US2535930A - Means for the automatic regulation of the action of machines for the continuous processing of materials - Google Patents

Description

2,535,930 EGULATION OF THE ACTION 0 Dec. 26, 1950 E. H. JONES MEANS FOR THE AUTOMATIC R F MACHINES FOR THE CONTINUQUS PROCESSING OF MATERIALS Filed July 16, 1947 5 Sheets-Sheet 1 Dec. 26, 1950 JONES 2,535,930

MEANS FOR THE AUTOMATIC REGULATION OF THE ACTION OF MACHINES FOR THE CONTINUOUS PROCESSING OF MATERIALS Filed July 16, 1947 3 Sheets-Sheet 2 6m mm om Qom mom By W {W J1 [fur/Icy:

Dec. 26, 1950 2,535,930

E. H. JONES MEANS FOR THE AUTOMATIC REGULATION OF THE ACTION OF MACHINES FOR THE CONTINUOUS PROCESSING OF MATERIALS Filed July 16, 1947 3 Sheets-Sheet S Inventor Altorneys Patented Dec. 26. 1950 MEANS FOR THE AUTOMATIC REGULATION OF THE ACTION OF MACHINES FOR THE CONTINUOUS PROCESSING OF MATE- RIALS Eric Harding Jones, Manchester, England, assignor oi one-half to The British Cotton Industry Research Association, Shirley Institute, Didsbury, Manchester, England Application July 18, 1947, Serial No. 781,394 In Great Britain December 5, 1944 17 Claims. 1

The invention relates to improved means for the type of automatic regulation of machines such as is exemplified in a continuous drier for sized cotton warps, in which the warps after sizing are passed over drying cylinders and the state of the sheet of warp is then estimated by an eectric instrument. the current through which affords a measure of the moisture content of the warp. Although in the description which follows reference will be made to the machine referred to above, it is to be understood that the invention is applicable generally to those machines whose actions can thus be measured electrically.

An object of the invention is to provide a method of and apparatus for controlling the automatic regulation of the machine, whereby good proportionality is obtained between the regulation of the machine and the deviation of the factor to be controlled from its correct value.

A further object of the invention is to provide improved means for carrying out a well-known general method of regulation, in which the property to be regulated is periodically sampled, and a correction applied approximately proportional to the discrepancy between the indicated magnitude and the desired standard, this correction and its indication being substantially completed before a new sampling is made (see a paper by Hazen in the Journal of the Franklin Institute, voi.-2l8, page 285, 1934). There are numerous known examples of the application of a stepwise method of correction, among which United States Patent Specification No. 2,466,446 relates to the drying of cloth.

In the accompanying drawings- Fig. 1 shows diagrammatically apparatus according to the invention,

Fig. 2 shows a modification of the sensitive part of the circuit shown in Fig. 1.

Fig. 3 shows diagrammatically further apparatus according to the invention.

Fig. 4 shows a detail modification for use in the embodiment shown in Fig. 3.

Figs. 5 and 6 are respectively elevation and section showing details of a contactor shown diagrammatically in Figs. 1, 2 and 3 as the contactors l2 and I3 with their common contact i4.

Figs. 7 and 8 are respectively elevation and plan of the reversing switches shown diagrammatically as X and Y in Figs. 1 and 3.

Referring to the drawings:

A continuous drying machine for sized cotton warps incudes a drying drum 3 around which passes the warp 4 which is engaged by electrical contact rollers 5 and 8 in circuit with an electrical indicator it. The current through the indicator i0, roller 5, warp 4 and roller 8, is made to pass through a potentiometer resistance H, and the potential difference between the ends oi a variable portion Ha of this resistance is made to operate a control motor I for regulation of the machine. The control motor i adjusts the variable-speed gearing t of a belt drive 2 connecting a driving motor i and the drum 3. The variable portion No of the resistance II will hereafter be referred to as the potentiometer resistance." The potential diflerence aforesaid which may fluctuate owing to variations of the moisture content of the warp 4, is periodically sampled by a contactor or pair of contactors. These contactors each consist of a pair of terminals which periodically make momentary contact with each other. Each contactor might, for example, consist of a terminal in the form of a metal tongue mounted on a revolving member so as to make contact with a stationary terminal. Where two contactors are used they are arranged in parallel portions of the circuit and come into operation alternately. For diagrammatic simplicity two movable contacts 12 and i3 are shown adapted alternately to make contact with a single fixed contact it.

