US2140933A

US2140933A - Automatic regulating device

Info

Publication number: US2140933A
Application number: US740586A
Authority: US
Inventors: Clark M Dennis
Original assignee: Individual
Current assignee: Individual
Priority date: 1934-08-20
Filing date: 1934-08-20
Publication date: 1938-12-20
Anticipated expiration: 1955-12-20

Description

Dec. 2o, 1933. C, M- DENMS 2,140,933

AUTOMATIC REGULATING DEVICE Dec. 20, 1938. c. M. DENNIS AUTOMATIC REGULATING DEVICE Filed Aug. 20, 1954 5 Sheets-Sheet 2 Filed Aug. 20, 1934 5 Sheets-Sheet 5 Uff Off

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(Muervr De. 20, 1938. c. M. DENNIS 2,140,933

AUTOMATIC REGULATING DEVICE Filed Aug. 20, 1934 5 Sheets-Sheet 4 INVENTOR.

Dec. 20,1938.

C. M. DENNIS AUTOMATIC REGULATING DEVICE Filed Aug. 2o, 1954 5 shets-sheet 5 INVENTOR.

Patented Dec. 20, 1938 UNITED STATES PATENT OFFICE Application August 2t,

'av claims.

My invention relates to improvements in automatic devices :for regulation and control of heating, chemical process operations, and many other operations in which it is desired either to main- 5 tain certain values constant, to change them in predetermined amount, or at a predetermined rate. it includes improvements by which the operation of existing control devices may he made more uniform and less subject to error. It also includes improved methods and apparatus for the electrical measurement of temperature, which maybe advantageously used in conjunction with other apparatus of my invention in the regulation of heating and cooling operations.

In connection with all control devices, and the heat or other variable quantity which is to be regulated, there is a time lag between occurrence of the change which requires compensation, and the compensating response of the control apparatus. During this period of lag a further change may occur, and the total amount of 'compensating response required is correspondingly increased. A similar condition exists .after response ultimately causes return to the control point. Lag of control operation causes the desired value to be not only reached but exceeded, and a continuous hunting, values, results. The time lag and amount of such hunting varies with the nature vof the variable to be controlled, and with the nature of the devices used for regulation. In some cases it is not objectionable; in most cases, however, objectionable fluctuations from desired control may result.

The type of objectionable hunting which is encountered in a wide variety of industrial control problems may, for convenience, be described in connection with the familiar example of irregular temperature control gained in a residence when the furnace is controlled by an ordinary thermostat. This irregularity is especially marked when heating is effected by means of a coal fired steam furnace. This may be illustrated by reference to Fig. 1, which shows in somewhat exaggerated form the type of heating curve resulting when furnace drafts are turned on in the morning, after furnace has been shut off and the house temperature has dropped say, to 60 F. during the night. The furnace drafts are turned on at time a, but there is an appreciable interval before the fire begins to burn strongly enough to generate steam, and a further interval before distributing pipes are warmed and radiatorslstart to heat. Actual rise in room temperature therefore may not begin until time b. With the radiators hot the room temperature rises with above and below desired.

1934, Serial No. '140,586

(Cl. 23d-*74) increasing rapidity until the control temperature of is reached at c and the thermostat causes the furnace drafts to close. The residual heat of re and radiators causes the temperature to continue rising, however, until a maximum of, say, 74 is reached at d, after which the temperature slowly falls until the thermostat operates to again open the furnace drafts at e. By this time re and radiators will have cooled to such extent that heat will not be immediately supplied. The hunting cycle of undercooling and overheating will continue through f, g, h, etc., in decreasing amount but with increasing frequency, until a minimum fluctuation, which varies with the equipment and conditions, is reached.

A somewhat similar behavior results when control devices now in common use are utilized for regulation of chemical and industrial processes, as, for example, regulation of proportional flow of an alkali to maintain exact neutralization of an acid flow which is subject to sudden variations. Lag in operation of a pH meter and motor controlled valves may permit large excesses or deflciencies to accumulate, with resultant undesirable hunting and delay before stability at the desired value is again reached.

Referring again to Fig. 1, it is apparent that if the original approach to the control temperature had been anticipated, and the furnace drafts first shut off at some suitably chosen point 7', the residual heat from the furnace and radiators would have been just sufficient to cause continued temperature rise along the broken line, :1L-k, until the desired temperature was reached but not exceeded at k. Similarly, if the furnace was turned on at some point Z, as the temperature was dropping from'too high a value, the necessary heat would be supplied by the time point m was reached. In any given installation the location of the suitable points y' andl will vary at different times, depending to a large extent upon the rate at which the' temperature is rising or falling. In mild weather, for example, the rate of heating Will be rapid and cut-off temperature 1 should be lower than in cold weather, when the rate of heating is slower and residual heat will cause less subsequent temperaturerise. Similarly, if the desired control temperature has for any reason been exceeded, the rate of cooling will be relatively l'ow in mild weather and the on point, l, should be lower than would be desirable in cold weather. Similar relations exist during approach tc desired values in control of acidity and in regulation of other industrial operations.

I have discovered means by which requirements of changing demand or approach to desired control values may be largely anticipated, and the amount of anticipation made to vary with the rate of change and, to a controlled extent, With the amount of excess or deciency to be compensated for. The basis of this part of my invention may be illustrated by means of Figs. 2 and 3. If all points of Fig. 2 are on a horizontal plane surface, and a is a Weight attached to a string, L -b, then as b is moved along the line A-B through successive positions b', b etc., the weight will follow through successive positions a, a along a tractrix curve. In theory the curve approaches the line A-B as a limit but reaches it only at infinity. In practice the distance from the weight to the line A-B becomes negligible at some point as c, after which the Weight will follow along the line. During the above the angle which the string makes with the line A-B becomes progressively smaller until it is substantially zero at c. The true equation of the tractrix curve is complicated, but the following simple equation is approximately correct for that part of the curve in which we are interested.

