US2279568A - Electrical signaling system - Google Patents

Description

EQB. IREL AND ET AL ELECTRICAL SIGNALING SYSTEM April 14,1942.

Filed Sept. 16, 1959 3 Sheets-Sheet 1 IN VENTORS.

EPIC BERTR] IRELAND ER! WYN JONES ATTORNEY.

p 1942- E. B. IRELAND EFAL 2,279,568

ELECTRICAL SIGNALING SYSTEM Filed Sept, 16, 1939 5 'Sheets-Sheef 2 INVENTORS ERIC 'BERTRAM IRELAND ERIC WYN JONES ATTORNEY.

g; E -q$ F --------R i E a; I I a April 14, 1 E. B.|RELAND EI'AL- ELECTR ICALSIGNALING SYSTEM Filed Sept. 16,. 1939 3 Sheets-Sheet 3 INVENTORS ERIC BERTRAM IRELAND RIC WY/V JONES 1 ATTORNEY.

Patented Apr. 14, 1942 UNITED STATES PATENT orrics f ELECTRICAL SIGNALING SYSTEM Eric Bertram Ireland, Liverpool, and Eric Wyn Jones, Nottingham, England, assignors to Associated Telephone & Telegraph Company, Chicago, 111., a corporation of Delaware Application September 16, 1939, Serial No. 295,176 In Great Britain September 1'7, 1938 11 Claims.

The present invention relates to electrical signaling systems and is more particularly con, cerned with systems for transmitting fire alarm signals to a central station from a plurality, of boxes located at different points all of which will usually be accessible to the public.

The invention has particular application to fire alarm systems of the closed circuit type in.

which a plurality of boxes are series connected in a loop circuit over which a current normally flows. With this arrangement a calling street box is arranged to transmit a series of impulses indicative of its code number to the central station where an indication of the number is given and to improve the reliability of the system it is usually arranged that the box is earthed during sending and the loop is interrupted according to th appropriate code on both sidesof the earth connection.

The general object of the invention is to provide improved arrangements whereby calls from short-circuited fire alarm boxes shall be satis-.

factorily handled with the minimum of interference with the normalworking of the system.

According to one feature of the inventionin a fire alarm system of the closed circuit type arranged so that when a box is pulled interruptions in a loop circuit and also intermittent connections to earth are produced, the code from a short-circuited box is satisfactorily received by arrangingthat when earth is intermittently applied to the circuit without the loop being in-.

terrupted, th connections are automatically al-.

tered so that the code represented by theintermittent earth connections produces operation of the code responding equipment. p

According to another feature. of the invention, in a fire alarm system of the.closed cir.- cuit type arranged so that when a box is pulled interruptions in the loop circuit and also inter-' mittent connections to earth are. produced, as

soon as a box is pulled earth is connected to the loop and serves to initiate a test whereby conditions are established such that if the loop is not, satisfactorily opened when the earth connection is removed, the circuits of the code re sponding equipment are altered so that the code represented by the intermittent earth'connections produces operation of the responding equipment.

A further feature of the invention in a' fire alarm system of the closed circuit type arranged so that when a box is pulled interruptions in the loop circuit and also intermittent connections to earth are produced, as soon as a box is pulled" earth is connectedto the loop and serves to in itiate a test whereby conditions are established such that if the loop is not satisfactorily opened when the earth connection is removed, a device responsive to the intermittent earthconnections is enabled to produce corresponding interrup-rl Considering the circuit operation of Figs. 1.

and 2, the general operation, in response toa normal fire call with all boxes in order will firstb dealt with. Assuming that .fire alarm box FA, Fig.1, is calling, the code wheel .begins .to rotate in a clockwise direction, as shown, driving the off-normal cam in. a counter-clockwise direction. These cams are arranged to operate the oif-normal contacts NI and N2 a short interval before the first operation of .the impulse contacts IMF! and IMPZ, thereby .to provide an initial test period. During this period earth via.

rectifier MBA is therefore connected over contact N! to both conductors of the first alarm loop. The high resistance earth test relay E thereupon voperates and at armature e'l operates.

