US2904782A - Lighting system for alarm boxes - Google Patents

Description

United States Patent Ofiice Patented Sept. 15, 1959 2,904,782 LIGHTING SYSTEM FOR ALARM BOXES Charles L. Craddock, North Hollywood, Calif.

Application November 13, 1956, Serial No. 621,923

15 Claims. (Cl. 340-288) My invention relates generally to alarm systems, and more particularly to alarm box systems that provide an attention commanding visual signal for each box.

The early discovery and reporting of a fire is one of the major considerations in reducing the amount of 'damage done by the fire. Very often fires are first discovered by people outside a burning structure, particularly during evening and night hours when buildings are often unoccupied. Such people, upon discovering a fire, however, often encounter ditficulty finding means of communicating with the fire department. Fire-alarm boxes are used in most cities in an attempt to make reporting a fire easier; however, such fire-alarm boxes are generally regarded with apathy by the public until the actual need to use such a box arises. Therefore people are not usually familiar with the locations of fire-alarm boxes and often have difficulty finding them.

There is, therefore, a need to provide an attentioncommanding signal adjacent fire-alarm boxes, first, so that upon repeatedly observing such a signal and associating it with a fire-alarm box, the locations of the boxes will become impressed upon the public. Then, when one discovers a fire, the knowledge of the location of fire-alarm boxes will greatly facilitate reporting. Further, even through the person who discovers a fire does not have knowledge as to the location of a fire-alarm box, an attention-commanding signal will make alarm-boxes much easier to locate.

Most fire-alarm systems consist of a group of firealarm boxes electrically connected in a serial circuit which is returned to the fire-alarm central station. This serial circuit is normally energized by means of a direct current of electricity. Turning in an alarm at any of the boxes has the effect of interrupting the normal flow of current in the circuit and providing current pulses in a particular code, identified with a particular box. In this manner, a signal at the fire-alarm central station is provided indicating the location of the fire-alarm box from which the alarm was given.

In its more general form, the present invention comprises a method of providing a flashing light adjacent a fire-alarm box to provide an attention-commanding signal. The light is illuminated by alternating-current electricity applied over the direct-current signal lines in such a manner that the direct current utilized to provide a fire alarm signal is not affected by the alternating current providing power for the lights.

It is, therefore, a major object of my invention to provide an attention-commanding signal originating from a point adjacent a fire-alarm box.

It is a further object of my invention to provide a flashing-light signal in conjunction With a fire-alarm box which may be simply installed, and which will not interfere with the normal operation of the fire-alarm box.

Another object of my invention is to provide an attention-commanding signal adjacent a fire-alarm box, which may be energized over the same electrical conductors that are used to carry alarm signals, without interfering with such alarm signals.

Another object of my invention is to provide an electrical (flasher signal in association with a fire-alarm box, which is economical both in installation and operation.

It is still a further object of my invention to provide a flashing-light signal in conjunction with a fire-alarm box, wherein the flashing-light signal is energized from a central source of electrical energy by means of wires utilized to carry the signal current to the alarm box andin such a manner as to not interfere with the alarm-signal. current.

These and other objects and advantages of my invention will become apparent from the following description thereof, and from the drawings illustrating the invention, in which:

Figure 1 is a perspective view of a fire-alarm box similar to that used in many cities, and to which a flashing-light has been attached;

Figure 2 is a schematic and block diagram of a system constructed in accordance with the principles of my invention; and

Figure 3 is a schematic wiring diagram showing a circuit which may be used in conjunction with the light on the box shown on Figure 1.

Referring now to the drawings, in Figure l I have indicated a fire-alarm box of a type widely used to report the occurrence of a fire. It is to be understood that the application of this invention is in no way limited to firealarm boxes of the type shown in Figure 1; however, this alarm box serves only to illustrate the manner in which a light may be mounted. That is, a fire-alarm box 10 may be of the type wherein a small door 12 is opened and a lever is pulled to report a fire. On such a firealarm box, may be mounted an enclosure 14 to house electrical circuitry for energizing a lamp 16 mounted on the enclosure.