If the distance which b travels along the line A-B is represented by Iv, the distance of a from A-B by ZI, and the length of the string by m, then in which n is a constant times a:

X (n: insa) The foregoing approaches closely to the tractrix curve after the angle a', b', A is less than about 30, from which it follows that there is a certain unit of travel of the point, b, which will approximately halve the distance of a from A-B each time it is repeated. The foregoing formula and statement are included here only to facilitate understanding of the operation of the invention to be described.

In Fig. 3, assume that A-B and C-D are parallel lines on a horizontal surface, and that E--G is a metal rod supported on the surface by a small wheel, E, and a movable pivot, F, which moves at a constant speed from left to right. Further assume that the lines A-B and C-D correspond to the 60 and 70 temperature lines of Fig. 1, and that the position of pivot F in relation to these lines varies with the actual temperature of the room which is under control, while at the same time the constant rate of motion from left to right is maintained. If the temperature starts to rise at a fairly rapid constant rate, the pivot F will move along some line as F-H, through

successive positions

1, 2 and 3. The wheel, E, will follow along a tractrix curve, EJ, lagging behind the motion of the pivot, while the free end of the rod, G, will lead the motion of the pivot toward the control temperature line, C-D, and will cross this line at the point K while the pivot is at point 3 corresponding to a temperature of, say, 66. If suitable contacts are arranged to cause the furnace to be shut off when the end of the rod, G, crosses C-D, the point 3 will correspond to the point y' of Fig. l and approach to the control temperature of 70 will have been anticipated by 4.

If the rise in temperature should take place at a slower uniform rate the pivot would move along some line as F--L and, because of the more acute angle at which this crosses C-D, G would not cross C-.D, and shut-off contact would not be made, until the pivot reached point 4 corresponding to some temperature higher than 3, say 68. In this case, because of slower heating rate, approach to the control temperature would be anticipated by only 2 when the shutoff contact was made. Under ideal conditions, with the control perfectly adjusted to the constants of the heating Ysystem, the residual heat of the latter would in either case be just suin'cient to cause further temperature rise to 70 after the furnace was shut olf, as indicated by curved line 3-M. If there was no residual heat, and the rise of room temperature stopped at 66 after the furnace was shut off, then the pivot would start to move along the line toward N, the drag wheel would start to approach this line along a tractrix curve, and the free end of the rod, G, would fall below C-D and again turn the furnace on. This process would repeat itself causing temperature to rise until the control temperature of 70 was reached.

If, on the other hand, the residual heat had been so great as to cause overheating, the pivot would move with room temperature along the line 3-6. The drag wheel would follow and, on a descending temperature, would cause G to cross C--D and turn the furnace on when pivot.

was at point @corresponding to some temperature above 70.\ In this case the furnace would have been shut off at the temperature of point 3, turned on at the temperature of point 6, with anticipation of both decreasing and increasing heat requirements.

Study of Fig. 3 Will show that for a given rate of temperature rise the amount of anticipation will depend upon a combination of factors. If the rate at which the pivot F is moved from left to right is increased, the effect will be the same as though the rate of temperature rise was decreased, that is, there will be less deflection of the arm and less anticipation. If the distance between E and F is relatively small, the curvature of the tractrix followed by E as the temperature changes will be relatively sharp and E will, within a short distance of travel, approximately follow the path of the pivot. In this case the angle which E-G makes with the line C-D will be chiefly determined, except for small changes, by the rate of change of temperature. If the distance between E and F is relatively large, then the tractrix path of E will only slowly approach the line along which the pivot moves. The anticipating lead of rod end G will in this case be chiefly proportional to the amount of temperature change, at the outset, and the rate of change will become the principal controlling factor only after this rate has continued for some little time. For any angle of E-G,'the amount of anticipation is directly proportional to the length of F-G.

From the foregoing it becomes apparent that there is considerable latitude in the design of a control, to operate in the manner described, to meet the requirements of different control problems. With suitable variations some of which will be indicated, this principle may be adapted to control of many variable quantities besides heat, such as acidity. pressure, speed, etc., and is further adapted to control rates of change independently of absolute quantity. In the illustration which has been given, for example, control contacts could be so mounted as to move with the pivot, F, and cause the furnace to be shut 0E or turned on when the rate of heating or cooling exceeded a certain value, regardless of the temperature. It further becomes apparent that by suitable choice of constants, including the speed at which pivot F moves from left to right, control may be gained over changes which take place slowly, over many hours, or rapidly, during a fraction of a second. Choice of constants must be determined by average operating conditions for each application. Theoretically perfect control will seldom be gained, but apparatus designed to employ the principle whichhas been described has a wide range of llexibility, and in most applications will virtually eliminate the objectionable hunting described in connection with Fig. l. Special devices to expedite stabilization at desired control values, and for other purposes, will be described in connection with speciiic designs of control apparatus.

The various designs and combinations of apparatus to be described show suitable applications of the foregoing principles, but many other designs may be employed to give similar results. My invention includes the principles, as well as the speciiic designs and combinations, which are described.

Fig. l together with Figs. 5 and 6 shows in semi-diagrammatic form a control apparatus employing the principle which has been described. A cylinder l attached to shaft 2 revolves on fixed bearings. The cylinder is revolved at constant speed in the direction of the arrow through gear chain 4 from shaft Ei, which is connected to a small synchronous motor M1, as for example an electric clock motor. Rolling on the surface of I is a small wheel, Il, which revolves freely in bearings, 1, in the forked end of a bar, 8. The latter is attached to shaft 8 which pivots freely in bearings of support 4I5 which is attached to a base of insulating material, Ill. A bronze spring 20 (Fig. 6) makes electrical contact from I5 to 8 through 9. Attached to the end of 8 is a flexible bronze strip I9 which makes contact with metal plates II or I2 mounted on an insulating support.

The insulating base I4 is attached to a metal block, IE (Fig. 6) through which screw I1 passes in a threaded hole. The screw I1 revolves freely in fixed bearings, supports the assembly I4, I5 and I6, and at the same time moves it from left to right in relati-on to cylinder I, or vice versa, depending upon the direction of rotation of the screw. Attached to the end of I1 is a cog wheel, 2|. A double ratchet, 22 is attached to the end of bar 23 which rocks in pivot 24 on the upper end of bar 21 (Fig. 5). This bar is supported on hinge 29, attached to the base, 28 and is connected through link 3U from pin 3| to the crank 32 which revolves continuously with the cylinder drive gears. As 5 turns, the bar 21, and the assembly attached to it, are continuously rocked back and forth in a direction normal to the axis of screw I1.

