US2052057A - Fire alarm system - Google Patents

Description

Aug. 25, 1936. F. REU: 2,052go57 AFIRE ALARM SYSTEM Aug. l:25, 1936. F. REID f 2,052,057

FIRE ALARM SYSTEM' Filed Nov. 7, 1929 2 sheets-Sheet 2 A rrr;

Patented Aug. l25, 11936 PATENT oFEiCE FIRE ALARM SYSTEM Frederick Reid,- Neasden, London, England Application November 7, 1929, Serial No. 405,472 In Great Britain January 4, 1929 6 Claims. (Cl. 1774352) This invention relates to fire alarm systems and is applicable to analogous, systems such as arnbulance call systems so that whenever the expression iireJ alarm system occurs herein it is to be understood as including such analogous systems and the expression fire alarm is to include analogous calls.

Such systems are divided broadly into two main classes, namely, closed circuit. systems in which the current supply is interrupted for the purpose of giving a fire. alarm, and "open circuit systems in which the line circuit is completed for current to flow therein for the purpose of giving the fire call. The former systems in general are constructed on the closed circuit metallic loop system, While the latter may be of either the metallic loop or earth return type.

The object of the invention is to improve the arrangement of open circuit systems whereby they may be adequately and continuously or frequently tested and to provide means for readily distinguishing fire calls from electrical faults.

Another object of the invention consists in the provision of means for facilitating automatic routine testing in open circuit systems and other details and arrangements hereinafter described or indicated.

The accompanying drawings illustrate one form of apparatus in accordance with the invention. v l

Figure. l shows a diagram of an open circuit're alarm system'dn accordance with the invention embodying an arrangement for automatic and 'regular routine testing of each re alarm circuit.

Figures 2, 3 and 4 show parts of apparatus on an alarm box whereby a signal is transmitted, and

Figures 5, 6 and '7 show routine testing arrangements for use in such circuits.

When applying my invention to open circuit systems I may provide my improvements in such systems independently of whether they are me- "inent now considered (as shown ior example in Figure 1).

As generally arranged the line is normally disconnected at -the fire alarm bemand a fire signal is sent by connecting the line tothe earth return either temporarily or until ;eleased in some manner, or in `accordance with a definite numerical code. The defects of such arrangements as hitherto adopted are:-

(1) That earth or electrical faults may cause false calls;

(2) That it is diflilcult to arrange for either a continuous. or 'frequent test of the continuity of the line under conditions identical with working conditions.,

In order to remedy these defects of existing systems in accordance with this inventions. suitable rectiiier is inserted in the earth return or metallic return at each box, and is arranged in relation to the station battery so that normally no current will pass in the line, but when a box is pulled to` give a re alarm the connections to the rectifier are reversed` by suitable means'in order that the current may then pass to actuate the alarmv apparatus and preferably the rectifier is held in its reversed condition by the locking of a cam or otherwise until released by a fireman or' responsible omcial. Such an arrangement is shown in Figures 2, 3 and 4 and comprises a camshaft a provided with a handle b which projects from the call box and is rotated in a counterclockwise sense to transmit an alarm signal. This reverses the circuit connections by relative .movement of contacts c and the shaft is held in its signalling position locked by a spring controlled pawl d until released by a responsible omcial. Such an arrangement permits of the application of simple means for testing the line since it will be clear that by reversing the station battery the current may be passed through the line at any desired time, the testing circuit including a suitable indicator (such as a milliammeter) to enable the observer to test whether the current isof proper strength, in which case the line may be regarded a's satisfactory.

The use of a rectifier at the fire call point also provides a ready' means of distinguishing re calls from earth faults. In one arrangement of the station apparatus, for example, a relay is connected ineach circuit to reverse the polarity of the line and cut off the i'ire alarm indicator in the operated position.

