US3626255A

US3626255A - Demagnetizer, solid state

Info

Publication number: US3626255A
Application number: US68625A
Authority: US
Inventors: Arthur K Littwin
Original assignee: LITTWIN FAMILY TRUST NO 1
Current assignee: LITTWIN DONALD F; LITTWIN MARGARET C; LITTWIN FAMILY TRUST NO 1
Priority date: 1970-09-01
Filing date: 1970-09-01
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07
Also published as: DE2143633C3; GB1367911A; DE2143633B2; DE2143633A1; JPS5732489B1

Abstract

A completely solid state demagnetizer including: a circuit including the object to be demagnetized and including a portion for applying DC to the object, and including portions operable for so applying the DC in successively opposite polarities; a first condenser of fixed capacity chargeable substantially instantaneously, and charged constantly by the power source; a second condenser progressively chargeable, of variable capacity, and having limits above and below that of the first condenser; the first condenser, when the second condenser is charged to a value less than itself, energizing the circuit portion operable for applying DC of a first polarity to the object; and the second condenser, when charged to a value greater than that of the first condenser; energizing the circuit portion operable for applying DC of the opposite polarity to the objects; an additional condenser means providing a decaying action for progressively and continuously reducing the value of the voltage applied to the object.

Description

United States Patent Arthur K. Littvvin [72] inventor Lincolnwood, iii.

[2 i Appl. No. 68,625

[22] Filed Sept. 1, 197i) [45] Patented Dec. 7, 1971 [73] Assignee Littwin Family Trust No. 1

Chicago, Ill.

s4 DEMAGNETIZER,SOLID STATE UNITED STATES PATENTS 3,086,i48 4/1963 Soneki 317/i57.5

Primary Examiner-L. T. Hix Attorney-Paul H. Gallagher ABSTRACT: A completely solid state demagnetizer including: a circuit including the object to be demagnetized and including a portion for applying DC to the object, and including portions operable for so applying the DC in successively opposite polarities; a first condenser of fixed capacity chargeable substantially instantaneously, and charged constantly by the power source; a second condenser progressively chargeable. of variable capacity, and having limits above and below that'of the first condenser; the first condenser, when the second condenser is charged to a value less than itself, energizing the circuit portion operable for applying DC of a first polarity to the object; and the second condenser, when charged to a value greater than that of the first condenser; energizing the circuit portion operable for applying DC of the opposite polarity to the objects; an additional condenser means providing a decaying action for progressively and continuously reducing the value of the voltage applied to the object.

DEMAGNETIZER, SOLID STATE OBJECTS OF THE INVENTION The present invention relates to demagnetizing of an-object of the general character in which DC is applied to the object in successive steps of opposite polarity and in which the voltage in the successive steps is gradually reduced, whereby at the final step the voltage is at or near 0, and the object is accordingly substantially demagnetized.

Dernagnetizing as just referred-to is generally known, as represented for example in my prior US. Pat. No. 2,825,854, dated Mar. 4, I958.

A broad object of the present invention is to provide a demagnetizing circuit and method of demagnetizing of the foregoing general nature, which is of completely solid state nature.

Another broad object is toprovide a solid state demagnetiz ing circuit of the character referred to having a novel arrangement of condensers in mutually opposed relation oneof which is of fixed capacity and the other of variable capacity, each of the condensers, when of a greater charged condition than the other, controlling the polarity of the DC applied to the object, and the two together operable for applying the DC'in mutually opposed steps throughout a series for accomplishing the demagnetizing operation.

Another object is to provide a solid state circuit for demagnetizing of the character just immediately referred to which includes means for maintaining the voltage on the condenser means at a point close to that necessary for activating each condenser over the other, so that upon buildup of voltage for the particular condenser, only a minimum of such buildup is required for triggering that condenser and so that it overcomes the opposed condenser.

A still further object is to provide a circuit for demagnetizing of the foregoing character including novel means for reducing the DC applied to the object, so that when the DC is reversed under control of the reversing means referred to, i.e., the condensers reduce the magnetism of the object in the successive steps.

A still further object is to provide apparatus of the kind just immediately referred to and including means for shutting off the demagnetizing circuit when the voltage of the DC as applied to the object is substantially at 0, wherein that shutting off means is independent of the reversing means, whereby to effectively shut ofi' the apparatus when the magnetism of the object to be demagnetized is substantially accomplished.

