US2397906A - Alarm installation with central power supply - Google Patents

Description

- April 9, 1946- c. F. AHLBERG EI'AL 2,397,905

ALARM INSTALLATION WITH CENTRAL POWER SUPPLY V I Filed Oct. 20, 1941' (MIFENJA TING R5115 TA lvcs INVENTOR Cumfiefiqx/x Ann/m AND 5 re/v AKE ML 5401/ ATTORNEY Patented Apr. 9, 1946 ALARM INSTALLATION WITH CENTRAL POWER SUPPLY Curt FredrikAhlberg, Appelviken, and Sten Ake Nilsson, Nockehy, Sweden, assignors to Telefonaktiebolaget L. M. Ericsson, Stockholm, Sweden, a company of Sweden Application October 20, 1941, Serial No. 415,806 In Sweden October 25, 1940 5 Claims.

The present invention relates to alarm systems with a central alarm station and local alarm installations.

Fire and burglar alarm systems are known in which alarm loops containing normall closed alarm contacts are extended to the premises to be protected. These line loops are put under socalled supervisory current control and alarm is indicated on a central board when break-down occurs in the line. Such break-down occurs at an alarm contact when it is put out of operation by heat or mechanical influence, but a breakdown may occur naturally in case of damage to the line. In the latter case a false alarm indication is given on the central board. The risk of false alarms is considerably reduced if the system is arranged with two parallel line loopswith twopoint alarm contacts whereby it is necessary for the alarm operation that a break-down occurs in both 100p circuits.

Such systems are very suitable for the supervision of premises forming an entire building, for instance a factory or a commercial building. If it is a question of the protection of several localities at some distance from each other or of a localit which for some reason is situated away from the centre of supervision (for instance a police or fire station) the lines become very expensive if they are to be built exclusively forthat purpose. A considerable reduction in the line cost may be gained if already existing lines are used and this reduction is obtained in many places where one or several communal fire telegraph loops are already available which are used for the transmission of alarm signals from automatic fire alarm plants. However, in such cases battery fed repeaters with code sign-a1 mechanism should be inserted between the alarm loops and the fire telegraph loop. This will reduce the line costs but, on the other hand, the repeater is added which renders this method uneconomical for small plants having only one or a small number of supervisory loops. Another drawback is that only a limited number of premises to be protected may be connected to one and the same fire telegraph loop, the impulse code not allowing for variations beyond a certain limit.

The present invention is intended for the use of spare lines in an existing telephone network for transmission of alarm signals from a number of dispersed places of protection to a supervisory centre. A system according to theinvention must fulfill certain conditions. Firstly, the line (central line) between the single or two-wire alarm loop itself and the central board must consist at the most of one two-wire telephone line. Secondly, the system must allow unintentional intermittent or lengthy break-downs, short-circuits, grounding or the like on the central line without a false alarm being indicated at the supervisory centre. Thirdly, all such faults as well as faults of the same kind in the alarm loops themselves must be' indicated at the centre in such a way as to enable determination of whether the faults have occurred in the central linear in the alarm loop.

The invention will now be described in greater detail with reference to the accompanying drawing, the figure of which shows an embodiment of a system which fulfills the aforesaid requirements.

Characteristic of the system is that the local alarm loop and the central line are connected to each other without having recourse to movable elements and without any local power supply being used for transmission of signals from the alarm loop to the supervisory centre. Further the central line and the alarm loop are automatically tested from the centre. In the embodiment shown the central line is tested on the occasion of an alarm by means of alternating current and a relay sensitive to alternating current whilst the alarm 'loopis tested with direct current and a relay sensitive to direct current.

On the drawing B1, B2 and B3 represent direct current supplies and O1 and O2 alternating current supplies. A81 and AS2 are two local alarm loops, the former of which is a single wire and the latter a double wire. Between the alarm loops and the central line CL an impedance network is inserted consisting of condenser C2, transformer TR and resistances 12, and m. For every central line CL the central station is equipped with the following devices:

A line compensation resistance r1;

Relays R1, R2 and R: which are normally connected in series with line CL;

Relays R4 and R5 which on break-down in the direct current circuit over CL, TR, AS1 andASz are connected to central line CL and test the latter, whereby relay R4, being shunted across condenser C1, is actuated by direct current but not by alternating current and relay R5 is energized both by direct current and alternating current;

An alarm relay Rs and a fault relay R7;

Signal lamp KL for short-circuiting, signal lamps ATL, KCL, CLL for diiierent central line breaks and signal lamp ASL for a single-wir alarm loop break;

A resetting switch A; and

.JR2 for botlrbatteriesBi and Beasiwell'asa con verter start relay S'R which, in known manner, is

slow-acting.

