US2485285A - Strip elongation indicator - Google Patents

Description

oct- 94 K. w. HARRIS 2,485,285

STRIP ELONGATION INDiOATOR Filed June 29, 1945 3 Sheets-Sheet 1 INVENTOR. 72 -./7 KEN/V5771 w. HARE/5 Oct. 18, 1949. K. w. HARRIS 2,485,285

STRIP ELONGATION INDICATOR Filed June 29, 1945 s Sheets-Sheet s a 5 Eg k VOL7'A6E IIIIII llllll INVENTOR.

KEN/V5 TH w. HA 22/5 A TTOlF/VEYS Patented Oct. 18, 1949 STRIP ELONGATION INDICATOR Kenneth W. Harris, Warren, Ohio, assignor to Republic Steel Corporation, Cleveland, Ohio, a corporation of New Jersey Application June 29, 1945, Serial No. 602,374 Claims. (cl. 175-183) My invention relates to lineal measuring devices and concerns particularly methods and apparatus for measuring distance between points on moving strips of magnetizable material such as steel strips.

An object of my invention is the accurate measurement and indication of the amount of elongation given to a strip of steel when it is rolled in a rolling mill, such as a temper rolling mill for example.

In temper rolling of strip steel, the strip is subjected to reduction pressures and pulling stresses that cooperate to elongate the strip in a range of 1% elongation up to elongation, the amount of elongation depending upon the temper of steel strip desired. In general, the greater the elongation, the higher the tensile strength obtained. It has been found in practice that if a known elongation is given a steel strip and the obtained temper is determined by tests in suitable apparatus, the mill operator can reproduce this temper within commercial tolerances by producing the same elongation in subsequent coils of strip steel of substantially the same analysis, heat treatment, width and gage.

In order to adjust the various mill components correctly so as to have the mill produce the desired elongation of a given strip, it has been common mill practice for mill operators to scribe the strip on the entry side of the mill with lines or marks some standard distance apart, such as 10 inches, as the strip is slowly paying oil the uncoilers and entering the mill. If the distance between the scribe marks and the strip is then measured after the strip has passed through the mill, the difference between the spacing of marks on the strip where they were made on the entry side of the mill, and the spacing between the marks after rolling, is the strip elongation. For example, if the scribe lines or marks are 10 inches apart on the strip entering the mill and 11 inches apart on the delivery side of the mill, the strip elongation is one inch, or 10% of the original value. This scribing and measuring operation must be carried out at very slow mill speeds, at approximately 100 feet per minute or less. It has been found that even though a mill is set up for say 10% strip elongation at slow mill speeds, the elongation may vary from the desired value when the mill is speeded 'up to top running speeds, such as 3,000 feet per minute. This variation may be due to various factors such as heating of the mill housings, heating of the mill rolls, slight variations in front or back tensions, electrical maladjustments of the control equipment or any of numerous other factors, impossible for the operator to detect and make necessary corrections for, to maintain the proper elongation. He has no way of accurately knowing what the value of strip elongation is at the high speeds. Therefore, it has heretofore been necessary for considerable quantities of steel to be temper rolled twice or even three times before the desired temper is obtained, simply because the mill operator does not obtain the proper strip elongation in the first rolling.

Tachometer generators driven by rolls in contact with the strip on the entry side and the delivery side of the mill have been proposed to indicate relative speed of the strip after it is elongated compared to the speed before it is elongated. For accurate control of tempering such tachometer generators would be required to indicate accurately over a speed range of to 3,000 feet per minute which represents a ratio of 30 to 1 between maximum and minimum indications.

It is an object of my invention to provide an improved elongation indicator, one which may be used for high speed rolling and which indicates accurately over a wide range of rolling speeds, and is as accurate at one speed as another. A further object is to provide an improved method of indicating elongation.

An object of my invention is to avoid the neoessity of measuring the elongation at one speed and rolling at another in temper rolling. A further object is to measure elongations accurately over wide speed ranges as great as 30 to 1 for example.

A further object is to measure distances or elongations on moving magnetizable strip material without scribing. A further object is to measure distances without any effect on strip which may introduce weakness or start defects or flaws.

An object of my invention is to mark magnetizable material magnetically and detect the marks by magnetically induced voltage.

A further object is to measure distances between magnetic marks by comparing phase relationship between voltages induced by the magnetic marks, the distance between which is to be measured. Still another object. of the invention is to provide an improved follow-up system for automatically indicating distance between voltage-inducing effects in strip material.

Still another object of the invention is to provide a continuous marking and distance measuring arrangement for moving strip material which is independent of slippage of mark actuating devices.

