US2937611A

US2937611A - Control systems

Info

Publication number: US2937611A
Application number: US539646A
Authority: US
Inventors: Schaelchlin Walter; Dennis M Boer
Original assignee: Individual
Current assignee: Individual
Priority date: 1944-06-10
Filing date: 1944-06-10
Publication date: 1960-05-24
Anticipated expiration: 1977-05-24

Description

b May 24, 1960 w. SCHAELCHLIN ETAL 2,9 f CONTROL SYSTEMS Filed June '10, 1944 2 Sheets-Sheet 1 t: v 34" J2 l a I H F l H H [I [L re Hy. 2.

WITNESSES: INVENTORS [Va/fer Jc/lae/cfi/l'fl 0%. A? nudge/101;: Miner ATTORNEY May 24, 1960 w. SCHAELCHLIN ETAL 2, 37,

comer. SYSTEMS Filed June 10, 1944 2 Sheets-Sheet 2 z INVENTCRS WITNESSES 9 Wa/fer Jc/me/M/m %.AMu aadgerm/ls'difioer ATTORNEY United States Patch CONTROL SYSTEMS Walter Schaelchlin, Pittsburgh, and Dennis M. Boer, East McKeesport, Pa., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed June 10, 1944, Ser. No. 539,646

9 Claims. (Cl. 114-221) The practice of planting mines in navigable waters for the purpose of destroying merchant shipping is well known. Such mines are provided with detonating mechanisms which are magnetically responsive to the magnetic field set up by the steel hull of a passing vessel. Accordingly, in those cases where it has been known or suspected has in the past been somewhat improved by the use of a pair of conducting wires adjacent each other or within the same sheath having end terminals trailing the ship at unequal distances.

A recent development in the structure of magnetic mines has provided such mines with a delayed action whereby such mines would be operated only after being subjected to a predetermined number of separate magnetic impulses. Assuming that such a mine had been set to explode on the fourth impulse, three vessels could pass over the mine safely before the mine would be responsive to a passing vessel. In some instances, the number of ineffective responses may even be selected to be considerably greater than three. Five, seven or nine ineflective impulses may precede the one impulse that sets oil the mine.

To effectively clear a field of such mines by sweeping operations, several traverses of the mine field by a sweeping vessel would be required, a single traverse being no longer reliable. In addition to the increased time required for sweeping, an undesirable element of doubt has been raised since the actual number of sweeping traverses necessary to clear the field could not be determined.

One of the principal somewhat specific objects of our invention is to provide an'app-aratus which is etfective to activate a delayed action mine on a single traverse of a plurality of synchronized controls on synchronously operating mine sweeping vessels. To this end, the sweep ing cables carried by each of the mine sweeping vessels are provided with means by which such cables may be periodically energized to impart a plurality of separate magnetic impulses to the mined area being swept. In this manner, mines in a given area being swept may be subjected to any selected desirable number of magnetic impulses to provide by such impulses the same or substantially the same efiect as would be provided by the passage of several ships. The sweeping vessels are thus enabled to accomplish in one traverse and over a considerable area that which has heretofore required several traverses of a single vessel.

' A further object of our invention is to provide mechanisms which are automatically operable to synchronously interrupt and synchronously re-establish the fields created by mine sweeping cables.

A further object of our invention is to provide a tim ing and synchronizing control for the mine sweeping de vices on each of the vessels, which devices include means for energizing the cables in a timed intermittent synchronous manner and which timing control is adjustable to vary the frequency of the current pulses flowing through the cable.

It is also an object of our invention to provide a control for a group of mine sweeping cables which is operable to alternately reverse the flow of currents through the corresponding cables to thereby intermittently reverse the magnetic fields which are set up between the terminals of such cables.

It is also an object of our invention to provide magnetic impulses of any desired wave form of either alternating or of direct current.

Another object of our invention is to provide a selected number of magnetic impulses arranged in any desired sequence for forward or reverse current during any one given sequence of operation.

Since it is extremely desirable to most effectively sweep an area that all the mine sweeping vessels operate in synchronism, independent timing is not a satisfactory solution and it is, therefore, an object of our invention to provide each mine sweeping vessel with a system of control such that any one of a group of vessels may operate as a master ship or a slave ship, the control being such that the impulses on the slave ships occur substantially in synchronism and are automatically synchronized if out of synchronism.