A solenoid coil 2S, having a divided winding is mounted on 21. An iron plunger is centrally suspended in the solenoid by wire 25 hanging from the end of bar 23. When no current is ilowing in either half of the solenoid the spring 33 holds both teeth of the ratchet out of contact with the cog wheel 2|, as the ratchet is moved back and forth with the rocking of 21. If current flows in the lower half of the solenoid the right hand end of 23 (Fig. 5) will be pulled down, the lower ratchet will be brought into contact with the teeth of 2|, and 2| will be caused to revolve in a clockwise direction. If current flows ence to control of temperature.

only in the upper half of the solenoid, wheel 2| will be moved in a counterclockwise direction. Depending upon the direction of rotation of 2| and the screw I1 to which it is attached, the block I6 and the assembly attached to it will be moved to the left or td the right in relation to cylinder I.

Attached to I4 is a flexible contact strip, I8, which makes contact with a wire wound resistance coil, I9. If the latter is incorporated in a suitable circuit for the electrical measurement of temperature, pH, etc., and the solenoid is connected to engage the ratchet in one direction or the other when the circuit is out of balance, the contact I8, and the assembly to which it is attached, will be moved as necessary to restore balance. The measuring circuit will be selfbalancing and the position of I8 on Iii will vary with the temperature or other variable which is being measured or controlled. Limit switches, which would be required in practice, are not shown. p

As contact Iii is moved the pivot d will be moved correspondinglyo The weight of bar 8 and wheel d, aided by light tension on contact spring IU will keep the wheel from slipping sideways on the surface or the cylinder l, if this is of suitable material, and, because of lesser friction, the end of ill which is in contact with II or I2 will therefore move in the same direction as I8 but at a faster rate. lf, as indicated above, the resistance I9 is connected in suitable circuit with a device sensitive to changes in the variable quantity being regulated and if the contacts II and I2 are suitably connected with means for increasing or decreasing the supply of corrective agent, we then have means of automatically duplicating the regulating conditions which were discussed in connection with Fig. 3 with refer- The wheel 6 of Fig. 4 corresponds to E of Fig. 3, 9 corresponds to F and I0 to G.

Closing of low temperature contact 53 similarly causes I4 etc. to move toward the right. Adjacent and local to the thermostatic element is a small electrical resistance heater, 51, which is partly in series and partly in parallel with resistance I9 through contact I8 which is attached to base I4. Resistance I9 and external resistance 58 are in series with each other and connected across suitable terminals of trans-- former 55 or other suitable source of current. As contact I8 is moved toward the left the amount of current bypassed from I9 through 51 will decrease, and vice versa. Within limits determined by suitable choice of resistance values, and voltage applied, there is some position of contact I8 on resistance I9 which will cause to flow in heater 51 an amount of current just suicient to warm thermostatic unit 50 to the temperature at which it will engage neither contact 54 nor contact 53. When the temperature of the medium being regulated is sufficient to maintain this open contact position, no heat is required in 51 and this temperature is the upper limit of the range of regulation. The lower temperature limit of regulation is that at which the current flowing in 51 when I8 engages the extreme right end of I9 is just sufficient -to heat 50 to the open contact position. Values arek so chosen that when the tractrix contact I0 is at mid position between II and I2, while the dram arm is normal vto the axis of the drum, I, the position of I8 on I9 will be such that heat supplied through 51 will be just sufficient to maintain 5 0 at open contact poall sition between 53 and 54 when the temperature of the controlled medium is at the desired level.

M2 is a motor or other suitable means for increasing or decreasing supply of heat from a main source. When I0 engages I2 current will be supplied to Mz through conductor 65, from 34 through the tractrx arm and contact I0 to I2, and conductor 64 to cause heat supply to be increased. When I 0 engages II a similar circuit will be closed through the conductor 63 to cause heat to be decreased.

In operation the effect of any change in the temperature of the controlled medium is to cause either

contact

53 or 54 to close, thereby operating solenoid 26, ratchet and

cog wheel

22 and 2|, and screw I'I to move contact I8 on resistance I9 in the direction and amount necessary to alter the heat in 51 until 5D is again in midposition, thus constituting a self balancing temperature measuring circuit. Pivot 9 of the tractrx drag arm is also mounted on the same moving base I4 with contact I 8, and moves in the same amount and direction. If we assume that the temperature of the controlled medium is substantially below the desired level, then I4 and the assembly mounted thereon will be in a position well to the right of that shown, and I0 will be in contact with I2, causing increase in main heat supply. As the temperature rises decreasing heat from 51 will be required to hold 50 in open contact position, and I4, etc., will automatically be moved toward the left, moving contact I8 and pivot 9 by like amount. The drag wheel, 6, in contact with revolving drum I will lag behind the lateral motion of the pivot, thereby causing contact I0 on the other end of the drag arm to lead the motion of I8 and 9, whereby it will engage the off contact, II, and shut off the main source of heat before the control temperature has been reached.

At the start of the temperature rise the arms 8 and I0 will have made an increasing angle with its original position as the wheel 6 followed motion of 9, in an approximate tractrx path on the drum. With a continuous and uniform temperature rise this angle increases until it reaches equilibrium at a value determined by the rate of change of temperature and the surface speed of the drum, I. With other factors constant the time and temperature change before the equilibrium angle is reached will vary with the distance from I to 9, but changing the length of the drag link does not alter the nal equilibrium angle. After the equilibrium angle is reached the point of contact of I 0 with H-or I2 will lead the position of I8 by a fixed amount determin d, together with the angle of the drag link, by the rate of change.

