US3548110A - Selecting means - Google Patents

Selecting means Download PDF

Info

Publication number
US3548110A
US3548110A US3548110DA US3548110A US 3548110 A US3548110 A US 3548110A US 3548110D A US3548110D A US 3548110DA US 3548110 A US3548110 A US 3548110A
Authority
US
Grant status
Grant
Patent type
Prior art keywords
means
relay
relays
circuit
marker
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
Inventor
Karl Axel Lundkvist
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Telefonaktiebolaget LM Ericsson AB
Original Assignee
Telefonaktiebolaget LM Ericsson AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Grant date

Links

Images

Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04QSELECTING
    • H04Q3/00Selecting arrangements
    • H04Q3/0004Selecting arrangements using crossbar selectors in the switching stages

Description

United States Patent Inventor Karl Axel Luntlkvist [51 Int. Cl H04q 3/00 Stockholm, Sweden [50] Field 01 Search 179/ 1 8AR, Appl. No. 639,760 l8.3,18.7,18.77;340/147, 1471" Filed May 19, 1967 Patented Dec. 15, 1970 N0 References Cited Assignee Telefonaktlebolaget LM Ericson Primary Examiner wmiam Cooper Stockholm Sweden Attorney-Hane & Nydick a Swedish corporation Priority June 2, 1966 m Sweden ABSTRACT: In order to avoid the use of relay chains and 7529/1966 pulse-stepping means for the selection of lines, markers, analyzers and registers in automatic telephone exchanges, there is disclosed apparatus for selecting one and only one of a gg fi i g rf c g. plurality of electric circuits. The selected circuit is marked via g its own marking circuit. Selection and marking are carried out U.S. Cl 179/18 in one step through the agency of bistable circuits.

WWW/Em REG L *1 RE 1! h 81 7 RE n f RR! oo- 2, MK max/s2 "'5: JW/TCH MH 7 RSM 1a r1 war v a g e Lg MR1 M RR2 b BM 5M! 5M i r z X -P26 ZSLp-Iv'v-up zgfi-t- I 5 x AL MR2 MR3 L R1 4%; 1. R, RMM e s! 2 A M J;l 17 wa -5 f R11 3*, l 111 M 71 A R70 2 I02 1 R8 I r 87 y -v 2 82 A- R6 I MH4 :2; R 12 SELECTING MEANS Thepresent invention concerns a means for selecting one electric circuit out of a plurality of such circuits, excluding all other circuits of the plurality, and for marking the selected circuit by connecting an electric potential to a marking conductor that is individual for the circuit. This problem appears especially in automatic telephone exchanges with cross bar switches and with markers or similar common selecting means. Within a group of lines only one connection at a time can be established and the intended line must be distinguished from all other lines by means of a circuit that is unique to the line. At some connections a plurality of free selectors and the like can be expected to carry out theconnection, but when only one selector is desired or required this selector must be selected and separated.

Up to now these selections have been carried out by means of relay chains, one relay for each circuit being included in the relay chain. The relays branch out from each other and are held in conduction paths that include a great number of contacts connected in series. These series of contacts can cause faults and operating troubles. Accordingly, the number of relays in a relay chain must not be too large.

One object of the invention is to arrange the relays in such a way that selection can be carried out among a plurality of circuits without the number of contacts connected in series exceeding what is practically suitable, for example 7 or 8 upon selection among 100 lines. Furthermore only one short selecting period is desired.

Another object is to dispense with the use of special means for the connection of lines and apparatus to the selecting means of the markers. By means of the invention the connection times of the markets will be reduced and the reliability of operation increased.

Briefly the invention contemplates apparatus for selecting one electric circuit out of a plurality of available electric circuits, excluding all the other electric circuits through connection of an electric potential to a marking conductor that is unique to the selected circuit. The apparatus comprises a number of groups of switching means where each switching means has at least two mutually exclusive stable positions. The first of the groups comprises a number of switching means corresponding to half the number of electriccircuits. The second group comprises a number of switching means corresponding to half the number of switching means in the first group, and the third group contains a switching meansfor two switching means in the second group, etc. up to a last-group with only one switching means. There is a repeatedly branched selecting network that branches at test conductor through two means for setting of the single switching means in the last group, and from each of the two setting means to a corresponding pair of setting means for each switching means in the last group but one, etc. up to those electric circuits among which the selection is to take place. The individual marking conductors on the one hand are connected each to its separate terminal in the first group of switching means and on the other hand, in dependence on a combination of the settings of the other mentioned switching means, which combination is individual for the marking conductor, are marked with theelectrical potential.