Further objects and advantages of our invention will become more apparent from a study of the following specification and the accompanying drawings, in which:

Figure 1 is a schematic showing of three mine sweeping vessels;

Fig. 2 is a diagrammatic showing of the relation of the power pulses, the initiating pulses and the synchronizing pulses;

Fig. 3 shows power pulses of the sinusoidal type, of the saw-tooth type, etc. and

Fig. 4 is a diagrammatic showing of the system of con.- trclll and power unit on each of the mine sweeping vesse s.

In Fig. 1 are shown mine sweeping vessels S1, MS and S2. The master ship is designated by MS whereas S1 and S2 designate the slave ships. In one actual application, five ships were used, two slave ships on each side of the master ship, but for the purpose of this discussion it sufiices to show one slave ship on each side of the master ship.

Each of the mine sweeping vessels is provided with a pair of adjacently disposed trailing cables of unequal length so that the magnetic fields set up between the

terminals

33', 34', 33, 34, 33", and 34" are substantially as indicated by the drawing. It will thus be apparent that as the vessels proceed through the mined region, the entire area is effectively swept by the magnetic fields se up.

To provide the necessary power impluses, the main generators on board the ships are connected to the cable. A source of electric energy for applying signalling impulses on the cable is also provided on each vessel. Electronic means are provided for picking up the signalling from the master ship. If the master ship sets up a signalling impulse on its electrodes 33 and 34, the pick-up units on the slave ships as well as the master ship, pick up this signal and set up a power pulse by suitably controlling the excitation of the generators on each of the ships. One of the electrodes, as 33, may be the hull of the ship.

A better understanding can probably be had by referring to Fig. 4 wherein the main generator GEN is shown connected to

cables

23 and 24 connected through the contacts 32 of the main line contactor MC to the terminals 33 and 34. The main generator field 22 is of a design to very rapidly build up the excitation of the generator and the exciter EXC supplying the energy to the field 22 is provided with a cumulative series field 20, a pattern field 17, having the adjusting rheostat 25, and a dlfierential field 28. This differential field 28 is connected to the terminals of the main generator to efiectively control the excitation of the main generator.

The control through the pattern field 17 of the exciter, aided by the field 20 of the exciter is designed to very rapidly build up the voltage of the exciter and not only that, it is so designed that, in the absence of the differential series field 28, the exciter would provide an excess excitation to the field winding 22 of the main generator. By this arrangement of the fields and their design, it is apparent that when the exciter is called upon to excite the main generator to produce a power impulse by the energization of the pattern field 17, the voltage of the generator will almost instantly build up to full value and in so doing the differential field 28 will decrease the effect of the pattern field so that the generator voltage of the main generator builds up to a fixed desirable value and is stabilized atv such value.

To provide the slave ships as well as the master ship with suitable signalling impulses, we provide a source of alternating current preferably of 500 cycles, evidenced by

buses

43 and 44, and this 500 cycle supply through a suitable transformer and timing capacitor 26 is connected to

buses

45 and 46 and when a signalling impulse is to be applied to the terminals 33 and 34, the

buses

45 and 46 are connected to these terminals through conductor 48 and contacts 47 of the first auxiliary relay 1AR.

To provide the proper polarity for the main generator, the pattern field 17 is disposed to be connected to a source of constant direct current potential through the polarity switches P and N, depending upon which one is operated. If it is desired to give a special shape to the power impulse, the pattern field must be correspondingly energized and to accomplish this, we provide the power pulse selector switch 13 for either connecting the pattern field 17 across the galvanometer terminals of a normally balanced Wheatstone bridge or, as shown in Fig. 4, for a square power pulse I, II, Ill, etc. of the type shown in the upper portion of Fig. 2. When a special shape of power pulse is desired the shape of the power pulse is varied by unbalancing of the Wheatstone bridge by the actuation of a cam 121 operated by the motor M. This motor M is normally, when the mine sweeping equipment is to be operated, operating at full speeds, but its control on the power pulses is efiected by means of a magnetic clutch which couples the sequence controller SC to the motor when desired.

To effect the proper timing, we provide a timer TM provided with means for adjustably varying the number of impulses and the sequence of operation. The timer means in themselves constitute no part of our invention but have been disclosed and claimed in Walter Schaelchlin application Serial No. 432,651, filed February 27, 1942, entitled Mine Sweeping Control, now Patent No. 2,397,209.