Still another object of the invention is to tenperstripmaterialtothedesireddegreeinasingle' rolling operation.

Other and further objects, featurl, and advantages will become apparent as the description proceeds.

In carrying out my invention'in accordance with a preferred form thereof, marks are placed on the strip being rolled at a known distance apart before the strip is elongated, and then the distance between the marks is measured after elongation, but instead of actually marking the strip with a scribe or other similar mechanical device which may cut int the strip or instead of producing surface marking which may rub oil,

localized magnetic fields are utilized to ili.ark"

the strip. Preferably electromagnets arranged to magnetize isolated spots of the strips transversely to its surface are employed for producing the magnetic mar For measuring the distance between marks, electromagnetic pick-up coils are employed and preferably the relationship between the localized magnetic fleld of a magnetic mark" and the pick-up coil is determined by the phase relationship of the induced voltage. For accurately placing two electromagnetic pick-up coils in the same relationship to two magnetic marks, the difference between which is to be measured, Lie induced voltages are compared in phase and the physical distance between the electromagnetic pick-up coils is adjusted to obtain phase coincidence. The movable pick-up coil has a carriage connected to a dial so calibrated as to indicate the percentage of elongation.

A better understanding of the invention will be afforded by the following detailed description considered in conjunction with the accompanying drawing and the scope of the invention will be pointed out in the claims appended hereto.

In the drawings:

Fig. 1 is a schematic diagram of the general arrangement of apparatus in accordance with one embodiment of my invention in a two stand tandem rolling mill;

Fig. 2 is a perspective view of apparatus at the mill entry side of the arrangement of Fig. 1;

Fig. 3 is a schematic plan view of the rolling mill illustrated in Fig. 1, showing the localized magnetic field pattern placed on the steel strip when a single coil localized magnetic field marking device is employed;

Fig. 4 is a schematic plan view of the rolling mill illustrated in Fig. 1, showing the localized magnetic field pattern placed on the steel strip when a double-coil localized magnetic field marking device is employed with both electromagnetic coils being energized simultaneously;

Fig. 5 is a diagram schematically showing the apparatus arrangement and the electrical circuits of equipment arranged for automatically detecting the phase relationship of two voltages induced in the pick-up coils with means for 'automatically adjusting the spacing between the two- 'pick-up coils to maintain the same phase relationship;

Fig. 6 is a graph representing induced voltage in one of the pick-up coils; and

Fig. 7 is a graph representing voltages induced in the other pick-up coil for diii'erent physical positions of the pick-up coil;

Fig. 8 is a schematic diagram of apparatus arrangement for visually indicating phase relationship between induced voltages in the pick-up coils by means of a cathode-ray oscilloscope.

Like reference characters are utilised throughoutthedrawingstodesignatelikeparts.

Inthetwostandtandemrollingmill f the sake of illustration in Fig. i there is stand of rolls ii for effecting aninitialred and elongation of a steel strip is and a stand of rolls it for eifecting thennal red and elongation of the strip It. The stri is preferably passed through the rolls il Ind from an uncoller It to a re-winding reel II. The strip passes in the direction of the arrow ll.

Electro-magnet means II are provided for magnetizing isolated spots or producing localised magnetic fields in isolated portions of the strip l2, and a pair of flux-responsive spaced pick-up coils II and it is provided for detecting the magnetic effects produced by the electromagnetic means l1. Preferably one of the pick-up coils, for example, the coil II, is movably mounted.

Suitable means are provided for intermittently energizing the electromagnet means I] in order to produce the electromagnetic eifects or "spots" fixed distances apart. Such means for intermittently energizing the electromagnet means ll may take the form of a rotary contact maker and breaker or commutator switch 1i connected in series with the electromagnet means l1 and a source of preferably direct current 22, and rotatively driven by a roller 2! frictionally contacting the strip i2. Preferably a backing roller 24 is provided for increasing the effectiveness of the frictional contact of the roller II with the strip II.

Preferably the magnetic marking means ll comprises pole pieces 25 and it placed on opposite sides of the strip I! so as to magnetize isolated spots of the strip transversely, across its thickness. The form of electromagnetic means illustrated in Figs. 2 and 3 comprises a core 21 carrying a magnetizing coil II and having an air gap in the core between the pole pieces 2! and I. which are preferably pointed or chisel-shaped or wedge-shaped to form a small spot of high magnetic intensity.

