US3214643A - Relay control circuit having time delay means - Google Patents

Description

G. L. BORELL 3,214,643

RELAY CONTROL CIRCUIT HAVING TIME DELAY MEANS Oct/26, 1965 2 Sheets-Sheet 1 Filed Feb. 14, 1962 INVENTOR. GEORGE .4. 50/9514 11 TTORNE Y5 ca. L. BORELL 3,214,643

RELAY CONTROL CIRCUIT HAVING TIME DELAY MEANS Cat. 26, 1965 2 Sheets-Sheet 2 Filed Feb. 14. 1962 F R M W WM 70 N m 0 U m B mm A K M W I P vm. WW 9N w N G N fi W \N N\ QM Q sm 1! TTORNE Y5 United States Patent i 3,214,643 RELAY CONTROL CIRCUIT HAVING TIME DELAY MEANS George L. Borell, Glen Rock, NJ. Almo Laboratories Co., Inc., 424 Madison Ave., New York, N .Y.) Filed Feb. 14, 1962, Ser. No. 173,201 3 Claims. (Cl. 317141) This invention relates to systems for controlling the delivery of a liquid material to a remote location where the amount of material so delivered is critical.

In general, the invention contemplates a system for replenishing in controlled amounts a liquid constituent of a bath in which the liquid is being progressively consumed and in particular one which automatically maintains a desired concentration of the liquid in the bath unless such maintenance is for some reason impossible of fulfillment in which case there is afforded a sensible indication.

The particular embodiment of the invention which is hereafter disclosed relates to dishwashing machines and employs the electrolytic properties of the detergent in the wash tank of the machine to detect and compensate for an insufiicient supply in the tank that is available for use in the washing operation. Because the new supply of detergent is not instantaneously so available on introduction to the tank even though the quantity may be suificient in amount to ultimately raise the concentration to the desired level, a time interval must be afforded to measure its uniform concentration. To this end the delivery is made in small increments or shots and after each shot the control system is reset for its succeeding one if necessary. This cycling operation of the system introduces a delay in the oif-to-on interval which afiords some time for a blending of the detergent in the wash water and hence a more accurate measurement of its true concentration. The principal advantage of cycling the delivery of the detergent to the wash tank is the prevention of excessive overshooting which would be present if the delivery were continuous.

A circuit supplied by an A.C. source has a pair of elec trodes in the wash tank which are made responsive to the conductivity of the wash solution as determined by the concentration of the detergent therein serving thereby to start the supplying of new detergent. A separate conductivity device in the detergent supply for stopping the delivery of detergent is dispensed with and in lieu thereof heat responsive elements are placed in the circuit for adjusting the impedance of the sensing circuit and thereby timing the feeding of detergent material to the tank. One of the thermal timing elements is a bimetallic switch which closes on cooling in the oif-to-on interval thus affording a time delay for blending the detergent in the wash water as aforementioned. The switch is connected in series with and between the conductivity device and a bridge-type rectifier in the circuit and, therefore, passes an A.C. current which is desirable for the elimination of arcing. Shunting the switch is a hot wire resistor which is the second thermal timing element in the circuit. This element is placed in the circuit in effect when the switch is broken and increases in impedance as its temperature rises during the on cycle. It is thus seen how the two thermal timing elements act cooperatively and sequentially to determine the length of the feed cycle.

A smoothing capacitor is a third timing element in the control circuit being employed to introduce a delay between feed cycles. This element is disposed in the rectifier output and across the relay coil which is in control of both the heater for the bimetallic switch and the detergent feed apparatus. Its primary function is to smooth the current in the relay to prevent it from chattering.

3,214,643 Patented Oct. 26, 1965 In addition, its capacitance is sutficiently large that it introduces a time delay during its recharging phase which starts at the termination of the feed cycles at which point the impedance in the control circuit is maximum and the voltage across the capacitor is minimum. The additional delay introduced by the capacitor during the offto-on cycle permits the blades of the bimetallic switch to return to near normal pressure and the resistor to return to near ambient temperature state before the cycle can be repeated and thereby affords the detergent feed apparatus sufiicient time to respond reliably to the relay control and stabilizes the mechanical operation of the switch. These elements are the sole components for the control of a single relay which in turn causes the cycling operation of the detergent feed apparatus. Since the elements are electrical and not electronic or thermionic in nature, they can be expected to have long life and be disposed in a circuit of relatively simple and economic arrangement.