The invention will be described in more detail with reference to the accompanying drawings wherein:

FIG. 1 shows a combined identifier and selecting means for connecting registers by means of crossbar switches to markers in an automatic telephone exchange.

FIG. 2 shows a selecting means for the same purpose as in FIG. 1 but designed with electronic components and without the aid of selectors and identifiers.

FIG. 3 shows how a marker selects a free line in an indicated traffic route. 7

FIG. 4 shows a block diagram for a telephone exchange.

Before describing the details of the apparatus, the general operation of the apparatus will be described with the aid of FIG. 4.

In FIG. 4, A1 is a subscriber's instrument, L1 a subscribers line and F1 a junction line. The lines L1 and F1 are connected through the agency of selectors SLA-SLIB, a link circuit SNR, selectors GVA, GVB, GVC and the line equipment FURl of the junction line F 1. The selectors SLA, SLB are set by connect relays MS. The selectors GVA, GVB, GVC are set by connect relays MG. Relays MS and MG :are controlled from a marker Ml-I. The marker Ml-I receives instructions from the originating register REGL.

At a call from the instrument Al, the line L1 is connected to a link circuit SNR by selectors SLA, SLB. The link circuit SNR is connected to a register REGL by selectors RSA, RSB. The register REGL is set by the subscrib-ers dial according to a called directory number. This number and data for identifying the link circuit SNR are transmitted to number register MR in the marker Ml-I under control of a selecting means RMM. With the help of relays MGR, the marker MH operates a selecting means Gul to select a junction line Fl. Data for the identification of line F1 is sent to line register HR in the marker MI-I, which with the help of the connect relays MG and the registrations in registers MRand HR sets selectors GVA, GVB, GVC to connect the link circuit SNR and the junction line Fl. Thus the lines L1 and F1 are connected and the register REGL will be released.

In FIG. 1, REGL is an add originating register with registering means RElREn for registering the digits of a called telephone number. M111 is a main marker intended for group selector connections, etc. and RSM is a crossbar switch for connecting a register REGL to a marker. .A plurality of registers REGL are provided and, forexample, four markers MH1-MH4 are presupposed. For each main marker there is provided a crossbarswitch operating bar in switch RSM, hav ing an operating magnet BM. For each register REGL there is found a selecting magnet SM1-SMn. Between the registers REGL and the main markers there is provided a bypass that is common to all registers REGL and markers MHl-MH4, having signal wires t1-tl0,tm.

The invention centers around selecting means RMM for connecting the registers REGL to the markers Mill-M114 by means of the crossbar switch operating bars in RSM. The selecting means RMM is composed of electromagnetic relays R1R12 which relays have two stable positions. The relays can be conventional polarized relays or relays having two electromagnets and a rocker armature that is common to these. The armature actuates a make-and-break contact. The relays should be fast-operating and for this reason they must be sen sitive with very few winding turns and small inductance. Preferably, the relays are polarized reed relays with contact springs of magnetic material.

When the register REGL is to be connected to a marker, the relay RRl will be operated. The contacts 15-16 are actuated. From each free marker Mill-M144 a circuit will be completed from source through the contacts 26,35, the winding of relay MR3, the rectifier e11 and through windings on the relays R10-Rl2, e.g. the upper winding of relay R11 and upper winding of relay R10; the upper winding of the relay R8 and the lower winding of relays R7, R6 and R4, the contact 15, a time relay, for example, a thermocontact r1, to negative source. The relays MR3, R4, R6, R7, R8 and R10, R11 set their contacts so that the following circuit is completed: from source the contact 27, the winding of the relay MR2, the contacts 111, 101, 81, 72, 62, 42, the winding of the selecting magnet SMl, the contacts 16 and 18, to negative source. The selecting magnet SM] and the relay MR2 operate in this circuit. The contacts 28--29 are actuated. The operating magnet BM is operated in a circuit through the con tact 29. The contacts a1,b1 corresponding to the selecting magnet SMl are actuated. A circuit is closed from number register MR through the winding b, the winding of the relay MR1, the contact b1, the winding of the relay RR2, to negative source. The relays MR1 and RR2 operate. The contacts 17--l8 and 25-27 are actuated. The relay RRl releases its armature and the selecting means RMM is released. The relay MR2 releases its armature. During the release time of the relay RR] the relays R10R12 are still energized and are switched to another free marker if such a marker exists.