A suitable mounting is provided for the pick-up coils l8 and II. For example, as illustrated in Fig. 8, a supporting base II, preferably non-magnetic, is provided carrying a pair of winding forms Ii and 32 for holding the pick-up coils is and II respectively. As illustrated, the winding form 3| is rigidly secured to the support 28, and an adjustable mounting is provided for the winding form 32, including an .iit.

adjusting screw 33 carried in a bracket 34 in the I support 2! and having a knurled hand wheel ll for adjusting the distance between the pick-up coils II and I8. Suitable means are provided for indicating variations in the spacing of the coils II and II. For example, a rack 36 may be pro-- vided which is secured to the winding form 32 of the movable pick-up coil is and a pinion 31 may be provided, engaged by the rack 38, and carrying a pointer 38, cooperating with a scale It. The scale 3! may be calibrated in terms of per cent elongation.

In order to enable the spacing of the coil II and it to be adjusted to conform to the spacing between magnetic marks produced on the strip i2, suitable voltage wave comparison means are amass art and comprise suitable voltage amplifying means together with means for alternately connecting one or-the other of two or more input voltages to a pair of output terminals. The electronic switch 42 as illustrated comprises input terminals '43, and 46, a pair of energizing terminals 46 connected to a suitable source of alternating current 41, and a pair of output terminals 48. The input terminals 43 and 46 are connected to the pick-up coil ll through conductors 40, II and 52, and the input terminals 44 and II are connected to the pick-up coil ll through conductors 52 and II. Internal vacuumtube circuits for switching the output terminals 66 from the input terminals 43 and 46 to the input terminals 46 and I5, and back again at a relatively highfrequency such as 2,000 cycles per second for example are not shown, since such circuits are well known to those skilled in the art.

The oscillograph 4| comprises suitable internal mechanism including a cathode-ray oscilloscope having a screen 64 which is visible in the drawing,

energizing terminals 66 which may be connected to the current supply source ll, input terminals l6 connected to the output terminals 48 of the electronic switch 42 and suitable beam-sweep frequency adjusting means (not shown), having a sweep speed setting hand and indicating pointer The manner in which the apparatus operates to enable a measurement of elongation to be made will be apparent from a consideration of the drawing with particular reference to Figs. 3, 6 and 'l. The form of rotary switch 21, illustrated in Fig. 2, comprises a drum 58 composed of insulating material, having a slot in which a segment 59 composed of conducting material is titted and which is adapted to contact a pair of brushes 6|. With each rotation of the drum 68, whenever the conducting segment 69 comes under the brushes 6|, the circuit is closed from the direct current supply source 22 through the energizing coil 28 of the magnetic marker II. An intense magnetic field is produced between the two tips of the pole pieces 25 and 26 across a localized spot in the strip l2. Inasmuch as amost all steel strip, iron-containing material, and some other magnetizable materials have some degree of magnetic retentivity, the effect of a momentary application of current to the coil 28 and a momentary setting up of magnetic field of great intensity through the strip I2 is to produce a localized permanent magnet or a retained localized magnetic field across the strip 12 with a pole of one polarity in a spot on the top surface of the strip l2 and a pole of the opposite polarity in a corresponding spot at the lower surface thereof.

When such spots of localized magnetization pass under the pick-up coils l8 and i6, voltages are induced in the pick-up coils. The intensity of the voltage depends upon the strength of the magnetization and also upon the speed with which the strip I2 is moving. A voltage of one polarity will be produced as the magnetization approaches a pick-up coil and a voltage of the opposite polarity will be induced as the magnetization leaves the pick-up coil. Accordingly, a roughly sinusoidal voltage impulse will be produced whenever a localized spot of magnetization passes under one of the pick-up coils l6 and it. Although the wave term may not constitute a true sine wave,'I find that the behavior of the 6 apparatus may be explained in terms of approximate sine wave induced voltages.

Since the rotary switch 2| is driven'by the frictional contact of the roll 22 with the strip l2, the speed of the switch 2] will be proportional to the speed of the strip l2 and a given number of current impulses will be passed through-the coil 26 for given distance of travel of the strip 12. Consequently, spots of localized magnetization 62 will be produced at fixed intervals along the strip l2. For example, arrangement may be such that the spots 62 are 10 inches apart. Whenever two adjacent spots pass under the adjacent coils II and I9, voltages will be induced therein. When one of such spots passes under the coil II, a voltage will be induced which may be represented by the sine wave illustrated in Fig. 6. A voltage loop 63 of one polarity is produced as the spot 62 approaches the pick-up coil l6 and a voltage loop 64 of the opposite polarity is induced as the localized magnetization spot 62 leaves the pick-up coil l6. At the instant represented by the vertical line 65 induced voltage falls to zero as the spot 62 passes directly under the coil l8.