These movable contacts might for example be mounted in a revolving member geared to the machine so as to revolve at a rate dependent on the speed of the machine. One end of the potentiometer resistance I la is connected through the contactor or contactors to one plate lid of a condenser C while the other end is connected through a source of potential I! to the other plate ilib. For any given value of the potentiometer resistance there will be a value of the indicator current such that the potential difference across its ends will exactly neutralise the potential of this source l1 so that this difference does not contribute to the charging of the condenser. By adjusting this resistance Ila the moisture content of the warp may be controlled according to the invention at various desired values. A centre tapped source of potential with halves 18a and lib is shown connected to the contacts l2 and i3 for a purpose described later,

An alternative method of making this adjustment is by means of a variation of the potential difference tapped oil from the source of potential I'l. Means for doing this are shown in Fig. 2 which represents a modification of part of the circuit shown in Fig. 1. In this figure i'la is a pv tntiometer resistance connected to the source sistance a variable tapping is made to the positive end the potentiometer resistance No.

When the moisture content is not at the predetermined control value each contact charges the condenser to an inital potential diflerence which will be the greater, the greater the deviation from this control value, so that the time taken after the contact is broken for the condenser to discharge through a suitable high resistance to a-definite voltage will be the greater. Means are employed whereby an electric motor is made to run for the period of this partial discharge and while running to operate so as to tend to correct the condition of the material passing through the machne. For example, the rotation of the motor might be made use of to traverse the belt of a pair of cone pulleys, so as to run the machine more or less quickly according as the moisture content of the warp was below or above the control value.

The preferred means comprises a triode valve whose change 01' grid potential is controlled by the potential difference between the plates of the condenser. a Wheatstone bridge formed from the valve res stance and three auxiliary resistances and a gas-filled triode valve activated by the out-of-balance potential of the bridge, so that the current through it works the motor. For convenience this valve will be referred to as a thyratron valve.

In the iorm of the invention as shown in Fig. 1 of the accompanyin drawings, the plates tea and Nib of-the condenser are connected through a high resistance is shown adjustable in Fig. 1, the plate lea being connected to the negative end of the potentiometer resistance lia through the fixed contact i l and the pair of alternative movable contactors i2 and i3 and also directly to the grid 2( of a triode valve M. The other plate 0% is connected through the source of potential ill referred to above to the positive and of the potentiometer res stance Ha. This end is also connected through a further source of potential 22 to the cathode 23 of the valve. the grid potential during the discharge of the condenser is made to depend upon the current through the potentiometer resistance at the moment of contact and therefore on the moisture content of the warp. Moreover, this further source of potential 22 may be adapted to make the valve 2! operate on a suitable portion of its characteristic curve. In the case of many types of valve 2i, this source of potential may be dispensed with.

The efiective internal resistance of the anode circuit of the triode valve 2i is incorporated in a Wheatstone bridge quadrilateral of which the other three arms are three resistances 2 3, 25 and 26. A source of D. C. is connected to those two opposite corners, of which one is connected directly to the anode 27 of the valve. The other pair of opposite corners of which, of course, one connects directly to the cathode of the valve, are connected by a resistance 28 through a reversing device X comprising arms 29 and 30 adapted to be engaged simultaneously with contacts 29a and 30a or 29b and 30b respectively, whose reversing action is synchronised with the alternate operation of the two contactors l2 and it so as to come into operation just before successive engagement of such contacts with the fixed contact it. This resistance 28 will be termed the activating resistance. 1

Owing to the action of the reversing devic 25 In this way it follows that whatever the direction of the outoi'-balance potential 01' the Wheatstone bridge, the difference of potential across the activating resistance will be of the'same sense and may be used to activate a gas-filled triode after one or other 01' the alternate engagement of the contacts i2 or it with the fixed contact it.