The use of a single conductivity device permits the delivery to be made directly from the original shipping container for the detergent which is particularly advantageous if the detergent is in liquid form since a powder detergent would have to be dissolved and dispensed from a separate container or transferred to the hopper of a dry-feeding mechanism. The action of these elements in response to heat yields a predetermined amount of detergent material during the initial cycle of operation. This amount is diminished once the thermal elements are heated and the delay inherent to their operation is thereby shortened. The shortened feeding cycles are constant for the entire remaining period of operation. Between cycling periods the thermal elements return to ambient temperature so that the initial feed cycle in the succeeding period will be normal and the remaining feed cycles uniformly shortened.

In addition the system employs visual and audible signals for the purpose of affording conspicuous indication of specific untoward operating conditions in the system. The circuit elements are so constituted and arranged, for ex ample, that the signals will rapidly cycle on and off after the first cycle if excessive dilution is occurring in the wash tank but will, on the other hand, lock in for continuous indication if the supply of detergent has been exhausted. Largely because of the stabilizing effect of the smoothing capacitor on the bimetallic switch, the audible indicator may be mounted directly on the chassis of the control system since any vibration in the chassis resulting from the indicators operation will not unduly impair the operating efficiency of the switch. Because the cycling is actuated solely by electrical timing elements rather than by change in liquid level, as in prior systems, the cycling is more readily distinguishable and, hence, more attention demanding.

One object of the invention is to provide a control system, which is both durable and economic to produce and operate, and which functions efiiciently to effect the delivery in discrete increments of a liquid material to a bath.

Other features and advantages of the invention will appear from the following description of the embodiment illustrated in the drawings, in which FIG. 1 is a sectional elevation of the Wash section of the wash tank and the detergent dispensing container from which liquid detergent is pumped into the wash tank, together with the control box in which the electrical control system for maintaining the desired detergent concentration is arranged, and

FIG. 2 is a diagram of the electrical control system.

A tray of dishes 1 is shown in the wash section of a dishwashing machine, on a conveyor which carries the tray to the rinse section on the right (not shown). Water containing detergent is pumped from the wash tank 2 and delivered forcibly upon the dishes through the spray means 3. An overflow pipe 4 determines the level of the water in tank 2. A drain board 5 leads the water which is delivered to the rinse section by pipe 6 from the rinse section into tank 2, or, as often is the case, into another tank which overflows into the wash tank. In large machines there are more than one tank receiving the rinse water and progressively overflowing one into another and eventually into the wash tank.

This constant addition of clean water to the wash tank dilutes the detergent concentration and periodically more detergent has to be added to the wash water. This is done automatically from a liquid detergent container disposed on the floor below the wash tank, the liquid detergent being forced by pump 8 through a hose 10 connecting the container 7 to the wash tank 2. The pump is controlled by a motor 11 which is actuated by the electrical control system.

To detect or sense the conditions in the wash tank 2, a pair of closely spaced electrodes 12 which are adapted to contact the contents in the wash tank and will be conductively bridged by the liquid which will afford a resistance which will vary inversely with the alkaline or detergent content of the liquid. The electrodes 12 in the tank 2 are suitably insulated and supported in a Well of the 'tank proximate the outlet opening in the tank for the liquid detergent.

Whenever the conductivity of the wash water in the tank reaches a certain minimum degree, it causes the pump to be actuated, as we shall see, to admit liquid detergent from the wash tank to the container 7. As conductivity in the tank increases due to the admission of detergent, the resistance across the electrodes 12 is reduced until delivery to the tank is shut off. As mentioned the delivery is made in predetermined increments and will continue in a cycling operation involving the making and breaking of a switch in series with the motor 11 until the selected conditions in the tank are satisfied. This cycling may continue indefinitely if water is being delivered from the rinse sec- .tion at such a rate that the desired detergent concentration cannot be effected and the cycling will cease altogether and the motor operated continuously if the detergent becomes entirely exhausted in the container 7, appropriate signals being provided so that the operator can readily determine the operation of the motor driven pump and distinguish thereby the specific reasons why the desired detergent concentration in the tank is incapable of attainment.

