US2983827A - Magnetic timing device - Google Patents

Description

May 9, 1961 F. s. MALlcK vmamme TIMING DEVICE 2 Sheets-Sheet l Filed May 19. 1958 J/wu/wkor grim/1MM May 9, 1961 F. s. MALlcK 2,983,827

. MAGNETIC TIMING DEVICE Filed May 19, 1958 2 Sheets-Sheet 2 IIIIIHIHIIIII|||||||H|||| m IIIIIIIIIIIlIlIIIIlHlIIIIII MAGNETIC TllVlING DEVICE yFrzylnklin S. Malick, Monroeville, lha., assignor to Allis- This invention relates generally to timing devices and in particular to those timing devices utilizing a magnetic core fto obtain a long time delay.

Magnetic amplifiers have long been used in applica tion where a high degree of reliability is desired. The reliability of a magnetic amplilier stems largely from the fact that it has no moving parts. Where such an ampliiieris embodied in a control circuit the overall reliability ofthe control circuit is greatly decreased by the inclusion of movingy parts such as relays, switches, or simil-ar devices. In the cases where a time delay is desired it has heretofore been necessary to use some sort of a timing relay. This invention overcomes the disadvantage of the timing relay by providing a completely sta-tic timing device vwhich has lan output suitable for direct utilization by :a magnetic amplier. This timer thereby avoids the necessity for contacts or other moving parts to convert the output of the timing device into an output compatible to the magnetic amplliiier type device.

It is therefore an object of this invention to .provide a new and improved timing device.

Another object of this invention is to provide a static timing device for use with a magnetic amplifier which eliminates the need for relay type devices.

It is another object of this invention to provide a control system in which the output may be delayedfafter the application of an input signal.

Other objects and advantages of this invention will become apparent from ythe following description taken in vconnection with the `accompanying drawings, wherein are set forth by way ofillustration and vexample-certain embodiments of this. invention. 'i

VIn the drawings,

Fig. 1 is a schematic presentation of the basicelements of my invention;

Fig. 2 is `a dnawing of the hysteresis curve for the core of Fig. 1;

Fig. 3 is a graphical presentation of the output Vot the core shown in Fig. 1;

Fig. 4 is a schematic drawing of a control system embodying my invention; and

Fig. 5 is a schematic drawing of another control system embodyn'ng my invention.

The basic theory of the magnetic timer isbest explained with reference to the circuit of Fig. 1. The core 6, shown schematically, has the hysteresis loop shown in Fig. 2. Any suitable direct Vcurrent source applies a'currentk ip to Winding Np. Therefore, winding Np has ampereturns equal to Npib. A second suitable direct current source applies a signal ip which causes the winding Np to `have ampere turns equal to Npip.

Assuming Erst that only the current `ip is flowing, the flux of the magnetic core will be at the negative 'saturation value es -as shown at point A of Fig. 2. Assume now that Npip is equal to twice the magnitude of Npip and opposite in sign. The ilux in the core will change to fthe positive saturation value +S in response tol the new value of 'total excitation applied'to'the magnetic-core.

l `United States Patent Oice 2,983,827 .Patented May 9, 1961 This flux change is not instantaneous but occupies a period of time. During the time the ilux is changing in the core from negative saturation to a positive saturation a voltage Es will be induced in winding Ns. This induced voltage Es will cause -a current is to ilow through the total secondary resistance Rs connected to the winding Ns. This relationship may be expressed mathematically.

During the time that the ilux in the core is changing, the hysteresis loop requires that the total ampere turns on the core must equal Nlp. Since there are only vthree sources of ampere turns ip, ip and is, -and since ip and ip have been determined as constants by defining them to be current sources, is must `adjust itself so that the followking equation is satisfied during the time `that the ux in the magnetic core is changing. (2) NItSNsl-s'iNpib-i-Npp The magnitude and direction which Nsz's must have is shown in Fig. 2. If we assume vertical sides to the hysteresis loop then is will remain constant `throughout the entire flux change from negative saturation to positive saturation.