One end of the activating res'stance 28 is connected, preferably through a safety resistance $9, to the grid 32 of a thyratron valve V, while the other end is connected through a source of potential 88 to the cathode 3Q oi the valve. The anode 35 and cathode 3d are connected up with a source of A. C. preferably the secondary 86 of a transformer. A D. C. control motor I is included in the circuit connected up through a reversing de vice Y having movable contact arms 87 and 88 engaging fixed contacts 37a, 371), 38a and 8% respectively and having their movements synchronised with the arms 29 and 39 in the cross arm of the Wheatstone bridge. A convenient arrangement is to have the field circuit 39 separately excited with D. C. and the armature coils 60 working in the valve circuit through the reversing device.

The use of A. C. in the circuit of the thyratron valve allows the potential across the activating resistance to resume control at each cycle. The reversal of the direction of the activated resistance in alternate contacts ensures that whether the moisture content be above or below the control value, there will be a tendency to activate the thyratron valve on one or other alternation. Moreover, owing to the motor reversing device, the motor will run in one or other direction ac-= cording as the moisture content is above or below the control value. To bring the grid voltage of the thyratron valve near to its critcal activating value at the-instants when contacts are made and to utilise a suitable part of the discharge curve of the condenser, separate sources of potential Mia and lab are inserted between the negative end of the potentiometer resistance and the two contactors. These are necessarily oppositely directed and their introduction necessitates separate contactors. In a simplified form of the invention one contactor only may be used, the reversal occurring on alternate contacts. Instead of arranging for the motor to be in the anode circuit of the thyratron valve a relay may be used, and in such case an A. C. motor could be used, together with mechanical reversing means if necessary.

The motion of the motor may be used to actu ate the belt of a pair of cone pulleys, or alter= natively it might be used to influence the supply of steam to the drying cylinders.

The unidirectional pulsating current produced when the thyratron valve is activated will cause the motor to run between successive contacts for a number of revolutions which will be greater or smaller according as the actual moisture content of the warp deviates more or less from the control value; and it is possible to obtain approximate linearity in the relations between the number of revolutions made in the interval between two contacts and this deviation. so minimising the tendency to hunting, and the time required to restore the moisture content of the warp to its correct value.

It is desirable that the rate of adjustment should also be proportional to the rate of passage of the material through the machine and that the interval between successive contacts should not be too long or too short compared with a,css,eso

the time taken to pass from where it is dried to where its moisture content is measured. These objects may be very simply attained by using a rotating member geared to the machine to actuate the contactors and reversing devices.

The invention may be applied to a dual system in which two means of control are used simultaneously; for example, in the case of the drier referred to above, speed and steam supply. Such dual control is useful where for extraneous reasons extremes of adjustment are undesirable; where, for example, with a drier, very low or high speeds of running should be avoided. In this special instance the arrangements described above would be used for the regulation of the speed, and the same motion which actuated the speed control might also operate a moving contact varying a resistance forming part of a total resistance through which a direct current was passing. This would give a variable potential on which would be based a duplicate of the arrangements described above in which, however, the motion of the motor would be'used to control the steam supply. Adiustment of this control would be made by adjustment of the current. Since in this instance the action of the control is slower than with the speed control, it would be advisable to operate the contacts less frequently. An alternative to duplicating the arrangements would be to bring the existing arangements into operation on the steam supply at suitable intervals by means of appropriate switching devices.

In carrying out the invention the various sources of potential, apart from that derived directly from the current through the indicator It, are preferably obtained from secondary windings of a transformer whose primary circuit is operated from A. C. mains, making use of rectifiers with smoothing condensers for the purpose of obtaining direct current. Means for carrying out the invention in this manner are illustrated in Fig. 3. This corresponds to the circuit shown in Fig. 1 with the modification illustrated in Fig. 2, and with the omission of the source of potential 22 shown in Fig. 1. In Fig. 3, features identical with those shown in Fig. 1 or 2 have been numbered as in those figures- It will be understood that the control motor of Fig. 3 is connected to the variabl speed gearing of a belt drive on the warp, as described with reference to Fig. 1.

