US2135921A - Automatic telephone system - Google Patents

Description

Nov. 1938. N. H. SAUNDERS ET AL 2,135,921

AUTOMATI C TELEPHONE SYSTEM Filed Sept. 12, 1955 CONN.

FINDER REPEATER 90 G1 IH IN VEN TORS Q L NORMAN H.SAUNDER$ RALPH R.FOWLER TO EXCHANGE B ATTORNEY.

1 Patented Nov. 8, 1938 UNITED STATES AUTOMATIC TELEPHONE SYSTEM Norman H. Saunders and Ralph R. Fowler, Chicago, 111.. assignors, by mesne assignments, to Associated Electric Laboratories, Inc., Chicago, 1ll., a corporation of Delaware Application September 12, 1935, Serial No. 40,196

21 Claims.

The present invention relates in general to automatic telephone systems, and more particularly to such systems as comprise two or more exchanges which are interconnected by trunk 5 lines. The object of the invention, briefly stated, is to provide new and improved trunk circuits for interconnecting two automatic exchanges.

A special feature of the invention is a new and improved repeater.

may be used at each end of a two way trunk line.

The repeater includes a number of improvements among which may be mentioned those having to do with the two way operation of a trunk line and others relating to the automatic transmission of standardized or corrected im pulses.

The invention will be described hereinafter with reference to the accompanying drawing, 20 which shows diagrammatically sumcient of the equipment and circuits involved to enable the invention to be explained and understood.

Referring to the drawing, the equipment there illustrated is all located in one exchange, which may be the type shown in the Ostline Patent No.

25 2,099,429, granted Nov. 16, 1937, or in the Saunders Patent No. 1,999,788, granted April 30, 1935. The exchanges described in these disclosures are small exchanges employing finder connector links for setting up connections. The exchange might also be a relay exchange of the type disclosed in the Ostline Patent No. 2,023,239 granted Dec. 3, 1935, and there are other exchanges to which the invention is applicable.

The drawing shows one end of a trunk line interconnecting two exchanges of the above mentioned character. There may be a number of these trunk lines, all the same as the one shown. The inter-exchange portion of the trunk line shown comprises two conductors 4| and 42. At the end which appears in the drawing the trunk line is provided with a repeater and a line circuit, both of which are so labeled in the drawing, and is multipled in the banks of connector switches and finder switches." The finder and connector branches of the trunk line appear at the right of the drawing, which also indicates one finder and one connector having access to the trunk line. The equipment at the other end of the trunk line may be exactly the same and for convenience it will be assumed that such is the case.

In the following description of the operation, the exchange at which the equipment shown in the drawing is located will be referred to as exchange A, and the exchange at the other end of the trunk line will be referred to as exchange B.

Assuming now that a subscriber in exchange A desires to call a subscriber in exchange B, he-

60 will remove his receiver, whereupon his line is One of these new repeaters.

picked up by the finder switch of a finder connector link. 'Ihe calling subscriber then dials the digit or digits assigned to exchange B, with the result that the connector of the link in use will be operated to select the group of trunk lines extending to that exchange, and will then proceed to select an idle trunk line in the group. Assuming that the connector indicated in the drawing is used, and that the trunk line shown is the trunk selected, when the connector wipers 24 engage bank contacts 8l9 a ground will be placed on the test wiper 4. A circuit is thus completed by way of 4, I0, 81, and I8.to the cut-off relay H5 in the line circuit. Upon energizing, relay l5 disconnects the line relay l4, and at 23 closes a circuit for relay iii. The operation of the latter relay has no significance at present.

The completion of the circuit of the cut-off relay l5, as above described, also grounds conductors 25 and 26 which extend between the line circuit and the repeater, terminating at the repeater in relays 49 and 39, respectively. Relays 49 and 39 therefore have their circuits closed simultaneously. Relay 39 is arranged to open the circuit of relay 40 at 50, but is slow to energize, and it follows that relay 4!! pulls up and locks itself at 45 before relay 39 operates.

