US3660909A

US3660909A - Dryer control

Info

Publication number: US3660909A
Authority: US
Inventors: Dale F Willcox
Original assignee: Controls Company of America
Current assignee: Eaton Corp
Priority date: 1970-12-18
Filing date: 1970-12-18
Publication date: 1972-05-09
Anticipated expiration: 1989-05-09

Abstract

The sensing rings mounted in the dryer drum are bridged by the tumbling clothes. The voltage is impressed on one of the rings and leaks to ground through the other ring allowing the bias on the grid of the triode to change until the triode passes enough voltage to actuate the relay. The resistance bridging the rings is integrated by reason of the capacitor in the circuit. The triode and relay operate as an electronic switch controlling energization of a power relay to shut off the dryer on receipt of the dry signal or to start a timer to provide an additional time delay period. In another version, the time to reach 20 percent moisture level is measured and the 20 percent moisture signal actuates the timer to continue running for a predetermined proportion of the measured period before shutting off the dryer.

Description

United States Patent Willcox [54] DRYER CONTROL [72] lnventor: Dale F. Willcox, Aurora, 111.

[73] Assignee: Controls Company of America, Melrose Park, Ill.

22 Filed: Dec. 18, 1970 [21] Appl.No.: 99,398

Related U.S. Application Data [63] Continuation of Ser. No. 383,542, June 29, 1964, abandoned, which is a continuation of Ser. No. 31,922, May 26, 1960, abandoned.

[52] U.S. Cl ..34/45, 34/48, 307/118,

318/483 [51] lnt.Cl ..F26b 13/10 [58] Field ofSearch ..34/45,48; 318/483; 307/1 18 [56] References Cited UNITED STATES PATENTS 2,045,381 6/1936 Elberty ..34/45 [451 May9, 1972 Primary Examiner-Carroll B. Dority, Jr.

Attorney-John W. Michael, Gerrit D. Foster, Bayard H. Michael, Paul R. Pue'rner, Joseph A. Gemignani, Robert E. Clemency, Andrew 0. Riteris and Glenn A. Buse ABSTRACT The sensing rings mounted in the dryer drum are bridged by the tumbling clothes. The voltage is impressed on one of the rings and leaks to ground through the other ring allowing the bias on the grid of the triode to change until the triode passes enough voltage to actuate the relay. The resistance bridging the rings is integrated by reason of the capacitor in the circuit. The triode and relay operate as an electronic switch controlling energization of a power relay to shut ofi the dryer on receipt of the dry signal or to start a timer to provide an additional time delay period. In another version, the time to reach 20 percent moisture level is measured and the 20 percent moisture signal actuates the timer to continue running for a predetermined proportion of the measured period before shutting off the dryer.

P'A'TENT'EDMAY 9 I972 3, 660 909 SHEET 3 OF 5 INVENTOR.

.Ft&. 6 DALE F. Wmuzox BYa :I

ATTORNEY P'A'TENTEBMAY 9 1972 3.660.909

SHEET l [1F 5 Mae-Gums iv i #016 'mo I00 90 8o '70 6o 50 4'0 30 '20 'lo 0 PERCENT MmSTURE.

F 7 INVENLIOR' \C-a. DALE F. WlLL X ATTORNEY PA'TENTEW 1972 3, 660.909

SHEET 5 OF 5 FUGHB INVENTOR. DALE. F. W\L.L.C OX BY uflmi ATTORNEY DRYER CONTROL This application is a continuation of my copending application Ser. No. 383,542, filed June 29, 1964, and now abandoned, which was a continuation of copending application Ser. No. 3 1,922, filed May 26, 1960, now abandoned.

This invention relates to a device adapted to control a drying operation.

The present device is adaptable to a great many uses where it is desired to dry or moisten a material to result in a predetermined moisture content. Clothes dryers are one example of a useful application of the present invention. Selecting the proper setting for a conventional clothes dryer timer control amounts to an educated guess based on the operators experience withloads of similar weight," wetness, type of material, etc. Even if one is highly expert in evaluating the various factors which dictate the proper drying time, certain imponderables such as fluctuating line voltage or a change in humidity can throw off his estimate. Experimentation 'with' parameters other than time, e.g., temperature or humidity in the dryer, has shown that these methods do not satisfactorily correlate with the actual moisture content of the clothes to form the bans of a control.

