US2724105A - Electric control or alarm systems - Google Patents

Description

1955 o. l. H. EKMAN ELECTRIC CONTROL OR ALARM SYSTEMS 2 Sheets-Sheet 1 Filed May 28, 1952 mxk tw IQ INVENTOR 0% J 7% filumw BWWJWN Y: Fm

ATTORNEYS NOV. 15, 1955 L H EKMAN 74J ELECTRIC CONTROL OR ALARM SYSTEMS Filed May 28, 1952 2 Sheets-Sheet 2 /V 1/65 IN] TO United States Patent Or 2,724,105 ELECTRIC CONTROL OR ALARM SYSTEMS Olof Ingemar Harald Ekman, Stockholm, Sweden Application May 28, 1952, Serial No. 2a0,4s2

6 Claims. (Cl. 340--227) The fire alarm systems heretofore generally used in which control wire loops with a maximum of about ten thermo-contacts per loop are individually connected to a central apparatus with separate control and alarm relays for each loop have lately been replaced by systems in which a number of loops or all the loops are connected in series so that they form a continuous loop with a great number of thermo contacts. By this arrangement, the costs of mounting and operation can be considerably reduced. Particularly, the number of relays and the total length of the wires of the loops may be reduced while maintaining as great control as possible.

The known systems of this kind suffer, however, from drawbacks. Resistive and capacitive impedances are provided at intervals along the loop and, upon an opening of the loop by the thermo-contacts, the location of the break can be determined by balancing the impedance of the loop from the central station to the break against impedances of known values at the central station. With long loops, the resistance of the wires and the distributed capacity between the same makes it particularly diificult to bring about a correct impedance balance of the system while attaining the highest reliability possible.

The object of the present invention is to overcome these drawbacks and to increase the sensitiveness of the system and make it easier to handle.

The invention relates to control and alarm systems with thermo-contact groups connected in series and is substantially characterized in that balance irnpedances are arranged at the terminals of the series to the central apparatus. Then it is important that such balance im pedances are arranged at both of the terminals of the series loop to the central apparatus.

An embodiment of a system according to the invention, mainly intended for a fire alarm system, is shown in the annexed drawings.

Figure 1 discloses a simplified wiring diagram of the system. Figure 2 discloses a front view of a group selec tor for the system. Figure 3 discloses in front view a detail of the same group selector with the appurtenant rotatable dial removed, Figure 4 discloses a side view of' the illuminating device in this group selector and Fig. 5 is a simplified diagram of a measuring bridge circuit established upon opening of a loop circuit between stations of the alarm system shown in Fig. 1.

In the wiring diagram in Figure 1 only the essential elements have been included, while earlier known details have been left out provided they are of no importance for understanding the invention.

In the drawing the central station apparatus is arranged below the dash-anddot line while the loops are arranged above the said line. The loops connected in series are connected between the four terminals Lau, Lbu, Lai and Lbi. The loop consists, in the usual manner, of a double wire and has an a-lead and a b lead, both ends of each lead being connected to a battery, not shown, at the central station. In the embodiment shown, ten group fire alarm boxes (secondary fire alarm boxes) 1-10 are arranged which are provided with manually disconnectable switches in each lead. In the group fire 2,724,105 Patented Nov. 15, 1955 ice alarm boxes series resistors R2, R3 R10 are provided in the a-lead and, moreover, parallel condensers C2, c3 C10 are connected between the .eads of the loops in these fire alarm boxes. The alarm loops are connected between the fire alarm boxes, only two of these loops, S5 and S10 being shown in detail. These loops contain a number of thermo-contacts T, the number of such contacts being adjusted to the length of the loop and to the conditions in the premises through which the loop. is drawn. Some ten thermo-contacts or more can without any difficulty be arranged in each loop.

Upon an opening of both leads a and b, either manually at one of the fire alarm boxes or automatically by a thermo-contact T in one of the loops, an alarm is sounded at the central station and the attendant connects one or the other end of the series loop into an alternating current bridge circuit and adjusts a bank of impedances of known values to balance the bridge, i. e. to connect into the bridge an impedance substantially equal to that of the two wire line between the break and the central station. As a check, he may then connect the other end of the faulty line into a similar bridge circuit.

