US3861056A

US3861056A - Control device

Info

Publication number: US3861056A
Application number: US215133A
Authority: US
Inventors: Otto R Behrens
Original assignee: Controls Company of America
Current assignee: Eaton Corp
Priority date: 1960-05-26
Filing date: 1972-01-03
Publication date: 1975-01-21
Anticipated expiration: 1992-01-21

Abstract

A control for sensing the moisture content of material utilizing a switching device responsive to a bias signal produced by a neon bulb.

Description

United States Patent Behrens Jan. 21, 1975 CONTROL DEVICE [75] Inventor: Otto R. Behrens, Skokie, Ill. [56] References Cited [73] Assignee: Controls Company of America, UNITED STATES PATENTS Melrose Park [IL 3,651,579 3/1972 Smlth 34 45 3,733,712 5/1973 Smith 34/45 [22] Filed: Jan. 3, 1972 Prima Examiner-Edward G. Favors l. 3 ry I App NO 215 Attorney, Agent, or Firm-Michael, Best & Fl'lCdl'lCl'l Related [1.8. Application Data [63] Continuation of Ser. No. 45,329, July 26, 1960, [57] ABSTRACT abandoned A control for sensing the moisture content of material utilizing a switching device responsive to a bias signal produced by a neon bulb [58] Field of Search 34/45, 48, 5, 53 4 Claims, 3 Drawing Figures CONTROL DEVICE This is a Continuation of application Ser. No. 45,329, filed July 26, 1960 and now abandoned.

This invention relates to a control for sensing moisture content of a material.

The principal object of this invention is to provide a control which will accurately sense the moisture content of a material over a wide range of moisture levels.

Such a control is applicable to many fields of use and is here illustrated as applied to a laundry dryer for turning off the dryer when a preselected moisture level is reached. The control provides very good accuracy over a wide moisture range but in some dryer drum designs the control can be fooled by a light load. Another object of the invention is to provide a modified control which is not fooled by a light load.

In laundry dryer usage there are occasions in which no heat is desired but drum operation vis wanted to fluff the contents. In the usual dryer operation the machine is controlled by a timer and such fluff operation is easily obtained. Where the drying operation is regulated by the present moisture sensing control there is no need for the usual timer but this omission would leave the dryer without the fluff feature. Another object is to provide a modified moisture sensing control which can be manually switched from its sensing function to a timing function. This is accomplished by the addition of only a switch and a capacitor to the basic electronic circuit.

FIG. 1 is a schematic wiring diagram of one embodiment of the invention;

FIG. 2 is a similar wiring diagram of a portion of a modified circuit; and

FIG. 3 is a portion of a further modified circuit.

Referring to FIG. 1 in detail, the control circuit is energized by actuating momentary switch to complete a circuit through secondary 12 of transformer 14, normally closed switch 16, and coil 18 of relay A to energize the coil and close switch 20 on contact 22 to establish a holding circuit. The holding circuit will remain closed so long as switch 16 is closed. This switch is actuated by relay B in a manner to be described hereinafter. The AC supply is rectified by diode 24 having

resistors

26, 28 in series to protect the diode against heavy in-rush current when the circuit is established. The pulsed DC leaving the diode is filtered by an RC

network including capacitors

30, 32 and

resistors

34, 36 to provide a filtered DC supply across resistance 38 which establishes the bias on switching diode 40. The voltage supply to the switching diode passes through a blocking diode 42 the purpose for whichwill appear hereinafter.

The switching diode is a Schockley type (US. Pat. No. 2,855,524) having a very high impedance when non-conducting or in the open condition, that is, when the bias is below the switching voltage of the diode. When the voltage impressed on the switching diode exceeds the switching voltage the diode becomes conduclive or closes and the voltage required to sustain conduction drops to a very low level. At this time the impedance is very low and, hence, thediode operates in much the same manner as the switch. When the diode conducts, current will pass through the coil 44 of relay B to open switch 16 and deenergize the control circuit. When the circuit is deenergized the diode is protected by means of capacitor 46 against the reverse induction caused by the collapse of the coil.