Solving Equation 1 for the value of t Thus, we find that the time required for the tlux to change equals:

sqbs RSB 'The currentis may be plotted against time as shown in Fig. 3. The graph represents that the current ip was applied at the time 1:0. When the tlux reaches the positive saturation point it can no longer change so the voltage Es 'and therefore also the current is decrease to zero. If the current ip is removed, it is obvious that exactly the samerelations hold but is is in a reverse direction as the ilux returns to the starting point A shown in Fig. 2. It will be recognized, of course, that winding Np might be divided into two separate windings of turns. The current source ipwould then feed one Winding and the current'source ip would feed another winding. This might 'be desirable in the case Where it is desired to keep two circuits electrically distinct to prevent interaction. In the drawing of Fig. 1, winding Np is shown as one winding for the sake of simplicity only. The ratio of Ni,J 'to Nip is 1:2 where it is desirable that the return of the In thisembodiment l'an alternating 'zcurrent zsource :1 tis *connectedfby means'o'fnaswitch 2 through conductors 3 p 3 and 4 to a magnetic amplifier 5. The magnetic amplifier has reactance windings and 111 and positive feedback windings 12 and 13 connecting alternating current source 1 to a load 14 through self-saturating rectifiers 15 and 16. The reactance windings 10 and 11 coact to conduct current on alternate cycles of the supply voltage. For example, during one half cycle the current will flow i of this current in control windings 41 and 42 is deterthrough reactance winding 10 and feedback winding 12 g cycle, current will reverse its fiow through'the load and 'ow through the rectifier 15, the feedback winding 13 and reactance winding 11 back to the alternating current source 1 through conductor 3.

Also wound on the same cores as the reactance windto the load y14 through rectiiier 16.A On the next' half and 26. The bias windings tend to drive the core of the i magnetic amplifier to saturation, thereby increasing the current through the reactance windings, as indicatedby the arrows adjacent windings and 21. Resistor 24, in series with these windings, limits the current owing in the windings to a predetermined value. in circuit with bridge rectifier 22 and bias windings 2f) and 21 serves to filter out undesirable components providing a more nearly constant direct current.

The direct current output voltage of bridge rectifier 22 also Yenergizes an input winding 30 on the magnetic timer core 31 through inductor 23 and resistor 32. This winding induces a flux in the magnetic core in a direction tending to drive the core to positive saturation. A reset winding 33 on the magnetic core 31 is connected to be energized by a signal derived from the output of the magnetic amplifier. This signal is picked off across the load 14 and converted to direct current by rectifier 34. Resistor 35 limits the current to a predetermined level. The polarity of the flux induced in the core by winding 33 is opposite that of winding 30 and tends therefore to drive the fiuX in the magnetic core to negative saturation. A current flows in winding 33 only when magnetic amplifier 5 is producing an output current through 4load 14. Since amplifier 5 is a snap acting amplifier due to the positive feedback windings 12 and 13, the resulting current in winding 33 will be largely a function of the size of resistor 35. l

The magnetic memory core 31 has an output winding 40 which is connected to control windings 41 and 42 on the magnetic amplifier. Control windings 41 and 42 are polarized so as to decrease the loutput of magnetic amplifier 5, as indicated by the arrows adjacent these windings. The magnitude of the current owing in control Windings 41 and 42 is sufficient to overcome the ampere turnsV of the bias winding and maintain the desaturation of theV magnetic amplifier. As mentioned earlier, the magnitude of the current in windings 40, 41 and 42 is determined by the rate of change of fiux in core 31. This cuts off Inductor 23 magnetic amplifier 5 and prevents an output current:

from flowing in reactance windings 10 and 11.

A typical operation of this circuit would be as follows. Magnetic core 31 is necessarily at negative saturation prior to the beginning of a cycle for reasons tobe explained later. When switch 2 is closed, power will be applied to rectifier bridge 22 from alternating current source 1. The direct current output of bridge. 22 will flow through inductor 23, the resistor 32 and winding 30 on the magnetic core 31. The current fiowing through winding 30 immediately starts to drive the magnetic core toward positive saturation. The resultant changing flux in the magnetic core 31 induces a current in winding 40 control windings 41 and 42 induce a ux in the core oft]- magnetic amplifier'S which drives the magnetic'amplifier Y to cut of so that no output is produced.` The vmagnitude mined by the rate of change of ux in core 31 and is sufficient to prevent any output from the magnetic amplifier. In other words, there is no current owing in the reactance windings and the entire supply voltage is absorbed by the magnetic amplifier.