If the balancing circuit is so adjusted that at a temperature of 70 contact I0 just touches the on-oi point when the drag link is normal to the axis of I, then as the temperature rises from some lower value this contact will lead the temperature rise and cause the heat to be shut oif at less than 70. As the rate of heating is decreased the equilibrium angle of the drag link will decrease. Revolution of cylinder I will cause the drag link and contact t0 swing toward normal position. If the instrument has been exactly adjusted to the overrunning caused by residual heat in the heating system, this swing will be balanced by the continued but slowing movement of 9 to the left, and contact will stay slightly on the off side until the temperature reaches 70, after which it will turn on or off as necessary to maintain that temperature. If the residual heat is insuicient to bring to control temperature, the on contact will be made and repeated as necessary until control temperature is reached. If for any reason the temperature rises above 70 the drag link will follow, with the drag wheel constantly tracing varying tractrx curves as it seeks equilibrium with changing rates and positions, and within a short period the drag link will be normal to the axis of the cylinder, in a position to the left of the control point, so that the contact will again lead as the temperature drops,

and the heat will be turned on while the temperature is above 70. Anticipation in varying relation to the rate and amount of change is thus gained.

It will be noted by reference to the tractrix curve of Fig. 2 that the rate at which the drag angle decreases falls off greatly as the nal equilibrium position is approached. In the apparatus of my invention this is ordinarily of no consequence, since it is usually best practice to not fully compensate for the lag in response of heating equipment, etc., and the control may be so adjusted that this lag ordinarily causes the control point to be reached and very slightly overrun after each off or on. If, however, the heat or other quantity under control is from a variable source, and the lag varies greatly at different times, the device as above described would cause rather slow approach to the control point when lag was small. This can easily be overcome, to any desired degree, by shortcircuiting a section of the control resistance I8 at the control contact point. If, for example, the control resistance is shorted between

points

43 and 44 of Fig. 4 by a copper band and is suitably adjusted, the effect will be as indicated diagrammatically in Fig. 7. The circuit will be balanced at 70 with contact I 8 touching any part of the shorting band. If the temperature is rising so that the drag link tends to follow path a-b, and if line A represents the location of the shut-off contact in relation to the margins of the 70 band, then when the drag pivot 9 reaches the edge of the band it must have not less than a certain lead angle to make shut-off contact. Shutoff before 70 is reached will take place only if the rate of temperature rise has been sufcient to make the drag link lead angle exceed this minimum value. The same will hold true if the temperature has been falling along the line c-d.

Referring to the approximate tractrx equation which has been given, it will be noted that i,

the rate at which the lead angle decreases progressively becomes `smaller as the angle itself is decreased. By causing the contact at the control temperature to be reached when the drag link and control contact angle are still appreciable, the rate at which control temperature is approached under controlled conditionsv is substantially increased. If this rate is below a minimum value,` which is determined by the Width of the resistance snorting band, in relation to other constants, no shut-off contact (or on contact, with falling temperature) will be made before the control temperature is reached, or at the exact control temperature. When *his tornperature is passed by a very slight amount, hcwf* ever, the Contact i8 must cross the full '-.idth cf,

the s'norting band in order to balance theI circuit, and in so doing will move contact I0 to 'turn heat on or olf as the case may be. The result is that, even when there is no lag in the heating system,

approach to control temperature follows paths as roughly indicated by the broken lines of Fig. 8 instead of the slowly converging full tractrix path of Fig. 2. It will be understood that in actual practice certain minor errors of the instrument, combined with variations in rates of heating or cooling may cause divergence from theoretical curves, but the results are substantially as indicated. By varying the width of the shorting band on the control resistance the minimum rate, below which there willI be no anticipation, may be varied as desired. By centering the band to one side of the break between contacts I I and I2 the minimum rate of approach from above may be made greater or less than that from below the control temperature.

I have discovered that a suitable apparatus, such as that above described, which employes what may be termed the tractrix principle, may be eiectively employed in conjunction with other suitable accessory apparatus to control temperature, acidity and many other variables, and will automatically anticipate requirements to such extent that hunting of the type indicated in Fig. 1 is greatly reduced or eliminated. Changes from one control value to another, or return to a fixed control value after sudden changes in demand, are made smoothly and quickly. Different types of self-balancing mechanism may obviously be used, and the control characteristics may be altered within wide limits by suitable design.v

Instead of using a self-balancing electrical circuit to control movement of the drag link pivot, 9 of Fig. 4, the latter may be attached directly` to the mechanism of a liquid expansion thermometer, pressure gauge or other measuring device which will move it in similar manner. In lack of a self-balancing circuit the rapid approach to control value which has been described cannot be gained by means of a shorting band, but a closely similar effect may be gained by attaching firmly to the movable base I4 a second contact, under I0, whichgalso wipes plates Il and I2. As the angle of l swings from one side to the other the contact I0 must slide over the second contact. In so doing it makes electrical contact with the latter, which at other times is electrically insulated from the wire 34, and control contact with II and I2 is transferred to the second contact spring which moves in direct relationto the change in temperature etc. under control.l By varying the width of the second Contact at the point where III touches and passes over it, and in so doing is lifted from direct contact with II and I2, the band effect above described may be almost duplicated.

This arrangement is shown in Figs. 9, 10 and 11. The lag and lead portions of the tractrix arm, 8 and I0 are shown as in Fig. 4, with the arm attached to pivot 9 in support I5 on the sliding base I4. Contact I8 on resistance I9 in a self balancing circuit are shown, as above -described, but in this case equivalent results may be gained if the assembly mounted on sliding base I4 is moved, in responseto changes in the variable, by other means. Also rigidly' attached to base I4 is an arm on which flexible contact 6I is mounted in such manner that it constantly engages contact II or I2 and, unlike II), moves directly with the pivot S. At 62 there is a widened portion or attachment to 6I, bent downward at its extremities, over which the contact III must slide in swinging from one side to the other relative to 6I. In the top view contact I0 is shown at an angle to one side, engaging contact I2. In the side view contact I0 is shown lifted on 62 from contact I2 while at some lesser angle with or directly above 6I. The operation is as follows.