The connection between register REGL and marker Mill is then held by the operating magnet BM that receives current through a resistance r2 via the contact 25. A pulse is sent from number register MR through the wire a, the contact a], the rectifiers elen,the relays RE1--REn to the signal wires tl-l '10,tm. The signals are received in number register MR and in- .dicate thecalled number that has been registered in originating register REGL.

" Each main marker MHl-MI-M has a slow operating steady current relay AL that keeps the contacts 35, 36 actuated when the marker is operated. In case of a faultin the'marker the current is interrupted by relay AL and the marker is disconnected from traffic. The number of main markers Ml-I 1-MI-I4 can be increased by adding relays or be decreased, for example to two, by removing the relays R1 1 and R12.

- The thennocontact r1 in the register REGL is actuated only if a call from the register is not followed by the operating of the relay RR2, i.e. by the connecting of the register to a marker. For example a contact fault may be found in one of the contacts 42, 62, 72, 81, 101, 111. The thermocontact r1 The invention is of course not limited to the identical em- ;bodiment shown in the FIG. The identifying of the calling circuit, originating register REGL, can be made by means of an electronic analyzer while the selection of a free apparatus, markers MH1MI-I4 is carried out according to the invention.

Upon selection of a free line in a traffic route a marker is identified and a free line is selected, a connection fundamentally according to FIG. 1 being arranged for each traffic route.

In FIG. 2 REGL is an originating register with registering means REl-REn. MHl is one marker among a number of, for example, six markers for the setting of selectors in a group selector stage. Between the registers REGL and the markers MI-II-MH4 there is provided a bypath with signal wires tl-r It), tm, common to all registers and markers. In the register REGL are found a calling means consisting of a relay RRI, a monostable circuit VT, a capacitor C1 and two resistances r1 and r2. In the marker MI-Il are found and"-circuits T1- --OTm, bistable circuits V1Vm, V0 and a connecting means MGR for the operation of group selectors. A calling means, for example a link circuit or the line equipment of an incoming" junction line is assumed to be connected to the register REGL.

" The invention is used for the selection of free markers by means of a selecting means RMM which'contains an andcircuit KI-K6 for each marker and a first group of bistable circuits V1V2 and a second group V3-V4 and a third group V5, having only one bistable circuit. Furthermore there are -or-circuits E1E5 for the setting of the bistable circuits V1V5.

When the marker Mill is free, the bistable circuit V0 is in the O-position and closes a circuit through the wire v1, the or -circuits Ell-E5, the resistance r3 and the winding of the supervisory relay ARI. It is presupposed that some marker is always free and holds the relay ARI operated by means of current" through the wires v1--v6, so that the alarm device AL is not-operated. Assuming the marker Mill is free and has been selected, then the bistable circuits V1, V4 and V5 will be in the- O-position and the conditions of the and-circuit K1 are fulfilled. Accordingly, the wire 31 is current carrying. Only sneer the wires sI- s6 at a time can be conducting current since each of the and-circuits K1 K6 is associated with only one of the six possible combinations of the bistable circuits V1V4, V5. If the markers corresponding to the wires v1 and v2, s1 and :2 are occupied, bistable v4 will be switched to the 1-position and the position of the bistable circuit V2 decides which marker is to be selected.

Since the electronic circuits operate at such high speed it may be presupposed that a free marker, if one exists, is always selected. Furthermore it is presupposed that each register REGL contains a time device, now shown in the FlG., which repeats a call directed to the markers from the register after a certain time if. a connection has been established which releases the register in a predetermined time.

After a registerfREGL, via the calling means, for example a link circuit, has received signals which indicate where a connection, connected to the register, is to be connected, the relay RRl will be operated temporarily. The contacts 11-12 are actuated. A short impulse is obtained'through the capacitor Cl and the resistance r2 to-the monostable circuit VT which is set into the l-position. Circuitsare closed from the bistable circuit VT, position. 1, through rectifiers el en, thev registering means RE1-REn, the wires tl-t10, rm to the and-circuits OT1--OTm of the marker MHI selected for this call. Simultaneously the wire r! is marked and forthis reason the conditions of certain and-circuits OT1-OTm, selected by means REl--REn, will be fulfilled and the corresponding bistable circuits V1--Vm are set into the l-position. The bistable circuit V0 is set into the l-positionby one of the circuits V1Vm and the connecting means MGR receives signals from bistable circuits V1Vm concerning data information for the calling means and for the called traffic route, for example a subscriber's group. The pulse from bistable circuit VT is then supposed to be terminated, and for that reason circuit VT returns to the O-position. A new marker is selected simultaneously, if such one exists I The register REGL has herebyleft the continued connecting process to the marker Mlil that establishes a connection within the telephone exchange. The calling means is indicated, for example, by a combination of wires up, uq and the called route by a wire at. The calling means for this connection is then actuated when the connection is established and releases the register REGL.