A better understanding of our system of control and particularly the contribution we make to the art can probably be had from studies of typical operating cycles for the various conditions of operation our system of control is called upon to effect. Let us assume that the generator and exciter are operating at full normal speed from the engines or turbines of the vessel, that the

directcurrent buses

1 and 12 are energized at full voltage, that the

buses

43 and 44 are supplied with the 500 cycle constant voltage alternating-current energy, and that manual operation is desired. In this case the attendant first operates switch 3 to closed position and operates 6 toward the left, as seen in Fig. 4. Switch 7 may then be ope'rated-eith'e'r toward the right or toward the left, depending upon the polarity of the power pulse desired. When switch 7 is closed for a positive power pulse, and the starting switch 3 is closed a circuit is established from the positive direct-current bus 1 through conductor 2, switch 3, conductor 4, switches 6 and 7, actuating coil 8 of the positive directional contactor P, conductor 9, actuating coil 11 of the control relay CR to the negative bus 12.

Operation of the positive directional contactor P establishes a circuit from the positively energized conductor 2 through segment 14 of the pulse-shaped selector switch 13, conductor 15, contacts 16, pattern field 17, energized in the direction indicated by the full-line arrow, rheostat 25, contacts 18 and current limiting resistor 19 to the negative bus 12. The pattern field 17 thus rapidly increases the excitation of the exciter and this exciter excites the generator field 22 through the series field 20 of the exciter. A moment later the generator voltage is up to full value and the excitation of the difierential field 23 on the exciter, but supplied from the main generator, stabilizes the voltage of the main generator at some fixed relatively high desired value. This generator voltage is supplied to

insulated cables

23 and 24. The terminals 33 and 34 are, however, not necessarily energized the instant the voltage on

cables

23 and 24 is at full value.

To effect the proper energization of terminals 33 and 34, we must take into account the fact that coil 11 of the control relay CR is connected in series with the actuating coil 8 and, therefore, energized substantially at the same instant.

Control relay CR immediately closes its contacts 31 whereupon a circuit is established from the energized conductor 2 through the actuating coil 30 of the main line contactor MC through contacts 31 to the negative bus 12. Operation of the main line contactor closes the contacts 32 and in consequence terminals 33 and 34 are energized by a power pulse from the main generator.

Another circuit is established from the energized conductor 4 through the motor M and conductor 42 to the negative bus 12. The operation of the motor M rotates the cam 121 but since, for the moment, we assume that the power-pulse-shaped controller 13 is in the position shown, no useful function is thereby accomplished.

The switch 6 is provided with suitable latching stops indicated quite schematically at 5 to hold this switch in the position desired. However, if the latch is tripped, the switch is returned to the oil position by suitable biasing means as springs.

If the manual control is to also provide the terminals 33 and 34 with negative impulses, the attendant merely alternately shifts switch 7 from the right to the left and back. If, as hereinbefore explained, a positive power pulse is utilized, the switch 7 is at the left and then if a negative impulse is to be supplied to terminals 33 and 34, switch 7 is moved toward the right. When shifted to the right, the actuating coil 35 of the negative directional contactor is energized and in consequence a circuit is established from the positively energized conductor 15 through contact 36, rheostat 25, pattern field 17, now energized in the direction indicated by the broken arrow, contacts 37, current limiting resistor 19 to the negative bus 12. The operation of the control relay CR and the main line contactor MC would, of course, be the same regardless of whether actuating coil 8 or actuating coil 35 is encrgized.

Assuming that it is desired to provide a particular shape to the power pulse curve, as indicated in Fig. 3, or one having a varying shape, then the power-pulse-shape controller 13 is moved to the left-hand position whereupon the pattern field is connected to the balance points represented by junction 124 and junction 122 of the Wheatstone bridge including the

resistors

19, 118, 119 and 117. This bridge circuit may be traced from the positively energized conductor 2 through resistor 11.7, segment and resistor 19 to the negative bus, the

resistors Y117 and 19 representing one pair of legs of the Wheatstone bridge. The other pair of legs of the Wheatstone bridge are connected, from the conductor 2 through the resistors 119 and 118 and segment 114 to the negative bus. The resistor sections 118 and 119 represent sections of a well-known regulating type of rheostat available to the trade under the trade name of Silverstat and includes a plurality of conducting leaf springs fixed in an insulating member and actuated by an actuator as 123 coacting with the cam 121. As the roller shown at the lower end of the actuator 123 traverses the cam, the balance ofv the bridge is disturbed and in consequence the field winding 17 is excited in accordance with the disturbance of the balance of the bridge. The preferred arrangement is usually to have the actuator 123 when in its mid-position so disposed with reference to the shunting elements for the resistor sections 118 and 119 that the same number are shunted on 118 as are shunted on 119 and any movement of the actuator 123 will thus alter the impedance of one with reference to the other of the legs of the Wheatstone bridge 118 and 119 in an opposite sense.