DESCRIPTION OF A-PREFERRED EMBODIMENT In the drawings:

The single figure is a diagram of a completely solid state arrangement for demagnetizing an object. I

Referring in detail to the circuit, .a magnetic chuck is shown (bottom center), of a kind commonly used in a machine tool, such for example as in a grinder and utilized in the reciprocating table for holding the workpiece to be ground. Such a chuck is represented in FIG. 5 of my prior patent referred to above (see No. 16, and the workpiece No. 17 in that patent). The magnetic chuck itself does not form a part of the invention, and is well-known, as is the overall and general arrangement and method for demagnetizing the chuck and the workpiece thereon. lnthe circuit the portion at the bottom enclosed in dot-dash lines and indicated at 12 represents the reversing means utilized in the demagnetizing operation, and the other portion of the circuit the control means for controlling that reversing means.

The circuit represented in the drawing includes a suitable AC source 14 from which

conductors

16, 18 lead, and in which are included switch means 20, 22 which may be ganged. Condensers 24, 26 include principal control elements for reversing the polarity of the DC applied to the chuck. The condenser 24 is connected between the

main lines

18, 16 through

conductors

27, 28, 29, 30 and 31, the conductors 27 and 31 having rectifiers 32, 33 therein. The condenser 26 is connected between the

lines

18, 16 through conductor 34 having a rectifier 35 therein, and leading to the cathode of an SCR (silicon controlled rectifier) 36. Leading from the plate are

conductors

37, 38, 39, the latter containing the condenser 26 and leading through conductors 30, 31 to the line 16. Connected across the

conductors

37, 30 is a conductor 40 containing series adjustable resistors 42, 44 which are connected across the condenser 26. 7

Another conductor 46 leads from the conductor 34 to another conductor 48 connected with the gate of the SCR 36 holding the SCR in conducting condition. The conductor 46 also connects with another conductor 50 leading to the plate of an SCR 52, and leading from the plate of the latter is another conductor 54 connected with an additional conductor 56 connected between the resistors 42, 44. Another adjustable resistor 58 is interconnected between the

conductors

54, 30. The gate of the SCR 52 is connected with another conductor 60 which is connected'with the conductor 56. A zener diode 62 is connected across the condenser 24.

.Associated with the condensers 2,4, 26 are transistors 64, 66 respectively (upper), and associated with those transistors are

SCRs

68, 70 respectively (top), and controlled in a manner referred to below. The rectifiers, transistors and SCRs may be referred to each and generically as valve means or gate means.

Connected between the main lines l6, l8 is a conductor 72 having series primaries 74F, 76F of transformers 74, 76, and the line has back-to-

back rectifiers

78, 80 therebetween. Also connected between the main lines isanother conductor 82 having series primaries 84F, 86F of transformers 84, 86, and including back-to-back rectifiers' 88, 90 therebetween. The secondaries of these transformers re found at the bottom of the circuit, having the same reference numerals with the subscript S.

The secondaries just referred to are incorporated in the portion 12 at the bottom of the circuit, and are individually connected with the gates of SCRs as follows: 748 with SCR 92, 76S with SCR 94, 84S with

SCR

96, and 865 with SCR 98. These SCRs are respectively arranged in back-to-back relation, i.e. the

SCRs

92, 94 providing unidirectional current in one direction to the chuck10, and the SCRs 9 6, 98 providing unidirectional current in the other direction. The chuck is connected with-a conductor 104 center-tap connected with a primary 106? of a transformer 106, the primary being-connected across the

main lines

16, 18, and connected respectively the SCR systems, viz, 92, 98 at one end and 94, 96 at the other end, completing circuit through the chuck. This transformer 106 includes secondaries 106S1 (top), 10652 (lower right), and 10653 (lower center).

Upon energization of the primary 106P (bottom) the chuck 10 is energized, and according to which of the secondaries directly connected with that primary are energized, the chuck is magnetized at one or the other direction: when the secondaries 74S, 768 are energized, the chuck is magnetized in a first direction, or first polarity, and when the secondaries 848, 868 are energized, the chuck becomes energized or magnetized in the opposite or second direction, or second polarity. The

back-to-back arrangement as to the secondaries 74S, 76S, and

the other secondaries 84S, 86S, together with the arrangement of the primary 106P in itself is known and the means for controlling the energization of those coils by the remaining portion of the circuit is of the essence of the invention.