In Fig. 3, 4| is the primary winding of a transformer connected to A. C. mains; and 42 to 48 are seven separate secondary windings. The winding 42 is connected to the A. C. terminals of a metal rectifier 42a, while the D. C. terminals are connected across a condenser 42b and a potentiometer resistance 420, from which a variable tapping is taken to an equal-resistance potential divider whose two halves 42d and 2e are equivalent respectively to the sources of potential l8a and 18b shown in Fig. l. The winding 43 is connected to the A. C. terminals of a metal rectifier 43a; and the D. C. terminals are connected across a condenser 43b and a potentiometer resistance "0, a variable tapping from which is equivalent to the source of potential II in Fig. 2.

In Fig. 3, the valve 21 is shown with its filament 23 directly heated from the winding 44, a centre tapping from which connects it to the resistance 25, this being adjustable for the purpose of balancing the bridge as explained below.

The operative potential of the Wheatstone bridge, whose direction is indicated by the signs and in. Fig. 1, is obtained from the winding employed to heat the cathode 45g. Centre tap ll by the use of a metal rectifier "a with smoothing condenser "b.

The equivalent of the source of potential 33 in Fig. l is derived from the winding 48, making use of a metal rectifier 45a, smoothing condenser 48b, and potentiometer 480.

The heater of the thyratron valve V is heated by means of the winding 41, a centre tapping being taken from this to the cathode 34. The anode circuit of the valve is connected to the winding 8 equivalent to the secondary winding 35 in Fig. 1 through the reversing switch Y and an adjustable resistance 50. In many applications of the invention'a slight delay in the operation of the regulating mechanism is desirable on restarting the machine after a stoppage. For example, in the application to the drying of warps in a sizing machine, such a delay is desirable till the excessively dry portion of warp in the drying chamber has been replaced by a normal portion. To effect such delay the circuit derived from the winding 48 is connected through a well-known formoi delayed action switcfit'l in which a bimetal strip 52 established contact with a member 58 only when it has attained a certain temperature; the strip being heated by the heating coil 54 which in the present instance is connected to th winding 41 in series with a switch 58 and resistance 55 which may be adjusted to give difrerentdesired periods of delay.

The switch 56 is ilxedto the re-starting mechanism on the machine in such a way that the delay period commences as soon as'the machine is restarted after a stoppage.

In place of the metal rectifier 450. a valve rectifier 4511 may be used in the manner illustrated in Fig. 4. Winding 45a: is connected to the plates e and f0! therectiiler and a winding ll is pings from the windings 5:2: and 49 yield the operative potential of the Wheatstone bridge, a smoothing condenser being employed, corresponding to the condenser 51) in Fig. 3.

For correct operation the Wheatstone bridge should be in balance when the contactors I2 and with Slb, 52a with 521) and 53a. with Nb, and

being thus in their lower" position. In the upperf position (when 5la is connected to ilc etc.) the testing circuit is established. In this case the connection of the circuit to the contactors l2 and I3 i broken (since the contact 5|c is not connected to any part of the circuit). In this upper" position the witches 52 and 53 disconnect th reversing switch X and connect the activating resistance 28 and the galvanometer G across the diagonal of the bridge independently assacso a simplified'side elevation (omitting the collar 62a in Fig. and a sectional plan along the line E--El of the device for operating the contactors. A shaft Bil is mounted in bearings and geared to the machine so as to run at a speed proportional to that of the drying cylinders. This shaft is provided with a fixed flanged sleeve tion which carries a fixed boss 60 whose two faces are provided with pegs Ma situated diametrically opposite each other. On each side of the boss are two similar cams 62 loosely mounted on the sleeve Ulla and retained contiguous to the boss ill by the flange oi the sleeve the and the collar (32a.

triode valve V will have a critical value for the potential of the grid, and will normally be biased by means of the source of potential 83 to a suitable potential below such critical value. The bridge circuit consists respectively of the elements 2G, 25, 26, and the thermionic valve, which latter will be proportioned so that for a predetermined suitable bias of its grid 26 such circuit will be substantially balanced and such grid po= tential will obviously be controlled largely by the source of potential iii. In principle, the com= bined function of such bridge circuit relative to the gas filled triode valve V is that such cir-= The cams t2 are provided with arcuate slots 62? Fig. 3. The two contacts 66a are connected electrlcally and constitute the junction id in Figs. 1 and 8, while the two contactors 63a constitute the contactors l2 and H3 in Figs. 1 and 3. The duration of these contacts is short and sensibly independent or" the speed of rotation of the shaft cc.