The main object of this invention is to provide a control which directly and accurately measures the moisture content of the material being processed.

This object is accomplished by providing a sensor device which directly measures the moisture content of the material. Part of the device consists of a pair of spaced conductive rings or bars mounted in the dryer so that the clothes bridge the gap. The clothes thereby form a resistance which is composed of the contact resistance between the clothes and the rings and the resistance of the fabric itself and this total resistance varies according to the moisture content of the clothes. The contact resistance greatly exceeds the inherent resistance of the fabric so the total resistance between the rings is not significantly affected by the physical position assumed by the fabric bridging the gap.

At 20 percent moisture content the contact resistance of all fabrics tested was approximately equal, and this was true regardless of the size of the load. This, then, becomes the control point underlying the present control. The conductive rings are connected to an electronic unit which measures the resistance and when the resistance rises to the predetermined value a relay is actuated to turn off the dryer (providing damp clothes) or to actuate one of two timers, described hereinafter, to dry down to the desired moisture content.

If the wash is dried on a straight time basis after the 20 percent moisture level is reached the humidity of the air, line voltage variations, etc., still affect the final moisture content.

However, the wash has a known moisture content (20 percent) when the timer is started and this improves over the conventional timer operated dryer in which there is no practical way to measure the initial moisture content of the clothes.

A proportional timer may also be used with the sensor unit. The proportional timer first records the time interval from dryer energization to the 20 percent moisture signal. Then the timer mechanism takes a proportion of this time interval and shuts off the dryer at the expiration of the proportionate time. The selected proportion is adjusted according 'to the final moisture content of the clothes desired. By use of the proportional timer, several of the variables common to straight timer systems, such as load size, line voltage and humidity, are eliminated.

Use of the present invention is described herein in connection with a clothes dryer, but it is equally adaptable to any similar drying operation and is also adaptable to operation in which moisture is added to a material.

Other objects and advantages will be pointed out in, or be apparent from the specification and claims, as will obvious modifications of the embodiments shown in the drawings in which:

FIG. 1 is a schematic view of a dryer control system in which the'dryer is optionally shut otf or permitted to run a presetinte'rval after the clothes in the dryer reach a given moisture content, as sensed by the electronic unit;

FIG. 2 is a schematic view of a dryer control system in which the moisture sensor is connected to a timer which records the time interval from dryer energization until the clothes reach a given moisture content and then continues the drying operation for the proper proportion of such interval to dry the clothes to a preselected final moisture content;

FIG. 3 is a side view of a dryer drum having a pair of spaced conductive rings mounted therein;

FIG. 4 is an electrical schematic view of the electronic sensingunit;

FIG. 5 is a top view of the proportional timer with the turntable removed showing the operative position of the turntable periphery in broken lines; 7

FIG. 6 is a side view of the proportional timer;

FIG. 7 is a graph of the resistance between the fabricbridged conductive rings plotted against the moisture content of the fabric;

FIG. 8 is an electrical schematic view of the proportional timer.

Referring to the drawings, the clothes dryer drum 10 has an inner conductive ring 12 grounded to the drum and a conductive ring 14 insulatively mounted in the drum and spaced from ring 12. A slip ring 16 is mounted on the exterior of the drum and electrically connected to ring 14 by wire 18. A brush 20 contacts slip ring 16 and is electrically connected to electronic unit or circuit 24 by wire 22.

Electronic circuit 24 has a power supply consisting of a rectifier 30 and a blocking capacitor 31 which combine to impress a voltage across a voltage divider network consisting of

resistors

36, 34 and 32. The values of these resistors are selected so that the cathode 28 of triode vacuum tube 26, connected between

resistors

36 and 34, has the proper biasing voltage impressed on it.

Another voltage divider network is connected to the power supply and consists of

resistors

36, 40 and 41. Resistor" 41 is the gap between the conductive rings in the dryer drum and this resistance therefore varies according to the moisture content of the clothes. The tube grid 38 is connected between

resistors

41 and 40 so that the voltage developed across resistor 41 is reflected at the grid.

Since the resistance measured at 41 is the'total resistance across the gap between the conductive rings, it would appear that this resistance would vary not only with the wetness of the clothes, but also according to whether the fabric bridging the gap was stretched taut or lying loosely across the gap since this varies the length of the conductive path. However, the resistance of the fabric itself is negligible compared to the contact resistance between the fabric and the conductive rings and, therefore, the manner in which the fabric bridges the gap between the rings is immaterial.