relay ER. Relay ER looks over its other winding to positive over armatures erl, efl,'gr3 and do! and also at armature er2 short circuits relay E so as to provide a holding earth for th box succession coils Bl or B2 and B3 under short-. circuited box conditions via the winding of the low resistance relay EX. Relay EX now operates and thereupon energises relay EB, Fig. 2, which brings up relay EC and this relay'in turn operates relay ED at armature ccl. Relay EC also at armature ec2 reverses the-polarity of the earth test circuit by connectingearth over relay ET to the opposite pole of theloop battery BA. Relays E and EX are thereby disconnected, so that relay EX releases at about the same time as relay ED is operated; Since earth is con-; nected to the loop over the rectifier MBA at the calling box, relay ETwill be unable to operate under this condition sincefthe rectifier To improve the op erating conditions for relay-ET in case a faulty will not be conductive.

liammeter MA and may be adjusted-by the variable resistance VR. The initiation of a telephone call from a street box causesa resistance to be inserted in the loop which reduces the: loop current to say 30 milli-amps whereupon relay T releases and operates relay TA. as will .be

described subsequently, the remaining series equipment still being held by this current; Relays RA and RE, the register PR and gong GG have all approximately the same operating and releasingvalues andwill'operate with a. current of th''orderof' 25 milli-amps and release with a current of 11' milli-amps and under normal conditions" they will respond satisfactorily to code impulsesL Under conditions where a box is'shunted by a leak resistance as sometimes occurs, the" loop current will not drop-to zero each time the box impulse springs open and conditionsmay arise where the relays. and puncher will receive sufiicient current during, the break periods to prevent their efiicient response. To safeguard the system from unreliable operation from this cause an additional supervisory relay RS. is provided which will only release if the loop current fans to less than say milli-amps. If this relayremains operated when the first break is delivered from the box, short-ci'rcuited box working using earth return is immediately brought into operationso that the complete code transmitted is correctly received. On the other hand if this relay releases, ordinary loop working will be retained since under this condition the loop current flow during break periods will clearly be so small as not to interfere with the:

proper operation of relay RA and the puncher and gong. Although relay RB is shown on. the drawing it is not concerned with the operations involved in"carrying out the present invention and only performs a useful function. under earthe'd line break conditions.

' Continuing the description of normal operation from the point when relay EC operated during the initial test period of the calling box, relay EX will be released" as pointed out previously and relays EB and EU will release in turn. Relay EB thereuponcompletes an operating circuit for the slow-to-operate relay EF while the release of relay EC reconnects relays E and EX on to the loop. However since relay E' is still short-circuited owing to the locking of relay ER, relay EX only will immediately operate and during the slow'rele'ase period of relay ED which commences to fall away on the release of relay EC, relay EWS will be operated. Relay EWS locks up at armature e'wsl over its second winding and at armature ewsZ- opens the circuit of the slow-tooperate relay EF before it has had time to oper- It, however, the operations described are initiated by a fault earth on the line rather than byvthe pulling of a' box, relay ET will operate whenthe battery polarity on the line is reversed. Relay ET thereupon at armature etl, removes the short-circuit from across relay ETR and so causes it to energise and lock up at armature etrl in series with relay EC. The latter relay thus remains held when relays EX and EB release so that no circuit is re-completed for relay EX and relay EWS cannot be operated over armatures escl and edl as in the normal case. Consequently relay EF operates shortly after the release of relay EB and at armature eJ2 lights the earth fault alarm lamp EAL, at armature efl releases relays ETR and EC and at armatures ef3 removes the short circuit from relay E so that ontherelease of relay EC relay E is again introduced into the earth test circuit. Relay E reoperates and ensures the maintenance of relays ER and'EF so that the earth alarm persists so long as the fault remains.

