US2525697A - Alarm system for hotels and the like - Google Patents

Description

Oct. 10, 1950 R E 2,525,697

ALARM SYSTEM FOR HOTELS AND THE LIKE Filed 'Harch 15. 1947 2 Sheets-Sheet 1.

SIN.

Oct. 10, 1950 E. M. LURIE ALARM SYSTEM FOR HOTELS AND THE LIKE 2 Sheets-Sheet 2 Filed Harch 13. 1947 patented Oct. 10, l d

OFFICE ALARM SYSTEM FOR HoTELs AND THE LIKE Eli M. Lurie, Laurelton, N. Y.

Application March 13, 1947, Serial No. 734,23

38 Claims. 1

This invention relates to improvements in fire indicator and alarm systems.

One object of the invention is to furnish improved means applicable to complex organizations such as office and apartment buildings for indicating at a central station or oifice, the occurrence of an undesired condition such as fire, at any of the diife'rent sections, floors, or rooms of the building.

Another object of the invention is to provide the system of the character described having electrical means comprising circuits carrying constant indicator or supervisory currents whereby anoperator is instantly notified of the occurrence of a break or defect in the system, and if it is desired, at the individual sections, floors or rooms of the building.

Another object of the invention is to provide an improved system of the nature set forth having improved means whereby signals are also caused at the different sections or rooms of the building in an automatic mannerwhen a fire or other undesired condition occurs, and whereby, if required, the operator may furnish an announcement to the different rooms or locations in the event of any emergency which may be independent of said fire or condition.

Another object of the invention is to provide an improved system wherein the signaling means in the different sections or rooms of the building may comprise lighting devices or electromagnetic speakers, the former to warn deaf persons, and the latter to furnish a suitable announcement.

Another object of the invention is to provide an improvement in the art whereby the supervisory current may be substantially increased upon the operation of a thermosensitive device or the like to cause a siren and amplifier or equivalent means to be energized, preferably by closing a normally open circuit therefore.

Another object of the invention is to provide improved means such that the supervisory current forms a continuous check of the condition of the loud speaker circuit, but without producing hum or other distortions in the loud speaker, particularly when the latter is not in use for transmitting announcements or the like; and the improvement further comprises the utilization of a direct current in such supervisory circuit whereby vibration in the speaker in response thereto is avoided.

Another object of the invention is to furnish an improvement whereby a plurality of radio receiver channels are adapted to selectively operspeaker member which when in ofi position is connected to energize the speaker member from the siren and amplifier or the like, and also to energize a neon light if desired.

Another object of the inventionis to furnish an improvement comprising a volume control switch adapted to permit the speaker member to be energized to transmit an" alarm signal in the zero position of the switch.

Another object of the invention is to provide an improvement whereby the supervisory circuit will not affect the speaker member to produce an objectionable hum therein, this circuit preferably carrying a direct current which may be associated with the speaker circuit to produce different novel effects.

Another object is to furnish a circuit system coordinated with the speaker member in an improved manner such that the impedance of various signal devices and the like will not affect the speaker.

Another object of the invention is to provide an improvement whereby the system is automatically connected to be energized by energy supplied from a storage battery in the event of failure of the regular source of house current.

Other objects and advantages of the invention will become apparent as the specification proceeds.

With the aforesaid objects in view, the invention comprises'the novel features, combinations and arrangements of parts hereinafter described in their preferred embodiments, pointed out in the subjoined claims, and illustrated in the an- 3 bodiments may be produced involving less than the whole.

It will be obvious to those skilled in the art to which the invention appertains, that the same may be incorporated in several different constructions. The accompanying drawing, therefore, is submitted merely as showing a preferred eXemplification of the invention.

eferring in detail to, the drawing, Figure 1 shows a system according to the invention with certain parts located at different sections or rooms of a building or hotel as here indicated in dot-dash lines, such rooms being denoted by the numeral it. In each of these rooms is provided a unit A these units being identical. While these units are shown in parallel arrangement to each other, they may also be arranged in series, although the former is preferable for reasons hereinafter apparent. Each unit A may include a signal element shown as an electromagnetic loud speaker ii and a sensing device l2 responsive to an undesired condition such as a fire, in which case the device l2 constitutes a thermosensitive member or switch. The member 42 is normally open, and is set so as to automatically close when a predetermined room temperature has been attained, to thus operate in the presence of a fire. The members ii and i2 may be connected into suitable protective circuits and are shown arranged in a single circuit 53 which includes a resistor l4 in series with the speaker H and in shunt with the member 112. Each circuit [3 may comprise response elements such as a relay l5 and an indicator, such as a lamp i6, which forms part of central response apparatus of the system located at the central station or control room. Across each of the members l2, I5, and [6 are connected the respective condensers l1, l8, and I9. The circuits i3 may connect together into a common circuit 20 of the central response apparatus having a source of direct current such as the common circuit 20 of the central response apparatus also includes additional response elements in the form of relays 22 and 23 of which the former is like the relay 1%. The purpose of these several relays will be presently described. Connected across the relays 22 and 23 is a condenser 2t, and a condenser 25 is connected across the battery 2 l. The purpose of the various condensers is to afford a low resistance path to audio or A. C. to the loudspeakers, bypassing the parts which are energized by D. C., and offering high resistance to D. C., and of course the speaker may include a matching transformer if desired.