When the fabric between the conductive rings has a high moisture content the resistance, and hence the voltage, across the gap between the conductive rings is quite low. When the gap voltage is low the voltage impressed on the grid is low and the tube is biased to cut off. As the fabric dries, the voltage across the gap increases and the grid bias increases thereby rendering the tube conductive. Current then flows through the tube to circuit breaking solenoid 46 which is actuated when the tube reaches a selected conductive level.

In very small loads the clothes may be momentarily tumbeld to a non-gap bridging position; to prevent this eventually from fooling the electronic unit into reporting that the clothes are dry, capacitor 42 is connected in parallel with resistance 41 and has a value such that the capacitor conducts sufficiently to develop a relatively low voltage across it and this voltage is impressed on the grid. Without the capacitor the very high voltage across the unbridged conductive rings would be impressed on the grid which would render the tube conductive. When the clothes again bridge the gap the capacitor stops conducting thereby becoming essentially an open circuit again and the voltage between the rings is again impressed on the grid. Capacitor 42 therefore builds a response time delay into the sensor device.

The graph in FIG. 7 shows how the contact resistance goes up sharply and uniformly for loads of all sizes when the moisture content of the fabric bridging the gap between the conductive rings is reduced to 20 percent. The steepness of the resistance curve at the 20 percent moisture level makes a good control point to sense and permits use of a tube of relatively low selectivity. v

Solenoid 46, which is actuated by the electronic unit when the 20 percent moisture level is reached, may be used to control dryer operation in one of several ways. Since 20 percent moisture content gives a damp-dry" wash, the solenoid may be used to actuate a switch to shut down the dryer.

Another possibility is to connect the solenoid to a timer which it starts in operation. Or, as diagrammatically shown in FIG. 1, a combination of these two systems can be used. It is possible to obtain good results by drying a load of clothes from 20 percent moisture down to a desired moisture content on a straight time basis although at first blush it may seem that, for example, wool would take longer to dry than nylon. With normal fabric weights drying time is almost solely a function of moisture content and, therefore, when wool and nylon start with the same moisture content (20 percent in this case) the drying time to say percent is the same. This system still requires an educated guess to be made as to timer setting but the most tricky variable, that of initial moisture content, is eliminated and the only significant variable remaining for consideration is load size. Another system, which eliminates the load size variable, is next described.

A third possibility, shown in F IG. 8, involves the use of what I call a proportional timer structurally shown in FIGS. 5 and 6. This timer measures the time it takes a load of clothes to dry from dryer energization to the 20 percent moisture level and then continues the drying operation for a proportion of such time interval sufficient to dry the clothes to a predetermined final moisture content. The dryer and proportional timer are both started by depressing button 50 which energizes circuit holding solenoid 52 thereby establishing a circuit to heater 56, dryer motor 58, sensing unit 24 and solenoid 60.

Turntable tilting arm 62 is connected between the armature of solenoid 60 and turntable support 64 so that, upon energization of solenoid 60, turntable 68 is tilted into contact with drive wheel 70. A spring 67 is connected between turntable support 64 and base 66 and biases the turntable into contact with return wheel 88 when solenoid 60 is de-energized.

Upon dryer energization, turntable support 64 tilts toward single pole, double throw switch 72 causing contact 65 to close a circuit to drive motor 74. Motor 74 drives wheel 70 which rotates the turntable in a clockwise direction. The turntable has a depending finger 76 which holds double pole, single throw switch 78 open when the dryer is off. Rotation of the turntable by drive wheel 70 after dryer energization moves finger 76 out of contact with switch 78, thereby permitting contact 80 to close a circuit between switch 72 and return motor 84. Contact 82 closes a circuit between circuit holding solenoid 52 and the power source when contact 80 closes.

The turntable is rotated clockwise by drive wheel 70 until the contact resistance of the fabric in the drum indicates that the moisture content of the fabric has been reduced to 20 percent. At this point electronic unit 24 transmits current, as described above, to circuit breaking solenoid 46 which breaks the circuit to solenoid 60 thereby releasing armature 61 so that spring 67 takes over and tilts the turntable into engagement with return drive wheel 88. When turntable support 64 moves away from switch 72, contact 65 opens the circuit to the drive motor and closes the circuit between the power supply and the return motor. The return motor drives wheel 88 which rotates the turntable counterclockwise.