Continuing the description of a bona-fide call,

no further operation ensues until the fire alarm box transmits the first break impulse of the train or trains constituting the box code and relay EX will then release and also the loop circuit relays T, RA andRS; The release. of relay RS indicates that no short-circuit exists on the box so that no circuit is completed to the short-circuited box working relay SC and the call is received at the central station over the loop in the normal manner. Relay P responds to impulses delivered from relay RA at armature ml and repeats them tothe indicator circuit 10 while the received code is punched" on the tape by the register PR and sounded on the. gong GG. Relay RS in responding to'the code impulses operates relay GR over armatures rs! and pl and this relay holds during pulsing due to its slug. When it operates, it releases relays ER and EWS by disconnecting the holding. earth thereto at armature m3 and the earth circuitrelays EX, E and ET are disconnected at armature gr2.

It will be understood that the armature of the fire alarm boxis made slow-to-release in order that the box will hold in when relay EC is momentarily operated during the earth discrimination test and removes the holding earth for the callingbox earth succession coil.

- changes over the loop circuit to earth return working, the two sides of the loop being connected in parallel over armature set and resistance YA. Hence since the box impulse springs are broken at this moment relay RA, the

gong. GG and the register PR will release; relays T and. RS also releases but these relays are not. concerned in the present operation. Suc

tain relay G which completes an, energising circuit for the slow-to-operate delay relay DA., It will be understood that although this relay previously received impulses during the coding-in it would not operate. During reception of the call relay GR was operated and due to its slug remained energised and therefore released relays ER and EWS as pointed out above. On the operation of relay DA after a period of the order of six seconds, relay SC is released and in turn opens the circuit of relay SCA which was operated when relay SC originally operated. The function of relay SCA is to prevent relay DA operating relay EW and so bringing about full line break earth working on the fire alarm loop which differs from short-circuited box earth working in a manner to be described. Relay SC on releasing restores the circuit to loop working, whereupon the line relays operate and release relay P which in turn disconnects relay DA. Due to its slug, relay SCA holds during this time and prevents earth being extended over armatures dal, seal and gl to operate relay EW. When the maintenance officer at the fire station subsequently operates the short-circuit call release key KSCR, relay SD will be released at key contacts KSCRI to extinguish the short-circuited box call indication lamp SBL.

The short-circuited box earth working as described above which is employed. whena call is received from a short-circuited box differs slightly from full earth working, this difference being mainly intended to give improved possibilities of succession working if a good box should call when a box shunted by a fairly high resistance is already coding-in. Under full earth working conditions, which are brought into effect in the relay DA. If a call is subsequently received either relay SA or relay SB (not shown) is operated in addition depending on whether the call is originated on the A or B leg. If the call is originated on the A leg, relay SA is operated to disconnect the B leg at armature sal and similarly for relay SB. By this means a second call originated simultaneously with the first and on the opposite leg is prevented from sending in its code and so spoiling the code already being received from the first box. If, however, one leg were disconnected for short-circuited box working as in the full earth working condition, it might not be possible for a second good box calling on the same leg as the first to hold the line relays operated in series with the resistance across the faulty box already coding and thus restores the loop working condition for succession working. It will be understood that if the line relays failed to remain operated 7 due to the high value of the resistance across the faulty first box, the second good box would fall out but would maintain a continuous earth via its rectifier on to the line and would thus tend to interfere with the response of the line relays to the earth pulses being transmitted from the faulty box already coding. With the short-circuited box working shown however, both legs of the loop are kept intact and succession working between a second good box calling and an already running box having a fairly high resistance shunt thereon can readily be effected, since when the second box calls with the first box already running, the earth extended from the-second box will immediately hold'the line relays operated round the other side of the loop and so bring in loop working is the mannerto be now described.

When a call is being received from a short-.

circuited box andanother call is originated at a good box in the loop, the seco nd box on running f on its test tooth will extend'c'ontinuous earth via its rectifier on to the loop for such a time as will hold the line relays long enough to allow relay GR to release, this relay normally receiving a pulse over armatures pl andrsl each time relay RS restores due to the pulsing from thefirst box. Relay GR thereupon operates relay SE over armatures yr! and s05 and this-relay at armature se2 releases relay SC to allow ordinary loop line conditions to be restored; At armature se3 any possibility of short-circuiting the high resistance relay E in the earth test circuit is prevented so rent to flow through the loop succession coils'to hold them in whichcase the first break delivered by the second box will release the short-circuited box. When the shorted box falls out, the second good box carries on coding-in; During this time relay GR will be again operated and releases reand when the rectifier earth connection at the.

lay SE which again prepares a locking circuit for relay 80. After coding from the second box has been fully received the releasefof relay GR causes earth to be reapplied to the earth circuit relays E and EX and the'short-circuited box will again bring up relay SC in the usual manner and will recommence to send in its'code.