Included in the circuit is switch means 108 (right, upper and lower), including two individual switches 108a and 108b, preferably. ganged together and movable between ON 'and DEMAG (demagnetizing) positions.

Leading from the first switch 108a is a conductor connected with the conductor 38 and leading to a variable resistor 112 and connected with another conductor 114 which includes an adjustable resistor 1 16, and also connected with a conductor 115. A return conductor 117 leads from the conductor 114 to the ON terminal of the switch 108a. Leading from the adjusting element of the resistor 1 16 is a conductor 118 connected with the base of the transistor 64 and leading from the emitter of that transistor is another conductor 120 connected with a conductor 122 which leads to the emitter of the transistor 66. Leading from the base of the transistor 66 are

conductors

124, 125 connected with the conductor 110. interconnecting the

conductors

118, 124 are

additional conductors

126, 128, respectively, including

resistors

130, 132, and connected with these conductors between the resistors is another conductor 134 which includes the secondary 10681 and is connected with another conductor 136 leading in one direction to a conductor 137 which includes a primary 138P and in the other direction to a conductor 139 including a primary 140P. The conductor 137 leads to the anode of the SCR 68 while the other conductor 139 leads to the anode of the SCR 70.

The transformer 138 includes a secondary 138S (center, left) while the transformer 140 includes a secondary 140S (center, right). The secondary 138$ leads to the base of a transistor 142 while the other secondary 140S leads to the base of a transistor 144. Leading from the emitter of the transistor 142 is a conductor 143 connected with the conductor 72 between the

rectifiers

78, 80, and similarly a conductor 145 leads from the emitter of the transistor 144 and is connected with the conductor 82 between the

rectifiers

88, 90. Leading from the collectors of the transistors 142, 144, is a conductor 146 connected with which is another conductor 148 center-tapped to the secondary 106S3.

Connected across the

main lines

16, 18 are

additional conductors

150, 152 leading respectively to the anodes of SCRs 154, 156, and the cathodes thereof are interconnected by

conductors

179, 181 which also connect with the conductor 148. The gates of the SCRs 154, 156 are connected at opposite ends to the secondary 106S3.

Leading center-tapped from the secondary 10683 is a conductor 160 connected with the emitter of a transistor 162 and connected with the base of that transistor is another conductor 164 leading to the collector of another transistor 66. The emitter of the transistor 166 is connected through a conductor 168 to the collector of the transistor 166 and to another conductor 170 leading to the ON terminal of the switch 108b. A conductor 172 leads from the base of the transistor 166 to the common terminal of the switch 108b. Leading from the DEMAG terminal of the switch 108!) is a conductor 174 connected with the secondary 106S2.

1n the use of a magnetic chuck it is utilized for holding a workpiece on which a work operation is performed, such as grinding, and for that purpose it must be fully magnetized. Although the principal purpose of the present invention is to demagnetize that chuck, and the workpiece thereon, it is necessary that the circuit also directly control all phases of control of the chuck, in order to perform the demagnetizing operation. Specifically, it may be desired to turn off the chuck to remove a piece for testing purposes and often that piece is again placed on the chuck and a further grinding operation is performed thereon. Thus the circuit is utilized for turning on and off the chuck as well as for demagnetizing it. The present circuit is interposed in the control circuit normally provided for energizing the chuck and operates to turn on and off that circuit. To put the circuit of the present invention into operation, in an initiating step, the switch means 20, 22, is of course closed which energizes all of the elements then directly connected with the

main lines

16, 18, including the primary 106P. Then depending on whether the grinding operation is to be performed, or a demagnetizing operation, the switch means 108 is thrown to corresponding position, and normally it is first thrown to ON position for energizing the chuck.