The return motor continues to run until finger 76 is driven back to its starting position where it opens contacts 80 and 82. Opening contact 80 shuts off return motor 84, and opening contact 82 de-energizes circuit holding solenoid 52 thereby shutting down the dryer. Finger 76 then remains in this position until the above described operating cycle is started again by depressing starting button 50.

Drive wheel 70 and return wheel 88 are fixedly connected by bracket 90 which is slidable on base 66 so that the drive and return wheels are movable radially as a unit with respect to the turntable. Percent moisture indicating indicia 94 are fixed on base 66 and pointer 92 is fixed on slidable bracket 90 which is moved to set pointer 92 to the desired final moisture content marked on indicia 94. Therefore, by moving drive wheel 70 to the extreme left so that pointer 92 is set on 20 percent moisture, wheel 70 engages the turntable near its periphery thereby'insuring a relatively slow rotation of the turntable. Obviously, when the timer is set for 20 percent moisture shut-down, the total clockwise rotation of the turntable betweendryer energization and the 20 percent moisture signal will be quite small. When wheel 70 is moved to the left, return wheel 88 is also moved left since the wheels are fixed relative to one another. This moves the return wheel close to the center of the turntable thereby imparting a relatively fast rotation to the turntable when it is drivingly engaged by the return wheel. This relatively fast return drive, coupled with the relatively small amount of tumtable rotation between dryer energization and the 20 percent moisture signal, makes return of the turntable to its starting point almost instantaneous and therefore the dryer is shut down at substantially the 20 percent moisture level when the proportional timer is set as described.

The return wheel ordinarily has a greater diameter than the drive wheel, and hence causes a quicker return time when connected to the turntable a given distance from the center than would a wheel having the same diameter as the drive wheel, since the desired drying time from 20 percent moisture to 0 is usually less than from dryer energization to 20 percent moisture.

The proportional timer described for use with electronic unit 24 has many advantages over straight timer operated dryers. However, initial moisture content of the clothes is a variable which is not eliminated by use of the above described system. The moisture content of clothes coming from automatic washers will vary with the make of washer and the conditions under which it is operated. It is therefore desirable to provide a compensator mechanism (not shown) which permits the dryer operator to calibrate the proportional timer to his washer. The compensator mechanism is used to vary the drive wheel speed. The speed of the drive wheel will be increased if the clothes are coming out of the dryer too dry according to the moisture content setting, and decreased if the opposite is true. This adjustment need only be made once and tends to eliminate the initial moisture content variable.

Although but a few embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. The combination with a dryer having a rotatable drum for containing material to be dried and means for rotating said drum to tumble said material,

electrodes supported in said drum for engagement with said material and with said material completing an electrical circuit across said electrodes,

means for applying direct current to said electrodes,

a capacitance connected in circuit with said electrodes and with said material completing a circuit across said electrodes for discharge of said capacitor,

means for gradually charging said capacitance at a rate less than its rate of discharge through said electrodes when said material has a high moisture content and which is greater than the rate of discharge through said electrodes when said material has a low moisture content,

control means operative when actuated to efl'ect a dryer control function,

and means responsive to the charge on said capacitance to actuate said control means when the charge on said capacitance reaches a predetennined value correspond- 1 ing to a predetermined moisture content.

2. A dryer control circuit for use in a dryer having a drum for containing material to be dried, said circuit comprising,

means for rotating said drum to tumble said material,

electrode means supported in said drum for engagement with said material,

means for applying direct current to said electrode means with the potential across said electrode means being determined by the amount of current leakage through said material,

a capacitance connected in circuit with said electrode means with the charge thereon corresponding to the potential of said electrode means,

and control means connected with and responsive to the charge on said capacitance, said control means being operated when the charge on said capacitance corresponds to a predetermined moisture content of said material to effect a dryer control function.

3. in a clothes drier control system including electrically energized means for altering the drying cycle, fabrics tumbled at random in said drier and a bistable electronic means for controlling said electrically energized means, the combination of a trigger means for said bistable electronic means including a circuit having a DC voltage source and a capacitor interconnected with said bistable electronic means and said DC voltage source, said capacitor being charged via a first circuit portion and discharged via a second circuit portion with one of said circuit portions interconnected with electrode means presenting at random a resistance which is a function of the moisture content of said fabrics in said clothes drier whereby said capacitor produces an output to control said bistable electronic means in accordance with the moisture content of said fabrics in said clothes drier.