. Considering nowthe case of a telephone call from a short-circuited box, the normal momentary increase of resistance in the loop circuit will be clearly ineffective owing to the short-circuit on the box, but at the same time earth over the box rectifier is momentarily connected to the line. It should be explained that in the case of a telephone call from a short-circuited fire alarm box the connection of the rectifier earth to the line would be effected manually by the fire or police officer initiating the call while in' the case" of a call from an ambulance telephone box situated in the same loop as the fire alarm boxes this would be automatically effected, fo-r instance in the manner described in British specification No.

471,759. The momentary connection of the recti-.

fier earth to the line causes relay SC to hamperated in the manner already described and this relay in turn operates reIays'SD and TA to display short-circuited box and telephone calls on the indicator panel by lighting the lamps SBL and TCL respectively. The operation of relay SC initiates short-circuited box working conditions box is removed, the line relays will release and bring up relay P which in turn operates relay G which completes a circuitto the delay relay DA. Relay DA on operating after its slow period operates relay EW over its left-hand winding to bring about thechangeover to earth working so as to provide feeding current to the telephone instru-,

ment, not shown, at the calling box. Relay SD also at armature sci-3 disconnects one winding of" the repeating coil RPC, which connects over leads l2 and I3 with the station telephone circuit, so

that when the telephone key KIS is operated,- speech may take place under this condition Clear downis subsequently effected by operating the short-circuited box release key KSCR, whereupon at contacts KSCRlj relay ISD is released and at contacts KSCRZ relayEW is released; Relay TA is released atv contacts KIfs hon theopera;

circuit is completed for the slow relay. DA and since relay EWS is not released by the operation of relay. GR afterthe predetermined period relay DA operates, and atjarmaturedal lightsthe socalled box earth lamp BEL. Relay Du also at armature dal' releases relay EWS and this relay thereupon extinguishes the lamp BEL and disconnects the circuit to relay DA so that thecycle,

of operations repeatsitself .andcauses the lamp to flash; In. actual. practice it. might be more convenient to prevent. the earth test circuit from being continually broken down, and set up again as in', the circuit shown. byfarranging that relays DA and. EWS, on operating together bring up a relaywhich. locks and maintains either. a continousor intermittent circuit for. thelamp BEL.

'Ifhe armature 002 in. the circuit of. relay DA'is to prevent thisrelaybeing] brought in when during succession workingone or more boxes fall out while another box is coding in." During this time it will. be appreciated. thata rectifier earth. is. maintained on theloop andiit may-be maintained long enough to allow relay. DA to operate ifthe circuit to this relay is. not. broken. by relay CO. which. is operated whenv a. full code. has been received, at the central station.

Referring now. to Eig, 3'thi simply shows the essential equipment required for handling shortcircuitedbox calls on straightiorward sectorbox, i. 6 non-succession workingsystems. On anormal call from a good box, relaysfRA, RBand'T release in accordance, with the operation of the impulsing. springs. and the punch register. PR and gong GG are operated in theusual. manner. Re-

lays BA and RBloperate slow relay RA whereby U the. earth testrelay E is disconnected at armature p112, and does not produce any effect on the auxiliary equipment.