For convenience in describing the operation, reference is made first to the DEMAG, or demagnetizing position and to establish that position, after the main switch means 20, 22 is closed, the switch means 108 is thrown to its full line position. A circuit is established from the main line 18 through the conductor 27, rectifier 32,

conductors

28, 29, 30, 31 to the line 16. This charges the condenser 24 instantaneously. At the same time, a circuit is established through conductor 34, SCR

36, this SCR being turned on through the conductor 46; the circuit continues through

conductors

37, 38, 39, the condenser 26, and conductors 30, 31. The condenser 26 charges slowly from its lower value of e.g., l0 volts to its upper value of, e.g., 40 volts, while the capacity of the condenser 24 may be of 25 volts. 7

The condensers 24, 26 are opposed, the negative sides thereof being connected with the conductor 30 and with an additional conductor which connects with the conductor 114. Upon the condenser 24 reaching its capacity charge, it controls the transistors 64, 66 as follows: from the positive side, through conductors 29, 28, adjustable resistor 116, conductor 118 applying a positive charge on the transistor 64 and turning it on; it continues through

conductors

120, 123, 145, 149, the collector of the transistor 66 and from the base thereof, through conductors I24, 125, 110, 39 to the condenser 26 and the negative of condenser 24. The transistor 64 is thus turned on and the transistor 66 is turned off. A similar circuit is established through the condenser 26 and the transistor 66 when the condenser 26 becomes charged and takes over, as referred to below. When the transistor 64 is turned on, it turns on the SCR 70, and similarly, when the transistor 66 is turned on, it turns on' the SCR 68. I 5

Upon turning on the the

SCRs

70, 68, the respective primaries P, 138P are energized, and in a first case, the energized primary 1401 energizes the secondary 140$ (center, right) and the latter completes a circuit through the transistor 144 and turns on the latter. The secondary 106S3 (center lower) is energized, which turns on the SCRs 154, 156 in respective half cycles, and upon turning on of the transistor 144, the primaries 84?, 86? are energized in respective half cycles, and they in turn energize the secondaries 84S, 86S (bottom) and establish a continuous circuit in those half cycles of a first polarity through the chuck l0 and the primary 106P for energizing the chuck. This energization occurs and persists throughout the range of effectiveness of the condenser 24, until the condenser 26 takes over. 7

Although the charge on the condenser 24 controls the transistor 64 as referred to, it remains constantly and fully charged by the main lines, and while the condenser 24 so controls the transistor 64, the charge on the condenser 26 builds up and when it reaches its maximum charge, e.g., 40 volts, it predominates and reverses the circuit arrangement, turning on the transistor 66 and the SCR 68, and turning off the transistor 64 and the SCR 70, in a circuit similar to the circuit including the condenser 24 as referred to above. Energization of the primary 1381 pursuant to turning on of the transistor 66 and SCR 68, energizes the secondary 138S (center, left) which turns on the transistor 142 and completes a circuit for energizing the primaries 74F, 761 in respective half cycles. The latter primaries in turn energize the secondaries 74S, 76S (bottom) and complete a circuit through the chuck 10 and primary 1061 in corresponding half cycles, and in conjunction with the secondaries 848, 865, as described above, maintain a DC circuit through the chuck. The voltage thus established is of the second polarity or opposite that of the first step.

Upon decay of the voltage of the condenser 26, as determined by the resistors 42, 44, 50 its minimum value which in the assumed example is 10 volts, it shuts off and the condenser 24 having remained charged, again predominates and establishes a controlling circuit through the transistor 64 and SCR 70. This continues until the voltage in the condenser 26 again builds up to its maximum capacity.

The effectiveness of the condenser 24, 26 on the reversals of polarity on the chuck are controlled by the transistors 162, 166 which in turn are controlled by the switch 108 b. The secondary 106S2 normally remains energized, placing a charge on the condenser 186, and when the switch 108!) is thrown to DEMAG position, it removes the voltage supply from the condenser 186 and the latter discharges, the negative bias controls the transistor 162 and therethrough, the transistor 166, and when this charge is expended, the transistor 166 shuts off. During the one and off periods of the condenser 186 and control thereby, the oneor the other of the secondaries 140$, 1388 is energized, and through the

primaries

84P, 86P, or 74P, 76P, control the polarity'the DC imposed on the chuck as described producing gradually decreasing periods of opposite polarity and the desired demagnetizing for predetermining the charge on the condenser 186, and the resulting decaying action is independent of the charge on cles and the condensers retain their charges throughout a plueither of the condensers 24, 26; when the action of the condenser 186 is terminated, the voltage of the chuck 10 is at 0,

or substantially zero, and any .further reversing action by the condensers 24, 26 thereon,is of no effect.