4. In the system of claim 3 the combination with said bistable electronic means of timing means operative to time the interval between initiation of the drying cycle and the triggering of the bistable electronic means by the trigger means and to continue operation of the electrically energized means for a predetermined percentage of said interval after the bistable electronic means is triggered to continue the drying operation past the point at which the moisture content of said fabrics has been reduced to a level low enough to trigger the bistable electronic means.

5. The combination of claim 3 in which the bistable electronic means controls the electrically energized means throughtiming means operative in response to triggering of the bistable electronic means by the trigger means to continue operation of the electrically energized means for a predetermined interval measured from such triggering.

6. The combination with a clothes dryer including a drum and motor therefor for tumbling fabrics at random and a heater, of a control system of regulating operation of the dryer, comprising, electronic means for controlling said heater, a circuit having a DC voltage source, a capacitor interconnected with said electronic means and said DC voltage source, said capacitor being charged via a first circuit portion and discharged via a second circuit portion with one of said circuit portions interconnected with electrode means positioned in the drum and presenting at random a resistance which is a function of the moisture content of said fabrics in said drum whereby the capacitor produces an output to trigger said electronic means in accordance with the moisture content of said fabrics in said drum and thereby terminate heater operation in accordance with such moisture content.

7. The combination of claim 6 including timing means operatively interposed between the electronic means and the heater, said timing means being operative to time the interval between initiation of a drying cycle and triggering of the electronic means and to thereafter continue operation of the heater and motor for a given percentage of said interval.

8. The combination of claim 6 including timing means operatively interposed between the electronic means and the heater, said timing means being placed in operation by the electronic means when the electronic means is triggered and being operative to continue operation of the heater and motor for a predetermined interval following such triggering.

9. In a clothes drier control system including electrically energized means for altering the drying cycle, fabrics tumbled at random in said drier and electronic means for controlling said electrically energized means, the combination of a trigger means for said electronic means including a circuit having a DC voltage source and a capacitor interconnected with said electronic means and said DC voltage source, said capacitor being charged via a first circuit portion and discharged via a second circuit portion with one of said circuit portions interconnected with electrode means presenting at random a resistance which is a function of the moisture content of said fabrics whereby said capacitor produces an output to control said electronic means in accordance with the moisture content of said fabrics in said clothes drier.

10. A moisture sensing control for use with apparatus for drying material and operative to control said apparatus in accordance with the moisture content of said material, said moisture sensing control comprising, sensing means arranged for engagement with the material being dried to complete a sensing circuit and the potential of said sensing means being determined by current flow through said material, means connected in circuit with and operative to apply a DC voltage on said sensing means, a capacitance connected in circuit with said sensing means for accumulating a charge which increases as the moisture content of said material decreases, switch means connected in circuit with said capacitance and responsive to a predetermined charge on said capacitance to change the operational state of said switch means, and control means connected with said switch means and operated by said switch means when the operational state of said switch means is changed to effect a dryer control function.

11. In a drying machine operable through a cycle of operation,

a chamber for containing articles,

means for drying said articles in said chamber during at least a portion of said cycle of operation,

electrodes for contacting and completing an electrical circuit through said articles, said electrodes spaced apart to receive therebetween the articles being dried so that the electrical resistance between said electrodes varies with the electrical resistance condition of the articles therebetween,

means for applying electrical voltage to said electrodes,

means for instituting said cycle of operation,

means in association with said chamber for moving said articles in random contact with said electrodes,

means for integrating the variations in applied voltage across the electrodes resulting from variations in resistance conditions of the articles therebetween to produce a signal,

means responsive to a signal of given magnitude to initiate termination of said cycle of operation.

12. A dryer control circuit in combination with a dryer having a drum for containing material to be dried, said circuit comprising,

means for rotating said drum to tumble said material,

electrode means supported in said drum for engagement with said material,

means for applying a voltage to said electrode means with the potential across the electrode means being determined by the amount of leakage through said material,

and control means connected with and responsive to the charge on said capacitance, said control means being operated to effect a dryer control function when the charge on said capacitance corresponds to a predetermined moisture content of said material.