Assume that in a drop of temperature from above control level, for example, contact swung to the lead angle shown to anticipate heat requirement, engage I2 and turn on additional heat from the main supply. If control is only through I0, and there has been any excess of anticipation, the tendency is for I0 to swing back and forth between I2 and II as its pivot moves to the right, alternately turning on and shutting off heat and slowing approach to control temperature as it makes decreasing angle with its neutraler mid position. With BI and 62 mounted as shown, however, contact I0 remains in control only until its angle with 6I decreases to a point where it starts to slide over 62 and in so doing is lifted from.I2 or II as the case may be. If, at the moment, IIJ has been engaging the on contact, I2, while 6I engages the off contact II, control will be transferred from I0 through 62 and 6I to II, shutting oif the heat. So long as further change is at the same or a lower rate there will be direct control through 6I without anticipation, expediting approach to control level. If the rate of change exceeds the predetermined value it will cause I0 to move away from contact with 62 and resume anticipating control.

One form of suitable assembly employing the foregoing in connection with regulation of temperature is for illustration further shown in Fig. 4. This assembly employs a temperature measuring and regulating device further described and claimed in a separate application. A bi-metallic thermostat bar 50 is located at the point where temperature is to be controlled. The bar 50 is mechanically adjusted so that at the -highest temperature of the range through which anticipating regulating is desired, its free end will lie between and be disengaged from the high temperavture and

low temperature contacts

54 and 53 respectively. The latter are connected to the two halves of the winding of solenoid 26, the circuit being completed, when bar 50 touches either contact, through the transformer 55 or other source of current and through conductor 41-56. When the circuit through 54 is closed the lower ratchet dog 22 engages gear 2I during each forward motion of the rocking support, and causes screw I1 to move the base I4 and the assembly mounted on it toward the left.

Many modifications of and additions to the tractrix mechanism are possible, to gain specific desired effects. If, for example, it is desired'to *gain regulation as described in connection with Fig. 4, but to set a predetermined maximum limit on the rate at which change may take place, rate limit contacts may be mounted on the sliding pivot base, I4, to be engaged by the drag arm in either direction when the predetermined rate of change is exceeded. Figs. 17 and 18 show a form of such limit contacts which may be used in an electrical control system such as that of Fig. 4, the moving base I4, arms 8 and I0, pivot 9 etc. of the two figures corresponding. Attached to the base I4 and insulated from each other except when in contact as will be described, are six spring contact strips, numbers 66 to 'II inclusive. Attached to the free ends of 61 and 10 are rods of insulating material, 12 and 13, against which the drag arm, 8, presses when the rate of change causes it to assume a suificient angle in one d1- 0 hasrection or the other. When arm 8 is between these limit positions contact 61 engages contact 68 and completes the circuit 35-63 from off contact plate I I to the motor, as shown in Fig. 4. Contacts 68 and 'I0 similarly engage to complete the on circuit. Under these conditions operation will be as previously described. If, for example, the temperature has been too high and starts to drop at more than the predetermined limit rate, before the fall has been suiiicient to cause the anticipating arm, I8, to engage the on contact, I2, then 8 will press against I2 and cause the circuit between 61 and 68 to open while at the same time making contact between 61 and 66. Since I8 is, under these conditions, in contact with II, the circuit 65--ID-I I-35 to 64 will be closed and cause heat to be turned on to check the rate of temperature drop. Similar behavior, to turn oi heat, results in the case of too rapid an increase in temperature from below control level.

Means for regulating to a predetermined rate of change is shown in Figs. 19 and 20. In this case, again, I4 and other similarly numbered parts correspond to those of Fig. 4 except that

terminals

35 and 36 are disconnected from contact plates II and I2 and connected, respectively` to contact plates 'I5 and 'I4 attached to the moving pivot base I4. A spring contact 16 attached to drag arm 8 engages one or the other of these contact plates and closes the corresponding circuits. If the opening between the contact plates is at one side of the center line, as shown, then the on circuit will be closed only when arm 8 makes an angle greater than a with its mid position, and at any lesser angle, or if on the other side, the off contact will be closed. Since contact of the drag wheel on the revolving drum causes arm 8 to maintain angle a only when the temperature is dropping at a denite rate it follows that with any departure from this rate on or oi contacts will be engaged as necessary until the desired rate has been regained. It will be understood that the foregoing examples in connection with heating and cooling are for illustration only, and that with substitution of equivalent apparatus it is possible to gain equivalent results in many other types of control problem.

Many other Variations of design are possible. If lag. rather than lead of control is desired, the control contacts II and I2 etc. may be placed between 6 and 9. A variety of modiiications to meet special control requirements will be obvious, as will suitable accessories such as limit switches to stop movement of I4 at either end of the screw I1.

Adjustment to different control Values may be gained in a Variety of ways, as by change in external resistance of the balancing circuit, movement of I3 and the attached contacts, or by dividing II and I2 into a greater number of contact plates and changing the connections to these plates as desired.

The foregoing descriptions have referred to control of heat etc. when control only of full on or full 01T is required. In many applications it is desirable to have partial or complete proportioning of heat, alkali ilow, etc., to constantly balance the demand. The anticipating features of the tractrix control may be combined with proportioning devices with especial advantage. Fig. 12 illustrates one form of suitable apparatus. The anticipating arm, I0, pivot 9, moving base I4 etc. are as previously illustrated and described.

A rod or cylinder of insulating material, l1, revolves constantly on shaft 18 mounted in fixed bearings. Mounted on the surface of 11 are two contact areas, and 8|, of conducting material and so tapered that on one side of 'I'I the conducting areas are adjacent and on the other side are appreciably separated, as indicated.

Brushes

83 and 84 make continuous contact with these two conducting areas and are in turn connected to the two halves, 85 and 86 of the divided field winding of a. motor for regulating the supply of heat or other variable under control, 81 being the commutator of the motor. When the variable is at the desired control level the tractrix contact arm I8 will lie in a position normal to the axis of the proportioning switch cylinder, TI, and during each revolution of the latter will be continuously insulated from the motor contacts, touching only the insulating area IIl--82. Any change from control level will cause arm I0 to move to one side and engage contacts 8U or 8I during part of each revolution of l1, thereby causing the regulating motor to revolve in desired direction during the time of such contact. The time of contact during each revolution of TI, and resultant period of motor operation, progressively increases with increasing departure of I0 from the mid position, and consequently causes inc reasingly rapid change in corrective supply to the controlled variable as the amount and rate cf departure from control level increase. Since the motor is inoperative when arm I0 is in midposition, regardless of its own position. stabilization will be gained when corrective supply just balances demand at the control level. The anticipation gained by means of the tractrix is especially desirable with this type of proportioning mechanism, which otherwise tends to overrun badly.