On energizing, relay 40 connects the trunk conductors 4i and 42 with the left-hand windings of the repeating coil by way of 44 and 48. Since the two left-hand windings of the repeating coil are connected together by way of the right-hand winding of the electropolarized relay 31 and contacts and 13, the right-hand winding of relay 31 is bridged across the trunk conductors 4i and 42. Responsive to the closure of this bridge, the line relay such as Id at exchange B operates, starts up a finder in exchange B, and makes the trunk line busy at that exchange. As a result the trunk line is extended through in exchange B to the connector of a finder connector link. These operations will be described more in detail and with reference to the drawing in the course of the explanation of a call originating at exchange B and directed to a subscriber in exchange A.

As a further result of the operation of relay 40, circuits are closed at 46 for the left-hand or polarizing winding of relay 31 and for relay 38. The direction of current flow over the trunk 4I-42 is such that relay 31 does not operate. Relay 38 energizes and locks itself by way of 53 and 5| as soon as relay 39 operates. In energized position relay 38 disconnects the conductors 85 and 86 from conductors 4| and 42 of the trunk and connects them through by way of contacts of the reversing relay 36 to the right-hand windings of the repeating coil. Conductor 85 is thus extended by way of 52, contacts controlled Upon energizing, relay 33 close; a forreiay 32 at 33. Relay 32, on energizing, locks itself at 33 so that it can stay up independent of ground at 32, and closes a circuit for the slow acting release relay 33 at 33. On energizing, relay 33 closes another circuit for itself by way of 32 and 33, and grounds conductor 23 at 34.

By the latter operation ground is extended back over 23, 31, I3, and l, to the release trunk conductor in the connector to maintain the connectar and finder of the link circuit in operated position after the falling back of the line and release relays of the connector. These relays deenergize following the switching through operation. Ground on conductor 23 also holds up the cut-off relay ii, and relays 33' and 33 of the repeater.

When the calling subscriber dials the next digit of called number, the calling line loop is interrupted a number of times depending on the value of the digit, and as a result theline relay 33 is deenergized a mmiber of times to produce a like number of interruptions in the bridge across trimk conductors 4| and 42, and thus repeat the digit over the trunk line to exchange 13. The repeating operation will now be described in detail.

When line relay 33 deenergizes at the begin- ,ning of the first interruption it breaks the circuit of relay 32 at 53 and relay 32 falls back. Relay 33 is slow to release and remains operated while relays 33 and 32 are responding to dialling. On falling back relay 32 closes a circuit for the slow acting relay 2] by way of 32, 33, and 31. Relay 21 energizes and stays operated until the digit is completed. In energized position, relay 2! closes a circuit for relay 23 by way of 32, 33, and 3|. Relay 23 therefore energizes and stays up until after relay 2! falls back.

The impulses, or interruptions, are repeated by relays 23, 33, and 3|, under control of relay 32. When relay 32 falls back it closes a circuit for relay 33 by way of 32, 33, 13, contacts controlled by 63', and contacts controlled by II. On energizing, relay 33 breaks the bridge across the trunk conductors II and 32 at 13, and at 12 closes a circuit for relay 23. Relay 23, on energizing, breaks the bridge at 15 and at H closes a circuit for relay 3| in parallel with relay 33. On energizing, relay 3| locks itself at 1|, and breaks the circuit of relay 33. Relay 33 falls back, closes a point in the bridge at 13, and breaks the circuit of relay 29 at 12. Relay 23 falls back'and closes the bridge at 15, thus ending the first interruption in the bridge across the trunk "-32.

In the meantime the line relay 33 pull; up again, recloses the circuit 'of relay 33 at 33, and at 33 recloses the circuit of relay 32. Relay 32, however, cannot energize until the relays 23, 33, and 3| have proceeded with their automatic operation to the point where relay 3| has locked itself and relay 33 has fallen back. At this stage, if the line relay 33 is up, a circuit is completed for relay 32 by way of I2, 13, and 33, and relay 32 reenergizes, breaking the locking circuit of relay 3| at 33. Relay 3| falls back, whereupon conditions are the same as they were before dialling startedexcept that relays 21 and 23 are holding on due to the slow release characteristics of relay 21. If the digit dialled is the digit'l no further interruptions will occur at the moment, and relay 21 will fall back, followed by the deenergization of relay 23. If the digit dialled is greater than 1, relay 21 will of course be maintained operated by an additional impulse or impulses from relay 32.