The reversal of the rectifier at the call point on' a` 4iire call causesI the relay to operate like a trembler bell as current vcan only ow when the relay is in the non-operated position. Pulses of current are therefore sent through the fire alarm indicator which is preferably a slow acting type, causing it tobe actuated.

An earth'fult'causes the relay to operate remain in its operatedposition, cutting off the fire alarm indicator which in consequence is not actuated.

Figure 1 shows one convenient arrangement of open circuit system according to the invention, which, for the sake of simplicity, is arranged as an earth return system, although as above indicated the invention is equally applicable to metallic return circuits. In Figure 1 I have shown two lines connected to the main station, each line having a call box and each line having its indicator I, its indicator control or reversing relay 8, its jack I3 and resistance I5, and its set of cam springs 2I-26, inclusive. The alarm signal controlled by indicator l may be common to a group of lines as shown as may also be relay I8, batteries 6n and 20, and signal I4 and jack I2 with its key I6. As indicated a cam operates springs 2| to 25 at one time to disconnect battery Se from the rst line and connect the test relay thereto while springs 2i to 25' are operated at another time by another cam to disconnect battery 6 from another line and connect test relay I8 thereto. Normally. in such an arrangement the battery 6 has its positive pole connected via contact I0, indicator l, contacts i, resistance I5, by line to the box, contacts k, rectifier 4, contacts l to earth; and its negative pole via relay 8, contacts 9 and contacts I3 also to earth.

The rectifier 4 in the fire alarm box is normally connected so that no current can ow to earth from the battery 6.

A fire call is made by pulling handle I which operates and locks cam 2 and reverses contacts k and l on switch 2'a permitting current to flow from the positive pole of battery 6 through the normal line circuit and new arrangement of contacts k and l to earth, returning through contacts I3, 9 and relay 8 to the negative pole of battery 6'. y

Relay 8 will operate and change over contacts 9 and III. Contacts 9 and IIJ reverse battery to line and as the rectier is now in inoperative condition for this direction of current ow the current to line will be small and relay 8 will restore when process is repeated. Relay 8 therefore vibrates like a trembler bell sending pulses of unidirectional current through indicator l which is slugged or otherwise made slow to operate. This will cause indicator le to operate giv-v ing a visual and audible signal of a re call, the audible signal being made by the closing of contact II on account of the operation of indicator 1*.

In the event of an earth fault on the line, relay 8 will operate and remain operated as current will ow through the earth fault even whenv the battery is reversed. Contact III cuts oif the indicator 1 so -that the latter is not operated by the steady current. An earth fault will therefore not give a re call. Plug I2 can be plugged into jack I3* to give a warning by the operation of indicator I4 when the re call point has been restored to normal. An adjustable resistance I5 can be employed i! desired to balance all lines to a common resistance (e. g. 500 ohms). A speaking key I6 and telephone I'I can be provided if desired and when used a telephone such as T can be inserted into the line by means of plug Y and jacks such as X and X if the fireman desires to converse with the central omce as isv common practice. Y

When plug I2 is inserted in jack I3 on receipt of a nre call due to the reversal of rectier 4 at call-point, the negative pole of battery C is connected via indicator I4, back contacts of key I6, tip of plug, short spring of jack I3 to line, whilst the positive pole of battery is connected via ring of plug and long spring of jack I3 to earth.

No current flows under these conditions as rectifier 4 has been reversed so that current can now only iiow from the line through the rectifier 4 to earth when the line is connected to the positive pole of the battery. Indicator I 4l is therefore not operated until the rectier 4 has been reset to normal by the reman at the call point.

The station attendant can, by throwing key I6, introduce a telephone transmitter and receiver I'I into the circuit. y

'I'he testing may be performed by hand but I prefer to arrange for an automatic testing to be carried out and where, as is usual, the system will include a number of boxes, an automatic routine test is preferably provided, it being understood that by routine tester I mean an automatic tester which when set into operation will run round a set of circuits and test each one individually. Obviously such routine test may be applied in many different ways since basically the .rectiers provided in accordance with the invention enable the lines to be tested under actual working conditions.