The tap on variable resistor 36 takes off voltage through one, some or all of

resistors

48, 50, 52, 54, 56, 58 to supply a voltage to junction 60. As shown in FIG. 1 resistors 48 through 58 are in series and hence, a relatively small voltage appears at junction 60. Lead 62 from junction 60 is connected to a conductive ring 64 in a dryer drum while the other ring 66 is grounded as shown. When wet material bridges these rings the current at junction 60 will rapidly leak to ground and the voltage at junction 60 cannot build up. However, as the clothes dry in the drum the voltage at junction 60 will gradually rise and the present control looks at the voltage (or the resistance between the rings) at this point for its control function. Junction 60 is connected to junction 68 through a resistance 70 and junction 68 in turn is connected to one side of the neon tube 72 as well as having capacitor 74 connected thereto. It will be apparent that as the voltage rises at junction 60 it will also rise at junction 68 and hence, on the neon tube. When the voltage across neon tube gets high enough the tube becomes conductive and allows current to flow towards the switching diode. The RC network including resistance 76 and

capacitors

78 and 80 sharpens the voltage passed by the neon tube into a spike which is blocked by blocking diode 42 and hence, must pass through the switching diode 40 in addition to the bias voltage. The spike plus the bias voltage is enough to render the switching diode conductive to operate relay B to open switch 16 and break the holding circuit which drops relay A switch 20 back to contact 23 to ground the circuit.

From this description it is apparent that the control looks at the voltage at junction 60. Since the material in the drum may not always bridge the rings there is a possibility of the voltage at junction 60 rising to the control voltage prematurely. It is for this reason that capacitor 74 is located between junction 68 and ground. Hence, as the voltage builds at junction 60, and hence, at junction 68, capacitor 74 must be charged and this affords a time delay function insuring against an artificial indication at the spaced

rings

64, 66. If wet material again contacts the rings it would leak offthe charge on capacitor 74 and place the capacitor in condition for accomplishing its time delay function again.

In the foregoing description all of resistors 48 through 58 were considered in the circuit, and hence, there is a maximum voltage drop between the variable resistor 36 and junction 60. This results in the smallest voltage appearing at junction 60, and hence, the resistance between

rings

64 and 66 must be very high in order to tire the neon tube. Therefore, this is the dryest setting of the control.

Push button switches

82, 84, 86, 88 and 90 are provided for selection of other moisture settings. These push button switches are interlocked so that closure of one to its lower contact will release the others for movement to their upper contacts. One additional push button may be provided to clear all of the switches to their upper contacts for placing all the resistors in series as illustrated in FIG. 1. Such push button operation is conventional and in this connection it may be noted that the momentary switch 10 can be actuated by the overtravel action of any such push button. Hence, only one push button need be made to both make the selection of the degree of dryness desired and to initiate operation of the control. It will be appreciated that if switch 90 is actuated only resistance 48 remains in the circuit and hence, a high voltage will appear at junction 60 which will permit the signal voltage to build up with relatively high leakage existing between the rings. Hence, this is the wettest setting. In the control illustrated the settings run between and 40% moisture content of the material between the spaced rings. Resistor 36 is shown variable to allow adjustment of the control but such adjustment is not necessary in all cases.

The arrangement shown in FIG. 2 is designed to accommodate very small loads which might not bridge the

conductive rings

64, 66 within the time delay provided by capacitor 74 as described above. Under these circumstances, the small load switch 100 is closed to place the extra capacitor 102 in parallel with capacitor 74 and thereby increase the time required to build the control voltage at junction 60 and hence, at junction 68. It will be noted that capacitor 102 is placed in operation by means of switch 100 and is effective at all dryness settings of the various switches 104 through 112. It will also be noted that even if switch 100 is open capacitor 102 is in the circuit when switch 104 (corresponding to the dampest setting) is closed on its upper contact. The reason underlying this feature is to prevent an artificial condition of short duration from signaling that the desired degree of dryness has been obtained. This sort of condition can be artificially obtained at a very wet setting of the control by a relatively dry material striking the rings while the majority of the materials in the drum are actually still quite wet.

It will be apparent that switches 104, 106, 110 and 112 operate to place

resistors

48, 114, 116, 118 and 120 in series as desired. Resistance 122 has a different function, however, in this design. This resistance is made quite high and is placed in circuit by clearing all the other switches by means of a push button as mentioned above with respect to FIG. 1 so that all the resistances, that is, 48, 114, 116, 118, 120, and 122 are in series giving a very low voltage at junction 60. This setting can be used to advantage when drying materials such as blankets the exterior of which will give a dry indication prior to the interior actually being dry. This is due to the thickness of the material involved. Another use of this branch including resistance 122 is that if the push buttons are manipulated so as to clear all of the push button switches inadvertently there is still a voltage available at junction 60 and the machine can ultimately turn off. If it were not for this feature, the user could possibly clear all the switches unknowingly and leave the machine so set up as to provide no voltage to junction 60 and, hence, render the control inoperative so far as its ability to turn off the machine is concerned.