Another feature of the invention is a means for accurately controllingthe points of effectiveness of the transistors 64, 66. The

resistors

130, 132 are connectedrespectively with the bases of the transistors and constantly provide a voltage thereon which is slightly less than the voltage required for turning them on. Thenupon the imposition of the voltage as provided by the condensers 24, 26 on the respective transistors, the latter need be only a very small increment whereby only a very small additional voltage is required under the control of the condensers 24, 26 to trigger the transistors. Accordingly the transistors are rendered more accurately responsive than would otherwise be provided for.

lclaim: g

1. Solid state demagnetizing means comprising a circuit adapted to beconnected with an electrical source and with an Object'to be demagnetized,'the circuit including means for applying DC to the object and for applying it in successive steps of opposite polarity,

a first condenser 'of fixed maximum capacity constantly chargeable and substantially instantaneously charged by the source,

a second condenser relatively slowly and progressively chargeable by the source, and adjustable through a range of maximum capacity extending above and below that of the first condenser,

and means responsive to and controlled by the first condenser operative, when the second condenser is charged to 'a value less than thatof the first condenser, for effecting application of DC of a first polarity to the object,

means responsive to and controlled by the second condenser operative, when it is charged to a value greater than that of the first condenser, for effecting application of DC of the opposite polarity to the object,

and means for reducing the value of the voltage appliedto the object during the reversals of polarity as controlled by the first and second condensers.

2. Demagnetizing means according to claim 1 and including a first and a second transistors related to the condensers, the condensers respectively controlling the transistors by rendering the corresponding transistor conducting and the other nonconducting, and, each condenser being operative for so controlling the respective transistorupon its predominance over the other, and the transistors operative for controlling the application of DC of respective opposite polarities to the object.

3. Demagnetizing means according to claim 2 and including first and second SCR's related to and controlled by the first and second transistors, and transformer means controlled by the SCR's and themselves controlling the application of DC to the object.

4. A demagnetizing means according to claim 1 adapted for connection with an AC source and wherein each condenser is operative throughout a range including a plurality of AC cyrality of AC cycles,and the charges decay independently of the AC cycles.

5. Solid state demagnetizingmeans comprising a circuit adapted to be connected with an AC source and with an object to be demagnetized,

a first charging transformer and rectifier means for effecting a DC of a first polarity and imposing it on the object, a second charging transformer and rectifier means for effecting DC of a second polarity and imposing on the obsource, rectifier means interposed between the source and the first condenser,

a second condenser relatively slowly and progressively chargeable by the source, and adjustable through a range of maximum capacity extending above and below that of the first condensen rectifiers means interposed between the source and the second condenser,

means responsive to and controlled by the first condenser operative, when the second condenser is charged to a value less than that of the first condenser, for energizing the first charging transformer and thereby magnetizing the object in the corresponding first polarity, means responsive to and controlled by the second condenser operative, when it is charged to a value greater than that of the first condenser, for energizing the second charging transformer and thereby magnetizing the object in the corresponding opposite polarity, valve means operatively interposed between the condensers and the charging transformers, I the first condenser during a predetermined value of charge thereon greater than that of the second condenser, being operable for holding the corresponding valve means in the respective conductive condition and the corresponding charging transformer in energized condition for imposing DC of a first polarity of the object,

. the second condenser during a predetermined value of chargcthereon greater than that of the first condenser, being operable for. holding the corresponding valve means in the respective conductive condition and the corresponding charging transformer in energized condition for imposing DC of the opposite polarity on the object,

and means for reducing the value of the voltage imposed on the object throughout a predetermined range independentlyof the periods of energization of the condenser means and corresponding energization of the charging transformers.

6. Demagnetizing means according to claim 5 wherein the means for reducing the voltage includes additional condenser means chargeable from the AC source, and means for controlling the discharging effect of the additional condenser means and corresponding range of the control of the first mentioned condenser means throughout a predetermined range.

7. Demagnetizing means according to claim 6 wherein the means for controlling the discharge of the additional condenser means establishes a range of effectiveness thereof greater than the range of discharge of either of the first and second condensers and independently thereof.