Figs. 7 and 8 illustrate suitable forms oi the switches X and Y. These consist of eight pairs of spring contacts of the type illustrated in Fig. 5 operated by two cams the and 65b fixed on the shaft so. These have the form shown in Figs. 2 and 8 being shaped to maintain contact over slightly less than 180 revolution of the shaft 6Q, being set with a phase difference of 180 and having a slight angular interval between the break of one switch and the make of the other, each interchange occurring shortly before the action of one of the contactors 63a. The manner in which "the eight pairs of contacts are made to operate as the two switches X and I, is illustrated diagrammatically in Fig. 9. In this the 16 "points of the eight pairs of contacts have been numbered to correspond to the 12 points of the switches X and Y in Fig. 1 or 3. The use of the eight pairs of contacts necessitates certain permanent electrical connections and these are indicated by the lines 50X, SiX, cor and MY, the use of the letters X and Y in these labels serving to indicate which pairs of contacts constitute the switch X and which the switch Y. The cams 65a, and 65b are here shown operating in one of their two modes of operation. The other mode is, of course, when 65b establishes its corresponding contacts and 6511 allows its contacts to be broken.

Thus, by rotation of the shaft 6d, synchronous operation of the ,switches X and Y is effected, and the correct timing of the operation of the contactors i2 and i3 is obtained.

Where the motor operates the belt of a conepulley speed changing device, it is desirable to insert limit switches which operate to break the motor circuit, for example, when the cone-pulley belt reaches either of its limiting positions; and similar switches are desirable where other regulating mechanisms are used.

In the examples shown in the drawings, the relative proportions of the parts of the circuit, and their principle of operation, areas follows:

Itis of course well known that the gas filled cult is to be used so that fluctuation of potential of the grid 26 will create balance disturbance ofthe bridge circuit, and the potentials across the diagonal of the bridge circuit are applied to the grid of the valve V so as to excite the same when the applied potential in conjunction with that of source 33 gives a resultant potential suficient to raise the grid of the valve V above its critical potential. The reversing switch X is introduced in the circuit so that increase or decrease of potential applied to the grid 2d of the thermionic valve may create positive potential for appllca tion to the grid of the gas filled valve V. Fuz thermore, the means for varying the potential to be applied to the grid 2d of the thermionic valve includes the sources of potential lfia and lflb for increment or decrement factors of predetermined value whilst the centre tapping between such sources to potential We and till) is adjustable along the potentiometer ll. When the machine for continuous processing to which the invention is to be applied is operating with the factor to be controlled at its correct value, the potential which would be applied to the grid 26 from the potentiometer resistance Ma, but excluding the increment or decrement potential from its or liib, is set so that it is the potential which will bring the bridge circuit into balance: thus the out-of-balance produced in the bridge circuit when the contactor engages will be a function of the increment and decrement potentials, and the bridge circuit is so proportioned that relative to the valve V the potential derived from its diagonal will be just insufilcient to activate the valve V. Obviously, the reversing switch X will be synchronised with the contactors i2 and i3 so that the change of direction of potential across the bridge circuit is counteracted to avoid re-= versal of the potential which would otherwise be applied to the grid of the valve V. If now the factor of the process to be controlled varies, then the potential obtained from the potentiometer resistance lia will increase or decrease. This increase or decrease is added to the increment or decrement potential applied to the grid Ell of the thermionic valve. If it is increased, then the out-of-balance produced during the increment function of the contactor will cause increase out-of-balance in the bridge circuit and the increased potential thereby applied to the grid of the gas filled valve V will activate the same, whilst during the decrement cycle of the contactor the out-of-balance will be reduced and the potential applied to the grid of the valve V potential drop across the condenser after it has The duration of exbeen charged and will depend upon the product of the capacity of C and the value of resistance It. Immediately after engagement of the contactor the voltage on the grid 20 of the thermionic valve 2| will be disturbed to its maximum extent and therefore will produce the maximum out-ofbalance in the bridge circuit and the maximum applied potential to the grid of the gas-filled valve V. The engagement of the contactor is only momentary for the purpose of charging the condenser, C and as soon as disengagement occurs, the condenser charge leaks away reducing the out-of-balance of the bridge circuit at a rate determined by the rate of leakage, and as soon as such out-of-balance results in a drop of potential at the grid of the valve V below its critical potential, such valve ceases to be excited. For any particular value of the increment and decrement potentials Na and lib there is the correct value of potential 33 which is just sumcient to prevent the valve V from becoming activated by the out-of-balance of the bridge circuit when either contactor is brought into action and the factor to be controlled is at its correct value. Moreover, the choice of the value of the Ila and llb and the corresponding value of potential 33'aflect's the length of the period during which the valve V is excited as the condenser charge leaks away-after the condenser has been charged owing to a deviation of the factor to be controlled from its correct value.