In Figure 2, I have indicated a diagram of a circuit for connecting a number of fire-alarm boxes, as shown in Figure 1,, to a fire-alarm central station. In the system of Figure 2, fire-alarm boxes are indicated by the numeral 18. Mounted upon eachof the fire-alarm boxes 18 is the necessary electrical circuitry for providing a flashing light, as indicated by signal-light boxes 20, which may be housed in the enclosure 14 of Figure 1 and which will later be described in detail. One such circuit for providing a flashing light is shown and described in my patent 2,717,336,.flasher circuit. The alarm boxes 18 are connected in a serial loop'by interconnecting conductors 22, 24, and 26. This serial loo-p is connected to the central office equipment 27 by a conductor 28 which is connected to the first alarm-box ,18 of the loop, and by a conductor 29 and a relay 30 connected to the last alarm box 18.v

During this normal operation of a fire-alarm system, as shown in Figure 2, a small direct current flows from the centralvoffice equipment 27, through the conductor 28, to the first of the alarm boxes 18. This current then passes through the alarm box to.the conductor 22 to be passed similarly .to the other alarm boxes 13 in the serial loop and returned to the central office equipment 27 through the conductor 29 and the relay 30. As long as this current continues-to flow, -no alarm signals are reported. When one of the alarm boxes 18 is operated, the serial loop is interrupted and the directcurrentflowing throughthe serial loop is then allowed to flow only in pulses which form a code signalidentified that particular alarm box. .This code signal may be decoded at the fire alarm central station housing the central office equipment 27 and utilized todirect the fire fighters to the location of the fire. It is in'iportantthat any visual signalling system associated with the'fire'alarm boxes 18 nected between the conductor 28 and the junction point 35 and the junction point 35 and the conductor 29.

Alternating current from the power source connected to the terminals 34 passes from these terminals through the primary winding of the transformer 36. The secondary winding of the transformer 36 is thereby energized to pass an alternating current through the contacts '38, and both the capacitors 39 and 37 to the conductors 28 and 29. The conductors 28 and 29 are connected to the serial circuit including all the alarm boxes 18, and

'thus provide a connection between the secondary winding of the transformer 36 and the alarm boxes.

The signal-light boxes 20 associated with each of the alarm boxes 18 are capacitively coupled between the conductors connecting the alarm boxes 18 into a serial loop and ground. Therefore, alternating-current applied to the serial loop passes through the signal-light boxes 20 via a capacitive alternating-current connection, then to ground. The direct-current in the serial loop is pre vented from passing into the signal-light boxes 20 by the capacitive connection, which is later shown and described in detail.

It is to be noted, that the two capacitors 37 and 39 serve to apply alternating current to both sides of the serial loop. This manner of power application maintains the alternating-current potential equal on the lines leading to the central office equipment 27. Therefore, no alternating current will flow into the central ofiice equipment. Such an arrangement is extremely desirable due to the fact that sensitive relay devices are often present in the central office equipment 27 and alternating-current could cause a malfunction of the equipment.

In the event that a fire is reported and one of the alarm boxes 18 opens the serial loop, the parted portions of the serial loop may not present equal impedance to the alternating currents passing through the two capacitors 37 and 39 and an unbalance between the potentials on conductors 28 and 29 may result. Therefore, it will be desirable to halt the application of alternating-current energy to the system when an alarm is given or the serial 7 loop is opened. This is efiected by means of the relay 30 opening the contacts 38. The relay 30 is of the slowconnect, fast-release type, and therefore requires that a direct current flow through the serial loop including the relay 30 for approximately thirty seconds before the contacts 38 will close to apply alternating-current potential to the serial loop. The relay 30 will however cause the contacts to be opened immediately when direct stops flowing in the conductor 29. Therefore, when a fire is reported or when an open circuit occurs in the serial loop, the current is interrupted in the serial loop, including the relay 30, and the contacts 38 are opened, thereby disconnecting the alternating-current source from the loop until the direct current has been re-established for some thirty seconds.

Since, in actual practice, serially connected fire alarm circuits are in an open condition only a very small percentage of the time, my invention makes possible the operation of an alternating-current operated attention commanding signal most of the time over these same circuits in a balanced feed connection which does not interfere with the normal electrical supervisory functions of the ofiice equipment of the serially connected fire alarm circuit. Thus the supervisory equipment will operate normally, waiting for an alarm, and in the meantime the public receives the benefit of the operation of the attention commanding signals.