8. Demagnetizing means according to claim 6 wherein the first and second condensers are constantly chargeable by the source, and the circuit includes means normally holding the charging transformers in deenergized condition, and manually controlled means for actuating the means for controlling the discharge of the additional condenser means and thereby energizing the charging transformers.

9. Demagnetizing means according to claim 8 wherein the period of discharge of the additional condenser means is greater than that of either the first or second condensers.

10. Demagnetizing means according to claim 9 and including transformer means for energizing the additional condenser means, this last transformer means being utilized also for controlling the charging transformers.

11. Solid state demagnetizing means including a circuit adapted for connection to an AC source and to an object to be demagnetized, comprising I a first condenser of fixed maximum capacity connected with the source, constantly chargeable and substantially instantaneously charged by the source, with rectifier means interposed between the source and the first condenser,

a second condenser relatively slowly and progressively chargeable, connected with the source and adjustable through a range of maximum capacity extending above and below that of the first condenser, with rectifier means interposed between the source and the second condenser,

a transistor associated with each condenser and controlled thereby,

an SCR related to each transistor and controlled thereby,

each condenser being operative to energizing its related transistor while deenergizing the opposite transistor and the transistors being correspondingly operative for energizing the corresponding SCRs when they themselves are energized,

transformer means for controlling the object including a main transformer energized directly by the source, and back-to-back transformers related to each of opposite polarities of DC and including associated back-to-back SCRs directly related to the back-to-back transformers,

a first pair of transformers having primaries in series connected with the source and having back-to-back rectifiers therebetween and including secondaries forming parts of the back-to-back transformers associated with the object,

a second pair of transformers having primaries in series connected with the source and having back-to-back rectifiers therebetween and including secondaries forming posts of the back-to-back transformers associated with the object, in the opposite polarity of the DC conductors respectively center-tapping the first pair of transformer primaries and the second set of transformer primaries, I

SCRs connected with the center tappings,

additional transformers having primaries controlled by the first mentioned SCRs and secondaries controlled by the last mentioned SCRs,

and means for controlling the application of DC to the object to be demagnetized including transformer means controlled by the last mentioned SCRs and including the second and third SCRs in a subcircuit, the transformers above mentioned being constantly energized under the control of the first and second condensers, throughout a range indeterminate in length,

control means for terminating the application of DC to the object to be demagnetized including an additional condenser operative when charged for energizing the last mentioned transformer and thereby energizing the transformer controlling the object to be demagnetized,

said additional condenser being constantly charged, and the circuit including means normally disconnecting the additional condenser from the last mentioned transformer,

and manually control means for connecting the additional condenser with the last mentioned transformer whereby that transformer is energized throughout the period of decay of the additional condenser and during that period the last mentioned transformer energizes the transformer directly controlling the object to be demagnetized and after the decay of the additional condenser it becomes deenergized and the circuit is opened to the object to be demagnetized,

the period of decay of the additional condenser being greater than at least the period of energization of each of the first and second condensers.

Claims

1. Solid state demagnetizing means comprising a circuit adapted to be connected with an electrical source and with an object to be demagnetized, the circuit including means for applying DC to the object and for applying it in successive steps of opposite polarity, a first condenser of fixed maximum capacity constantly chargeable and substantially instantaneously charged by the source, a second condenser relatively slowly and progressively chargeable by the source, and adjustable through a range of maximum capacity extending above and below that of the first condenser, and means responsive to and controlled by the first condenser operative, when the second condenser is charged to a value less than that of the first condenser, for effecting application of DC of a first polarity to the object, means responsive to and controlled by the second condenser operative, when it is charged to a value greater than that of the first condenser, for effecting application of DC of the opposite polarity to the object, and means for reducing the value of the voltage applied to the object during the reversals of polarity as controlled by the first and second condensers.

2. Demagnetizing means according to claim 1 and including a first and a second transistors related to the condensers, the condensers respectively controlling the transistors by rendering the corresponding transistor conducting and the other nonconducting, and each condenser being operative for so controlling the respective transistor upon its predominance over the other, and the transistors operative for controlling the application of DC of respective opposite polarities to the object.

3. Demagnetizing means according to claim 2 and including first and second SCR''s related to and controlled by the first and second transistors, and transformer means controlled by the SCR''s and themselves controlling the application of DC to the object.