If the calling, box is shortecircuited however relay E operates by. wayoi the earth at the box. when. a call is initiated and atarmature elcompletes a circuit for relay ER which in turn pulls up relay. J which, locks, over. it lower winding. Relay J, at armature 9' 2 completes a circuit for thetime delay relay EAwhich is utilised to bring in. an, earth alarm indication, after a period of the order of twelve seconds as will be. described subsequently. Relay. ER at. armature e12: operates, relay M of the countingrelays and this relay in turn prepares. a circuit for relay N which at this, stage is short-circuited by. the positive potential extended from. armature ef3. It is assumed. that three-digitbox codes are to be catered for and on the transmission'of the hundreds digit, relay E responds to the impulses but relay ER due to. its slug holds. operated during this time. It will be appreciated that due. to the short-circuit on the box relays RA, RB and T are unable to release so. that relayPA is not operated. During the interdigital pause the impulsing springs.

atthe box. remain openso that. relay E releases, and duringthistime relay ER 'willin turn release and remove the short-circuit from relay 7 N. which operatesv in series with relay M which holds energised in this circuit. On the trans mission of the tens .digit relay E pulses and again er tes, ela R wh h e sgrel a P a d. this relay in turn prepares a circuit for relay Q which at this time is short circuited, In thefin .ter-digitalpause following the tens digit, relay Q operates in series. with relay P. which remains held and after the reception of the units digit relaysR and S will be operated in a similar'ma'hner. The operation of all'the relays MS indi j 'tes at on r c. ll. om a s r rwi ed.

box is in factbeing received, and relay Sat armature sl prepares a circuit for the short-circ uited box working relay SX.

11; Will beunderstood that each street box m l n i de n, ke a tetal f. r e. ra smi sions of its box, number andhence when the first.v

make impulse of the hundreds digit is transmitted 0n the second round, relay E is again oper:

ated and brings up relay ER oncemore sothat. relay S2; is operated and locks up over its lower winding On the first break impulse, relay' E releasesand now operates relay EP sincea circuit is completed for it over armatures el and sx5 and this relay thereupon breaks the loop cireuit at armature epl and thus repeats the pulse on to the line relays and punchregister.

Relay PA now operates butin this case, the circuit,

for relay E is maintained over armature Relay RA also at armature pal disconnects any 'further operating circuit for relay S X though this operation serves no'useful function inthe present circumstances. When the code wheel reaches the second make of the hundreds dig"? earth is re-applied totheline and relay Ejre operates since although relay EP is operated at this time to disconnect the loop on the B leglthe earth will feed round the A leg. Relay E on dp erating releases relay El? which re-makes the loop circuit thereby re-energising the gong,

register and the line relays.

The second two codes transmitted from the box are thus translated from earth pulses into loop pulses by relay EP and are correctly ceived on thepunch register and gong, the first code transmitted being lost in order to diserim inate between a genuine call and momentary earth leakageson the line.

At the-conclusion of the code sending, relay E restores and maintains relay EP operated thereby breaking the loop circuit. Since. no further pulses are received on the punch register, after a further short delay period provided mechanically thereon, this restores to normal and momentarily closes a pair of contacts pr tdoperate relay RR, which at armatures TH and rr2releases the'relays SX, MS and J; Relay S on re:

leasing releases relay EP the loop circuit is thus re-made in readiness forfurther callsf Relay SX' when it operated initially energized relay SCB which remains locked over its lower wind mg and thus maintains the short-circuited box call lamp SBL lighted until the cancel key KSCR is operated by the station attendant.

In the case of an earth fault on the line, relay.

E remains steadily operated and brings up relays ER and J in turn. Relay J completes, a

circuit for the delay relay EA and since relay PA is not now. operated if the fault persists for twelve seconds or more relay EA operates and operates relay EF. Relay EF locks up to the lamp EFL at armature ef2. or two momentary earth leakages n the line earth fault key EFK and lights the earth fault In the case of one which may be followed by continuous earth, a

number of the impulse train counting relays 5' MS may be operated and locked, but these relays-will be released at armature ef3 when relay EF is operated.

" Itwill be understood that this latter method earth working on a line break. 'We claim: 1. In a fire alarm system, a call point and a central station, two conductors connecting said call point to said central station, said conductors normally connected together at said call point,

means at said call point for repeatedly interrupting the connection between said conductors during the sending of a code to said central station, means for grounding said conductors at the call point whenever they are connected to- 5 gether during the sending of a code, saidground being disconnected from both conductors whenever said conductors are disconnected from one I another during the sending of a code, a source of current at said central station normally connected between said two conductors to cause cur-" rent to flow over said conductors in series when they are connected together at said call point, means at said central station responsive to interruptions of the current flow over said conductors in series, means operated at times to disconnect one of said conductors from said source at said central station and to connect it to the other conductor, said last means also ef- Iective at said times to ground said source thereby to cause current to flow from said source over said two conductors in parallel whenever said conductors are grounded at said call point, said third means then responsive to the interruptions of current flow over said two conductors in parallel whenever the ground is disconnected from said conductors at said call point.