A similar voltage wave is induced in the coil l9. If the spacing between the magnetic spots. 62 is the same as the spacing between the coils l8 and 19, a voltage wave 61 will be induced in the movable coil I! which is in phase with the voltage wave 66 as illustrated in Figs. 6 and 7. However, if the spacing between the coils l6 and I6 is less than the spacing between the magnetic spots, a magnetic spot will pass under the coil l6 before the spot behind it has passed under the coil It, so that a voltage 61 will be induced in the coil [9 which has an earlier phase than the voltage 66 induced in the coil IS. The voltage induced in the coil is is represented by the full 9 line 61 in Fig. 7 for the in-phase condition, and

by a dotted line 61 for the advanced phase condition where the spacing between the coils I 6 and I9 has not been adjusted to correspond to the spacing between the spots of magnetization 62. .Visual indication of the voltage waves 66 and 61 is obtained upon the screen 56 of the oscilloscope ll. This is accomplished by adjusting the sweep-frequency setting hand 51 to correspond to the speed of the rotary switch 2| so that by taking advantage of the phenomenon of persistence of vision, a lineal trace 66 will appear on the screen 56 corresponding to the voltage 66.

However, if the voltages 66 and Glare not in phase two wave traces will appear upon the screen of the oscilloscope 4i corresponding in relative position to the waves 66 and 61' 0! Fig. 7. The adjusting wheel 35 is then turned in one direction or the other as required to bring the two wave traces into coincidence. The percent of elongation may then be read from the scale 39.

It will be understood that the apparatus may initially be calibrated by passing a strip l2 through the rolls H and I3 with the rolls set to produce no reduction, and no elongation, in order to determine the point on the scale 39 corresponding to zero elongation. The percentage elongation is the ratio between the distance moved by the coil holder or winding form 32 from the zero elongation position, to the distance between winding forms 3| and 3-2 when the form 32 is set in the zero elongation position. Thus as soon as the zero elongation point on the scale 39 has been ascertained, the points for various percentages of elongation may be obtained by physical measure- 7 ment of the distances between the winding forms 8| and 82 for diflerent positions of the pointer 88 on the scale 88.

Maniiestly the magnetic marker I1 does not mar the strip surface or produce cuts which may later develop into dangerous flaws.

As illustrated in Fig. 3, the apparatus may be operated in such a manner as to produce a continuous repetition of evenly spaced magnetic spots 82 upon the strip I2, utilizing a single electromagnetic coil 21 with a single pair of pole pieces 28 and 28. However, my invention is not limited to the specific arrangement thus far described and particularly illustrated in Fig. 3. For example, if desired, as illustrated in Fig. 4, magnetic marking means I1 may be provided comprising two separate magnetic cores 89 and 1| with separate air gaps having pole pieces corresponding to the pole pieces and 28 of the single magnetic core 21. Preferably, one of the magnetic cores H is so shaped or so positioned as to produce a magnetic spot 12 which is further from the edge of the strip I2 than the magnetic spot 18 produced by the magnetic core '88. Preferably also the cores 89 and H have energizing coils 14 and 18 connected in series with suitable switching means and the current source 22 so as to produce the magnetic spots 12 and 13 simultaneously: Thus regardless of the frequency of the switch 2i and independently of any slippage which may take place in the driving of the switch 2|, successive pairs of magnetic spots 12 and 18 will be produced for each energization of the coils 14 and 15, which spots 12 and 18- are spaced longitudinally a fixed distance corresponding to the longitudinal spacing between the magnetic cores 88 and TI. Although a frictionally-driven rotary switch 2i has been shown also in connection with the arrangement of Fig. 4, it will be understood that the invention is not limited thereto and any suitable type of intermittently acting switch may be utilized for energizing the magnetic marker coils 14 and 15 simultaneously. It is to be understood that when the double magnetic marker arrangement of Fig. 4 is employed, the pick-up coils I8 and I9 will be positioned at different distances from the edge of the strip I2 in order that the spots of localized magnetization 12 and 13 may pass directly under the coils I8 and I8 respectively. The comparison of the phase of induced voltages and the adjustment of the hand wheel is carried out in the same manner when the magnetic spot arrangement of Fig. 4 is employed as when the magnetic spot arrangement of Fig. 3 is employed.

' Preferably, however, for the sake of greater precision and increased speed of manipulation, an automatic phase indicating and pointer adjusting arrangement is provided such as illustrated, for example, in Fig. 5.

For automatically and continuously detecting differences in phase between the voltages induced in the coils I8 and I8 and readjusting the relative position of the coils to maintain phase coincidence, electronic phase detection circuits and a motor-driven follow-up system, are preferably employed as illustrated in Fig. 5. The apparatus illustrated in Fig. 5 comprises a reversible direct current adjusting motor 8|, coupled to the screw 38, and a pair of co-related electronic circuits 82 and 83 responsive to the voltage outputs of the coils I8 and i8 respectively and electrically connected to the motor 8| for driving it in whichever direction is required to maintain phase coincidence between the output voltmamas 8 ages of the coils l8 and II. Themotor 8| may be provided with a speed adjusting field rheoetat 88.