Reference will now be had to Figure 3 which shows one form of a capacitor-isolated signalling circuit which may be placed within the signal-light boxes 20 of Figure 2. This system will provide a flashing signal when connected to a source of alternating current, but will not receive direct current. Considering the circuit of Figure 3 in greater detail, a terminal 40 is adapted to be connected to the serial loop, e.g. conductor 22. This terminal will, therefore, receive both an alternating and a direct current voltage. Direct current is prevented from passing into the circuit by a capacitor 41; however, alternating current passes through the capacitor 41 and is applied to oppositely poled diodes 42 and 43. A capacitor 44 is connected across the diodes 42 and 43 and has one terminal connected to a grounded conductor 46. Connected to the other terminal of the capacitor 44 is one terminal of a variable resistor 54), the other terminal of which is connected to one terminal of a fixed resistor 51, and the other terminal of this fixed resistor is connected to a junction point 52. A conductor 53 connects junction point 52 to another junction point 54 and a capacitor 55 is connected between junction point 54 and the diode 42. Thus,

resistors 50 and 51 are connected in series, and capacitor 55 is connected in parallel with the resistor circuit, thereby providing an RC circuit.

A capacitor 56 is connected between junction point 54 and conductor 46, and junction point 52 is connected by conductor 57 to anode 60 of the electron discharge tube 61. The grid of the electron discharge tube 61 is connected through resistor 62 to the conductor 57. Finally,

the cathode 64 of the tube 61 is connected to a junction point 65, and the capacitor 66 is connected between this junction point and the conductor 46.

As will be hereinafter described, high voltage pulses appear between junction 65 and the conductor 46, and conductor 67 connects the junction 65 to one terminal of the primary of a transformer 70. The other terminal of the primary of the transformer 70 is connected to conductor 46, and the secondary terminals of the transformer are connected to the two terminals of a gaseous conduction tube 72, one of these conductors, if so desired, being in turn connected to conductor 46.

When alternating current is applied to the terminal 40 the condenser 41 is charged during the negative halfcycle, through the diode 43. During the positive halfcycle, the voltage applied at the terminal 40 is serially added to the voltage developed across the capacitor 41.

As a result, a voltage, substantially doubled from the voltage applied at the terminal 40, is passed through the diode 42 to the capacitor 44. In this manner, the capacitor 44 is charged; however, the charging current is limited somewhat by the diode 42. During each positive halfcycle of the alternating current passing through the diode 42, the voltage developed across the capacitor 44 rises exponentially and then decreases in such a manner as to form a so-called saw-toothed wave form. As the voltage across the capacitor 44 increases, the voltage between the junction point 52 and the conductor 46 likewise increases, since tube 61 is initially non-conducting and no large current is drawn through the resistors 50 and 51. However, capacitor 56 which is connected between junction point 52 and conductor 46 is being charged during this period and when the voltage appearing between junction point 52 and conductor 46 reaches some critical value, the electron discharge tube 61 becomes conductive, and capacitors 44 and 56 discharge through it. The discharge continues until the voltage between the junction 52 and the conductor 46 decreases to a value insuificient to continue the discharge, whereupon the tube 61 becomes non-conducting. At this point, capacitor 44 has discharged its charge through resistors 50 and 51, so that the voltage at junction point 52 is less than the voltage at the diode 42. As a result, capacitor 55 is charged and this charge will tend to set the voltage to which the capacitor 44 may discharge. Thus, the resistors 50 and 51 and the capacitor 55 are the fundamental elements of a timing circuit which by establishing the level to which the capacitor 44 may discharge establish the time cycle of the circuit.

The function of the capacitor 44 is toprovide a' supply of current that may be discharged relatively rapidly, and in an amount greater than that capable of being provided by the source of power applied at the terminal 40. The function of the capacitor 56 is similar, and its effect is to reinforce or increase the brilliance of the discharge occurring in the gaseous discharge tube 72, since capacitor 56 discharges directly through the electron discharge tube 61 While capacitor 44 discharges through resistors 50 and 51.

The operation of the electron discharge tube 61 is somewhat similar to that of a thyratr'on. The control electrode of the tube 61 is connected through a resistor 62 to conductor 57 and this conductor is likewise connected to the anode or plate 60 of the tube. Consequently, when the tube 61 is not conducting, no current flows through the resistor 62. Thus, the grid and the anode of the tube 61 are at the same potential, and the grid acts as the trigger electrode for the tube 61. When the junction point 52 reaches a predetermined value, the same voltage which appears on the grid of the tube, triggers or starts the discharge in the tube 61 and current flows between the anode and cathode of the tube. Current also flows through the grid of the tube and the resistor 62 to the conductor 57; however, the presence of the resistor 62 causes a voltage drop to appear across the terminals of the resistor, so that a lower voltage appears upon the grid than upon the anode of the tube 61 when the tube is conducting. This, however, does not stop the discharge within the tube 61 once it has been initiated.