It is presupposed that the connecting means or relays MGR in the marker Mlll is equipped with means for code control. If marker Ml-Il receives a faulty, for example an incomplete, item of information,.so that no connection can be carried out, marker MI-I1 will be released immediately and register REGL again makes a new call.

In FIG. 3 there is shown a partof a marker Ml-I including relays MR1MR4 and a line register HR for a larger traffic route, a part of the line equipment Fl of a junction line anda selecting means Gul for that traffic route to which the line Fl belongs. The means G141 is composed of polarized electromagnetic relays R1R8 each provided with two windings I and II and two stable positions andtwo make-andbreak contacts connected accordingto the FIG. Furthermore there are found control relays URI UR2 and a resistance r2. The means is constructed for four markers and an indefinite number of lines F,F., etc. I

When the marker NIH is to establish a telephone connection, potential will be connected to the marking wire ul in the FIG. that corresponds to that traffic route to which a connection is desired. The following circuit is completed: line ul, contact 24, the upper windingof the relay MR1, which has a low resistance, and its lower winding that has a high resistance, the winding I of the relays R1 and R3, the resistance r2, the winding of therelays R4, R8, for example through the winding I of relay R4, the winding I of R5 and the winding 1 of relay R7,'the contacts 215 and 200 and the resistance r3, to

the exchange battery which is indicated by V/2. A considerable voltage drop through the resistance r2 then prevents further markers MH from being connect to the selecting means Gul. If more than one marker is connected simultaneously one of these is selected by means of the relays R1R3.

By means of the relays R4-R8 a free junction line is selected in a circuit from battery V/2, the contacts 25, 15, the connecting point P. for example winding 1 on relays R4, R5, R7, the contacts 215, 200, the resistance r3, to negative source The following circuits are completed: position source the winding of relay MR3, the contacts 22, 11; partly through contacts 111,421, the upper winding of relay UR2, contacts 131, 141, 151, partly through contacts 113, 123, the lower winding of relay UR2, contacts 133, 143, 153; and the contact 214, the winding of relay FUR2, to negative source The relays MR3 and FUR2 operate in this circuit. The windings of the relay UR2 counteract each other and therefore relay UR2 does not operate as both parallel circuits in selecting means Gul are closed. The contacts 31 and 221- 224 are actuated. The resistance r3 is short-circuited.

Through a common bypath consisting of wires r101,

1102.....r a signal is sent from the selected junction line equipment F1 to the calling marker MH. The signal is continued during the make-time of the relay FURl and indicates on the one hand a group of lines, to which the line equipment F1 belongs, and on the other hand the position of line F1 within this group of lines. For this purpose the following circuits are completed: positive source the contacts 221, 211, the wire r101, the right winding of the relay l-lRl, the rectifier e1, the contacts 21 and 31, the resistance r1, to negative source and from positive source the contacts222, 212, the wire 1102, the right winding of the relay HRZ, the rectifier e2, the contacts 21, 31, the resistance r1, to negative source The contacts 51, 52 and 61, 62 are actuated. -The signal is registered in marker HR by the relays l-lRl and HR2 being held in the following circuits: positive source the contact 12, the winding of MR2, the contacts 52 and 62 respectively, the left winding of relays HRl and HR2 respectively, the contact 41, the winding of relay MR4, to negative source The relay MR2 operates. The contacts 21-25 are actuated. The selecting means Gul is released. The relays MR2, HR! and l-lR2 are held in a circuit through the wire ul and the contact 23.

Simultaneously with the operating relay MR2 the relay F URI operates. The contacts 2l1-215 are actuated. The line equipment F1 is marked busy. The relay FURl is held in operated condition during the release time of the relay FUR2 which is slow-releasing. During the release time of relay FUR2 the marker MP1 is supposed to have time to carry through the connection of the telephone communication. Then the contact 200 in the line equipment Fl will be actuated, which hereby remains busy-marked after relays FURl and FUR2 have released their armatures.