The electronic circuit 82 comprises an amplitying stage 88 and a power stage 88. The amplifying stage 88 may comprise a suitable voltage responsive amplifying electric discharge device such as a vacuum'tube having a control electrode or grid 81 resistance-capacity coupled to the coil I; The common conductor 82 of the coils I8 and .I 8 is preferably grounded as illustrated by the ground connection 88.

Although my invention is not limited to electronic tubes of a particular type, preferably for the sake of obtaining suflicient power to control the operation and direction of rotation of the motor 8I, the power stage 88 comprises an electronic discharge device of the type carrying current independently of control voltage upon ignition thereof, such as a thyratron, gas or vapor filled tube for example. The tube 88 comprises an anode 88, a cathode 8i and a control electrode or grid 82. For energizing the electronic circuit 82, a plate power source 88 is provided which is connected on the negative side to the ground connection 88. The vacuum tube 88 is connected to the plate supply 88 through an anode resistor 98.

The anode 89 of the thyratron tube" is connected to the positive terminal of the plate supply 93 and its cathode BI is grounded through a cathode resistor 88 which is by-passed by a condenser 88. The control electrode or grid 82 is resistance-capacity coupled to the anode 81 of the vacuum tube 88 by means of a coupling condenser 88 and a grid resistor 98. The circuit of the thyratron 88 is connected for controlling the polarity and magnitude of current supply to the armature winding of the motor 8I. Preferably a differential arrangement is provided comprising a separate generator I8I connected to the armature of the motor 8I by a pair of conductors I82 and having a differential field winding, comprising opposing field coils Ill and I88. The coil I83 is connected in series with the anode lead or the thyratron tube 88. Suitable rotary driving means such as a three-phase motor III for example is provided for the generator I8I, which is preferably of the high-speed voltage-build-up type such as those sold as amplidyne generators.

The electronic circuit 88 is similar to the electronic circuit 82 comprising an amplify s stage I88 and a power stage I81, comprising a vacuum tube and a thyratron type of tube respectively. The tubes I88 and I81 have connections corresponding to the connections of the tubes 88 and 88. The amplifier tube I88 has its input connection from the pick-up coil I8 and the thyratron tube I81 has its anode lead connected in series with the second differential field coil III of the amplidyne generator I8I. It is to be observed that the resistor 851s a common cathode resistor for the tubes 88 and I81. A bleed resistor I88 is provided between the positive terminal at the plate supply 88 and the cathode II of the tube 88 which is also the cathode connection of the tube I81. The resistances of the resistors 85 and I88 are so chosen as to bias the control grids of the tubes 88 and I81 sufficiently negative to prevent them from becoming conductive until potentials are applied to the control grids.

For effecting the desired control of the driving motor 8I by the thyratron tubes 88 and I81,

relays are provided in the tube circuits. These relays include relays represented in the drawing by their actuating coils I08, III, H2, H8 and II4, having contacts represented by the same III and .2 are time-delay pick-up, instantane-.'

ous drop-out relays, having normally closed contacts Illa and II2a respectively. Preferably the pick-up time delay is approximately 1'6 second. The relays H8 and H4 are instantaneous pickup, instantaneous drop-out relays, having normally open contacts Il8a and Illa respectively. The actuating coil of the relay I09 and the relay contacts II8a and II4a are connected in series across the plate supply 98. The normally closed relay contacts I09a are connected between the positive terminal of the plate supply 93 and the junction terminal I15 of the opposing generator field coils I08 and I04. The normally closed relay contacts IIIa and II2a are connected in se-' ries with the anode leads of the thyratron tubes 88 and I01, respectively.' .The actuating coils of the relays III and H9 are connected in parallel in the anode lead of the tube 86 and the relay actuating coils II2 and I I4 are connected in parallel in the anode lead of the thyratron tube I01.