, If either of the pulse polarity contactors, that is, the directional contactors P and N are energized, the excitation circuitfor the pattern field may be traced from junction 122 through segment 116, conductor 15, contact 16 (assuming that P has been energized), pattern field 17, rheostat 25, contacts 18 to the junction 124. This control of the wave shape of the power pulse is not dependent upon manual operation of the system and may be utilized whether theship is a slave ship or master ship. It dependsprimarily upon the position of the pulse shaped controller 13.

vIf the system of control shown in Fig. 4 is tooperate as a slave of the master ship, the switches 6 and 7 are left in the position shown and the master-and-slave switch 66 is moved to the closed position. Since we are to consider slave operation, it will be apparent that the master ship at someother point in the region of the sea being swept will provide the necessary signalling impulses onterminals 33 and 34. These impulses establish a signalling impulse current from cable 23 to conductor 48, back contact 49 of the first auxiliary relay 1AR through the electronic amplifying equipment ER and conductor 51 to the terminal 34. When a signal is received, contacts 52 are closed for the duration of the signal.

It might be well to point out at this stage that the master ship is actuated by its own signals and this comes about as follows. The signalling potential on

buses

45 and 46 is continuous but on the master ship, the timer TM provides suitable short time energization of the auxliary relay 1AR and in consequence the

buses

45 and 46 are connected to the terminals 33 and 34 of the master ship. The terminals 33 and 34 as well as the corresponding terminals on the slave ships are thus energized.

This signal tension or potential thus provided to the terminals 33 and 34 of the master ship cause a signalling current to flow from terminal 33 through cable 23, conductor 48, resistor 50, the, electronic amplifier and relay ER andconductor 51 to the terminal 34. On the master ship. since the signal is rather strong, the resistor 50 is inserted to make the signal comparable to that received onthe slave ships. On the slave ship auxiliary relay lAR will not be energized and, as already stated, contacts 49 will be closed.

I When the signalling impulse closes the contacts 52, a circuit is established from the energized conductor 4 through the back contact 53 of contactor E, conductor 54, the back contacts 55 of the main line contactor MC, junction '75, contacts 52, conductor 56, back contacts 57 of contactor G and the actuating coil 58 of the time limit relay TR to the negative bus 12.

I The operation of the time limit relay establishes a circuit from the positiveconductor 56 through conductor 59, make contacts 60 of the time limit relay TR,

the back contact 61 of contactorG, junction -76, aetuatis apparent because junction 76 is positive and through the closure of contact 64 the right-hand junction of coil 94 is also positive. Similarly, since junction 75 is positive and contacts 63 are closed, the left-hand junction 175 of coil 94 is also positive.

Since the time limit relay TR has a time constant of about .5 of a second, or any other selected value, and the contactor J has an additional time constant after the dropout of time limit relay TR of about .2 of a second, or any other selected desirable time constant, the contacts 65 will close while contacts 69 are closed, whereupon a circuit is established from the positive conductor 4 through contacts 65, the master-and-slave switch 66, the pulse drive clutch coil 67, conductor .68, contacts 69, actuating coil 70 of relay A, the back contacts 71 of relay D, segment 72 of the power-pulse-sequence controller SC, the selector switch 73, which we can assume to be in the dotted line position, and conductor 74 to the actuating coil 8. Since the actuating coil 8 is operated, the power pulse for the generator and exciter proceeds in exactly the same manner as for manual control.

Operation of the relay A opens the contacts 81 to prevent any energization of actuating coil 77 when segment 78 is moved to a position so as to bridge the contact finger associated with that segment. The'relay A also closes contacts 84, shunting the contact 69 whereupon the energization of the pulse-drive clutch coil 67 is made thereafter independent of the position of contactor J. Coil 70 thus remains energized until segment 72 is moved to a position not engaging its contact fingers, in which position the contact fingers for the segment 78 are in engagement with the associated fingers. However, since contacts 81 are open, coil 77 is not energized and in consequence the actuating coil 8 is deenergized and the power pulse ends.