4. A demagnetizing means according to claim 1 adapted for connection with an AC source and wherein each condenser is operative throughout a range including a plurality of AC cycles and the condensers retain their charges throughout a plurality of AC cycles, and the charges decay independently of the AC cycles.

5. Solid state demagnetizing means comprising a circuit adapted to be connected with an AC source and with an object to be demagnetized, a first charging transformer and rectifier means for effecting DC of a first polarity and imposing it on the object, a second charging transformer and rectifier means for effecting DC of a second polarity and imposing on the object, a first condenser of fixed maximum capacity constantly chargeable and substantially instantaneously charged by source, rectifier means interposed between the source and the first condenser, a second condenser relatively slowly and progressively chargeable by the source, and adjustable through a range of maximum capacity extending above and below that of the first condenser, rectifiers means interposed between the source and the second condenser, means responsive to and controlled by the first condenser operative, when the second condenser is charged to a value less than that of the first condenser, for energizing the first charging transformer and thereby magnetizing the object in the corresponding first polarity, means responsive to and controlled by the second condenser operative, when it is charged to a value greater than that of the first condenser, for energizing the second charging transformer and thereby magnetizing the object in the corresponding opposite polarity, valve means operatively interposed between the condensers and tHe charging transformers, the first condenser during a predetermined value of charge thereon greater than that of the second condenser, being operable for holding the corresponding valve means in the respective conductive condition and the corresponding charging transformer in energized condition for imposing DC of a first polarity of the object, the second condenser during a predetermined value of charge thereon greater than that of the first condenser, being operable for holding the corresponding valve means in the respective conductive condition and the corresponding charging transformer in energized condition for imposing DC of the opposite polarity on the object, and means for reducing the value of the voltage imposed on the object throughout a predetermined range independently of the periods of energization of the condenser means and corresponding energization of the charging transformers.

11. Solid state demagnetizing means including a circuit adapted for connection to an AC source and to an object to be demagnetized, comprising a first condenser of fixed maximum capacity connected with the source, constantly chargeable and substantially instantaneously charged by the source, with rectifier means interposed between the source and the first condenser, a second condenser relatively slowly and progressively chargeable, connected with the source and adjustable through a range of maximum capacity extending above and below that of the first condenser, with rectifier means interposed between the source and the second condenser, a transistor associated with each condenser and controlled thereby, an SCR related to each transistor and controlled thereby, each condenser being operative to energizing its related transistor while deenergizing the opposite transistor and the transistors being correspondingly operative for energizing the corresponding SCR''s when they themselves are energized, transformer means for controlling the object including a main transformer energized directly by the source, and back-to-back transformers related to each of opposite polarities of DC and including associated back-to-back SCR''s directly related to the back-to-back transformers, a first pair of transformers having primaries in series connected with the source and having back-to-back rectifiers therebetween and including secondaries forming parts of the back-to-back transformers associated with the object, a second pair of transformers having primaries in series connected with the source and having back-to-back rectifiers thErebetween and including secondaries forming posts of the back-to-back transformers associated with the object, in the opposite polarity of the DC, conductors respectively center-tapping the first pair of transformer primaries and the second set of transformer primaries, SCR''s connected with the center tappings, additional transformers having primaries controlled by the first mentioned SCR''s and secondaries controlled by the last mentioned SCR''s, and means for controlling the application of DC to the object to be demagnetized including transformer means controlled by the last mentioned SCR''s and including the second and third SCR''s in a subcircuit, the transformers above mentioned being constantly energized under the control of the first and second condensers, throughout a range indeterminate in length, control means for terminating the application of DC to the object to be demagnetized including an additional condenser operative when charged for energizing the last mentioned transformer and thereby energizing the transformer controlling the object to be demagnetized, said additional condenser being constantly charged, and the circuit including means normally disconnecting the additional condenser from the last mentioned transformer, and manually control means for connecting the additional condenser with the last mentioned transformer whereby that transformer is energized throughout the period of decay of the additional condenser and during that period the last mentioned transformer energizes the transformer directly controlling the object to be demagnetized and after the decay of the additional condenser it becomes deenergized and the circuit is opened to the object to be demagnetized, the period of decay of the additional condenser being greater than at least the period of energization of each of the first and second condensers.