The manner in which the phase responsive circuits 82 and 89 maintain the voltages in phase in the pick-up coils I8 and I9 will be apparent from a consideration of the diagram of Fig. 5. With the pick-up coils I8 and I9 in the proper spacing relationship so that the induced voltages of the two pick-up coils are in phase, the induced voltage in pick-up coil I8'starts to drop negative at exactly the same instant as the voltage in the pick-up coil I9, referring to curves 88 and 81 in Figs. 6 and 7, respectively. The signal voltage from the pick-up coil I8 depresses the potential of the grid 81 of the vacuum tube 80,

- causing the plate current thereof to decrease and causing the plate voltage to rise. This rise in plate voltage, acting through the coupling condenser 98, temporarily raises the potential of the grid 92 of the thyratron tube 88, which is normally biased'below the critical value at which the tube fires or becomes conductive. In exactly the same manner and at the same time the induced voltage in the pick-up coil I9 starts to drop negative, the plate current in the vacuum tube amplifier I06 decreases, causing an increase in its plate voltage. This increase in plate voltage likewise causes the grid of the thyratron tube I01 to rise positive. Simultaneously, the grid voltages in the thyratron tubes exceed their critical value, causing both thyratron tubes 86 and I01 to fire. Considering the assumed flow of current in the conventional, arbitrary sense, contrary to fiow of electrons, current is thereby allowed to flow from the positive terminal of the plate supply 98 through the normally closed relay contacts I09a,- the amplidyne field coil I03, the actuating coil of the time-delay relay III, its normally closed relay contacts la, the thyratron tube 88, the cathode resistor 95, back to the negative terminal of the plate supply 93. The relay III will allow current to flow through its operating coil for a definite time 6 second for illustration) before it operates to open its normally closed contact Illa in series with the operating coil interrupting the current flow through the thyratron 86 and thereby resetting the thyratron tube for another operation. Simultaneou ly with 10 the initiation of current flow through the thyratron tube 88, current is initiated in the tube I01. It fiows from the positive terminal of the plate supply 98 through the normally closed relay contacts I08a, the amplidyne generator field coil I04. the actuating coil of the time-delayrelay II2, its normally closed contacts I He, the thyratron tube I01 and the cathode resistor 90, back to the negative terminal of the plate supply 08. Since the generator field coils I08 and I04 are wound in opposition, no armature'voltage is generated in the current driving motor 8I receives no voltage, and

does riotrotate to reposition the movable pick-up coil I If the two pick-up coil voltages 88 and 81 are exactly in phase and all electrical components are properly matched and electrical adjustments are properly made, the operating coils III and H2, that is the relay actuating coils III and H2, will carry current for second for example, and then operate at exactly the same instant, interrupting the current flow through the thyratron tubes 86 and I01. Simultaneouslywith the current passing through both thyratron tubes, current will also pass through the actuating coils oi the instantaneous pick-up time-delaydrop-out relays H3 and H4, closing contacts on these relays, that is contacts 3:1 and H411, which are in series with the relay operating coil I09. The relay I09 will operate instantaneously opening the normally closed contacts I09a in the common circuit between the generator fields I08 and I04 and the positive terminal 01' the plate supply 98. The relay I09 remains energized with its normally closed contacts I09a in the open position for a pre-determined time, for example, one to three seconds adjustable even though the actuating coils of the relays H8 and I I4 are de-energized immediately when contacts Illa and HM open after second time delay. Thus the corrective apparatus is not allowed to re-cycle until the time delay drop-out relay I09 has re-set closing its normally closed contact I09a. Therefore, when the elongation is properly indicated this apparatus will automatically check the strip elongation each one to three seconds according to the time setting of the relay I09.

For the purpose of further illustrating the operation of the apparatus, it may now be assumed that the strip elongation increases. With the same pick-up coil spacing used as for the previously describedoperation, and the centers of spots of localized magnetic field farther away than the centers or the pick-up coils, due to the increased elongation of the strip I2 in the mill, it will be apparent that the induced voltage 61' in the pick-up coil I9 will start to drop negative before the induced voltage 88 in the coil I8 starts to drop negative as the strip carrying the localized magnetic fields passes .under the pick-up coils I8 and I9. In this case, the amplifier tube I08 has its grid fall negative before the amplifier tube 86, raising its plate voltage. Therefore the condenser II6 starts to charge up through resistor I20 before the condenser 98 start to charge through the'resistor 99. Accordingly, the grid in the thyratron tube I01 reaches the necessary positive value to fire the thyratron tube I 01 ahead of the thyratron tube 88. Thereupon current passes from the positive terminal of the plate supply 98, through the normally closed contacts I09a, the amplidyne generator field coil I04, the actuating coil of the relay I I2, its normally closed contacts Illa, the thyratron tube I01, and the 1-1 cathode resistor 95 back to the negative terminal of the plate supply 93. The relatively heavy current passing through the cathode resistor 99, causes a voltage drop across the resistor raising the cathode potentials of the tubes 86 and I01 so that the cathode of the thyratron tube 06 is driven positive with respect to the negative terminal of the plate supply 93. This will not, however, substantially aiIect the current fiow through the thyratron tube I01 which has already been ignited. The voltage in the condenser 98 which has been lagging behind that in the condenser H6, finally rises sufiiiently to raise the grid potential of the thyratron tube 06, but the cathode of the tube 86 is now so highly positive, due to the previously described voltage drop across the cathode resistor 95, that the tube 86 cannot conduce current. Consequently, only the generator field I04 receives current and the generator IOI supplies voltage of the proper polarity to run the direct current driving motor 8| in the direction to move the coil I9 further away and thus return the two pick-up coils to in phase voltage relationship. However, the thyratron tube I01 passes current through the amplidyne generator field coil I04 only until the relay II2 has had time to operate 6 second, for example). The