The battery 2i of the central response apparatus is of a relatively low voltage causing flow of a relatively low sensing or supervisory current in the common circuit 2% and the branch circuits I3 connected thereto. Since the sensing current is a direct current it will not cause vibration of the speaker member ii, and will thus avoid any objectionable hum. The diaphragm of the speaker member may be under a constant tension, but this will be relatively negligible since the current is very small due to the provision of the various resistances in the line. Should the thermostatic switch device I2 close, the current will be substantially increased to cause ample illumination of the lamps 16, but this current will not cause any damage to the speaker member. The supervisory current may cause a slight glow of the indicating or lamp members It, and thus afiord an indication that the circuits l3 and '20 are in proper operating condition.

To provide fault signal to indicate a break in any of the above mentioned circuits, a bell or other indicator 26 is utilized which may be connected into the main line or source of volt current, this line being indicated at 27. From the latter extends a branch circuit 23 comprising fault responsive means shown as having a switch 29, and a switch 3| in another branch circuit and a further switch 33 in a further branch circuit 32. The relays l5 and 22 hold the switches 29, 3!, and 33 in a normal open position, these switches being of a spring type and tending to automatically close when their respective relays become deenergized. It will be perceived that the arrangement is such that upon the closing of any one of the switches 29, 34 or 33, the bell 26 is caused to ring. Because the relays [5 are in the individual circuits l 3 for the rooms l0, they will constitute indicators to show quickly the room in which the defect or break in the circuit has occurred, attention being directed to this condition by the bell 26. The relay 22 may be omitted, or the relays 15 may be omitted and only the relay 22 used. Because the circuits l3 connect in parallel relation into the common circuit 29, the relay 22 can afford no indication as to the locality at which the break in the supervisory circuit has occurred. An ammeter 34 may be connected into the circuits 2!] to indicate the total amount of current flowing, and this would afford an indication of a break in any of the supervisory circuits by showing a diminished amount of current. The condenser 24 may be in operative relation to this ammeter.

The responding apparatus of the central station also comprises a signal transmitting system shown as a siren 35, a microphone 35a. and an amplifier 36, the latter being shown as having a transformer whose secondary is in the circuit 20. The siren and amplifier are connected to the main line 2? in parallel relation to each other by their individual branch circuits 3? and 38 and the siren output is connected through microphone 35a to the amplifier 36 at 39. The supervisory direct current in the circuit 20 will have no effect upon the amplifier and the latter is normally deenergized because the circuits of the amplifier and siren include a common branch 40 having a normally open switch M.

The relay 23 is inoperative to cause closing of the switch 3! in response to the supervisory current. Upon operation of the thermostat, switch l2 closes causing a shunting of its resistor l4 and a substantial flow of current, sufficient to fully energize the relay 2;. The latteractsuponthe armature 2 to close the switch 4 5. Thus the siren and amplifier are energized and their output is suifi ciently great to properly activate the speaker member if irrespective of the supervisory current that may be flowing. Accordingly, the operator may send any suitable alarm, announcement and instructions to the occupants in the various rooms in the building or hotel, and if preferred a suitable preset announcement or oscillation signal may be transmitted as a warning. It will be appreciated that the supervisory current may be so small as to offer no material opposition to the signal energy from the amplifier 35.

In the event that the battery 2! becomes deenergized, the switches such as 29, 3|, 3'! of the response relays I5, 22 automatically close to cause ringing of the alarm and all the lamps I6 will be dark and the ammeter 34 will show zero, thus quickly indicating the source of trouble.

In the event that the regular house current in assess? the line 27 should fail, due to damage caused by fireor otherwise, an auxiliary unit 25 comes into operation to supply energy from a storage battery 46. To the latter is connected a circuit 4'! comprising motor-generator unit 48, and cooperative herewith is a switch device 49. The latter is diagrammatically shown as including a member 58 pivoted at 5! and having an armature 52 for a relay 53. A tension coil spring 5d urges the armature away from the relay 53. The latter is connected by a circuit 55 into the circuit 5'! and is normally energized to swing the lever switch member as to close the switch 56 in order to maintain a connection between the main building line 57 and the main house line 217. The switch member 5E9 also carries a switch 58 for a circuit 59 comprising the generator at. There is also a. switch ti operated by the member 49 for controlling the circuit Ail of the motor 62. It will now be apparent that if there is a failure of current in the in line 57 which feeds house line 21, the relay 53 is deenergized, whereupon the spring 54 swings the switch arm counterclockwise to close the switches 5e and 5 i. Thus the circuit is closed between the battery and the motor 52, and the circuit is closed between the houseline El and the generator fit. Certain corresponding contacts of the switches 53 and 53 may be interconnected as at 63, 84 so that the generator current feeds into the house line 2? in the same manner as in the case of the main line 51.