Bias windings 20 and 21 are connected through resistor 24 to -be energized by the direct current output of the bridge rectifierV 22. Windings 20 and 21 tend to drive the magnetic amplifier to full output by saturating the core of magnetic amplifier 5. The ampere turns of the bias windings 20 and 21, however, are not sufficient to overcome the ampere turns of the control windings 41 and 42 and therefore the magnetic ampliier remains cut off. When the winding 30 has Vdriven the core 31 to positive saturation the fiux ceases to change and the voltage induced across winding 40 drops to zero.

Thisv means that there will be no current flo-wing in control windings 41 and 42. The ampere turns of the bias winding therefore will tend to drive the magnetic amplifier to full output.

As soon as current starts to iiow in the reactance Windings 10 and 11 the positive feedback windings 12 and 13 take over and quickly increase saturation of the core until the magnetic amplifier is delivering full output to the load 14. The magnet-ic amplifier will remain at full output until the switch 2 is opened.

As soon as an output current fiows through the load 14, the voltageV developed across the load energizes a reset winding 33 on memory core 31 ywhich drives the core to negative saturation once again. This, of course, induces a current in winding 40 connected to control windings 41 and 42 however, the ampere turns of control windings ,41 and 42 are not suflicient to overcome the sum total ampere turns of both the ybias windings 20 and 21 and the feedback windings 12 and l13. The time required to reset the magnetic core is governed by the size of the resistor in series with the winding and the voltage induced across the load of the magnetic amplifier. When the switch is opened, the exciting current to magnetic amplifier 5 is removed and the load is thereby K deenergized. Reclosing the switch initiates another timing cycle since the core is at negative saturation.

It will be obvious that the load 14 of the magnetic amplifier 5 can be the control winding on another magnetic amplifier, a relay winding, motor or other similar load. The drawing illustrates the use of a winding of a relay 44 as the load 14.

'Fig 5 shows a control circuit that is generally similar to the circuit of Fig. 4 except that the circuit of the reset winding 33 is isolated from the circuit of the magnetic amplifier 5 and the load 14 that is controlled by the magnetic amplifier. The reset winding 33y is connected Vto thedirect current terminals of the bridge rectifier 22 ythrough a resistor 35 yand the contacts 45 of the relay ywinding 33.

What is claimed is: K

'1. In acontrol system, a static timing device comprising a saturable magnetic core, input winding means on said core, amplifier means having an input and lan output; an output winding on said core lfor developing a voltage responsive to a changing iiux in said core, a source of direct current, means Vfor supplying said input winding means with a direct current from said source to drive said core to magnetic saturation, said output winding being coupled to said amplifier input to form a circuit for carrying current in said output winding in response to the current in said input winding-and according to the time elepai, Whilsd input Winding is SQPPled with direct current, and means responsive to the output of said amplifier to energize said input winding means and reverse the saturation of said core.

2. In a control system, a static timing device comprising a saturable magnetic core, an input winding on said core, an output winding on said core for developing a voltage responsive to a changing iiux in said core, a source of direct current, means for supplying said input winding with a direct current from said first source to drive said core to magnetic saturation, amplifier means responsive to the voltage induced across said output winding by the changing flux in said core, la reset winding on said core, means responsive to the output of said amplifier to energize said reset winding to reverse the saturation of said core.

3. In a control system, `a static timing device comprising a saturable magnetic core, an input Winding on said core, an amplifier having an input and an output, an output winding on said core for developing a voltage responsive to a changing flux in said core, a source of direct current, means for supplying said input winding with a direct current from said source to drive said core to magnetic saturation, said output winding being coupled to said amplifier input to form a circuit for carrying current in said output winding in response to the current in said input winding and according to the time elapsed while said input winding is supplied with direct current, and means responsive to the output of said amplifier to reverse the magnetomotive force of said input winding thereby driving said core to reverse saturation.

