, each of said SCR'"'"''"'"'S having a control leg;

e. diode means electrically coupled in series with said first SCR;

f. a first capacitive element electrically coupled to said means for generating a trigger signal and to said control leg of said first SCR, said first capacitive element being adapted to charge when said trigger voltage appears; and

g. a second capacitive element electrically coupled across said diode means and to said control leg of said second SCR, said second capacitive element being adapted to charge when said first SCR conducts, whereby, following the appearance of said trigger signal, the sequential firing of said first and second SCR'"'"''"'"'S causes said solenoid to be energized by said power source until said concentration of said material in said fluid reaches a desired level, said desired level causing said amplitude of said analog signal to fall below said predetermined trigger level.

3. The circuit of claim 2 wherein following the appearance of said trigger signal, the voltage stored in said first capacitive element causes said first SCR to fire when the latter is forward biased during a first half-wave of said AC power source, and the voltage stored on said second capacitive element causes said second SCR to fire when the latter is forward biased during a second half-wave of said AC power.

4. The circuit of claim 10 wherein said material is a detergent and said fluid is a water solution of said detergent in a washing tank of a dishwashing apparatus, and said responsive means comprises:

i. a low impedance probe sealedly secured through a hole in a wall of said tank at a position below the water line, said probe having an insulated inner conductor with first and second ends, said first end thereof being disposed within said water solution and said second end thereof being disposed exterior to said tank; and

ii. voltage dividing means electrically coupled to said second end of said probe, the output of said voltage dividing means being said analog signal, the amplitude of said analog signal being inversely related to the conductivity of said water solution and to the concentration of said detergent therein, said responsive means being relatively insensitive to temperature variations of said water solution.

5. The circuit of claim 2 having in addition thereto means for issuing an alarm signal whenever the concentration of said material in said fluid falls below a predetermined alarm level, said alarm means being electrically coupled to said analog signal and being adapted to respond when the amplitude of said analog signal reaches a level corresponding to said predetermined alarm level.

6. In a control system for regulating the supply of a material in a fluid, wherein an AC solenoid is utilized to control the dispensing of said material into said fluid, an AC solenoid control circuit comprising:

a. 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;

b. a 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 probe being sealedly secured through a hole in the wall of a tank into which said fluid is injected at a position in which said fluid will at least intermittently bathe said first end of said probe when said fluid is injected, said second end of said probe being disposed exterior to said tank;

c. first switching means electrically coupled to said second end of said probe and providing a second AC power signal by switching half cycles of said first AC power signal when said fluid 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;

d. means responsive to the concentration of said material in said fluid providing at its output an analog signal whose amplitude is a function of the concentration of said material in said fluid, said responsive means being energized by said first AC power signal;

e. means for generating a trigger signal when the amplitude of said analog signal exceeds a predetermined trigger level, said means for generating a trigger signal being electrically coupled to said output of said responsive means and being energized by said second AC power signal;

f. second switching means electrically coupled in series between said solenoid and said AC power, said switching means being adapted to receive said trigger signal and to respond thereto by switching said AC power across said solenoid for one full cycle of said AC power next following the appearance of said trigger signal, said second switching means being energized by said second AC power signal, whereby said second switching means causes said solenoid to be energized by said AC power source until said concentration of said material in said fluid reaches a desired level, said desired level causing said amplitude of said analog signal to fall below said predetermined trigger level.