relay II; is not operated, owing to the thyratron tube 86 having been prevented from passing current as previously described; the normally open contacts on the relays H311 and Illa will not close simultaneously so that the actuating coil of the relay I09 was not energized. Therefore, when the relay II2 opens its contacts Il2a after 1%; second of time delay, the generator field I04 is de-energized, and the generator voltage returns to its original value which is not sufilcient to D- erate the power positioning motor 9 I. As the strip elongation changes and therefore the spacing of the spots of localized magnetic fields on the delivery side of the mill changes, the apparatus immediately starts correcting th coil spacing, that is the pick-up coil spacing, through an impulse to the driving motor of 1% second duration, or whichever other value is determined by the characteristics of the relays III and II2.

If the movement of the pick-up coil I9 by the repositioning motor 8| is not sufiicient to establish the in phase relationship, the motor will again be energized for 1% second to move the coils I8 and I9 still further apart, and this jogging" action will be repeated until in phase relationship is again established.

If the'strip elongation decreases on the other hand, the voltage of the pick-up coil I9 will drop negative before that in the pick-up coil I 9 so that the thyratron tube 86 will pass current before the thyratron tube I01. Consequently, the thyratron tube I0'I will be locked out in the same manner that the thyratron tube 96 was locked out in the previous example, and the amplidyne generator field coil I03 will be energized instead of the coil I04. This will cause the amplidyne generator IM to produce a voltage of the opposite polarity from that previously described, and the repositioning motor BI wil1 run in the reverse direction for 1 6 second at a time and continue to jog in this direction until "in phase" relationship of the two induced voltages in the pick-up coils is re-established. The change in pick-up coil spacing by the direct current coil repositioning motor 8| will move the rack 36, turning the pinion 31 so that the pointer 30 is rotated to a position indicating the percentage elongation.

In order that the indications of elongation may 12 be reproduced at a distance, or mayactuate reduction setting controls for the rolls II and IS, a resistance I I1 is preferably arranged along the scale 39, and a contact is formed on the pointer adapted to slide along potentiometer III as the pointer 30 is located by the movement of the rack 90. The potentiometer resistance In is connected across a suitable constant voltage supply, such as the supply 22, and a suitable remote indicating device such as a voltmeter H0, or a voltage responsive roll control is provided which is electrically connected between one end of the potentiometer resistance Ill and the contact on the pointer 30, by conductors II9 which extend to the point where the voltmeter II! is to be located. Changes in position of the pointer 98 will. result in changing the reading of the 'voltmeter H8, which is calibrated preferably in values of percentage elongation.

When the pick-up coils I0 and I9 again reach the proper spacing relationship for the induced voltages in the pick-up coils I8 and I9 to be "in phase, the apparatus checks the pick-up coil spacing each one to three seconds, depending upon the timing for which the relay-I09 has been set, as previously described. If the elongation thereafter changes, the pick-up coil relative spacing is altered with the high speed impulses to the direct current coil-repositioning motor 9I. The pick-up coil I9 is moved in the proper direction with relation to the pick-up coil I8 until in phase" relationshipis again established. The new position of the pick-up coil I9 with respect tothe pick-up coil I8 causes the rack 90 to turn the pinion 31 rotating the contact on the pointer 39, sliding it along the potentiometer III to a new position and a new elongation is indicated on the voltmeter III.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its principle of operation and showing its application, but it will be obvious to those skilled in the art that many modifications and variations are possible, and I aim therefore to cover all such modifications and variations as fall within the scope of my invention which will be defined in the appended claims.

I claim:

1. An indicator for a moving strip of magnetizable material, comprising in combination means for marking first and second magnetic spots on the material at a fixed distance apart, first means for detecting the location of the first magnetic spot, second means for detecting the location of the second magnetic spot, and means responsive to the phase relationship between re spouses of said first and second detecting means.