Adjustment of the values of Ila, llb and 33 thus enable the period of activation of the valve Vto be adjust-' ably limited to the early stages of the condenser discharge thus enabling a better proportionality to be obtained between the period of actiregion of rapid voltage change the operation of the thyratron is more precise and a high value of potential 33 insures greater stability of the thyratron in the unactivated condition.

The duration of excitement. of the valve V is thus a function of potential variation in the potentiometer resistance I la. The anode circuit of the valve V includes a. reversing switch Y which is synchronised with the reversing switch X so, that relative to increase or decrease of potential in the potentiometer resistance Ha the motor or other actuating mechanism represented in this case by the armature l and field 39 is actuated in forward or reverse direction to bring about movement of control mechanism to vary the factor of the process which is to be controlled.

I claim:

1. The method for the automatic regulation of the action of machines for the continuous processing of materials wherein a property of the material, such as its moisture content, is caused to vary a potential in part of an electric circuit and such potential variation is used to regulate the machine, including the steps of obtaining a series of electric charges periodically from such potential, effecting leakage of each charge, and using each leaking charge to control automatic regulation of the machine approximately proportional to such charge.

2. The method for the automatic regulation of the action of machines for the continuous processing of materials wherein a property of the material, such as its moisture content, is caused to vary a potential in part of an electric circuit and such potential variation is used to regulate the machine, including the steps of 10 obtaining a series of electric capacity charges periodically from such potential, effecting leakage of each charge, and using each leaking charge to control automatic regulation of the machine approximately proportional to such charge, the proportional control of the machine being obtained from the duration of the charge value above a predetermined potential.

3. The method for the automatic regulation of the action of machines for the continuous processing of materials wherein a property of the material, such as its moisture content, is caused to vary a potential in part of an electric circuit and such potential variation is used to regulate the machine, including the steps of obtaining a series of electric charges periodically from such potential, effecting leakage of each charge, and using each leaking charge to control automatic regulation of the machine approximately proportional to such charge, the proportional control of the machine being obtained from the duration of the charge value above a predetermined potential and the control of the machine being not otherwise proportional to the actual potential of the charge.

4. The method for the automatic regulation of the action of machines for the continuous processing of materials wherein a property of the materiaLsuch as its moisture content, is caused tovary a potential in part of an electric circuit and such potential variation is used to regulate the machine, including the steps of obtaining a series of electric charges periodically from such potential, effecting leakage of each charge, and using each leaking charge to control automatic regulation of the machine approximately proportional to such charge, the proportional control of the machine being obtained from the duration of the charge value above a predetermined potential, and the rate of leakage discharge being adjustable for vary-, ing the proportional control.

5. The method for the automatic regulation of the action of machines for the continuous processing of materials, wherein a property of the material, such as its moisture content, is caused to vary an electric current, a potential variation resulting from such current variation is applied periodically to a leaking condenser, the charges are caused to leak from the condenser, and each leaking charge, if sufficient, is used to operate the action-regulating mechanism of the machine in a direction and during a period which will be a function of the potential charges.

6. The method for the automatic regulation of the action of machines for the continuous processing of materials, comprising causing variation of a property of the material, such as its moisture content, from a predetermined control value to vary a potential in part of an electric circuit above and below a predetermined value, periodically obtaining electric charges from such potential variations, effecting leakage of each charge, and using each leaking chargeto effect a correcting regulation of the machine apaaaaoso processing oi materials, comprising causing variation of a property of the material, such as its moisture content, from a predetermined con trol value to vary a potential in part of an elec-= tric circuit above and below a predetermined value, periodically obtaining electric charges from such potential variations, eilecting leakage of each charge, and using each lealring charge to eirect a correcting regulation of the machine approximately proportional to such charge, the proportional control of the machine being obtained from the duration oi. the charge value above or below a predetermined potential, each charge above said predetermined potential be= ing used to correct the action of the machine in one sense and each charge below said pre= determined potential being used to correct the action oi the machine in the opposite sense.