Certain advantages of the invention may be realized by omitting the electromagnetis speaker members H and the amplifier 35 and the siren 35, since the relays it, 22, and can be used in coordination with the thermostatic devices l2 according to the circuits herein disclosed to furnish an alarm system embodying a supervisory circuit. Although the speaker members I i are shown in circuit with the devices 1 2, they may also be disposed in wholly separate circuits embodying the amplifier and siren members and subject to the control of the relay 23 and its switch ii, and in that case the speaker members will not be influenced at all by the supervisory current. The embodiment of the invention shown in Fig. 1 permits the use of a much more compact circuit, and it provides for a check-up of the circuits of the speaker members by the supervisory current. In the various forms of the inventionas referred to herein, the device as may be employed.

In Fig. 2 is shown a modification of the invention generally similar to that of Fig. 1 except that it combines therein the employment of various radio receiver channels having electromagnetic speaker members 65which may be used totransmit music or alarm signals. A particular feature of this modification is that the alarm signal or announcement can be transmitted regardless of the position of the station selector switch or of the volume control switch or both.

Each room or section of the building may contain a unit B comprising the speaker member 65. Such building may include a plurality of like units )3 connected in series. The units B shown are connected in parallel for reasons hereinafter apparent. Although only two such units have been shown, it will be understood that the system may employ a great many of them all combined into a single circuit as hereinafter indicated. A circuit 56 for the speaker member may include a volume control switch 57 later described and a station selector switch "63 of any suitable character. The switch -58 is diagrammatically shown as including a plurality of arms havinga suitable pivotal mounting 68a, these arms being engageable with a series of pairs of contacts 69 for different radio channels. When the switch E8 is turned to a cut-off position, it engages a pair of contacts "Hi, the purpose of which will be presently described. From the contacts 69 extend difierent circuits or radio receiver channels H connected to respective amplifiers having their individual radio receivers or equivalent devices 13. Any suitable switches 14 may be provided with contacts 15 for connecting the amplifier circuits 16 t0 the receiver circuits 71. These switches 14 are provided with other contacts b8 connected to a circuit 79 of amplifier 8i] and a microphone I I la for a siren ill. The switch is is preferably automatically shifted from contacts is to contacts '18 to connect the siren ll to an amplifier l2. This operation may also be manually performed. A switch such as M is provided for each of the channels ii. Normally the tenants in the building'manipulate the switches 58 to connect the speaker member 55 to a selected channel and control the volume of reception by means of the switches 51. The switches it permit the receivers 73 to be cut on so that an alarm signal may be transmitted for all of the channels ii.

To indicate an undesired condition, such as fire, each room is provided with a suitable thermosensitive means 3| serving as a switch in its individual circuit 322 which leads to the control room of the building. Each of these circuits is adapted to carry a constant low voltage small current, for which reasona resistor 83 is connected across each thermostatic switch ill. Preferably a condenser 34 is connected across the resistor so that the latter shall not materially influence the impedance of the circuit. Extending from the off-position contacts "iii, of the switch 58, is a circuit 85, and between the latter and the circuit 82 is a transformer edit. The circuit 85 may contain a neon light Ma or similar signal device which is adapted to be energized by a very The light forms a small current of low voltage. visual alarm indicator for persons who maybe deaf. The direct current of the supervisory circuit 82 will not cause this light to be energized even though the circuit be closed by the engagement of the switch at the ofi" position contacts 10. However, at certain times, as hereinafter described, the amplifier 89 sendsan alternating current signal through the circuit 82 to energize the light or signaltda, and the latter is intended to be of such nature as to be responsive under these conditions. i

The circuits 82 may be interconnected at 86, iii to form a common circuit :95 in the control room, into which the circuits 82 extend. This common circuit 35 includes a battery 88 to furnish the direct current for the supervisory circuits including the common circuit. The voltage in these circuits is adjustable by a variable resistance 89. Each circuit 32 may have an indicator such as a lamp 90 located in the control room, and across each lamp is connected a condenser 9 Likewise a condenser 92 may be connected across the variable resistance 89 and across the ammeter 94 which is used to indicate the total amount of the supervisory current. In the individual circuits 82 are disposed signals S or relays 91 having switches i 55. Across these relays are connected condensers Bid. A similar relay may be furnished if desired in the common circuit95 and either or both arrangements may be employed. The common circuit 95 mayalso include a relay as having a? a switch I85 comprising a spring armature I86. A condenser 98 is connected across the battery 88. The purpose of the condensers 9I, 92, 93 and 91a is to produce circuits which will not affect the impedance caused by the speaker members 65, although the latter may have a matching transformer if desired. The amplifier 8B is connected in the common circuit 95 at its output transformer in the usual manner.