Semi-proportioning, by turning supply on and oi during xed time cycles for periods the relative length of which are in proportion to demand, may be gained, together with anticipation, by using the tractrix mechanism with a revolving cylinder switch of the type illustrated in Fig. 13. Operation is similar to the described above, but in this case as the cylinder 88 revolves on shaft 89 the contact IO alternately engages conducting areas 90 and SI which are separated by insulated space 92. Motion of IIJ to the right of mid position increases the length of periods during which the motor is turned in, say, on direction and decreases offi operation, and vice versa.

It is obvious that considerable latitude is permissible in shaping of contact areas and speed of switch revolution to meet specic conditions.

In many control devices now commonly used proportioning is gained by a double potentiometer circuit, one part of which is varied in proportion to demand, and the other balanced by the response of the control motor, The tractrix control as first described and illustrated in Fig. 4 may advantageously be used in connection with such devices by substituting the motor control potentiometer resistance for the contacts II and I2 of that figure. Fig. 14 indicates the arrangement diagrammatically. The numbers correspond to those of Fig 4. a is for example a thermocouple, b a galvanometer relay controlling the selfbalancing potentiometer circuit I8, I9, etc. The position of contact arm IU of the tractrix unit on one half of the motor potentiometer circuit regulates the operation of the proportioning control motor through contact c which engages the other portion of the motor control resistance, c

2. A regulating device employing the tractrix control principle, comprising an arm which is at one point connected by frictional contact with a moving surface, is pivoted at another point which moves laterally to but does not follow the motion of the surface in response to changes in value of the variable being controlled, and at another point or points which lead or lag behind the motion of the pivot point engages contacts for regulation of the variable under control, all substantially as described.

3. An automatic regulating mechanism comprising an arm which is at one point connected by frictional contact with a moving surface, is at another point attached to a pivot, the arm engaging one or more regulating contacts at points which lead or lag behind the motion of the pivot, the pivot being connected to a contact with an electrical resistance in circuit with a device sensitive to changes in the value of the variable being regulated and also in circuit with means for causing the pivot to move in one direction or the other lateral to the motion of the surface when the circuit is unbalanced, the circuit values being such that change in value of the regulated variable will affect the sensitive element in such manner as to unbalance the circuit and cause the pivot and contact to move in the required direction and amount until the circuit is again balanced, a source of electrical current of approximately uniform potential, and a short circuiting band or widened area of uniform potential on the control resistance at the approximate point where the pivot contact touches when the circuit is balanced at the desired value of the regulated variable.

4. An anticipatory regulating mechanism comprising an arm which is at one point connected by frictional contact with a moving surface, is pivoted at another point which is moved laterally to the motion of the surface in response to changes in value of the variable being regulated, and at another point or points which lead or lag behind the lateral motion of the pivot engages electrical contact means which regulate compensation for departure of the variable from the desired condition, a second contact arm which moves directly with the pivot and engages the same regulating contacts, the second contact arm being disconnected from the electrical control circuit except at times when the pivoted arm is directly above such arm or makes less than a predetermined angle with such arm, and means whereby the pivoted arm is liftedl from direct engagement with the regulating contacts and makes control contact indirectly through the second arm when the angle is less than a predetermined amount.

5. An anticipatory regulating mechanism comprising an arm which is at one point connected by frictional contact with a moving surface, is pivoted at another point which is moved laterally to the motion of the surface in response to changes in value of the variable being regulated, and at another point or points which lead or lag behind the motion of the pivot engages contact means which regulate compensation for departure of the variable from desired condition, independent contact means which are mechanically connected to and move with the pivot being provided, and so located with respect to the pivotcd contact arm that they will be engaged when rate of change of the regulated variable causes said arm to exceed a predetermined angle, said independent contact means being connected to means for retarding rate of change of the regulated variable regardless of absolute value of such variable, until such time as the rate of change and angle of the pivoted contact arm have fallen below predetermined values.

6. A-rnechanism for regulating rate of change of a variable condition, comprising an arm which is at one point connected by frictional contact with a moving surface, is pivoted at another point which is moved laterally to the motion of the surface in response to changes in the value of the variable being regulated, and, at another point or points which lead or lag behind the lateral motion of the pivot, engaging means for increasing or decreasing the value of the regulated variable, such means being mechanically connected to follow the motion of the pivot, and so located with reference to the pivoted arm that they will be engaged by the latter at a predetermined angle and tend to cause the value of the regulated variable to increase or decrease at a predetermined rate.

7. An automatic system for regulating temperature, comprising a centrally pivoted arm which is in frictional contact with a moving surface near one end and near the other end engages contacts to operate mechanism for increasing or decreasing'heat supplied from a main source to the regulated medium, motor driven means for moving the arm pivot in one direction or the other lateral to the motion of the surface, a thermostatic element provided with contacts which actuate said means for moving the arm pivot when temperature of the thermostatic element is above or below predetermined value, an electrical resistance heater adjacent and local to the thermostatic element, said heater being partly in series and partly in parallel with a control resistance connected across a source of current through a variable contact mechanically connected to the arm pivot, the relative values of heater and control resistances being such that change in heat supplied to the thermostatic element from the heater is substantially proportional to movement of contact on the control resistance, a shorting band or widened area of uniform potential on the control resistance at the Contact position approximately corresponding to desired temperatures of the medium being regulated, separate means actuated in conjunction with means for controlling heat from the main source whereby wattage of current flowing in the thermostat heater is increased Vin predetermined amount during periods when the main heat supply is turned on, clock controlled means for periodically and progressively varying wattage of thermostat heater current through a predetermined range substantially independent of other control adjustments, and separate clock controlled means for varying the thermostat heater current at desired times and in desired amounts, the separate variations of heater current being eil'ected through variations in the control resistance which is parallel with the heater, independent of the arm pivot contact with such resistance.