The cathode 64 of the tube 61 is connected in series with the primary of the transformer 70, and when the tube 61 is non-conducting, the potential of the cathode is substantially equal to that of conductor 46. However, the primary of the transformer 70, has a certain resistance, and when current first fiows from the tube 61 through the primary, this produces a voltage drop that causes the capacitor 66 to be charged. As the tube 61 conducts, the first surge of current decreases or decays, and a lower voltage drop appears between the terminals of the primary of transformer 79. As this occurs, the capacitor 66 returns the energy stored in it, to the circuit and the charge on the capacitor is then discharged through the primary of the transformer 70. Thismeans that the lamp 72 is illuminated a slightly longer time. The effect of the capacitor 66 is thus to decrease the initial surge of current to the primary of the transformer 70, and to continue the passage of current through that primary for a longer period of time.

The flashing rate of this system may be controlled by varying the resistor 50. In this manner the time to discharge the capacitor 55 may be varied. Each of the different capacitors and resistors, however, has its own effect on the flash rate, some increasing and some decreasing the frequency of flashing.

It is to be understood that the flashing light system shown in Figure 3 is only exemplary of the type flashing light systems which may be utilized in the system of my invention and various other systems may satisfactorily be used.

It will thus be seen that I have shown and described a fire alarm box lighting system fully capable of achieving the objects in securing the advantages heretofore set forth. Many modifications and variations will occur to those skilled in the art, but these are included within the broad scope of my invention. Consequently, I do not 6 wish to be restricted to the particular forms described and shown except as limited by my claims.

I claim:

1. In a fire-alarm system of the class described wherein plural fire-alarm boxes are connected in a serial manner to receive a direct current from central oflice equipment, the improvement which includes: means for coupling a source of alternating current to said serial circuit; a plurality of signal means each connected to said serial circuit and positioned adjacent one of said firealarm boxes, said signal means being such as to selectively receive only alternating-current energy; means: for detecting the flow of direct current in said serial circuit; and means for disconnecting said source of alternating current from said serial circuit when a direct current is not detected in said serial circuit.

2. In a fire-alarm system of the class described Wherein plural fire-alarm boxes are connected in a serial circuit to receive a direct current from central oifice equipment, the improvement which includes: capacitive alternating-current coupling means adapted to be connected to a source of alternating current and connected to said serial circuit; a plurality of flashing-light signals each identified with a particular one of said fire-alarm boxes; plurality of alternating-current coupling means each connecting one of said flashing-light signals to said serial circuit; and means for disconnecting said source of alternating current from said serial circuit during a period when direct current is not flowing in said serial circuit.

3. In a fire-alarm system of the class described wherein plural fire-alarm boxes are connected in a serial circuit to receive a direct current from central office equipment, the improvement which includes: first and second capacitors for coupling a source of alternating-current to a pair of points in said serial circuits; a plurality of flashing-light signals each identified with a particular one of said fire-alarm boxes; plurality of alternating-current coupling means each connecting one of said flashing-light signals to said serial circuit; and means for disconnecting said source of alternating current from said serial circuit during a period when direct current is not flowing in said serial circuit. v

4. A fire-alarm system of the class described including: a plurality of fire-alarm boxes interconnected by an alarm circuit; central otfice equipment connected to said alarm circuit for energizing said alarm circuit with 'a direct electrical current; a first alternating-current coupling means adapted to couple a source of alternating current to said alarm circuit; a plurailty of flashing-light signal means adapted to be energized by an alternating current; a plurality of second alternating-current coupling means connected between said alarm circuit and said flashing-light signal means; means for detecting the presence of a direct'current flowing in said alarm circuit; and means for disabling said first alternating current coupling when a direct current is not detected in said alarm circuit.

5. A fire-alarm system of the class described including: a plurality of fire-alarm boxes connected in a series circuit; central office equipment having first and second electrical terminals connected to said series circuit to pro- ,vide direct-current energy to said series circuit; first and second capacitors serially connected between said first and said second terminals; means adapted to connect a source of alternating-current energy to a junction point between said first and said second capacitors; a plurality of flashing-light signal devices each associated with one of said fire-alarm boxes; and a plurality of alternating-current coupling means, each for coupling one of said flashing-light signal devices to said series circuit.