2. An elongation indicator for a magnetizable strip material being passed through reduction rolls comprising in combination means for marking first and second magnetic spots on the material at a fixed distance apart, first and second detectors for producing electrical responses to passage of magnetic spots thereunder, one of said detectors being movable for adjusting the distance between detectors to conform to the distance between magnetic spots, and means responsive to diiference in phase relationship between said electrical responses for automatically varying the position of the movable magnetic spot detector.

3. An indicator for a magnetizable material being passed through reduction rolls comprising in combination means for marking a magnetic spot on the material, second means for marking a second magnetic spot on the material at a fixed distance from the first marking, means for producing an electrical response to passage of the first magnetic spot, means for producing an electrical response to the passage of the second magnetic spot, one of said responsive means being movably mounted, and means responsive to difference in phase relationship between said electrical responses for automatically varying the position of the movable responsive means.

4. An indicator for a moving strip of magnetizable material comprising in combination means for marking a magnetic spot on the material at a substantially fixed distance from the edge of the material, second means for marking a second magnetic spot on the material simultaneously with the first marking at a greater distance from the edge of the material than the first marking and at a substantially fixed distance from the first marking, measured in the direction of the length of the strip, means for detecting the first magnetic spot, means for detecting the second magnetic spot, and means for comparing the time of response of one of said detecting means with that of the other of said detecting means.

5. An indicator for a moving strip of magnetizable material comprising in combination means for making a magnetic spot on the material at a substantially fixed distance from the edge of the material, second means for making a second magnetic spot on the material simultaneously with the first marking at a greater distance from the edge of the material of the first marking and at a substantially fixed distance from the first marking measured in the direction of the length of the strip, means for detecting one of said magnetic spots, movable means for detecting the other of said magnetic spots, means responsive to the time relationship between responses of said detecting means, and means for gauging distance between said detecting means.

6. An elongation indicator for magnetizable strip material being passed through reduction rolls comprising in combination means for marking a magnetic spot on the material at a substantially fixed distance from the edge thereof, second means for marking a second magnetic spot on the material simultaneously with the first marking at a greater distance from the edge thereof and at a fixed distance along the length of the material from the first marking, a'first detector for producing an electrical response to passage of the first magnetic spot thereunder, a movable detector for producing an electrical response to passage of the second magnetic spot thereunder, and means responsive to diflerence in phase relationship between said electrical responses for varying the position of the movable magnetic spot detector.

7. An elongation indicator for magnetizable strip material being passed through reduction rolls comprising in combination, means for marking magnetic spots spaced apart upon the material, a pair of spaced magnetic flux detectors, one of which is movable, a driving motor for adjusting the position of the movable magnetic flux detector, a pair of electric discharge device circuits each responsive to one of said magnetic flux detectors, and means differentially responsive to said discharge device circuits for controlling said motor.

8. In combination, a pair of alternating voltage sources to be maintained in phase, means for eiiecting relative phase variation of said sources to bring about phase coincidence, operating means for said phase adjusting means having oppositely acting control windings, a pair of control circuits, each having a control element responsive to one of said voltage sources, one of said control windings being included in one of said control circuits, and the other said control windings being included in the other of said control circuits, means responsive to energization of either of said control circuits for preventing subsequent excitation of the other of said control circuits whereby one or the other of said control circuits and control windings is energized to operate the phase adjusting means to restore phase coincidence, and means responsive to simultaneous excitation of said control circuits for intermittently deenergizing and reclosing said control circuits to check phase relationship periodically.

9. In combination, a pair of alternating voltage sources to be maintained in phase, means for effecting relative phase variation of said sources to bring about phase coincidence, operating means for said phase adjusting means having oppositely acting control windings, a pair of control circuits, each having a control element responsive to one of said voltage sources, one of said control windings being included in one of said control circuits, and the other said control windings being included in the other of said control circuits, and means responsive to energization of either of said control circuits for preventing subsequent excita-' tion of the other of said control circuits, wherein time delay means are provided in each of said control circuits for re-opening the circuits 3, predetermined length of time after energization thereof whereby a jogging" action is produced to bring about gradual step-wise readjustment of the phase relationship until phase coincidence has been produced.

10. A strip elongation indicator comprising in combination means for producing electro-magnetic effects in localized spots of a strip at fixed distances apart, a pair of voltage inducing means mounted an adjustable distance apart, responsive to passage of said aiiected spots thereunder, to induce voltages therein, means for adjusting the spacing of said voltage inducing means to conform to the spacing of the electro-magnetically affected spots in the strip, and means responsive to phase difference between voltages induced in said voltage inducing means to adjust the position of said voltage inducing means in a direction required to produce phase coincidence.

KENNETH W. HARRIS.

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

UNITED PATENTS v zeiboll Apr. 23, 1946

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