13. A dryer control circuit in combination with a dryer having a drum for containing material to be dried, said circuit comprising,

means for rotating said drum to tumble said material,

electrode means supported in said drum for engagement with said material, means for applying a voltage to said electrode means with the potential across the electrode means being determined by the amount of leakage through said material,

means for integrating the potential across the electrode means as the potential varies with variation in the leakage through said material to produce a signal,

and means responsive to a signal of given magnitude to initiate termination of the drying operation.

14. Apparatus according to claim 13 in which the means for initiating termination of the drying operation includes, a timer for timing the termination period, said timer being adjustable to adjust said period and, hence, adjust the degree of dryness of said material at the conclusion of the drying operation.

15. in a drying apparatus operable through a cycle of operation,

a drum for containing fabrics,

means for rotating said drum to tumble said fabrics,

means for drying said fabrics in said drum,

means for instituting said cycle of operation of the apparatus,

electrodes positioned within said drum for contacting and completing an electrical circuit through said tumbled fabrics,

said electrodes spaced apart to receive therebetween the fabrics being dried so that the electrical resistance between said electrodes varies with the electrical resistance condition of the fabrics therebetween,

means for applying electrical voltage to said electrodes,

means including capacitance means for generating a control signal responsive to the electrical resistance condition of said fabrics contacting said electrodes maintained over a period of time of sufficient duration for random pieces of said fabrics to be tumbled into contact with said electrodes,

and means responsive to said control signal for initiating termination of said cycle of operation.

16. In a drying machine,

a chamber for articles to be dried,

electrodes for contacting and completing an electrical circuit through said articles,

said electrodes spaces apart and adapted to receive therebetween the articles being dried so that the electrical resistance between said electrodes varies with the electrical resistance condition of said articles therebetween,

means for supplying electrical voltage to said electrodes,

moving means in association with said chamber for causing relative movements and random contact between said electrodes and said articles to obtain a' representative sampling of the electrical condition of the articles,

control means for initiating termination of said drying machine,

means for accumulating energy,

means connected to said electrodes for discharging said energy accumulating means at a rate corresponding to the electrical resistance across said electrodes,

means for charging said energy accumulating means with energy at a predetermined rate which exceeds the discharge thereof when the articles contacting said electrodes are at least partly dried,

and means responsive to a predetermined amount of energy accumulated by said energy accumulating means for controlling said drying machine.

17. In a clothes drier control system including electrical energized drying cycle altering means, fabrics tumbled at random in said drier and a bistable electronic means for controlling said altering means, the combination of a transducer means for producing random pulses of electric energy as a function of the moisture content of said fabrics in said clothes drier, and trigger means for said bistable electronic means interconnected with said transducer means and said bistable electronic means comprising a circuit having a DC voltage source and a capacitor electrically connected to said bistable electronic means, said capacitor being charged and discharged, respectively, at first and second relative rates of charge, one of said rates of charge being a direct function of the said moisture content of said fabrics, said circuit producing an output voltage representative of the difference in the said charging rates.

18. A control system for altering the drying cycle of a clothes drier when the moisture content of fabrics being dried therein reaches a predetermined level, said fabrics being tossed about in a random manner within said drier during the said drying cycle, comprising an electrically energized means for altering said drying cycle, a bistable electronic means selectively energizing said electrically energized means in one of its states to alter said cycle and permitting said cycle to continue unaltered in the other of its states, transducer means for producing random pulses of electric energy as a function of the moisture content of said fabrics, and trigger means for said bistable electronic means interconnected with said transducer means and said bistable electronic means, said trigger means comprising a circuit having a DC voltage source and a capacitor electrically connected to said bistable electronic means, said capacitor being charged and discharged, respectively, at first and second relative rates of charge, one of said rates of charge being a direct function of the said moisture content of said fabrics, said circuit producing an output voltage representative of the difference in the said charging rates.

i l 3! 1 i

Claims

1. The combination with a dryer having a rotatable drum for containing material to be dried and means for rotating said drum to tumble said material, electrodes supported in said drum for engagement with said material and with said material completing an electrical circuit across said electrodes, means for applying direct current to said electrodes, a capacitance connected in circuit with said electrodes and with said material completing a circuit across said electrodes for discharge of said capacitor, means for gradually charging said capacitance at a rate less than its rate of discharge through said electrodes when said material has a high moisture content and which is greater than the rate of discharge through said electrodes when said material has a low moisture content, control means operative when actuated to effect a dryer control function, and means responsive to the charge on said capacitance to actuate said control means when the charge on said capacitance reaches a predetermined value corresponding to a predetermined moisture content.