8. An automatic system for regulating temperature, comprising an arm at one point in frictional contact with a moving surface, and pivoted at another point which moves in response to changes in the temperature being regulated', a thermostatic element which engages electrical contacts when the temperature of said element varies from predetermined values, an electrical resistance heater adjacent and local to said thermosatic element and-partly in series, partly in parallel through a contact mechanically connected to the arm pivot with a control resistance connected across a source of current, motor operated means actuated by the thermostat contacts to move the arm pivot and control resistance contact as necessary to maintain the thermostatic element at approximately constant temperature during changes in temperature of the surrounding regulated medium, and contact means for increasing or decreasing heat supplied to the regulated medium from a main source when such contacts are engaged by an extension of the pivoted arm at a point which leads or lags behind motion of the pivot.

9. An automatic regulating device comprising an arm which is at one point connected by frictional contact with a moving surface, is pivoted at another point which is moved laterally to but does not' follow the motion of the surface in response to changes in value of the variable being regulated, and at another point or points which lead or lag behind the motion of the pivot engages tapered contact areas on a revolving proportioning switch, means being provided whereby the value of the regulated variable is progressively increased or 'decreased during the times of contact of said arm with one or the other contact areas.

10. An automatic regulating device comprising an arm which is at one point connected by frictional contact with a moving surface, is pivoted at another point which is moved laterally to but does not follow the motion oi the surface in response to changes in value of the variable being regulated, and at another point or points which lead or lag behind the motion of the pivot engages a tapered contact area on a revolving periodic proportioning switch, means being provided whereby the value of the regulated variable is increased during times of contact of arm with said area and decreased at other times, or vice versa.

11. An anticipatory regulating mechanism comprising an arm which is at one point connected by frlctionai contact with a moving surface, is pivoted at another point which is moved laterally to the motion of the surface in response to changes in value of the variable being regulated, and at another point or points which lead or lag behind the lateral motion of the pivot engages contact means which regulate compensation for departure of the variable from desired condition, a second contact arm which moves directly with the pivot and engages the same regulating contacts as the mst arm, the second contact arm being disconnected from control contact except at times when the pivoted arm makes less than predetermined angle with such arm, and means whereby the pivoted arm is disengaged from control contact and control is transferred to the second arm when the two arms make less than predetermined angle with each other.

12. An automatic regulating device comprising an arm which is at one point connected by frictional contact with a moving surface, is at another point attached to a pivot which may be moved laterally to the motion of said surface, said arm at one or more points which lead or lag behind the lateral motion of said pivot engaging means to alter the condition of the variable being regulated, a contact which moves in harmony with the lateral motion of said pivot and engages an electrical resistance in circuit with .a device sensitive to changes in value of the regulated variable, means whereby said circuit becomes balanced only when the lateralposition of said pivot and said contact corresponds with the value of the regulated variable, means whereby unbalance of said circuit causes corrective motion of pivot and contact until said circuit is balanced, while at the same time causing leading or lagging engagement of said pivoted arm with means which correctively alter the condition of the regulated variable.

13. An anticipatory regulating mechanism comprising an arm which is at one point connected by frictional contact with a moving surface, is pivoted at another point which is moved laterally to the motion of the surface in response to changes in value of the variable being regulated, and at another point or points which leador lag behind the lateral motion of the pivot engages means which regulate compensation for departure of the variable from the desired condition, a second arm which'moves in harmony with the pivot but is disengaged from regulating means when rate of change and angle of the first arm exceed predetermined minimum values and means whereby the second arm is caused to engage the regulating means when rate of change and angle of the iirst arm fall below predetermined values while first arm is at the same time disengaged from the regulating means.

14. An automatic regulating device comprising an arm which is at one point connected by frictional contact with a moving surface, is pivoted at another point which is moved laterally to but does not follow the motion of the surface in response to changes in value of the variable being regulated, and at another point or points which lead or lag behind the motion of the pivot engages an electrical resistance in the circuit with proportioning means whereby the supply of corrective agent is made to vary. in harmony with position of said arm on said resistance.

15. An automatic regulating device comprising an arm which is at one point connected by frictional contact with a moving surface, is pivoted at another point which ismoved laterally to but does not follow the motion of the surface in response to changes in value of the variable being regulated, and at vanother point or points which lead orlag behind the motion of the pivot engages means which varies the supply of the corrective agent, in proportion to the movement and position of the contact arm at. the point of such engagement.

16. An automatic system for'regulating temperature comprising a centrally pivoted arm which is in frictional contact with a moving surface nearrone end and near` the lother engages contact to operate mechanism for increasing or decreasing heat supplied from a main source to the regulated medium, motor driven means for moving the arm pivot in one direction or the other lateral to the motion of the surface, a thermostatic element provided with contacts which actuate said means for moving the arm pivot when temperature of the thermostatic element is above or below predetermined value, an electrical resistance heater adjacent and local to the thermostatic element, a source of current and a control resistance engaged by a contact moving in harmony with the arm pivot whereby current flowing in the thermostat heater may be varied.

17. An automatic regulating device comprising a self-balancing electrical circuit connected with means sensitive to changes in the variable being regulated, means for anticipating changes in demand, substantially in proportion to rate of change, means whereby regulation is controlled substantially in proportion to such anticipated -demand when rate of change exceeds predetermined value, and a short circuiting band or widened area of uniform potential on the balancing resistance whereby anticipation is cancelled and approach to control point is expedited when rate of change and amount of departure fall below predetermined valuesl8 An automatic regulating s'ystem compris ing means sensitive to change in value of the variable being regulated, connected means which lead or lag behind changes in the true value of the variable by amounts which vary with the rate of change, connected means which vary in direct harmony with changes in value of the regulated variable, and means whereby the leading or lagging element controls supply of the corrective agent when rate of change exceeds predetermined values and means whereby the supply of the corrective agent is controlled by the member which moves in direct harmony with changes of the variable at times when rate of change is less than predetermined value.