In the circuit described, the amplifier 88 is normally deenergiaed and the supervisory direct current has no efiect thereon nor upon the speaker members 65. The supervisory current may cause a faint glow in the lamps 88 to indicate that the circuits 82 are unbroken. The volume control switch 51 may be like that shown in my pending application, Serial No. 703,438 filed October 15, 1946 for Radio Receiving Amplifying System and Variable Volume Control Switch Therefor. This may be a circular resistance member [E38 having a rotary switch arm I85 connected into the circuit 66. The resistance Illt is tapped at diagrammatically opposed poinI-s through resistances it? and Iil2a into the circuit 66. Accordingly the switch arm may be turned continuously in either direction to vary the volume between low or zero volume positions at the resistances I02, IEiZa the latter being utilized to pass a small signal current that will not produce an appreciable audible effect t the speaker member 65.

Resistance I82, which may be omitted, limits the maximum voltage to speaker 65 and hence the maximum volume of sound, while resistance 32a is com uted for a minimum volume of sound to be produced by the speaker when the switch El is in off position. Should the switch 68 be in off position at the contacts 18, the amplifier 86 will send a signal through circuits 82 and -5 and thence into circuit 85 and into the circuit 65 to produce the relatively powerful alarm signal or announcement, and also cause illumination of the neon light 84111. When this occurs, the supervisory current will have no material effect, and this current and the signal energy from the amplifier 59 may flow simultaneously into circuits 82 and 95.

If a fire occurs at any one of the units B, its thermostatic switch 8i closes causing the flow of a substantially greater direct current in the circuits 82 and 85. This causes illumination of the lamp 98 corresponding to the particular switch 85 and thus indicating to the operator the location of the fire. It also causes the relay 98 to be so powerfully energized as to attract the armature I85 and close the switch I95, it being understood that the normal supervisory current is unsufficient to cause such operation. This operation of the armature 985 causes movement of the switch Hi to disconnect the amplifier 12 from the radio receiver '53 and to connect the amplifiers F2 to the siren III. A schematic drawing of the switch I4 shows the switch arms it? thereof as having double pole, switch arms it? for operative engagement with either of the pairs of contacts I5 and I8, the contacts I8 being connected to the circuit I I4 of the siren H I. The switch arm I87 may be regarded as pivoted at I68, and a series of such switch arms may be pivotally interconnected by a rod I89 which is linked to the armature I56. A tension coil spring Ht serves to return the switch arms it? to the position shown. It will be understood that this showing of the switches it is primarily for convenience in the drawing and that any suitable lost motion arrangement may be provided at the arms or at the armature for proper operation of the rod W9. The rod I89 may be manually operated back or forth according to certain emergency conditions.

The closing of the switch I by the relay 96 causes operation of the oscillator, or siren device I I l which is connected through a manual switch IHb into a circuit H2 leading from the main building line H3 that carries any suitable house current preferably a 110 volt A. C. current. When the switch I85 closes the circuit H2, there is also closed the circuit H4 which comprises the amplifier 88 and the siren circuit.

Should a break occur in any of the circuits 82 or 95, the switch II5 will close to close the circuit I I6 which leads from the main building line H3 which includes a bell or signal H1. The spring switch H5 is normally kept open by the relay 9? which is energized by the constant supervisory current. Closing of the switch H5 will thus indicate a break in a circuit or a failure of the battery 88. The different relays 91 are located in the control room, and as soon as the bell III rings, the operator may readily examine all of the relays to determine which is closed and this may be used to indicate the particular circuit 82 in which the break might occur. Thus a more satisfactory indication would be obtained than by observing the lamps which may have only a very slight glow that goes out when a break occurs in their respective circuits.

In the absence of any house current due to failure caused by fire or otherwise, the device 45 hereinbefore described will operate to furnish energy from a battery 48 so that the motor generator 48 will supply current of proper voltage to the building line H3.

The operation of the device will now be briefly described. The supervisory current has no effect upon the speakers 65, but if a break occurs in the branch circuit 82, the relays 91 will be deenergized so that the bell I Il will sound. If the thermostatic switch 8| closes, the relay 86 will be energized to close the switch I85 to energize the siren and amplifier, III, 86, and also swing all the switches I l from their respective radio receiver channels I I into connection with the amplifier 88 whereby the alarm is transmitted through the speakers 65. Since the device I I Ia may also represent a microphone, the operator may send a suitable announcement through the speakers. In course of such operation, the supervisory current need have no effect. In ordinary use the tenant of the building may turn the station selector switch 68 to any desired radio channel II or to an ofi position of the contacts ID. If the switch 68 is connected to one of the channels II, the alarm signal will be transmitted from the siren or microphone I l I to the different amplifiers I2. If the switch 68 is in the off position, the siren I I I will cause the amplifier 88 to transmit the signal or announcement through the circuits 82 and 95, switch 68 and circuit 55 to the speaker member 65, and the neon light 84a will be energized. If the volume control switch 61 is in off position, the signal energy, regardless whether it comes from the channels II or from the amplifier 88, will flow through the resistances I02 to operate the speaker 65. If the house current should fail, the device 45 will automatically supply energy from a battery 46 through a motor generator. Should the battery 88 fail, the bell i I! will sound, and it will be understood that this battery 88 may be replaced by taking the current from the line H3 through a suitable step-down transformer and a rectifier in the Well understood manner.

wavy character differentiating said signals 'ironr changes in the level of sensing current; means whereby said circuit, said sensing elements and said response apparatus are setta'cle and ad justable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of sensing elements including means whereby sai ing s r ents are actuated by abnormal conditions at the respective location for changing the normal level of said sensing current and thereby actuating response apparatus to activated condition; a plurality of signalling elements at said different locations including whereby said signalling elements are operated to produce a signalling action when actuated by response signals transmitted from said response apparatus and to remain substantially inoperable by the presence or absence of sensing current.

2. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at a plurality of diiierent protected locations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals, means whereby said re sponse apparatus is operable in an active condition in which it transmits electric response signals of wavy character differentiating-said signals from changes in the, level of said sensing current;

A means whereby saidcircuit, said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormalconditions at the respective location for changing the normal level of said sensing current and thereby actuating said response apparatus to activated condition; a plurality of signalling elements at said different locations including means whereby said signalling elements are operated to produce a signalling action when actuated by response signals transmitted from said response apparatus and to remain substantially inoperable by the presence or absence of sensing current; said response apparatus including .fault responsive means operative by a change of said sensingcurrent from said normal level to indicate presence of a fault on said circuit.

3. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between'response apparatus and a plurality of sensing elements positioned at a plurality of difierent protected locations; means whereby saidresponse apparatus is operable in an inactive condition in which it does not transmit signals, means whereby said response apparatus is operable. in an active condition in which it 10 transmits electricresponse signals of wavycharacter differentiating said signals from changes in the level of said sensing current; means whereby said circuit, said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response app ratus remains inin- ,active condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at therespective location for changing the normal level of said sensing current and thereby actuating said response apparatus to activated condition; a plurality of signalling elements at said diiferent locationsiincluding meanswhereby said signalling elements are operated to produce a signalling action when actuated by response signals transmitted from said response apparatus and to remain substantially inoperable by the presence or absence of sensing current; a plurality of channels for transmitting different electrical program signals; individual selector elements for the respective signal elements at said different locations selectively settable indifferent settings and including means for actuating the associated si nal element to produce a signalling action either by signals transmitted through said protective circuit or through one of said channels; said system operating to transmit response signals from said response apparatus to said signal elements in each of said settings of said selector elements.

4. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at a plurality of different protected locations; means whereby said response apparatus is operable is an inactive condition in which it does not transmit signals, means whereby said response apparatus operable in an active condition in whichit transmits electric response signals of wavy character differentiating said signalsfrom changes inthe-level of said sensing current; meanswhereby said circuit, sai-dsensing elements and said response apparatus aresettable and adjustable to maintain said sensing current at a normal level at which saidresponse apparatus remains in inactive condition; each of said nalling action when-actuated by response signals transmitted through said circuit and to remain substantially inoperable by the presence or absence of sensing currents in saidcircuit. v

5. In an electrical protective system having a protective circuit connected and arranged to carry sensingcurrent between response apparatus and a plurality of sensing elements positioned at a plurality of diflerent protected locations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals, means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character differentiating said signals from changes in the level of said sensing current; means whereby said circuit, said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of said sensing current and thereby actuating said response apparatus to activated condition; a plurality of signalling elements at said different locations connected to said circuit including means whereby said signalling elements are operated to produce a signalling action when actuated by response signals transmitted through said circuit and to remain substantially inoperable by the presence or absence of sensing current in said circuit; said response apparatus including fault responsive means controlled by said sensing current to indicate presence of a fault on said circuit.

6. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at a plurality of different protected locations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals, means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character differentiating said signals from changes in the level of said sensing current; means whereby said circuit, said sensing elements and. said response apparatus aresettable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of said sensing current and thereby actuating said response apparatus to activated condition; a plurality of signalling elements at said dilTerent locations connected to said circuit including means whereby said signalling elements are operated to produce a signalling action when actuated by response signals transmitted through said circuit and to remain substantially inoperable by the presence or absence of sensing current in said circuit; a plurality of channels for transmitting difierent electrical program signals; individual selector elements for the respective signal elements at said different locations selectively settable in different settings and including means for actuating the associated signal element to produce a signalling action either by signals transmitted through said protective circuit or through one of said channels; said response apparatus including a control means perative upon actuation of said response apparatus to cause transmission of response signals to said signalling means irrespective of the setting of said selector elements.

7. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of diiferent protected locations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit/signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character diiferentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signalling elements at said different locations including means whereby said signalling elements are operated to produce a signalling action when actuated by response signals transmitted from said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; said sensing current being substantially unidirectional, said signals being alternating electric signals.

8. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of different protected locations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character differentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signalling elements at said different locations including means whereby said signalling elements are operated to produce a signalling action when actuated by response signals transmitted from said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; said response apparatus being actuated to anactive condition by an increase of said sensing current above said normal level.

9. In a protective system as claimed in claim 8, said sensing current being substantially unidirectional, said signals being alternating electric signals.

10. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of difierent protected locations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character differentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said diiierent locations including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; said response apparatus including fault response means operative by a change of said sensing current from said normal level to indicate presence of a fault in said circuit; said sensing current being substantially unidirectional, said signals being alternating electric signals.

11. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of diiferent protected cations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character difierentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adiustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said different locations including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; said response apparatus including fault response means operative by a change of said sensing current from said normal level to indicate presence of a fault in said circuit; said response apparatus being actuated to transmit response signals in response to an increase of said sensing current and being actuated to indicate a fault in response to a decrease of said sensing current.

12. In a protective system as claimed in claim 11, said sensing current being substantially unidirectional, said signals being alternating electric signals.

13. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sen-"111g elements posi tioned at the plurality of diiierent protected 10- cations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character differentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and. thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said different locations including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to; remain substantially inoperable by the presence or absence of sensing current; said response apparatus including fault response means operative by a change of said sensing current from said normal level to indicate presence of a fault in said circuit; said circuit including a plurality of different circuit portions connected at said different locations to said sensing elements and said fault responsive means including a plurality of different sensing elements selectively actuable by the sensing current in the difierent circuit portions to indicate presence of a fault in a circuit portion.

14. In a protective system as claimed in claim 13, said sensing current being substantially unidirectional, said signals being alternating electric signals.

15. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of different protected 10- cations; means whereby said r'esponse apparatus is operable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character diiferentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said different locations including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; said response apparatus including fault response means operative by a change of said sensing current from said normal level to indicate presence of a fault in said circuit; said circuit including a plurality of different circuit portions connected at said different locations to said sensing elements and said fault respon ive means including a plurality of different sensing elements selectively actuable by the sensing current in the diiTerent circuit portions to indicate presence of a fault in a circuit portion, said response apparatus being actuated to transmit response signals in response to an increase of said sensing current and being actuated to indicate a fault in response to a decrease of said sensing current.

16. In a protective system as claimed in claim 15, said sensing current being substantially unidirectional, said signals being alternating electric signals.

l'i. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of diiferent protected locations; means whereby said response apparatus is oper able in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active contive condition in which it transmits electric response signals of wavy character differentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said difierent locations including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; a plurality of channels for transmitting different electrical program signals; individual selector elements for the respective signal elements at said different locations selectively settable in different settings and including means for actuating the associated signal element to produce a signaling action either by signals transmitted through said protective circuit or through one of said channels; a means whereby said system is operative to transmit response signals from said response apparatus to said signal elements in each of said settings of said selector elements; said sensing current being substantially unidirectional, said signals being alternating electric signals.

18. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of different protected locations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character differentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said different locations including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; a plurality of channels for transmitting different electrical program signals; individual selector elements for the respective signal elements at said different locations selectively settable in different settings and including means for actuating the associated signal element to produce a signaling action either by signals transmitted through said protective circuit or through one of said channels; a means whereby said system is operative to transmit response signals from said response apparatus to said signal elements in each of said settin s of said selector elements; said response apparatus being actuated to transmit response signals in response to an increase of said sensing current and being actuated to indicate a fault in response to a decrease of said sensing current.

19. In a protective system as claimed in claim 18, said sensing current being substantially unidirectional, said signals being alternating electric signals.

20. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of different protected locations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character diiferentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said different locations connected to said protective circuit and including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; said sensing current being substantially unidirectional, said signals being alternating electric signals.

21. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of different protected locations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character differentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said different locations connected to said protective circuit and including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to remain l7 Substantially inoperable by the presence or absence of sensing current; said response apparatus being actuated to transmit response signals in response to an increase ofsaid sensing current and being actuated to indicate a fault in response to a decrease of said sensing current.

22. In a protectivesystem as claimed in claim 21, said sensing current being substantially unidirectional, said signals being alternating electric signals.

23. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of differentprotected locations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character differentiating said signals from changes in the level of saidsensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; eachof said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said different locations connected to said protective circuit and including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; said response apparatus including fault responsive means controlled by said sensing current to indicate presence of a fault on said circuit; said sensing current being substantially unidirectional, said signals being alternating current signals.

24. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of diiferent protected locations; means whereby said response apparatus is operableuin an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character differentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions, at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said different locations connected to, said protective circuit and including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to re-, main substantially inoperable by the presence or absence of sensingcurrent; said response apif a l8 paratus including fault responsive means controlled bysaid sensing current to indicate presence of a fault on said circuit; said response apparatus being actuated to transmit response signals in response to an increase of said sensing current and beingactuated to indicate a fault in response to a decrease of said sensing current.

25. Ina protectivesystem as claimed in claim 24, said sensing current being substantially unidirectional, said signals being alternating electric signals.

26. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality ofsensing elements positioned at the plurality of different protected locations; means wherebysaid response apparatus is operable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character diiferentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settableand adjustable to maintain saidtsensing current at a normal level at which said response apparatus remains in inactivecondition; each of said sensing elements including means wherebysaid sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said different locations connected to said protective circuit and including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to remain. substantially inoperable bythe presence or absence of sensing current; said response apparatus including fault responsive means controlled by said sensing current to indicatepresence of a fault on said circuit; said circuit including a plurality of different circuit portions connected at said different locations to said sensing elements and said fault responsive means including, a plurality of different sensingelements selectively actuable by the sensing current in the different circuit portions to indicate presence of a' fault in a circuit portion.