The electrical circuit by which the pump is controlled and maintenance of the desired detergent concentration in the wash tank is efiected is diagrammatically shown in FIG. 2.

It is a low voltage system fed by a low voltage transformer 13 which is a voltage step down instrument having a 22-volt secondary and a 115-volt primary. The transformer can, of course, be designed with a 230-volt primary if required. Wires 14 and 15 constitute the two .sides of the supply line and electrodes 12 are connected across the line in series with a variable 100-ohm resistor 16 and a ZO-ohm resistor 17 which determine the distribution of the voltage drop in the connection across the line including the electrodes. A switch 18 is disposed in the wire 14 connected to the secondary of the transformer and a pilot light 20 and current limiting resistor 21 are connected in series with the switch 18 and across the secoperation employed in some previous designs. A capacitor 26 is connected in shunt with the relay 23 to smooth out the pulsating rectified voltage and serves to prevent relay chatter.

The control relay 23 includes a contact 27 which is connected by wire 28 to one side of the supply line and which is adapted to contact a terminal on conductor 29 which is connected to the other side of the supply line. A thermal element 30 of thermal time-delay relay 31 is disposed in the line connecting conductor 29. A normally closed bimetallic switch adapted to open when heated is a second element of the thermal time-delay relay 31 and the two elements of this device are enclosed by a sealed envelope. The bimetallic switch 9 is connected between one side of the electrodes 12 and the full wave rectifier 22. Shunting the thermal time-delay relay 31 and connected between the sensing electrodes 12 and the full wave rectifier 22 is incandescent lamp 33. This lamp has a filament 33a which is a hot Wire resistor, its temperature response establishing a 200 ohms resistance at cold temperature and a 500 ohms resistance at hot temperature. The motor 11 for the pump 8 is connectable across the supply line by the relay 23, one lead for the motor 11 being connected to the wire 14 of the supply line and the other lead for the motor being connected by conductor 34 to the terminal of the conductor 29 which, on energization of the relay, is engaged by contact 27 to connect the motor .to wire 15 on the other side of the supply line.

Also connectable across the supply line through the switching elements of the relay 23 is the signal bell 35 and signal light 36, these indicators being connected on one side to the wire 14 and to the switching elements of the relay 23 on the other side by the conductor 34.

It will be seen, therefore, that in operation there is a succession of shots of a small quantity of liquid detergent delivered into the wash tank 2, from the detergent container 7 until an alkaline condition is reached where the drop across the electrodes 12 is no longer sufficient to energize the relay 23 and energize the motor 11 for the pump 8. Where a succession of shots is required, the drop across the electrodes 12 continues within the relay energizing range. Each delivery shot corresponds to a cycle of operation of the thermal time-delay relay 31 and the incandescent lamp 33 during which the bimetallic elements of the switch 9 of the time delay-relay 31 initially carry the full current at practically no impedance, the current, however, being subsequently carried by the shunting, incandescent lamp 33 as the impedance across the bimetallic elements increases to infinity. Since the resistance of the hot wire resistor 33a increases to about 500 ohms at the end of the cycle, the current through the relay coil 24 will be reduced at the end of each cycle. Whether the current is sufliciently reduced to cause the relay to open its switching elements depends on the voltage drop across the electrodes 12. Except under the specific condition that the detergent has been exhausted, the current will be sufficiently reduced to open the switching elements so that the thermal time-delay relay 31 will be reset for the succeeding cycle. On the first feed cycle, there will be required approximately three seconds for the relay to open and an additional three seconds for the hot wire resistor of the lamp 33 to be heated up to full ohmage. On every succeeding feed cycle, including the final one, the total time for this to occur will be about two seconds since both elements have been preheated. The time interval between rapidly for two second intervals. If the cycling continues for a period of time, it will aiford an easily recognizable indication that the detergent delivery to the wash tank is being excessively diluted by the water going in from the rinse section of the apparatus, or that a fillvalve is open inadvertently.