2. In a fire alarm system, a call point and a central station, two conductors connecting said call point to said central station, said conductors normally connected together at said call point, means at said call point for repeatedly interrupting the connection between said conductors during the sending of a code to said central station, means for grounding said con- 5 ductors at the call point whenever they are connected together during the sending of a code, said ground being disconnected from both conductors whenever said conductors are disconnected from one another during the sending of a code, a source of current at said central station normally connected between said two conductors to cause current to flow over said conductors in series when they are connected together at said call point, means at said central station responsive to interruptions of the current flow over said conductors in series, other means at the central station operated responsive to the first disconnection of ground from said conductors at said call point during the sending of a code, 7

means operated ccnjointly by said last means and said third means to disconnect one of said conductors from said source at said central station and to connect it to the other of said conductors if said third means does not operate 7 responsive to the first disconnection of said conductors from one another during the sending of a code, said last means also efiective, upon operation, to ground said source thereby to cause current to flow from said source over said two conductors in parallel whenever said conductors are grounded at said call point, said third means then responsive to the interruptions of current flow over said two conductors in parallel whenever the ground is disconnected from said conductors at said call point.

.3. In a fire alarm system, a call point and a central station connected together by two conductors, a device at the central station for responding to electrical impulses transmitted from said call point during the sending of an alarm therefrom, said responding device normally connected in a circuit including said two conductors in series and operated responsive to impulses transmitted over said two conductors in series during the sending of an alarm from said call point, and means operated whenever said call point is short-circuited during the sending of an alarm to change the connections of said responding device to said conductors to render it responsive to impulses transmitted over said two conductors in parallel.

4. In a fire alarm system as claimed in claim 3, wherein the sending of an alarm from said call point is initiated by grounding said conductors at the call point, means at the centralstation operative responsive to a ground on said conductors to determine whether said ground is due to the initiation of an alarm or to a fault.

5. In a fire alarm system as claimed in claim 3, wherein the sending of an alarm from said call point is initiated by connecting ground through a rectifier to both of said conductors at said call point, means at said central station for determining Whether a ground on said conductors is due to the initiation of an alarm or to a fault, said means including a source of direct current at said central station connected across said conductors, a test device for each of said conductors, and means for grounding each of said conductors at said central station through its respective test device, both of said test devices being operated if the ground on said line is due'to a fault, said rectifier preventing one of said test devices from operating if the ground on said line is due to the initiation of an alarm.

-6. In a central fire alarm station, two conductors incoming from a call box circuit, a responding device normally connected in a circuit including said two conductors in series and responsive to electrical impulses transmitted over said two conductors in series, and means operated at times for changing the connections of said device to said two conductors, said means effective to ground said device thereby to render it responsive to electrical impulses transmitted over said two conductors in parallel at said times.

7. In a fire alarm system, a call point connected to a central station by a metallic loop circuit, means at said call point normally operated to repeatedly interrupt said loop circuit during the sending of an alarm from said call point, thereby to transmit impulses over the two sides of said circuit in series, a responding device normally connected in series in said loop circuit and operated by said impulses, means at said call point effective during the sending of an alarm therefrom if said call point is short-circuited to transmit impulses over the two sides .of said responding device to said circuit to cause 1 it t0, respond to said impulses transmitted over the two sides of said circuit in parallel. n