Since a very large number of calls is connected in dependence on the selecting means Gul, certain precautionary measures are taken. After the line equipment F1 has been selected and connected to a telephone connection, the'relay FURl is held in a circuit positive source through the contacts 101 and 213 and the lower winding of relayof FURL At the next call to the traffic route from a marker the relay URI is operated in a circuit from the calling marker, for example through the contact 14 on the relay MR1, the relay FURl in the line equipment selected immediately before being released but not selected if another free line is provided. Thus one and the same line, perhaps a faulty line, is not selected over and over again.

After a line equipment F1 has been selected and its relay FUR2 has operated, the resistance r" will be short-circuited by the contact 224. There is thus prevented the possibility that the signal sending equipment from F 1 to 'marker MH is disturbed by changes in the busy condition of the group of lines, for example if one or two of the line equipments F2-F4 after having indicated busy condition when equipment F1 was selected, are marked free which could imply operation of the relay R5.

The contacts 111-154 in selecting means Gul are controlled by relay UR2 that operates if interruption arises in one of the two parallel circuits through selecting means Gul. Then the contact 102 and an alarm device TC will be actuated.

The registering in the marker Ml-l of data information for the line selected by selecting means Gul requires controlling. Such a control function is fulfilled by the relay MR4 that operates if more than two of the relays HRl-HRn are operated simultaneously. Then the contacts 41, 42 areactuated and the registering is canceled and after that, the call will be renewed. A similar function can be fulfilled by contacts 51, 61 and by relays connected thereto which cancel the registering when only one of the relays l-lRl-l-lRn operates. In FIG. 3 it is however assumed that the relay MR2 is not able to operate if only one of the relays l-lRL-l-lRn is operated upon a registering. When the relay FURl in the equipment F1 has operated, in this case a new line will be selected and then a new registering is obtained in line register HR. This registering becomes normally a registering containing three relays and is for that reason released by relay MR4 and then, a third line will be selected. Hereby it is achieved that at a contact fault considerable switchings of the relays R4-R8 in selecting means Gul will take place. Operation of relay MR4 causes alarm by a current impulse through the contact 42 to an alarm device AL.

I claim:

1. Apparatus for selecting one and only one of n electric circuits (SMl to SMm) at a time and applying a marking potential to the selected circuit, comprising a plurality of groups of switching means (R1 to R4, R5 and R6, and R7), each of said switching means being settable to one of two mutually exclusive stable states, each of said switching; means including a pair of inputs, each of said inputs being associated with a different one of the stable states whereby a switching means is settable to a particular stable state upon receipt of a signal at the input associated with that particular stable state, eachof said groups having a number of switching means corresponding to a different one of the numbers N=n/2, where m'is an integer ranging from 1 to value such that N=1, a repeatedly branched selecting network for interconnecting the inputs of said switching means whereby each input of a switching means of any one group but the group with M2 switching means is connected to the two inputs of a switching means of the group having twice the number of switching means, means for selectively applying a switching signal to atleast one input of at least one of said switching means (upper coil of relay R8 and circuits to the right thereof), and each of said electric circuits being connected to a difierent one of the switching means of the group having N/2 switching means (leads connected to contacts of relays R1 to R4).

2. A selecting network comprising at least three electromagnetic relays, each of said relays comprising two windings balancing each other, one end of one of the windings being connected to a corresponding end of the other winding to provide a common terminal, an armature which is switchable to one of two positions each associated with the flow of current through only an associated one of the two windings, a movable contact connected to said armature, and a pair of fixed contacts whereby said movable contact connects to one of said fixed contacts in accordance with the position of said armature, a current source having an output terminal and a return terminal, the free end of one winding of a first of said relays being connected to the common terminal of a second of said relays, the free end of the other winding of said first relay being connected to the common terminal of the third of said relays, means for connecting one terminal of said current source to the common terminal of said first relay, switching means for selectively connecting the free ends of the windings of said second and third relays to the other terminal of said current source, means connecting one fixed contact of said first relay to the movable contact of said second relay, means connecting the other fixed contact of said first relay to the movable contact of said third relay, a common electric circuit connected to the movable contact of said first relay and a plurality of further electric circuits, each of said further electric circuits being connected to a different one of the fixed contacts of said second and third relays whereby said common electricv circuit is connected to one and only one of said further electric circuits whenever at least one of the free ends of the windings of said second and third relays is connected to the other terminal of said current source.