The operation of the system will now be de:-"

scribed.

7 By intact central line CL and alarm ElOOPSYASI- and A82, a supervisory current flows in a circuit I I from battery B1 through relays R1; R2 anon: whichwith resistance n is' adjusted to a determined value. Relays R1 and R2 which formerly, by pushing of the button A and closing the contacts I4, I 5 have been energized over a circuit. 12: with relatively high current keep the armatures attracted for the lower supervisory current, Whilst R3 is not able to attract its armature for the supervisory current- This condition is shown in the drawing. 7 y 7 It now short-circuiting. or a sufficiently powerful leakage follows. betweenv the two branches of the central line CL; relay Rs is energized by a higher current and operates itsv armature l6. and lights the lamps KL. and SFL over the circuits 41,18;

In the case-of a single wirebreak-down in; the alarm loop ASz, the relay R2 releases itsarmature 2| owing to the current decrease whereby lamps ASL and LL are illuminatedrover the. circuits 22,. 23a

If adouble-wire: breakv in the loop Ass 01' a break-down in loop ASi occurs; the relays :Ri' and Rz release their armature with the following result:

Relay SR. is actuated over the contact 25 and closing of the contacts. of: relay SR closes av Cir-- suit of a starting device (not'shown) for the converters; Relays Rs-and Rs. are, over. contact" 28,

connected to the CGIITSI'HLHHG CLina circuit over 31.01, m, one of the: branches: of C13,. condenser 02- and the other branch. ofCL. The circuit is set under both direct. and alternating voltage but alternating. current; alone. can. pass throughthe relays, the condenser 02' blocking the direct cur rent. Relay Rs operates but notrelay R4, whereby relay Re is energized: over contact 21' andthe alarm lamps AL. and. A'IL are illuminated over contacts 28 and-'29; I

on. break-down. in. central line 01. thezsame tacts 32 and 33 and the lamp 'SFL. in a: circuit over the contact 34-. 1 7

After all; above-mentioned. circuit alterations the relays may be reset; to normal position by pushing. key- A. In case of a complete breakdown botl'rih th'lofop Astandinithe line: CL; the combined; direct; and alternatingvoltage remains on the centi'akline; 'Shouldthe'breaks he. of short duration the relay R4515" actuated. on remova'lof thebreak whereby relays: R1 andRaoperate: in a circuit: from battery B2 over. contact 35: and: are again set under supervisory current. i Wherr. the relayzRiattracts. its armature, relays R1; and R5 release their armaturesfandi. the converter stops,

but that one of the relays-ReandrRv:whiclrhas been actuated retains its armature inicircuitset; 31 causing the existingssignal itoreaspmoe main. On the other hand signal SFL or KCL does not remain in this case.

After a short-circuit break-down of short duration the relay R3 retains its armature due to the supervisory current being able to magnetize the relay sufficientlyto lock'it but netenough for attraction. After a short single-wire break-down in the loop ASz, the relay R2 is for the same reason unable to attract its armature.

Thus both signals KL and ASL remain operative after faults of short duration.

On a leakage to earth from one of the two branches of central line CL or from some alarm loop, the relay JR1 operates in a circuit from earth to battery B3, which is connected to earth and the lamp JFi is illuminated over contact 4|. If the leakage is not located in the lower branch of the central line, the relay R3 also attracts its armature and the lamps KL and SFL are illumihated; Should, the leakage disappear, the signals. KL and SFL, however, remain whilst the lamp JFi is extinguished, the relay R3 as above still. being actuated;

Since all lines are connected in parallel to the battery E1, the relay JRl .will be set under the total leakage current from these lines to earth. It might therefore happen that the relay JR].

attracts its armature without thev leakage in every line: having reached an inadmissible value. In that. event, it. is convenient to switch the faulty lines to battery B2 andconverter 02 through the switch B0, The earth fault relay JRz may there by be constructed for a higher energizing current than the relay JR1 so that it'does not attract its armature until a direct connectionto earth has occurred on a line; 7