8. .In a fire, alarm system, a call, point connected to a central station by, ametallic 100p circuit, a source of current in saidloop circuit, a:

ground connection to said A loop circuit at the can point, means. at the call :point for repeatedly interrupting saidloop circuitduring the sending of an alarm from saidcall point, said means effective also to disconnect ws id roundir ma least one side of saidloop circuit each time said loop circuit is interrupted, an jungrounded re- .Spondingdevice at said central.stationgconnected in series in said loop circuit and normally opermated over the. .metallic, looni ir i x lusiv y 1 res on ive t ea h in e ruption of said l op rcui c y saidfirst me nsha erounded re pond n device at said cen ral station conne ted. to; Said can si e ith llcopccircuitand op ra ed re po .A csivet c c rstd sco nec on of. v r ndfrcom said one side by said fir st means upon initiation of the sending of an alarm from said call point, and

means controlled conjointly by said two respondin g devi ces if said. first device fails to operate cQncurrently with said operation of said second deviceto ground said first .device,, thereby to cause said firstdevice to respond to the repeated disconnections of said groundifrom said one side of said loop cir cuit by said first means 7 9. In a fire alarm system, av call. point'connected to a central station Joya metallic loop circuit a source of current insaid loop circuit, a ground connection to saidloop circuitat the call I point means at the call point for repeatedly interruptingi said loop Circuit during the. sending of, an alarm. from said ,calldpoint, said means ef- ,f e ctive alsoto disconnecttsaid groundcfrom. at least one side of said loop circuit. each time said loop circuit is interrupted, an, ungrounde'd respending device at said central station connected inseries in said loop circuit andcnormallyioperated, over the metallic loop circuit;,exclusively responsive to each interruption; of said lo op;circuitby said firstameans agr'ounded responding device at said central station, connected to.said

one side of the loop ,circuitHand-c at times operated responsive to each disconnectioncof ground from said one sideby said firstmeans, and means controlled by said last responding device at said t me to i r fie saie 99p u ta ac tra t pn. u on P3152 5 Q aid a device, therapy to insure the operation of said s n nd n devii hu. 11;;

.01 1 0% re a a mls t tmb a a-99in? 91. eq e t a ce tr ta wmbra att li i. i99 circuit, a source of current in s aid loop circuit, a ound co n i n. to s d .l9ena ait t. the ca oint me n a t e an. 129 t f r, r pea edl interrupting said lO p circuit d ng the sending l t a a arm; om: aid ..=.a l m i t. Sa d mean e t v a s t d sc nn t said. ree twee least one side of said loop circuit eachfiime' said loop circuit is n e n nte r l uncr wded-1esponding device at said central station connected in series in said loop circuit and normally operat eve e m t l 1 012, r uit v elu ire T$FQY c a h iQPflEWfiPQQZ 99 Z$?iI- w t y i r m ns a ounded e eee n 0.118 e 9 the 1 2 cir u a sier re eq 16 9.9 iv to ea d ec i n.- ..r9 s1.. bm;a o e. d ub a d fi tlm an urin the-S nd n .Q a arm I r m vi a q. call p nt .i sai c 1 90 1 i o t ei wit d me ns n led: oun d .rc ie n in c dev ce, i9, Wh h r S i O era io o e d: und i 'e e nde v q s o ea 'nled b t ssa s s;o .v n alarm. f om aid ll mi aby; ae a t. on a 92. em ts andnmeaas c tr ed; y sa ro nd d r sp nd n :sieri t s d a t; m an det min h t a q er t qn 9 5 di r q p n i yi' ai oc asi n d y he send n er e alarm fr m. s id. ce p int to terruntsa 19 ci i ama d c ntra statien .p on; as' e n of sai gr und kl s o dina deri s her ei eratesa q lmgrw d d e ond n v e e p te the che rtei qu tat a d c l-p i V. 1,- A fl e znc r emc s c aimedz azclai l0 whe cmr aid fir tm ansison ated d rin h eendin p alarm tqn epeated tra smit, a r qetermine toda andwhem n saiddc e m .i m n inc ude a .co nt rel yphainon rt d f ite cc danc wi h v he fir ttr nsmission'of said code when an alarm is sent-from said call point while said call pointis shortfcircuited, thereby to distinguish :Operationibisaid grounded responding device. due to. the'lsending of an alarm from operation: ofisaid' grounded device due to a fault in the loop circuit.

amcijsaaaamaams.

ERIC WYN JoNEs.

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