The moment a second signal is received and contacts 52 close, the cycle for the time limit relay TR and contactor J is repeated, but this time, since segment 72 is not in engagement with its fingers, coil 77 is energized opening the contacts 82 and closing the contacts 85. The energization of coil 77 is thus made independent of the position of contact 69, the actuating coil 35 is energized until segment 78 disengages the fingers associated with it, at which time the fingers associated with segment 89 are bridged. It will be noted that the actuating coil 35 is in this instance energized, but this is dependent upon the position of selector switch 79. The preferred arrangement is to alternate the power pulse, first negative and then positive and to effect this, selector switch 79 is assumed to be in the proper selected position. When the third signal is received, actuating coil 88 is energized through segment 89, selector switch and conductor 74 through the actuating coils 8 and 11 to the negative bus. Relay C opens its contacts 83 to prevent the energization of actuating coil 91 of the relay D and it also closes its contacts 86 to assure its continued energization until segment 89 disengages the fingers associated with it. Upon the fourth signal,,.actuating coil 91 is energized through segment 92 and selector switchwith the operations on the master ship, the synchronizing control we show will have no eflfect when a synchroniz assists ing signal is received, but let us assume the slave ship is out of synehronism so that when the fourth power pulse has been had on the master ship, the time mechanism sets up a plurality of synchronizing signals on the terminals 33 and 34 of the master ship, which signals are of substantially the nature as the usual signals except that instead of one signal lasting a fraction of a second, signals are sent out at the rate of about per second. When the signals of about 10 per second are sent out, the time limit relay TR is energized but does not have time to become deenergized and, therefore, remains in its energized position, namely in the position to maintain its contacts and 63 closed and its contacts 65 open. Since the contacts 60 are closed, and contacts 61 for the time being are closed, the actuating coil 62 is energized when the contacts 52 are closed in the first instance. Upon the very first instant that contacts 52 open, however, a circuit is established from positive junction through contacts 63, junction 175, actuating coil 94, contacts 64, actuating coil 62 of contactor I to the negative bus. Contactor G, therefore, operates to close contacts whereupon a circuit is established from positive junction 75 through contacts 52, conductors 56 and 59, contacts 60 of relay TR and contacts 95 of contactor G, actuating coil 96 of contactor H to the negative bus. This energizing circuit is, of course, established on the second closure of contacts 52 of the synchronizing signals.

The operation of the contactor H causes the closing of contacts 97, providing a more direct connection for the actuating coil 94 of contactor G, and the closure of contacts 100 of the contactor I-I establishes a circuit for the synchronizing clutch coil 99, the moment the contacts 65 of the time limit relay close, but their closure is effected in a relatively short time by reason of the fact that contactor G being now energized opens the circuit for the actuating coil 58 of the time limit relay at contacts 57.

Contacts 65 thus close while both contactors G and H are still energized to establish a circuit from energized conductor 4 through contact 65, switch 66, synchronizing clutch coil 99, contacts 100 of contactor H, coil 101 of contactor E, conductor 102, segment 103 of the sequence controller to the negative bus 12. This circuit through segment 103 will of course not be completed even though the synchronizing signals are received if the segment is in the position shown, but for any slave ship, or for that matter the master ship, not in synchronism with the synchronizing signals, some other segment than segment 72 will be in contact with its corresponding fingers and the contact fingers coacting with segment 103 will be in engagement. Since the synchronizing clutch coil 99 is energized, the sequence controller SC will continue to operate. To make certain that its operation does continue until all the elements of controller SC are in the position shown in Fig. 4, coil 101 of contactor E is energized and this contactor closes its contacts 104 making the energization of coil 101 independent of the position of contactor H and also closes its contacts 105 making the energization of the synchronizing clutch coil 99 independent of the position of contact 65. The motor M will thus continue to drive the controller SC until all the elements are in the position shown, whereupon coil 101 is deenergized, the

segment 103 and all the elements of the controller are again in the position to receive the first power pulse initiating signal.

When the ship is a master ship, the control hereinbefore discussed is substantially exactly the same as for the slave ship, except that the magnitude of the signals is reduced correspondingly by the insertion of resistor 50 in pick-up circuit. However, the timer mechanism on the master ship is used for controlling the time and sequence of the power pulses and signals of all the ships.