6. A fire-alarm system of the class described including: a plurality of fire-alarm boxes connected in a series circuit; central office equipment having first and second electrical terminals connected to said series circuit to provide direct-current energy to said series circuit; first and second capacitors serially connected between said first and said second terminals; means adapted to connect a source of alternating-current energy to a junction point between said first and said second capacitors; a plurality of flashing-light signal devices each associated with one of said fire-alarm boxes; a plurality of alternating-current coupling means, each for coupling one of said flashing-light signal devices to said series circuit; means for detecting the presence of direct current in said series circuit; and means for disconnecting said source of alternating-current energy from said junction point when direct current is not detected in said series circuit.

7. A fire-alarm system of the class described including: a plurality of fire-alarm boxes connected in a series circuit; central oifice equipment having first and second electrical terminals connected to said series circuit to provide direct-current energy to said series circuit; first and second capacitors serially connected between said first and second terminals; transformer means adapted to connect a source of alternating-current energy between a junction point between said first and said second capacitors and ground potential; a plurality of flashing-light signal devices each associated with one of said fire-alarm boxes; a plurality of capacitors each for coupling one of said flashing-light signal devices to said series circuit; means connecting said flashing-light signd devices to ground; means for detecting the presence of direct current in said series circuit; and means for disconnecting said source of alternating-current energy from said junction point when direct current is not detected in said series circuit.

8. A fire-alarm system of the class described including: a plurality of fire-alarm boxes connected in a series circuit; central office equipment having first and second electrical terminals connected to said series circuit to provide directcurrent energy to said series circuit; first and second capacitors serially connected between said first and said second terminals; transformer means adapted to connect a source of alternating-current energy between a junction point between said first and said second capacitors and ground potential; a plurality of flashing-light signal devices each associated with one of said fire-alarm boxes; a plurality of capacitors each for coupling one of said fiashing-light signal devices to said series circuit; means connecting said flashing-light signal devices to ground; a relay device connected to be controlled by the flow of direct current in said series circuit, said relay device having contacts for disconnecting said source of alternating current energy from said junction point when direct current is not flowing in said series circuit.

9. A system according to claim 8 wherein said relay device comprises a slow-connect, fast-release relay.

10. A11 attention commanding signaling system applicable to a direct current serially connected metallic circuit, and consisting of means for connecting alternating voltage between said metallic circuit and earth, such connecting means possessing balanced high pass admittance to the two ends of. such direct current metallic circuit, and such connecting means further possessing means for becoming disconnected from said metallic circuit when the flow of direct current in said metallic circuit falls below a predetermined value; and further consisting of attention commanding signals with high pass admittance characteristics, connected between the metallic circuit and earth at various points along said metallic circuit.

11. A system according to claim 10 wherein said means for becoming disconnected from said metallic circuit when the flow of direct current in said metallic circuit falls below a predetermined value, is also a means for connecting said alternating voltage to said metallic circuit when the flow of direct current in said metallic circuit rises above a predetermined value.

12. A system in accordance With claim 10 wherein the disconnecting and connecting means responsive to the value of direct current flowing in said metallic circuit possesses means for causing considerable difference in time of response for disconnecting as compared to the time of response for connecting.

13. A system in accordance with claim 10 wherein the connecting means possessing balanced high pass admittance to the two ends of such direct current metallic circuit consists of two equal capacitors connected in series, the two outer terminals of said two series connect capacitors being connected respectively to the two ends of said metallic circuit and the common center terminal of said series connect capacitors being connected to one side of said alternating voltage.

14. A system in accordance with claim 13 possessing disconnecting and connecting means for becoming disconnected from said metallic circuit when the flow of direct current in said metallic circuit falls below a predetermined value, is also a means for connecting said alternating voltage to said metallic circuit when the flow of direct current in said metallic circuit rises above a predetermined value.

15. A system in accordance with claim 13 possessing disconnecting and connecting means wherein the disconnecting and connecting means responsive to the value of direct current flowing in said metallic circuit possesses means for causing considerable difference in time of response for disconnecting as compared to the time of response for connecting.

References Cited in the file of this patent UNITED STATES PATENTS 246,163 Livingston Aug. 23, 1881 715,537 Bedell Dec. 9, 1902 1,242,756 Angold Oct. 9, 1917 1,314,339 Laidley Aug. 26, 1919

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