The relays respond to the remaining interruptions of the digit the same way. At the beginning of each interruption relays 33 and 32 fallback. The latter relay closes a circuit for relay 33, whereupon relays 33, 23, and 3| pull up successively and relay 3| locks. Following the operation of relay 3|, relays 33 and 23 fall back successively. At the end of each interruption relay 3| pulls up again, followed by the energization of relay 32 contingent on relay 33 having restored. It will be seen that the length of the repeated interruptions produced by opening the bridge at I3 and 13 is independent of the length of the interruptions in the circuit of line relay 33, and has a constant value determined by the operating characteristics of relays 23, 33, and 3|. A repeated interruption.

starts with the opening of the bridge at 13 on the energization of relay 33 and it lasts while re ay 23 is pulling up, relay 3| is pulling up, relay 33 is falling back, and relay 23 is falling back, the interruption being ended when the bridge is closed at II by the deenergization of relay 23.

In view of the foregoing it will be understood that some care is necessary to insure that the relays have the proper operating and release characteristics, and it will be desirable to give some values that have been found to work well in practice. An example that may be cited is a commercial repeater designed to produce repeated interruptions having a constant length or duration of .060 second. With this length of interruptionrand with a dial speed of 10 impulses, or interruptions, per second, the ratio of the open periods to the closed periods is as 60 to 40. That is, the repeater output during dialling is what is known as a 60 per cent break and a 40 per cent make. Since the open period or break remains constant the ratio of make to break changes with the dial speed, and excessive variations of dial speed are not permissible. The range within which the repeater will work satisfactorily is about 8 to 12 impulses per sec- The desired constant break of .060 second is secured by using the following values: Relays 33 and 3| are each wound to a resistance or 210 ohms, and relay 23 to a resistance of 300 ohms. The non-inductive resistance 33 shunting relay 3| is 2000 ohms, resistance 31' shunting relay 33 is 1000 ohms, and resistance 33' shunting relay 23 is 2000 ohms. While not material to the length of break, it may be stated also that the line relay 33 has a resistance of 200 ohms and relay 32 a resistance of 210 ohms. The latter relay is shunted by a resistance 33 of 2000 ohms. The battery voltage is assumed to be about 46 volts. With the above values standard adjustments may be used which last for a long time,

that other sets of values could be used, a change in one relay being compensated for by a change at another.

Some further operations which take place during the repeating of a digit will now be explained. At 88 relay 21 short-circuits the upper righthand winding of the repeating coil, which improves the operation of relay 34. With the same object, the impedance element 35 is shunted by resistances 84 and 85' at 83 and 19. The impedance element 35 functions to balance the line circuit in a well-known manner during the talking periods and for this reason is of the same impedance value as the impedance value of the line relay 34. The shorting out of an impedance such as 35 to improve the response of the line relay in the other side of the line has been done before, but in this repeater the mere short circuiting of the impedance 35 would not work. If impedance 35 were short circuited in the usual way by relay 21 during dialling, the removal of the short circuit at the end of a digit would suddenly introduce the impedance into the circuit of line relay 34, causing the current to fall momentarily and producing a slight or transient deenergization of the line relay. A very short deenergization such as this, only a small fraction of the length of a standard interruption, does no harm in an ordi-v nary repeater; but in this repeater only a very momentary falling back of relay 34 is sufiicient to deenergize relay 32, which initiates a series of operations resulting in the transmission of a standard length impulse. To avoid any possibility of a false deenergization of line relay 34, therefore, relays 21 and 28 are arranged to remove the shunt from impedance 35 in two stages. During the dialling of a digit, impedance 35 is shunted by resistances 84 and 85' which may be 50 and '100 ohms, respectively. When the digit is completed, relay 21 falls back and removes the 50 ohm shunt of resistance 84. An instant later relay 28 falls back and takes off the 700 ohm shunt of resistance 85. This arrangement has been found to be suificient to prevent any false deenergization of relay 34 under ordinary conditions. For more severe conditions, it is apparent that another slow acting relay could be added to secure removal of the shunt in three stages instead of two.

Other operations which may be mentioned are the shunting of the right-hand winding of relay 31 at 18 during dialling, and the use of a priming circuit for line relay 34 to assist this relay in energizing quickly during dialling. The object of the first mentioned operation will be obvious. As to the second, it will be noticed that whenever line relay 34 falls back during the dialling it connects itself in series with relay 32 at 58, a resistance 98' being included in the circuit.- Resistance 98' may have a value of 3000 ohms and relays 34 and 32 cannot operate in series with this resistance. The current flow established in relay 34, however, primes the relay and enables it to respond more readily when the line circuit is closed after each interruption.