3. A selecting circuit comprising at least three electronic bistable device's, each of said bistable devices having two outputs which emit a signal associated with one of the two stable devices, second OR-circuit means for connecting the third and fourth of said sources to the second input of said third bistable devices, at least four AND-circuit means, each having at least two inputs and one output, the two outputs of said first bista- -.ble device being connected to first inputs of first and second of said AND-circuits respectively, the two outputs of said second .bistable device being connected to first inputs of third and fourth of said AND-circuits" respectively, one output of said third bistable device being connected to the second inputs of said first and second AND-circuits, and the other output of said third bistable device being connected to the second inputs of said third and fourth AND-circuits whereby a signal is emitted from the output of one and only one of said AND-circuits when a signal is emitted from at least one of said sources.

4. The apparatus of claim 1 further comprising means for registering an activated switching signal applying means and for registering an electric circuit to be selected and timing means for temporarily deactivating said activated switching signal applying" means if the electricei 'cuit to be selected is not selected ina given time.

5. The apparatus of claim! further comprisingmeans for selecting another of said electric circuits whenever a first of said electric circuits cannot be utilized.

6. The apparatus of claim 2 wherein each of said electromagnetic relays further comprises another movable contact connected to the armature thereof and two further fixed contacts, said contacts being 'so connected to form circuits in parallel to the circuits of the other contacts thereof, and alarm means that is activated upon a fault in one of the circuits.

US3548110A 1966-06-02 1967-05-19 Selecting means Expired - Lifetime US3548110A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
SE752966 1966-06-02

Publications (1)

Publication Number Publication Date
US3548110A true US3548110A (en) 1970-12-15

Family

ID=20271610

Family Applications (1)

Application Number Title Priority Date Filing Date
US3548110A Expired - Lifetime US3548110A (en) 1966-06-02 1967-05-19 Selecting means

Country Status (5)

Country Link
US (1) US3548110A (en)
BE (1) BE699424A (en)
DE (1) DE1537001B1 (en)
GB (1) GB1183941A (en)
NL (1) NL6707478A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4633042A (en) * 1984-07-26 1986-12-30 Electrotel, Inc. Electronic micro-controller conversion module for step by step switching apparatus
US20070146104A1 (en) * 2004-03-08 2007-06-28 Lee Ray F Active radio frequency coil for high field magnetic resonance imaging

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL215176A (en) *
NL267039A (en) * 1960-07-18
DE1212163B (en) * 1964-12-01 1966-03-10 Telefunken Patent Stable multi-switch for equal frequent evidence of similar devices in telecommunications, in particular telephone systems

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4633042A (en) * 1984-07-26 1986-12-30 Electrotel, Inc. Electronic micro-controller conversion module for step by step switching apparatus
US20070146104A1 (en) * 2004-03-08 2007-06-28 Lee Ray F Active radio frequency coil for high field magnetic resonance imaging
US7876101B2 (en) * 2004-03-08 2011-01-25 New York University Active radio frequency coil providing negative resistance for high field magnetic resonance imaging

Also Published As

Publication number Publication date Type
NL6707478A (en) 1967-12-04 application
BE699424A (en) 1967-11-16 grant
GB1183941A (en) 1970-03-11 application
DE1537001B1 (en) 1970-05-21 application

Similar Documents

Publication Publication Date Title
US3562435A (en) Switching system with automated main distributing frame
US2518022A (en) Translator
US3178516A (en) Call forwarding arrangement
US2354682A (en) Electric selection controlling circuit
US1498544A (en) Electrical selective system
US2813929A (en) Automatic signalling system
US2149646A (en) Automatic telephone system
US2242776A (en) Telephone system
US3310633A (en) Arrangement for selecting transmission paths in multi-stage switching grids
US2857467A (en) Alternative trunking in telephone systems controlled by overflow trunks and common directors
US2909607A (en) Automatic telephone system with automatic transfer
US2351551A (en) Telephone system
US2421919A (en) Telephone routing system
US1492995A (en) Telephone system
US2261370A (en) Telephone system
US2377453A (en) Telephone system
US2691066A (en) Automatic telephone system
US3133995A (en) Call awaiting signal telephone circuits
US3288939A (en) Crosspoint switching array and control arrangement therefor
US2344634A (en) Telephone intercept system
US3808381A (en) Continuity testing circuit for testing transmission paths
US1593387A (en) Telephone-exchange system
US2424281A (en) Relay allotter for finder switches
US3129293A (en) Automatic telecommunication switching systems
US2788394A (en) Party line telephone systems