Itwilltbe seen from the above firstly that an alarm (lamp AL, bell AK) is not emitted by lasting or intermittent faults on thecentral line; secondly, that faults which prevent the transmission of alarm signals are indicated as major faults by the lamp SFL; thirdly, that faults which do not prevent the transmission of alarm signals are indicated as minor faultsi by the lamp LL; fourthly; that faults of short duration are signalled. by'me'ahs of'continuing signals. thus calling: forexam-ination of the lines; and finally, that faults of short duration do not interrupt the emission of. ultimate. alarm signals'sinceat least the relayRi,iand'possibly also the relay R2, upon the removalof anlarbitrary fault, attracts its arma ture, even shouldthe resetswitch not have been previously operated. 6b a com lete break-down in the alarm loops which of so shorta duration that the loops are closed when relays R4 and R5 become connected for' testin g and thusboth should be actuated; as

an alarni si nal may be transmitted, the resist-' tactzisnowwiaened, wherefore, e'venshould the alarm contact: in the loop'be' closed,an' alarm signal is" emitted. at: the centralboarclj Inthe example of an: alarmzsystem according to the invention and shown 'in': the drawing; the branches'emanating. from the centralistati'orr of line 6L. in the IGcaILpIantQWhichlis. to'th'e right on the drawing are connected to each other a condenser C2, whereby these two branches will -iorm a single-wire loop circuit for alternating current. This loop circuit is then electrically connected at the local plant to loop circuits A81 and AS2, This electrical connection is constituted by the windings on transformer TR and of resistance r2, r3. Alarm loops A81, A32 may consequently be supervised or tested from the central station by the aid of direct current. Naturally, other arrangements than those given in this example may exist in the local plant without affecting the principIe of the invention. Consequently, the two central line branches may be connected to each other over a choke coil which thus replaces condenser C2, whereby the local alarm circuits become connected to this coil from the central board emanating loop circuit for direct current over a condenser and resistance. The local loop circuits are thereby connected in parallel with the choke coil and may be supervised from the central station by means of alternating urrent.

According to a different embodiment, the central line branches may be connected to each other over the primary winding of a transformer and the local loop circuits connected to the secondary winding of the transformer. According to still another modification, the two central line branches may be connected to each other over an ohmic resistance, whereby the local alarm circuits in series with other ohmic resistances are connected in parallel to the first-mentioned ohmic resistance.

In the embodiment described, a test made over the central line is carried out when an indication has taken place. Under certain circumstances it may prove advantageous to undertake further tests.

We claim:

1. An alarm system comprising a central alarm station, sources of alternating and direct current in said station, local alarm loops with two-wire lines outside the station, a central two wire line extending from said station and connected to said local alarm loops and forming a central loop circuit, a blocking device for the direct current in said loop circuit at the connection between the central line and the local alarm loops, a relay device in said central station connected with said central line and operable by said direct current, a second relay device operable by the alternating current and connected between said central line and said alternating current source after opera tion of the first relay device, signal circuits controlled by said relay devices, and signal devices in said signal circuits for indicating whether changes in the line conditions have taken place in the central loop circuit or in the local alarm loops.

2. An alarm system as claimed in claim 1 in which the blocking device is constituted by a condenser and in which the local alarm loops are in series with a resistance connected in parallel with said condenser.

3. An alarm system as claimed in claim 1 in which the two wires of the central loop circuit at the connection to the local alarm loop are connected to each other over the primary winding of a transformer, the local alarm loops being connected to the secondary winding of the transformer.

4. An alarm system as claimed in claim 1 in which a supervisory device at the central alarm station is so arranged that a supervisory circuit for direct current is closed from said. device and that on change of current in said supervisory circuit the alternating current becomes connected to the central two wire line.

5. An alarm system as claimed in claim 1 in which the first mentioned relay device includes relays through which supervisory current is closed from the direct current source to the central two wire line, certain of said relays being so constructed that the normal supervisory current is unable to energize such relay, butif such relay is energized by a higher energizing current, the normal supervisory current is *sufilcient to maintain such relay energized and its armature attracted.

CURT FREDRIK AHLBERG. STEN AKE NILSSON.

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