Continuing now with the general explanation, the digits of the called number are repeated in the manner described and result in the completion of the connection to the desired subscribers line in exchange B. When the called subscriber answers, the connector in use reverses the direction of current flow over the trunk line 4I- 42 in the usual manner, causing the operation of the electro-polarized relay 31. On operating, relay 31 closes a circuit for reversing' relay 38, which reverses the direction of current flow in the calling subscriber's line. At this point it may be mentioned that if the calling party should accidentally operates or move his dial so as to send one or more impulses, which would cause relay 31 to fall back due to being short circuited, the energized position of reversing relay 36 is not disturbed because of the provision of a locking circuit by way of 55 and 11.

When the calling subscriber hangs up his receiver, the release relay 33 falls back following the continued deenergization of relays 34 and 32. Ground is thus removed from the holding circuit at 64, and the link circuit in use by the calling party is restored to normal in the usual manner. When relay 32 in the repeater falls back, relays 21 and 28 of course energize and relays 29, 38, and 3| go through their operations, but the interruption produced thereby in the bridge across the trunk does no harm. Relays 21, 28, and 3| are deenergized by the falling back of relay 33, which opens the circuits of the former relays at 52 and 83. The removal of ground from conductor 25 at 64 by the falling back of relay 33, also lets relays l and 48 fall back. The latter relay removes the bridge from conductors 4| and 42 and initiates the release of the equipment in exchange B.

If the release of the connection should take place while current is reversed on trunk line 4l-42, no lock up can occur, due to the arrangement involving slow to release relays 39 and 38. When relay 33 falls back, the line relay I4 is promptly connected up by the falling back of relay l5, and if the trunk line were connected through at this time the line relay of the distant connector would hold up in series with the line relay l4, energizing this latter relay also. Such operation is prevented because relay 48 falls back promptly on the falling back of relay 33 and initiates the release at the distant exchange, while the slow acting relays 39 and 38 hold on for an interval and hold the trunk line open at 52 and 54 long enough for the distant connector to release and reverse the direction of current fiow back to normal. The holding open of the trunk at 52 and 54 involves also the maintaining of the incoming line conductors connected through to the repeating coil by way of contacts of the reversing relay 36. Since relays 31 and 36 are energized when relay 48 falls back, assuming the release takes place while current on trunk line 4 l42 is reversed, and since it takes an instantforrelays-31 and 36 to deenergize, contacts 58 and 41 on relay 48 are provided to disconnect line relay 34 and impedance 35 from the repeating coil and prevent any possibility of the false operation of relay 34 in series with relay l4.

In order to complete the explanation, the operation of the repeater and line circuit on a call from exchange B to exchange A will be considered.

When the trunk line is seized at exchange B, the repeater on that end -of the trunk places a bridge across the trunk line just as explained in the discussion of the previous call. The bridging of the trunk line results in the operation of the line relay l4 at exchange A. Upon energizing, relay l4 grounds conductors 26 and 81 at 18, the ground on 81 serving to make the trunk line busy in the banks of the connectors. Ground on 26 operates relay 39, which opens the circuit of relay 48 at 58. It will be noted that on a call coming from exchange B conductor is not grounded immediately, so relay 38 prevents relay 40 from operating. The line relay H also connects at I1 the cut-ofi relay I5 to test contacts such as IS in the banks of the finders, thus placing a test potential on these contacts, and at I8 closes a finder start circuit including conductor 90. An idle finder is then started up in known manner in search of the trunk line. Assuming the finder in use is the one indicated in the drawing, when the test wiper 1 reaches test contact II, the findertest relay energizes in series with cut-oi! relay l5 and stops the finder. Relay l5 locks itself at 2|, removes the shunt resistance at 22, and disconnects the line relay ll, which latter relay now falls back. The cut-ofl relay I5 is held energized by ground from the finder and later from the connector of the link, the circuit including the finder test wiper I. These circuits are known and are fully explained in the disclosures hereinbei'ore referred to. It will be noted that as soon as the finder connects with the trunk line the conductor 25 will become grounded but by this time the relay 39 has energized andhence relay 0 cannot pull up.