27. In a protective systemas claimed in claim 26, said sensing current being substantially unidirectional, said signals being alternating electric signals.

28. In an electrical protective system having a protective circuit connected and arranged to carry sensingcurrent between response apparatus and aplur-ality of sensing elements positioned at the plurality of different protected locations; means whereby-saidwesponse apparatus isoperable in an inactive condition in which it does not transmit signals and means whereby said signalsfrom changes in thelevel of said sensing current; means whereby said sensing elements a M and said response apparatus are settableand adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elementsincluding means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating 7 said response apparatus to activated condition;

and a plurality of signaling elements at said diiierent locations connected to said protective circuit and including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; said response apparatus including fault responsive means controlled by said sensing current to indicatepresence of a fault on said circuit; said circuit including a plurality of diiierent circuit portions connected at said different locations to said sensing elements and said fault responsive means including a plurality of diiierent sensing elements selectively actuable by the sensing current in the different circuit portions to indicate presence of a fault in a circuit portion, said response apparatus being actuated to transmit response signals in response to an increase of said sensing current and being actuated to indicate a fault in response to a decrease of said sensing current.

29. In a protective system as claimed in claim 28, said sensing current being substantially unidirectional, said signals being alternating electric signals.

30. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of different protected locations; means whereby said response apparatus is operable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active condition in which it transmits electric response signals of wavy character differentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each of said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said different locations connected to said protective circuit and including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted from said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; a plurality of channels for transmitting different electrical program signals; individual selector elements for the respective signal elements at said different locations selectively settable in different settings and including means for actuating the associated signal element to produce a signaling action either by signals transmitted through said protective circuit or through one of said channels; a means whereby said system is operative to transmit response signals from said response apparatus to said signal elements in each of said settings of said selector elements; said sensing current being substantially unidirectional, said signals being alternating electric signals.

31. In an electrical protective system having a protective circuit connected and arranged to carry sensing current between response apparatus and a plurality of sensing elements positioned at the plurality of diiferent protected locations; means whereby said response apparatus is op erable in an inactive condition in which it does not transmit signals and means whereby said response apparatus is operable in an active 'con dition in which it transmits electric response signals or" wavy character differentiating said signals from changes in the level of said sensing current; means whereby said sensing elements and said response apparatus are settable and adjustable to maintain said sensing current at a normal level at which said response apparatus remains in inactive condition; each oi said sensing elements including means whereby said sensing elements are actuated by abnormal conditions at the respective location for changing the normal level of sensing current and thereby actuating said response apparatus to activated condition; and a plurality of signaling elements at said different locations connected to said protective circuit and including means whereby said signaling elements are operated to produce a signaling action when actuated by response signals transmitted lrom said response apparatus, and to remain substantially inoperable by the presence or absence of sensing current; a plurality of channels for transmitting difierent electrical program signals; individual selector elements for the respective signal elements at said different locations selectively settable in different settings and including means for actuating the associated signal element to produce a signaling action either by signals transmitted through said protective circuit or through one of said channels; a means whereby said system is operative to transmit response signals from said response apparatus to said signal elements in each of said settings of said selector elements; said response apparatus being actuated to transmit response signals in response to an increase of said sensing current and being actuated to indicate a fault in response to a decrease of said sensing current.

32. In a protective system as claimed in claim 31, said sensing current being substantially unidirectional, said signals being alternating electric signals.

33. In a protective system as claimed in claim 1, at least some of said signaling elements including an electrically actuated sound reproducing device for generating sound corresponding to signals transmitted through said circuit; and a volume control arrangement for at least one of said sound reproducing devices comprising a resistance structure extending along a loop-like endless path and forming a substantially continuous endless resistance path, a contact element continuously movable along said continuous path and arranged to establish electrical contact engagement with successive elements of said endless resistance path, a relatively fixed element of said endless resistance path being connected to one supply circuit portion of said circuit supplying signals to said reproducing device, circuit connections for completing supply connections from said circuit to said reproducing device including a circuit connection connecting said contact element to one terminal of said sound reproducing device, and a rotatably actuated control member manually actuable for moving said contact element endlessly along said endless resistance path so that in each omplete cycle of movement of said contact element over the entire length of said endless resistance path from a position corresponding to mini-mum volume of then gradually decrease to a minimum volume.