In one particular construction, for example as shown in Figures 5,. 6 and 7, I may provide a master clock e' which will close a contact, e. g. f', f2, f3, f4, say, once every1 15 minutes for the purpose of starting the test and will then by means of ratchet wheel g' (stepped by the ratchet lever system h of the electromagnet 7" energized by the closed circuit), cause cams k', k2, k3, etc. which are on the same shaft as the wheel g' each to close a set of contacts l', l2, Z3, etc. whereby the different circuits are reversed for testing. The cams are set at angles to one another on the shaft in order that only one circuit is tested at a. time. The stepping of the wheel g' may be effected one tooth per second until it has made one complete revolution. As soon as the stepping switch of a particular line operates to reverse the circuit, the fire alarm indicator for that line will be cut off, and one coil of a testing (differential) relay will be connected to line with reversed battery so that the current which then flows through the line will be balanced against a current through the other coil of the testing (differential) relay, and if the current in the line is not equal to the standard Working current within a prescribed margin the line will be faulty and a fault indicator will drop and, if necessary, a fault bell may be made to ring.`

In another particular construction specially suitable for systems where the lines are to be tested at frequent intervals I employ a motor driving through a reduction gear to operate the test switches.

Figure 1 embodies one arrangement which may be used for the automatic and regular routine testing of each re circuit.

When springs 2|, 22, 23, 24, 25 by cams such as lc', k2, k3, etc., Figure 7, are changed over the station battery 6 and fire indicating apparatus are cut out of circuit and a testing battery 2Il with the positive pole earthed (i. e. reversed with respect to station battery) is connected to the normal line circuit via one coil of a diilerential relay I8 and through'the other coil of I8` to a rectier I9 and a resistance 28 which exactly balances the line..resistance. Rectifier I! is introduced into the routine testing compensation cir- 75 cuit in order to give a proper balance. vIl! the line is free from faults the differential relay Ilv ferential relay I8 from battery 2li respectivelyl through rectifier i9, spring 2l, resistance 26 to earth, and spring 23, resistance i5", rectifier to earth, lthus giving rise to an unbalance, operating relay I8 and closing contact 28 which drops fault indicator 21 associated with the line being tested. A contact 29 associated with each line is broken when the, fire indicator 'I is actuated to prevent :fire calls also actuating the fault indicator.

`Each line is provided with a set ofsprings 2 I, 22, 23, 24. 25. These sets are operated in succession by cams of the kind shown in Figure 7 driven for example by a ratchet drive operated by a magnet controlled from a clock.

It is proposed to arrange a group of ten lines on one cam assembly and arrange to test each line in turn one every minute.

The period of test need not exceed one second so that the testing would not delay any call .for more than one second and on the average only one call in sixty would be so delayed.

The mechanical arrangement forr driving the routiner and the period of test are ofcourse subject to wide variation in accordance with the requirements of any system.

As previously p'ointed out the mechanical devvices illustrated in Figures 2 to '1, inclusive, are

merely-one form of well known mechanism which may be utilized. The clock controlled sequence switches such as indicated in Figures 5, 6 and 'I are well known in the telephone art and merely consist of a series of cams on a shaft which shaft is rotated by a magnet operating a pawl and ratchet and controlled from contacts on an electric clock such as a program clock. The detailed mechanisms are not a part of my invention.

It will be understood that the details of the testing arrangementA thus given are purely by way of illustration as obviously the. periods of test may be varied and the particular mecha.- nisms employed for automatically bringing each line into test may also be modified within wide limits, the essential feature of the invention being that in an opencircuit system the line or lines may be subjected to test automatically and as frequently as may be considered desirable.