It will be understood therefore that on. an incoming call from exchange B the repeater at exchange A is not used. The trunk conductors 4| and 42 continue through the repeater to the banks of the finders, and after a finder has picked up the trunk line, to the line relay oi the associated connector- The connection is completed by operating the connector responsive to the digits repeated over the trunk line by the distant repeater in the manner previously explained.

The invention having been described, that which is believed to be new and for which the protection oi. Letters Patent is desired will be pointed out in the appended claims.

What is claimed is:

1. In a telephone system, two exchanges, finder and connector switches in each exchange, a two-way trunk line connecting said exchanges, a repeater associated with said trunk line at each end thereof, and two branches of said trunk line at each end, one branch accessible to connector switches to extend an outgoing connection from an exchange via the associated branch repeater and the other branch accessible to finder switches to find the trunk line over which an outgoing connection has been extended from another exchange.

2. In a telephone system, an exchange including finder and connector switches, a trunk line extending to another exchange, a first branch over which said trunk line may be seized by a connector to extend an outgoing connection to the other exchange, a repeater operable to repeat impulses when the trunk line is seized by a connector, a second branch of said trunk line accessible to said finders when an incoming connec-- tion is received, line circuit equipment controlled over the trunk line when an incoming call is received from the other exchange to cause a finder .to find and seize said second branch, and means in the-repeater for discriminating between outgoing and incoming calls to connect the same into the trunk line only on outgoing calls.

3. In a telephone system an exchange comprising finder and connector switches, a two-way trunk line connecting said exchange with another exchange, a repeater, means responsive to the seizure of said trunk line by a connector for inserting said repeater therein to provide a holding circuit for said connector, a line relay energized over said trunk line when the same is seized at the other exchange, means controlled by said line relay for starting a finder switch in search of the trunk line, and means controlled by said line relay for preventing the insertion of said repeater.

4. In a telephone system, an inter-exchange trunk line, a repeater, two conductors normally connected together, a quick-acting relay energized over one conductor and a slow-acting relay energized over the other, said slow relay having means to break the circuit of the quick relay, means for grounding said conductors simultaneously. when the trunk line is seized at one end, whereby the quick relay is energized, means whereby said quick relay locks itself and connects the repeater in the trunk line, and means for grounding the conductor associated with the slow relay while the other conductor is free of ground when the trunk line is seized at the other end, whereby the slow acting relay is effective to prevent the operation of the quick relay and the connection of the repeater in the trunk line.

5. In a repeater, a line relay and an impedance coil bridged a cross the incoming line in series with a battery, contacts on the line relay for repeating impulses over the outgoing line, means for shunting the said impedance coil during the operation of said line relay in repeating a series of impulses, and means for removing the shunt at the end of a series in a plurality of stages, whereby the momentary false deenergization of said line relay which might result if the entire shunt were removed at once is effectively prevented.

6. In a telephone system, two exchanges, a two-way trunk line connecting said exchanges, a repeater at one exchange including a repeating coil, a relay in said repeater responsive to the seizure of said trunk line to bridge one side of said repeating coil across the trunk line, a line relay in the other exchange operated by the closure of the bridge, and a busy test circuit completed by the operation of said line relay, whereby upon seizure of the trunk line it is made busy at the other end by the successive operation of only two relays, one in the repeater atthe end seized and the other being the line relay at the other end.

'7. In a repeater, means responsive to the seizure of the repeater for closing a bridge across the outgoing line, a line relay energized over the incoming line, a series of relays responsive to the deenergization of said line relay, and circuit arrangements whereby said series of relays open said bridge for a predetermined interval which is independent of the length of time said line relay is deenergized.

8. In a repeater, a line relay, a series of three other relays, circuits for automatically and successively energizing said other relays and for successively deenergizing two of said other relays responsive to the momentary deenergization 01. said line relay, and an impulse bridge held open by contacts on said two relays while the same are energized.

9. In a repeater, a line relay, a plurality of other relays, means responsive to the momentary deenergization of said line relay for automatically energizing a plurality of said other relays in succession and for deenergizingthem in the same order, and an impulse repeating bridge including contacts on one oi! said plurality of relays.

10. In a repeater, a line relay, a second relay initially responsive to said line relay u n re of the repeater, an outgoing trunk line, automatic impulse repeating means for transmitting impulses over said trunk line controlled by said second relay, and circuits effective during the repeating of a digit for making the response of said second relay to said line relay contingent o the operation of said repeating means.