2. A dryer control circuit for use in a dryer having a drum for containing material to be dried, said circuit comprising, means for rotating said drum to tumble said material, electrode means supported in said drum for engagement with said material, means for applying direct current to said electrode means with the potential across said electrode means being determined by the amount of current leakage through said material, a capacitance connected in circuit with said electrode means with the charge thereon corresponding to the potential of said electrode means, and control means connected with and responsive to the charge on said capacitance, said control means being operated when the charge on said capacitance corresponds to a predetermined moisture content of said material to effect a dryer control function.

5. The combination of claim 3 in which the bistable electronic means controls the electrically energized means through timing means operative in response to triggering of the bistable electronic means by the trigger means to continue operation of the electrically energized means for a predetermined interval measured from such triggering.

11. In a drying machine operable through a cycle of operation, a chamber for containing articles, means for drying said articles in said chamber during at least a portion of said cycle of operation, electrodes for contacting and completing an electrical circuit through said articles, said electrodes spaced apart to receive therebetween the articles being dried so that the electrical resistance between said electrodes varies with the electrical resistance condition of the articles therebetween, means for applying electrical voltage to said electrodes, means for instituting said cycle of operation, means in association with said chamber for moving said articles in random contact with said electrodes, means for integrating the variations in applied voltage across the electrodes resulting from variations in resistance conditions of the articles therebetween to produce a signal, means responsive to a signal of given magnitude to initiate termination of said cycle of operation.

12. A dryer control circuit in combination with a dryer having a drum for containing material to be dried, said circuit comprising, means for rotating said drum to tumble said material, electrode means supported in said drum for engagement with said material, means for applying a voltage to said electrode means with the potential across the electrode means being determined by the amount of leakage through said material, a capacitance connected in circuit with said electrode means with the charge thereon corresponding to the potential of said electrode means, and control means connected with and responsive to the charge on said capacitance, said control means being operated to effect a dryer control function when the charge on said capacitance corresponds to a predetermined moisture content of said material.

13. A dryer control circuit in combination with a dryer having a drum for containing material to be dried, said circuit comprising, means for rotating said drum to tumble said material, electrode means supported in said drum for engagement with said material, means for applying a voltage to said electrode means with the potential across the electrode means being determined by the amount of leakage through said material, means for integrating the potential across the electrode means as the potential varies with variation in the leakage through said material to produce a signal, and means responsive to a signal of given magnitude to initiate termination of the drying operation.

15. In a drying apparatus operable through a cycle of operation, a drum for containing fabrics, means for rotating said drum to tumble said fabrics, means for drying said fabrics in said drum, means for instituting said cycle of operation of the apparatus, electrodes positioned within said drum for contacting and completing an electrical circuit through said tumbled fabrics, said electrodes spaced apart to receive therebetween the fabrics being dried so that the electrical resistance between said electrodes varies with the electrical resistAnce condition of the fabrics therebetween, means for applying electrical voltage to said electrodes, means including capacitance means for generating a control signal responsive to the electrical resistance condition of said fabrics contacting said electrodes maintained over a period of time of sufficient duration for random pieces of said fabrics to be tumbled into contact with said electrodes, and means responsive to said control signal for initiating termination of said cycle of operation.

16. In a drying machine, a chamber for articles to be dried, means for drying said articles in said chamber during at least a portion of said cycle of operation, electrodes for contacting and completing an electrical circuit through said articles, said electrodes spaces apart and adapted to receive therebetween the articles being dried so that the electrical resistance between said electrodes varies with the electrical resistance condition of said articles therebetween, means for supplying electrical voltage to said electrodes, moving means in association with said chamber for causing relative movements and random contact between said electrodes and said articles to obtain a representative sampling of the electrical condition of the articles, control means for initiating termination of said drying machine, means for accumulating energy, means connected to said electrodes for discharging said energy accumulating means at a rate corresponding to the electrical resistance across said electrodes, means for charging said energy accumulating means with energy at a predetermined rate which exceeds the discharge thereof when the articles contacting said electrodes are at least partly dried, and means responsive to a predetermined amount of energy accumulated by said energy accumulating means for controlling said drying machine.