8. Apparatus for the automatic regulation of the action of machines for the continuous processing or materials, comprising an electric cir= cult containing an adjustable resistance element arranged so that the potential across it is a function of the property of the material to be regulated, such as its humidity, an electric condenser, means for charging the condenser periodically from the said resistance element with any difference of potential in said resistance element from a predetermined value and means responsive to such potential difierenoe for controlling regulation mechanism of the machine proportionally with each such charge.

9. Apparatus for the automatic regulation of the action of machines for the continuous processing oi materials, comprising an electric circuit containing an adjustable resistance ele-= ment arranged so that the potential across it is a function of the property of the material to be regulated, such as its humidity, an electric condenser, a leakage circuit for the condenser,

means for charging the condenser periodically from the said resistance element with any diflerence of potential in said resistance element above a predetermined value, and actuating means responsive to a predetermined minimum potential of the condenser charge for bringing into actuation the regulating mechanism of the machine as a function of the duration of the condenser charge above such minimum potential.

10. Apparatus for the automatic regulation of the action of machines for the continuous processing of materials,comprising an electric circuit containing an adjustable resistance element arranged so that the potential across it is a function of the propertyof thematerial to be regulated,such as its humidity, an electric condenser, a leakage circuit for the condenser, means for charging the condenser periodically from the said resistance element with any difierence of potential in said resistance element above a predetermined value, and actuating means responsive to a predetermined minimum potential of the condenser charge for bringing into actuation the regulating mechanism of the machine as a function of the duration of the condenser charge above such minimum potential, actuation of the regulating machine being not otherwise proportional to the actual potential of the condenser charge.

11. Apparatus for the automatic regulation of the action of machines for the continuous processing of materials, comprising an electric circuit containing an adjustable resistance element arranged so that the potential across it is a function of the property of the material to be regulated, such as its humidity, an electric condenser,

a leakage circuit for the condenser, means for charging the condenser periodically from the said resistance element with any difierence of poten= tial in said resistance element above a predetermined value, and actuating means responsive to a predetermined minimum potential of the condenser charge for bringing into actuation the regulating mechanism of the machine as a fum tion of the duration of the condenser charge above such minimum potential, said actuating means including a thermionic valve with its grid connected to the condenser, and a bridge circuit with the anode circuit of the valve included in one limb of the bridge.

12. Apparatus for the automatic regulation of the action of machines for the continuous proc= essing of materials, comprising an electric circuit containing an adjustable resistance element arranged so that the potential across it is a func tion of the property of the material to be regu= lated, such as its humidity, an electric condenser, a leakage circuit for the condenser, means for charging the condenser periodically from the said resistance element with any difierence of po tential in said resistance element above a predetermined value, and actuating means responsive to a predetermined minimum potential of the condenser charge for bringing into actuation the regulating mechanism or the machine as a function of the duration of the condenser charge above such minimum potential, actuation of the rogu lating machine being not otherwise proportional to the actual potential of the condenser charge, and said actuating means including a thermionic valve with its grid connected to the condenser, and a bridge circuit with the anode circuit of the valve included in one limb of the bridge.

13. Apparatus for the automatic regulation of the action of machines for the continuous processing of materials, comprising an electric cir-= cuit containing an adjustable resistance element arranged so that the potential across it is a function of the property of the material to be regulated, such as its humidity, an electric condenser, means for charging the condenser periodically from the said resistance element with any difference of potential in said resistance element from a predetermined value, and means responsive to such potential difference for controlling regulation mechanism of the machine proportionally with each such charge, characterised in that said means for charging the condenser includes means for maintaining the condenser, relative to the resistance element, at the predetermined potential to be derived from the resistance element.