If the controlis to be used as a master control, then switch 6 is positioned to the light, switch 66 is closed because switch 66 is effective for both master and slave operation. When switch 6 is closed, a circuit is established from the energized conductor 4 through switch 6, conductor 106, contacts 107, the armature of the timer motor of timer TM to the negative bus 12. This timer is both adjustable in the number of its operation and its time constant, but the preferred arrangement is such that contacts T1 close for a fraction of a second and then are maintained open for about 15 seconds. The speed of operation of motor M and controller SC is so selected that when the closure of T1 initiates a signal T1 and the power pulse has started the power pulse is on for about five and one-half seconds and then 01f for about nine and one-half seconds, so that the secend time T1 closes it precedes by a short interval of time the time instant when it is desired to have a second power pulse. After the preferred closure of four times, T2 closes to produce the synchronizing signals T2 which operation will be hereinafter explained.

The instant T1 closes, a circuit is established from the energized conductor 106 through contacts T1, actuating coil 108 of the auxiliary relay lAR to the negative bus 12. The auxiliary relay is for an instant energized and closes the contacts 47 and opens the contacts 49 and 109. A moment later contacts 47 are opened and contacts 49 and 109 are again closed. The instant contacts 47 are closed a signal is impressed on terminals 33 and 34 and that signal is picked up by the electronic device to close contacts 52. When contacts 52 close, the operation of the controller is as hereinbefore explained such that a power pulse follows the signal. Since T1 is closed but a short interval of time, the actuating coil 108 is deenergized shortly thereafter and no further signal is impressed on terminals 33 and 34.

After four power pulses have been impressed upon terminals 33 and 34, contacts T2 close whereupon a circuit is established from conductor 106 through contacts T2, contacts 109, actuating coil 111 of the second auxiliary relay 2AR and adjustable resistor 112 to the negative bus. Capacitor 113 is connected in parallel to the actuating coil 111 and the resistor 112 so that an instant later when the contacts of the auxiliary relay close to energize the actuating coil 108, contacts 110 will remain closed long enough as the condenser or capacitor 113 discharges through the coil 111 to make certain contacts 109 are open, but since the energization for coil 111 at this instant is dependent entirely upon the time the capacitor 113 discharges, it will be apparent that an instant later contacts 110 open, deenergizing the actuating coil 108 and again opening contacts 47. The instant contacts 47 open, the signal is discontinued but coil 111 is again energized through contacts 109. It is thus apparent that the auxiliary relays 1AR and 2AR operate alternately in rapid succession for as long as contacts T2 are closed. Contacts T2 need only remain closed long enough to provide a sufiicient number of signals to synchronize the master ship and the slave ships to the action of the timer, whereupon when T1 closes, producing the first power pulse initiating signal, all of the power pulses will, through the electronic pick-up device, operate at the same time. Since the synchronizing signals occur after every four power pulses, it is apparent that positive synchronous operation is maintained.

From the foregoing, it will be apparent that we have provided a system of control wherein any selected number of power pulses and any number of ships may be definitely synchronized in their operation to produce the magnetic fields to detonate mines that are provided with electromagnetic delayed action devices.

We are, of course, aware that those skilled in the art, particularly after having had the benefit of the teachings of our invention, may devise similar systems of control for accomplishing the novel results accomplished by our control, and we, therefore, do not wish to be limited to the particular circuits herein shown, but wish to be limited only to the scope of the claims as hereto appended.

We claim as our invention:

1. In a mine sweeping control utilizing a plurality of mine sweeping vessels each being provided with a pair of spaced electrodes for producing a magnetic field simulating the passing of a merchant vessel, in combination, means for producing a signal current in the electrode circuit ofone of the vesselsselected as a master ship, electronic means associated with each of the electrode circuits of each vessel for picking up the signal current, electric means, responsive to the signal current, for causing a relatively heavy power impulse current to flow between the electrodes of each of the vessels, timing means on the master ship for repeating the signal and power impulses on the master ship and each of the slave ships at selected number of times, and means responsive to the timing means for periodically controlling the synchronous olperation of the power pulses on the master and slave s ips.