Because it has been found that in dishwashing machines having an automatic detergent feed control for liquids, there is no ready means for easily determining that the detergent container has become exhausted, it was found desirable to provide a signal to indicate this particular fact. To this end, it will be seen that the signal indicators are locked in continuously instead of cycling when the liquid detergent is exhausted. This is accomplished because the voltage drop across the electrodes becomes very large when there is a Weak detergent solution in the wash tank and, as a consequence, the current through the relay 23 increases to the point where the switching elements of the relay are continuously closed even though the hot wire resistor is at its maximum resistance. Accordingly, a continuous ringing of the bell and a continuous illumination of the lamp 36 will give an easily identified indication that the liquid detergent supply is exhausted.

While the particular embodiment which has been above described and shown in the drawings has proven satisfactory, the invention may be otherwise embodied without departing from its scope as defined in the following claims.

What is claimed is:

1. A time delay circuit means comprising a conductivity sensing device, a rectified control circuit connected to said conductivity device and to a load control means, said circuit including a relay in control of the load control means, and said conductivity sensing device for establishing the relay in one state for a given interval of time, causing said relay to change to its opposite state at the end of the given interval of time, and circuit breaking means for affording a time delay in returning the relay to said one state but for a diminished time interval, said load control means having a thermal control element in control of said delay means.

2. A time delay circuit means comprising a set of sensing electrodes, a rectified control circuit connected to said electrodes and to a load control means, said circuit including a supply, said electrodes and a voltage distributing resistor connected across said supply, a full wave rectifier connected in parallel with said electrodes, a delay having a thermal responsive element connected between said electrodes and said rectifier and a bimetallic switch shunting said thermal responsive element, a heater in control of said bimetallic switch, a relay switch in control of said heater, a relay adapted to operate said relay switch and connected to the output of said rectifier and a smoothing capacitor disposed across said relay.

3. A time delay circuit means comprising a set of sensing electrodes adapted to contact a solution in a tank, and a control circuit connected to said electrodes and to a load control means, said circuit including a supply, said electrodes and a voltage distributing resistor connected across said supply, a full wave rectifier connected in parallel with said electrodes, a delay having a hot wire resistor with a positive thermal coefiicient connected between said electrodes and said rectifier and a thermal time-delay relay having a bimetallic switch connected across said hot wire resistor and a heater in control of said bimetallic switch, a relay switch connectable across the supply and in control of said heater, relay means connected across said rectifier and operative to control said relay switch and a smoothing capacitor disposed across said relay means.

References Cited by the Examiner UNITED STATES PATENTS 2,476,329 7/49 Sitzer 317-132 2,476,330 7/49 Sitzer 317-132 2,482,820 9/49 Wolfson et a1. 307-132 2,593,825 4/52 Albrecht 137-95 2,672,188 3/54 Cassidy 317-132 2,786,968 3/57 Kabak 323-68 2,817,806 12/57 Borell 317-141 2,830,615 4/58 Borell 137-392 2,832,068 4/58 'Warren 317-132 2,932,774 4/60 Rice 317-141 3,017,564 l/62 Barney 323-68 3,067,410 12/62 Louis 317-132 SAMUEL BERNSTEIN, Primary Examiner.

ISADOR WEIL, NEIL C. READ, MAX L. LEVY,

Examiners.

Claims (1)

1. A TIME DELAY CIRCUIT MEANS COMPRISING A CONDUCTIVITY SENSING DEVICE, A RECTIFIED CONTROL CIRCUIT CONNECTED TO SAID CONDUCTIVITY DEVICE AND TO A LOAD CONTROL MEANS, SAID CIRCUIT INCLUDING A RELAY IN CONTROL OF THE LOAD CONTROL MEANS, AND SAID CONDUCTIVELY SENSING DEVICE FOR ESTABLISHING THE RELAY IN ONE STATE FOR A GIVEN INTERVAL OF TIME, CAUSING SAID RELAY TO CHANGE TO ITS OPPOSITE STATE AT THE END OF THE GIVEN INTERVAL OF TIME, AND CIRCUIT BREAKING MEANS FOR AFFORDING A TIME DELAY IN RETURNING THE RELAY TO SAID ONE STATE BUT FOR A DIMINISHED TIME INTERVAL, SAID LOAD CONTROL MEANS HAVING A THERMAL CONTROL ELEMENT IN CONTROL OF SAID DELAY MEANS.

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