14. Apparatus for the automatic regulation of the action of machines for the continuous processing of materials, comprising an electric circuit containing an adjustable resistance element arranged so that the potential across it is a function of the property of the material to be regulated, such as its humidity, an electric condenser, means for charging the condenser periodically from the said resistance element with any difference of potential in said resistance element from a predetermined value, and means respon sive to such potential difierence for controlling regulating mechanism of the machine proportionally with each such charge, characterised in that the means for charging the condenser includes means for maintaining the condenser, relative to the resistance element, at the predetermined potential to be derived from the resistance element, and in that variable potential means are provided for varying the said predetermined potential of the condenser.

15. Apparatus for the automatic regulation oi! the action of machines for the continuous processing of materials, comprising an electric circuit containing an adjustable resistance element arranged so that the potential across it is a function of the property of the material to be regulated, such as its humidity, an electric condenser, contactor means for applying such potential to the condenser periodically and alternately with superimposed increment and decrement potential of predetermined value, a leakage resistance connected to such condenser, a thermionic valve having its grid connected to the condenser so as to be biased in part by the potential between its plates, a bridge quadrilateral incorporating three resistances and the internal resistance of the thermionic valve, a source of potential for operating the bridge applied with positive polarity to the anode of the valve and negative polarity to the diagonally opposite corner, the resistance between this corner and the cathode of the valve being adjustable, the two opposite other corners being connected by a reversing switch through a diagonal resistance whose ends are connected by a smoothing condenser, the alternating actions of the reversing switch being synchronised with that of the contactor means, a gas-filled triode whose grid is biased in part by the out-of-balance potential across the diagonal resistance and in part by an auxiliary source of potential, a safety resistance between the grid and the neighbouring end of the diagonal resistance, an alternating source of potential in the anode circuit of the gas-filled triode, a further reversing switch synchronised with the contactor and first mentioned reversing switch, a reversible electric motor adapted to be actuated by the excitement of the gas-filled triode in direction controlled by the said further reversing switch and adapted for the actuation of regulating mechanism for the machine to regulate the property to be controlled oi the material, the elements of the bridge circuit being normally proportioned so as to be balanced by the application to the thermionic valve of a potential corresponding to the required predetermined value of the property to be regulated and the increment and decrement potentials being proportioned so that the positive potential applied to, the grid of the gas-filled triode by the balance disturbance created by them in the bridge circuit is just below the critical potential for excitement of the gas-filled triode.

16. Apparatus for the automatic regulation of the action of machines for the continuous processing of materials, comprising an electric circuit containing a resistance element arranged so that variation of the property of the material to be regulated, such as its humidity, causes proportional variation of the potential across the resistance element above and below a predetermined value, an electric condenser, means for maintaining the condenser at the predetermined potential to be derived from the resistance element, means for charging the condenser periodically from the resistance element with any dit- Ierence in the potential in the resistance element above and below the predetermined value, and means responsive to the condenser charge for controlling regulation mechanism of the machine proportionally with each charge from a potential variation, each charge above the predetermined potential correcting the action of the machine in one sense and each charge from a potential variation below the predetermined potential correcting the action of the machine in the opposite sense.

17. Apparatus for the automatic regulation of the action of machines for the continuous processing of materials, comprising an electric circuit containing a resistance element arranged so that variation of the property of the material to be regulated, such as its humidity, causes proportional variation of the potential across the resistance element above and below a predetermined value, a leaking condenser, means for maintaining the condenser at the predetermined potential to be derived from the resistance element, means for charging the condenser periodically from the resistance element with any difference in potential in the resistance element above and below the predetermined value, and means responsive to the condenser charge for controlling regulation mechanism of the machine proportionally with each charge, each potential difference above the predetermined value correcting the action of the machine in one sense and each potential difierence below the predetermined value correcting the action of the machine in the opposite sense, and the proportional control of the machine being obtained from the duration of the charge value above a predetermined potential.

ERIC HARDING JONES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,194,937 Hawkins Mar. 26, 1940 2,244,722 Norcross June 10, 1941 2,311,673 Lilja Feb. 23, 1943 2,346,437 Krogh Apr. 11; 1944 2,466,446 Laurie Apr. 5, 1949 FOREIGN PATENTS Number Country Date 563,480 Great Britain Aug. 16, 1944

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