In FIG. 3 an air fluff switch 150 is provided as a push button switch acting to clear the selection switches 152, 154, and 156. Under these conditions, the

resistances

48, 158, 160, 162 are in series and the resistance provided by 162 is of a high magnitude. Therefore, the voltage available at 60 is again quite low and capacitor 164 is also placed in parallel with capacitor 74 while the sensing rings 64, 66 are cut out of the circuit. This air fluff switch, therefore, provides a mechanism for disconnecting the electrodes from the circuit and substituting therefor an electronic timing circuit which must charge

capacitors

74 and 164 before neon tube 72 can fire. This can be designed to give ten minute operation, for example, and then turn off the machine. Such an arrangement avoids the requirement for a separate mechanical timer for accomplishing an air fluff operation.

Heat may be provided during the air fluff operation, if desired. The air fluff switch may, however, be tied into the heater circuit to cut out the heater during air fluff operation. Obviously a separate heater switch could also be provided to give the user the choice of heat or no heat.

The high resistance 162 can also be utilized to advantage in the event the push button switches should be inadvertently cleared as described in connection with FIG. 2. Thus if all the switches are open voltage still appears at junction 60 to allow the machine to turn off (albeit at a very dry condition).

It will also be appreciated that the electronic timer portion of the circuit can be separated from the sensing circuit to provide a simple, straight timer having no moisture sensing function. Different time periods could be provided by providing a selection of resistances.

This control is superior to prior vacuum tube type controls since no current is passed to the relay until the sensing point is reached. Thus the relay operation is better. Furthermore, the neon bulb has a more clearly delineated firing point than the combination of a vacuum tube and relay so the control point from the electrical sense is sharper. Therefore, the present control is capable of more accuracy and will also sense accurately over a greater range.

I claim:

1. A control for determining moisture content of material, comprising, spaced electrodes adapted to be bridged by a material the resistance of which varies as its moisture content varies, electrical circuit means for supplying said electrodes with an electrical D.C. voltage, a capacitor connected in circuit with the electrodes so the charge thereon will increase as the resistance between the electrodes increases, a solid state switching device having conducting and nonconducting conditions and responsive to a bias signal to switch from one condition to another condition, a neon bulb connected in circuit with said capacitor andresponsive to a predetermined charge on the capacitor to produce a bias signal, said solid state switching device connected in circuit with said neon bulb and operated by the bias signal produced by said neon bulb to switch from one condition to another condition, and control means connected in circuit with said solid state switching device and operated by the change of condition of the switching device for performing a control function.

2. A control according to claim 1 in which the switching device is a switching diode connected in circuit with said neon bulb and normally biased below its switching voltage, said pulse increasing the voltage across the diode above the switching voltage whereby the diode becomes conductive.

3. A control according to claim I wherein said control means comprises a switching relay.

4. A control according to claim 1 wherein said solid state switching device is a Shockley diode.

3,861,056 Dated January 21, 1975 Patent No.

Inventor s Otto R. Behrens g 1 of 3 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Sheets 1 and 2 of the drawings should appear as shown on the attached sheet.

Signed and Scaled this seventeenth Day Of February 1976 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (orrnnissioner nj'Paremx and Trademarks Pmminm s SHEET 1 G? 2 Page 2 of 3 PATEHTEU JANZ I 1975 SHEEI 2 BF 2 Page 3 of 3

Claims

1. A control for determining moisture content of material, comprising, spaced electrodes adapted to be bridged by a material the resistance of which varies as its moisture content varies, electrical circuit means for supplying said electrodes with an electrical D.C. voltage, a capacitor connected in circuit with the electrodes so the charge thereon will increase as the resistance between the electrodes increases, a solid state switching device having conducting and non-conducting conditions and responsive to a bias signal to switch from one condition to another condition, a neon bulb connected in circuit with said capacitor and responsive to a predetermined charge on the capacitor to produce a bias signal, said solid state switching device connected in circuit with said neon bulb and operated by the bias signal produced by said neon bulb to switch from one condition to another condition, and control means connected in circuit with said solid state switching device and operated by the change of condition of the switching device for performing a control function.

3. A control according to claim 1 wherein said control means comprises a switching relay.