2. In a mine sweeping control utilizing a plurality of mine sweeping vessels each being provided with a pair of spaced electrodes for producing a magnetic field simulating the passing of a merchant vessel, in combination, means for periodically producing a power pulse initiating signal current in the electrode circuits of all the ships, means responsive to the power pulse initiating signal current in the electrode circuits of all the vessels of a group doing rmne sweeping operations for simultaneously producing a power pulse current between the electrodes of the ships to produce magnetic fields in the area being swept simulating the passage of a plurality of merchant vessels to thus cause detonation of mines of the delayed action type in the area being swept.

3. In a mine sweeping control utilizing a plurality of mine sweeping vessels each being provided with a pair of spaced electrodes for producing a magnetic field simulating the passing of a merchant vessel, in combination, means for periodically producing signal current impulses of relatively short duration in the electrode circuits of the mine sweeping vessels, control circuits on each vessel, a source of electric energy for the control circuits,

electronic means responsive to the signal current impulses for periodically connecting the control circuits to the source of electric energy, means responsive to the energization of the control circuits for producing periodic power impulses across the electrodes to produce a magnetic field in the area being swept at each power impulse simulating the passage of a plurality of merchant ves- 1 sels, and means operable from the control circuits for alternately altering the electrodes.

4. In a mine sweeping control utilizing a plurality of mine sweeping vessels each being provided with a pair of spaced electrodes for producing a magnetic field simulating the passing of a merchant vessel, in combination, means for periodically producing signal current impulses of relatively short duration in the electrode circuits of the mine sweeping vessels, control circuits on each vessel, a source of electric energy for the control circuits, electronic means responsive to the signal current impulses polarity of the power pulses of the for periodically connecting the control circuits to the source of electric energy, means responsive to the energization of the control circuits for producing periodic power impulses across the electrodes to produce a magnetic field in the area being swept at each power impulse simulating the passage of a plurality of merchant vessels, means for'controlling wave form of the power impulses, and means operable from the control circuits for alternately altering the polarity of the power pulses of the electrodes.

5. In a mine sweeping control utilizing a plurality of mine sweeping vessels each being provided with a pair of spaced electrodes for producing a magnetic field simulating the passing of a merchant vessel, in combination, means for periodically producing signal current impulses of relatively short duration in the electrode circuitsof the mine sweeping vessels, control circuits on each vessel, a

source of electric energy for the control circuits, electronic means responsive to the signal current impulses for periodically connecting the control circuits to the source of electric energy,.means responsive to the ener-1 mine sweeping vessels each being provided with a pair of spaced electrodes for producing a magnetic field simulating the passing of a merchant vessel, in combination, means for periodically producing signal current impulses of relatively short duration in the electrode circuits of the mine sweeping vessels, control circuits on each vessel, a source of electric energy for the control circuits, electronic means responsive to the signal current impulses for periodically connecting the control circuits to the source of electric energy, means responsive to the energization of the control circuits for producing periodic power impulses across the electrodes to produce a magnetic field in the area being swept at each power impulse simulating the passage of a plurality of merchant vessels, means for controlling wave form of the power impulses, means operable from the control circuits for alternately altering the polarity of the power pulses of the electrodes, and means for periodically synchronizing the power impulses produced.

7. In a mine sweeping control for producing a plurality of magnetic fields in the area being swept simulating the passage of several merchant vessels, in combination, a pair of terminals disposed in the region being swept, means for producing periodic signal potentials across the terminals to cause periodic signal currents to flow between the terminals, and means, responsive to the signal current, for producing a relatively large magnetic field producing current to flow between the terminals following each signal current.

8. In a mine sweeping control for producing a plurality of magnetic fields in the area being swept simulating the passage of several merchant vessels, in combination, a pair of terminals disposed in the region being swept, means for producing periodic signal potentials across the terminals to cause periodic signal currents to flow between the terminals, means, responsive to the signal current, for producing a relatively large magnetic field producing current to flow between the terminals following each signal current, and means for selectively producing a varying magnetic field producing current to give any selected wave form to the power pulse produced by magnetic field producing current.

9. in a mine sweeping control for producing a plurality of magnetic fields in the area being swept simulating the passage of several merchant vessels, in combination, a pair of terminals disposed in the region being swept, means for producing periodic signal potentials across the terminals to cause periodic signal currents to flow between the terminals, means, responsive to the signal current, for producing a relatively large magnetic field producing current to flow between the terminals following each signal current, other terminals disposed in adjacent areas to be swept of mines, and means for synchronizing the production of power pulses in other terminals with the power pulses in the first pair of terminals.

No references cited.