4. In a control system, a static timing device comprising a saturable magnetic core, input winding means on said core, an output winding on said core for developing a voltage responsive to a changing iiux in said core, a first source of direct current, means for supplying said input winding means with a direct current from said iirst source to drive said core to magnetic saturation, amplifier means responsive to the voltage induced across said output winding by the changing flux in said core, a second source of direct current, means responsive to the output of said amplifier to energize said input winding means from said second source to reverse the saturation of said core.

5. In a control system, a static timing device comprising a saturable magnetic core, an input winding on said core, an output winding on said core for developing a voltage responsive to a changing ux in said core, a reset winding on said core, a source of direct current, means for supplying said input winding with a direct current `from said source to drive said core to saturation, a magnetic amplifier having a bias winding, a control winding and reactance windings, means for energizing said bias winding from a direct current source to increase the output of said amplifier, means connecting said control winding to be energized by the voltage developed across said output winding to reduce the output of said amplifier, means connected to said reactance windings and said reset winding to reverse the saturation of said core in response to an output current through said reactance windings.

6. In a control system, a static timing device comprising a saturable magnetic core, an input winding on said core, an output winding on said core for developing a voltage responsive to a changing flux in said core, a reset winding on said core, a source of direct current, means for supplying said input winding with la direct current from said source to drive said core to saturation, a magnetic amplifier having a control winding, a bias winding, a feedback winding, and reactance windings, means for energizing said bias winding from a direct current source to increase the output of said amplifier, means connecting said control winding to be energized by the voltage developed across said output winding to reduce the output of said amplifier, means connecting said feedback winding to be energized by the output of said magnetic amplifier to further increase the output of said amplifier, means isolated from said magnetic amplifier to energize said reset winding and reverse the saturation of said core in response to the output of said amplifier.

7. `In a control system, a static timing device comprising a saturable magnetic core, an input Winding on said core, an output winding on said core for developing a voltage responsive to a changing iiux in said core, a reset winding on said core, a source of direct current, means for supplying said input winding with -a direct current from said source to drive said core to saturation, a magnetic amplifier having a control winding, a bias winding, a feedback winding and reactance windings, means for energizing said bias windings from a direct current source to increase the output of said amplifier, means connecting said control winding to lbe energized by the voltage developed across said output winding to reduce the output of said amplifier, means connecting said feedback winding to be energized by the output of said magnetic amplifier to further increase the output of said amplifier, means responsive to the output of said magnetic amplifier to energize said reset winding to reverse the saturation of said core.

8. In a control system, a static timing `device comprising a saturable magnetic core, an input winding on said core, an output winding on said core for developing a voltage responsive to a changing flux in said core, a reset winding on said core, a source of direct current, means lfor supplying said input winding with a direct current 'from said source to drive said core to saturation, a magnetic amplifier having a control winding, a bias winding, a feedback winding and reactance windings, means for energizing said bias windings from a direct current source to increase the output of said amplifier, means connecting said control winding to be energized by the voltage developed across said output winding to reduce the output of said amplifier, means connecting said feedback winding to be energized by the output of said amplifier, a reset winding on said magnetic core, means connecting said reset winding to be energized by the output of said amplifier to reverse the magnetic saturation of said core.

9. In a control system, -a static timing device comprising a saturable magnetic core, an input Winding on said core, a source of direct current, means for supplying said input winding with a direct current from said source to drive said core to magnetic saturation, an output winding on said core for developing -a current in response to a changing flux in said core, a current responsive amplifier connected to said output winding, a reset winding on said core means responsive to the output of said amplifier to energize said reset winding and reverse the saturation of said core.

References Cited in the tile of this patent UNITED STATES PATENTS 2,027,312 FitzGerald Jan. 7, 1936 2,615,066 Milne Oct.'21, 1952 2,786,147 Kaufmann Mar. 19, 1957

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