19. In measuring and control instruments, the combination with measuring means of a revolving drum, a wheel revolving in contact with said drum, means whereby said wheel is withheld from following the motion of the surface of said drum but said wheel may follow its line of rolling Contact lateral to said surface when the plane of said wheel is turned at an angle to the line of motionvof said surface, and means responsive to said measuring means whereby the angular deflection of the wheel and its motion lateral to the moving surface of the drum are guided in response to changes in value of the measured quantity.

20. In a regulating instrument, the combination with means responsive to changes in value of the regulated quantity of a revolving drum, a wheel revolving in contact with said drum, means whereby said wheel is withheld from following the motion of the surface of said drum but may follow its line of rolling contact lateral to the motion of said surface when the plane of said wheel is turned at an angle to the line of motion of said surface, means whereby said responsive means causes said wheel angle to change as necessary to cause the lateral motion of the wheel with respect to the drum surface to approximately follow the direction, amount and rate of changes ir the regulated condition, means for applying an agent to correct departure of the regulated condition from desired value, and means whereby during change in value of the regulated condition the application of the corrective agent is in part controlled as a function of the angle which said wheel is caused to take in following such change.

21. In a regulating instrument, the combination with means responsive to changes in the regulated condition of a revolving drum, a wheel in contact with and revolving against said drum, a pivoted arm to which said wheel and its supporting mount is suitably attached, means connected to said responsive means whereby the path of said Wheel on said drum is controlled as necessary to cause said arm to assume an angle which is a function of the rate of change taking place in the regulated condition, means for applying a corrective agent, and means whereby application of said corrective agent is in part a function of the angle assumed by said arm.

22. In a regulating instrument, the combina tion with means responsive to changes in the regulated condition of a lever arm, means whereby one point on said arm is moved laterally from its median position in response to direction and amount of departure of the regulated condition from desired value, means whereby said arm is angularly deflected about said point in response to the direction and rate at which change is taking place, means for applying a corrective agent, and means whereby application of said corrective agent is controlled by the movement of a second point on said arm.

23. In a regulating instrument, the combination of means responsive to change in the regulated condition, means for applying a corrective agent, a control member for regulating such corrective application, means whereby the movement and position of said control member is a continuous function of the direction and amount of departure plus the direction and rate of change during departure of the regulated condition from desired value, and means whereby the movement and position of said control member is a continuous function of the direction and amount of departure minus the direction and rate of change during return toward desired value.

24. In measuring and control instruments, the combination with measuring means of a revolving drum, a wheel revolving in contact with said drum, means whereby said wheel is withheld from following the motion of the surface of said drum but said wheel may follow its line of rolling contact lateral to said surface when the plane of said wheel is turned at an angle to the line of motion of said surface, means responsive to said measuring means whereby the angular deection of the wheel and its motion lateral to the moving surface of said drum are guided in response to changes of value of the measured quantity, a pivoted lever arm, means whereby the pivot point of said arm is moved in response to changes in value of the measured quantity, and means whereby said arm is angularly deflected from a position normal to the line of motion of said pivot by the angular deflection of said wheel during periods when the value of the measured quantity is changing.

25. In measuring and control instruments, the combination with measuring means of a revolving drum, a wheel revolving in contact with said drum, means whereby said wheel is withheld from following the motion of the surface of said drum but said wheel may follow its line of rolling contact lateral to said surface when the plane of said wheel is turned at an angle to the line of motion of said surface, means responsive to said measuring means whereby the angular deflection of the wheel and its motion lateral to the moving surface of said drum are guided in response to changes of value of the measured quantity, a pivoted lever arm, means whereby the pivot point of said arm is moved in response to changes in value of the measured quantity, means' whereby said arm is angularly deiiected from a position normal to the line of motion of said pivot by the angular deflection of said wheel during periods when the value of the measured quantity is changing, means for applying a corrective agent to maintain or re-establish the desired value of the measured quantity, and means whereby application of said agent is controlled by movement of a control point on said lever arm other than said pivot point from the position at which said control point lies during periods when the measured quantity has desired value and no change in value is occurring.

26. In measuring and control instruments, the combination with measuring means of a revolving drum, a wheel revolving in contact with said drum, means whereby said wheel is withheld from following the motion of the surface of said drum but said wheel may follow its line of rolling contact lateral to said surface when the plane of said wheel is turned at an angle to the line of motion of said surface, means responsive to said measuring means whereby the angular deflection of the wheel and its motion lateral to the moving surface of said drum are guided in response to changes of value of the measured quantity., a pivoted lever arm, means whereby the pivot point of said arm is moved in response to changes in value of the measured quantity, means whereby said arm is angularly deflected from a position normal to the line of motion of said pivot by the angular deflection of said wheel during periods when the value of the measured quantity is changing, means for applying a corrective agent to maintain or re-establish the desired value of the measured quantity, means whereby application of said agent is controlled by movement of a control point on said lever arm other than said pivot point from the position at which said control point lies during periods when the measured quantity has desired value and no change in value is occurring, and means whereby the application of said corrective agent is proportional to the movement of said control point -on said arm within a predetermined range.

27. In measuring and control instruments, the

combination with measuring means of a revolving drum, a wheel revolving in contact with said drum, means whereby said wheel is withheld from following the motion oi' the surface of said drum but said wheel may follow its line of rolling contact lateral to said surface when the plane of said wheel is turned at an angle to the line of motion of said surface, means responsive to said measuring means whereby the angular deection of the wheel and its motion lateral to the moving surface of said drum are guided in response to changes of value of the measured quantity, a pivoted lever arm, means whereby the pivot point of said arm is moved in response to changes in value ofthe measured quantity, means whereby said arm is'angularly deflected from a position normal to the line of motion of said pivot by the angular deection of said wheel during periods when the value of the measured quantity is changing, means for applying a corrective agent to maintain or re-establish the desired value of the measured quantity, means whereby application of said agent is controlled by movement of a control point on said lever arm. other than said pivot point from the position at which said control point lies during periods when the measured quantity has desired value and nochange in value is occurring, together with means whereby the rate at which said corrective application is increased or decreased is a function of the amount of departure of said control point from the position in which said control point lies when desired value exists and no change is taking place.

CLARK M. DENNIS.