34. Ina-protective system as claimed in claim 2, at least some of said signaling elements including, an electrically actuated sound reproducingdevice for generating sound corresponding to signals transmitted through said circuit; anda'volui'ne control arrangement for at least one of said sound reproducing devices compris ing a resistance structure extending along a looplike endless path and forming a substantially continuous endless resistance path, a contact element continuously movable along said contin uous path and arranged to establish electrical contact engagement with successive elements of said endless resistance path, a relatively fixed element of said endless resistance path being connected to one supply circuit portion of said circuit supplying signals to said reproducing device, circuit connections for completing supply connections from said circuit to said reproducing device including a circuit connection connecting said contact element to one terminal of said sound reproducing device, and a rotatably actuated control member manually actuable for mov ing said contact element endlessly along said endless resistance path so that in each complete cycle of movement of said contact element over the entire length of said endless resistance path-from a position corresponding to minimum volume of sound output-the volume of sound output will gradually increase to a maximum volume and then gradually decrease to a minimum volume.

35. In a protective system as claimed in claim 3, at least some of said signaling elements including an electrically actuated sound reproducing device for generating sound corresponding to signals transmitted through said circuit; and a volume control arrangement for at least one of said soundreproducing devices comprising a resistance structure extending along a looplike endless path and forming a substantially continuous endless resistance path, a contact ele-- ment continuously movable along said continuous path and arranged to establish electrical contact engagement with successive elements, of

said endless resistance path, a relatively fixed element of said endless resistance path being connected to one supply circuit portion of said circuit supplying signals to said reproducing device, circuit connections for completing supply connections from said circuit to said reproducing device including a circuit connection connecting said contact element to one terminal of said sound reproducing device, and a rotatably actuated control member manually actuable for moving said contact element endlessly along said endless resistance path so that in each complete cycle of movement of said contact element over the entire length of said endless resistance path from a position corresponding to minimum volume of sound outputthe volume of sound output will gradually increase to a maximum volume and then gradually decrease to a minimum volume.

36. In a protective system as claimed in claim 4, at least some of said signaling elements including an electrically actuated sound reproducing device for generating sound corresponding to signals transmitted through said circuit; and a vol ume control arrangement for at least one of said sound reproducing devices comprising a resistance structure extending along a loop-like endless pathi and-iforminga substantially continuous endless resistance path, a contact. element con tinuously movable along ,said continuous path and: arranged to ,establishelectrical contact'engagement with successive elements ofsaid endless resistance path, a relatively fixed element of said endless resistance path being connected to one supply circuit portion of said circuit supplying signals ,to, said reproducing device, circuit con-l nections for, completing. supply connections from said circuit to said;reproducing device including: a circuit connection connecting said contact elementto, oneterminal of said sound reproducing device, and a rotatably actuated control member manually actuable for moving said contact element endlessly along said endless resistance path so that in each complete cycle, of movement of said contact element over the entire length of said endless resistance pathirom a position corresponding to minimum volume of sound output-the volume of sound output will gradually increase to a maximum volume and then gradually decrease to a minimum volume.

37. In a protective system as claimed in claim 5, at least some of said signaling elements including an electrically actuated sound reproducing device for generating sound corresponding to signals transmitted through said circuit; and a volume control arrangement for at least one of said sound reproducing devices comprising a resistance structure extending along a loop-like endless path and forming a substantially continuous endless resistance path, a contact element continuously movable along said continuous path and arranged to establish electrical contact engagement with successive elements of said endless resistance path, a relatively fixed element of said endless resistance path being connected to one supply circuit portion of said circuit supplying signals to said reproducing device, circuit connections for completing supply connections from said circuit to said reproducing device including a circuit connection connecting said contact element to one terminal of said sound reproducing device, and a rotatably actuated control member manually actuable for moving said contact element endlessly along said endless resistance path so that in each complete cycle of movement of said contact element over the entire length of said endless resistance pathfrom a position corresponding to minimum volume of sound outputthe volume of sound output will gradually increase to a maximum volume and then gradually decrease to a minimum volume.

38. In a protective system as claimed in claim 6, at least some of said signaling elements including an electrically actuated sound reproducing device for generating sound corresponding to signals transmitted through said circuit; and a volume control arrangement for at least one of said sound reproducing devices comprising a resistance structure extending along a looplike endless path and forming a substantially continuous endless resistance path, a contact element continuously movable along said continuous path and arranged to establish electrical contact engagement with successive elements of said endless resistance path, a relatively fixed element of said endless resistance path being connected to one supply circuit portion of said circuit supplying signals to said reproducing device, circuit connections for completing supply connections from said circuit to said reproducing device including a circuit connection connecting 23 said contact element to one terminal of said sound reproducing device, and a rotatably actuated control member manually actuable for moving said contact element endlessly along said endless resistance path so that in each complete cycle of movement of said contact element over the entire length of said endless resistance pathfrom a position corresponding to minimum volume of sound outputthe volume of sound output will gradually increase to a maximum volume and then gradually decrease to a minimum volume.

ELI M. LURIE.

REFERENCES CITED Number 24 UNITED STATES PATENTS Name Date Vansize Mar. 10, 1885 Harley July 9, 1912 Flagg et a1 Oct. 7, 1913 Goldstein June 12, 1917 Derby et al. May 5, 1925 Derby May 5, 1925 Turner Jan. 23, 1934 Lurie Apr. 14, 1942 Reeve July 20, 1943.

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