11. In a repeater, a line relay, a second relay energized by said line relay when the same responds to the seizure of the repeater, said second relay deenergizing when said line relay falls back at the beginning of an interruption, repeating means responsive to the deenergization of said second relay for producing an interruption of predetermined duration in the outgoing line, and circuit arrangements for preventing the reenergization of said second relay responsive to the reenergization oi. the line relay until the operation of said repeating means has reached a definite stage.

12. In a repeater, a line relay, a second relay energized by said line relay when the same responds to the seizure of the repeater, said second relay deenergizing when said line relay falls back at the beginning of an interruption, repeating means responsive to the deenergization of said second relay for producing an interruption of predetermined duration in the outgoing line, circuit arrangements for preventing the reenergization of said second relay responsive to the reenergization oi' the line relay until the operation of said repeating means has reached a definite stage, and means for preventing said repeating means from fully completing its cycle of operation until said second relay has become reenergized.-

13. In a repeater,- a line relay, a second relay energized by said line relay upon the seizure of the repeater, a release relay initially energized by said second relay, and a circuit closed by said release relay over which the same is subsequently controlled by said line relay.

14. In combination, a repeater, a trunk line normally extending through said repeater, means responsive to the seizure of the trunk line for opening the trunk line at the repeater, for connect ng a line relay bridge across the trunk line on the seized side of the break, and for connecting an impulse repeating bridge across the trunk line beyond the break, means for promptly opening said repeating bridge upon the release oi. the trunk line by the seizing means, and means for maintaining the open condition of the trunk line at the repeater for a predetermined time after the repeating bridge is opened.

15. In a repeater, a line relay, a plurality of other relays, means responsive to the deenergization of said line relay for automatically and successively energizing said other relays and for deenergizing them in the same order, and an impulse repeating bridge including serially related contacts on two of said other relays.

16. In a repeater, a line relay responsive to digital series of interruptions, means including a pair. of auxiliary relays controlled by said line relay for repeating said interruptions, contacts on one 01' said auxiliary relays for beginning each repeated interruption and contacts on the other auxiliary relay for ending each repeated interruption.

17. In a telephone system, two exchanges, a

two-way trunk line extending between said exchanges, a repeater associated with said trunk line at each end thereof, connector switches in each of said exchanges individually operative to select said line to extend a call thereover, finder switches in each of said exchanges individually operative to search for and seize said line when a call is received thereover, and means for selectively rendering the repeater at the exchange receiving the call inoperative.

18. In a'telephone system, two exchanges, a two-way trunk line extending between said exchanges, a repeater associated with said trunk line at each end thereof, connector switches in each of said exchanges individually operative to select said line to extend a call thereover, finder switches in each of said exchanges individually operative to search for and seize said line when a call is received thereover, and means controlled by the finder that seizes said line for selectively disconnecting the repeater at the exchange receiving the call from the circuit of said line.

19. In a telephone system, two exchanges, a two-way trunk lineextending between said exchanges, a repeater associated with said trunk line at each end thereof, connector switches in each.

of said exchanges individually operative to select said line to extend a call thereover, finder switches in each of said exchanges individually operative to search for and seize said line when a call is received thereover, means associated with the finder switch operated to seize said line for preventing the connector switches at the same exchange from connecting with the line to extend a call thereover, and means controlled by the operated finder switch for rendering the repeater connected to the trunk line at the exchange receiving the call inoperative.

20. In a repeater, incoming and outgoing lines, a line relay, a battery and a line balancing impedance element, said selector, battery, and impedance all connected in series and bridged across said incoming line, said line relay including means for repeating impulses over said outgoing line, means for shunting said impedance element during the operation of said line relay in repeating a series of impulses, said impedance element so connected that it would cause false operation of said line relay from one of its two positions to the other it said shunting means were removed in its entirety at the same instant, and means for removing said shunting means in a plurality of stages to prevent such false operation.

21. A repeater adapted to interconnect a pair of line circuits to transmit control impulses therebetween comprising, a line relay responsive to impulses received over one of said line circuits, a plurality of relays responsive to operation of said line relay from one oi. its two positions to the other for repeating said impulses over the other of said line circuits, and control circuits for interconnecting said plurality of relays and said

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