In the foregoing descriptiony it is assumed that the line will normally be connected to earth through a rectifier connected, for example, so

. that current can only pass to earth when the line .is negative to earth but some features of the inaccordance with any practical requirements thatV may have to be'fulfilled.

Further, any convenient form of rectier may be employed in accordance with the invention, although I have found that very satisfactory resultsmay bei-obtained by the use of copper oxide rectiers:

I claim c 1. An open circuit fire alarm system comprising a cali point, a central station, an electric circuit connecting the two, .a source of current in said circuit. a rectifier at said call point sc ar- 5 ranged in said circuit vthat no currentI normally flows, means at said cali point for reversing the connections to the rectifier in order to cause a signalling current to flow over said circuit, y,and receiving means atthe station operated, under 10 -the influence of said signalling current, temporarily to reverse the connections of said source to the line to temporarily stop the flow of signalling current thereover, said receiving means intermittently operated responsive to said source connec- -l5 tions reversal to give a fire alarm in case the current flow is stopped by said reversal and operated steadily to prevent a fire alarm responsive to said.' reversal in case the flow of current is due to causes other than the reversal of the rectifier. 20 connections and therefore current flow is not stopped by said reversal.

2. In a fire alarm system, a plurality of lines connecting call points to a central station, a battery and alarm equipment connected to each 25 line atthestation, a rectifier in each line at the call point;` normally connected to prevent current. flowing` from' the battery over such line,y means at each call point for reversing the connection of the rectifier of that line to permit current to 30 flow to operate the alarm equipment of that line, test equipment for successively connecting a battery of reversed polarity to the lines, 'arelay in the test equipment operated only in case of a fault in the line, an indicator controlled by said 35 relay, and means controlled'by the alarm equipment vof a line for preventing operation of the test equipment indicator if it is associated with that line when the rectifier thereof is reversed.

3. In a fire alarm system, a line connecting a rcall point to a central omce, a batterygand a signal connected to the line at the omc "a Arectifier in the line at the call point normally zrcventing any current from flowing from tha-battery over the line to operate the signal, means' atthe call a5 point for reversing the connections oi the rectifier to the line to thereby permit current to flow over the line to operate the signal, another signal at the omce, means for disconnecting the first signal from the line and connecting the second ,50 signal thereto, said second signal so connected toA the line as to be inoperative when the rectifier is reversed, said second signal operated responsive to the reversal of the rectier-to its normal connection to the line. 1; 55

4. In a nre alarm system, aline connected between a call point anda central station, a rectiiler in the line at the station, a battery connected in the line at the central station, said rectiiier normally preventing current flow from the batce tery over the line, a control relay and an alarm relay connected to the line at the station, means at the call point for reversing the rectiner to transmit a nre alarm by causing a current to flow in the line, said control relay operated responsive 65 to said current flow to reverse the connections oi said battery in the line to test the line for accidental grounds, said control relay continuously operated responsive to an accidental ground on the line to prevent any further operation of said V70 alarm relay and intermittently operated in case the line is normal to control the alarm relay.

5. In a re alarm system, a line connecting a main station to a call point,-a rectifier in the line at the call point and a battery connected thereto 7 battery to the line, said relay operated steadily if a direct ground is present on the line when the battery is so reversed and said relay operated intermittently when the battery is reversed re sponsive to said current flow if no direct ground is present on the line, and an alarm controlled by said relay when intermittently operated.

6. In a re alarm system, a line leading from a central station to a call point, alarm equipment and a source of current supply at the station for said line. a rectifier in said line at the call point normally preventing operation of the equipment. means at the call point for reversing the connections of the rectifier to its line, means in the station responsive to the reversal of the rectier for reversing the connections of said source to the line, means at the station operating in one manner responsive to said reversal of the source and to saidreversal of the rectifier connections to cause an operation of said alarm equipment, said means at the station operating in another manner responsive to said reversal of the source to prevent operation of the alarm equipment for such line in case an accidental ground is present on the line.

FREDERICK REID.

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