In accordance with this invention, balance impedances are arranged in the loop at the two terminals of the series loop at the central apparatus. Thus, series resistors Rm and Rh are connected in the a-lead, while parallel condensers Luci and Lin are provided between the leads. The leads then are conducted to a group selector switch GSO which controls the connection of the leads to the two group selectors VGS and HGS which constitute means to identify the particular fire alarm box or loop at which the leads a and b are open. In the embodiments shown, these group selectors are made as reflections of each other. 3

The group selector to the left VGS contains a ladder or chain composed of nine resistors connected in series and ten parallel condensers, the latter connected with one terminal to contacts arranged in a circle, which can be connected and disconnected by means of a contact bar which can be turned by means of the knob 101 of the group selector. A sliding contact G rests against this bar. The tenth balance resistor VSR is connected to the chain of resistors in the group selector and is connected in series with two individually parallel-connected balance condensers Luc and VSC the wires of whichare connected and disconnected by contacts 102 which, when the bar 100 is turned round, are actuated by a cam 10 on said bar.

As to the right-hand group selector conditions are en tirely analogous as is shown in the drawing The group selectors are connected to a bridge which contains the condensers VBCi, VBCz and Luc for the purpose of effecting cooperation with the left-hand group selector VGS. The bridge branch (neutral wire) of this bridge contains the transformer VTF in the secondary winding of which a dim glowing lamp VGL is connected. In a similar manner the right-hand group selector HGS is connected to a bridge which contains the condensers Lic,

HBCz, HBCI and in the bridge itself (neutral wire 1) the transformer HTF with the dim glowing lamp HGL. The condenser VSC is shunted over the terminals of the left-hand group selector to the bridge and can be disconnected by means of the contact 102. The same is the case as far as the condenser HSC for the right-hand group selector HGS is concerned.

The condenser Luc is in an analogous manner con nected and disconnected by means of one of the contacts 102 by turning the bar 100 the cam 103 of which conmeets and disconnects the contacts 102. The condenser Lic is in the same way connected and disconnected by means of a contact 102 by turning the bar 100 of the right-hand group selector HGS.

' The system is energized by a D. C. battery and the terminals to the said battery are marked with and The grounding (or the connections to the central point of the battery) are marked conventionally. A motor generator MG is connected to the battery with its D. C. motor part and gives off A. C. (signal current) of suitablefrequency, for example 1000 cycles per second for checking the balance of one or the other of the bridge circuits which may be established by switch GSO. All the essential parts of the system are D. C.-controlled. The motor generator MG is started by a special starting relay GSR upon an opening of the leads a and b.

The station attendant throws the switch GSO in one sense or the other when an alarm is sounded to indicate an opening of the leads a and b, for example in the sense to connect the left-hand section of the opened loop into the bridge of the group selector VGS. The bridge is energized with alternating current from the motor-generator, and the attendant adjusts the contact bar 100 rntil the bridge is balanced by connecting into circuit at the central station amounts of resistive and capacitive impedance substantial'y equal to the lumped and distributed impedances of leads a and b from their left ends at the central station out to the break. At bridge balance a relay drops out to energize signal lamps in one of th" group selectors, and the position of the knob 101 at bridge balance affords an indication of the open loop of the alarm system.

The left-hand transformer VTF is with its primarv winding connected in paralle with a re tifier V" "hi"? in turn feeds a brid e relay VBR. The ri hth ad tr former HTF is in analogous manner connected in naralle with a rectifier Hli which feeds a brid e relay HER for the right side. The contact to the left-hand bridge relav VBR controls the cir"uit for two signal lamps VSL and VOL in shunt. The right-hand bridge relay HBR controls in the same way the circ it for two si n l amp HSL and HOL for the ri ht side.

The shown example relates for examp'e to a series loop withfor example ten partial loops connected in series However, in very great systems one or more series loops each comprising several partial loops can be connected in the way indicated by arrows at the points A.

Figures 2-4 show how the illuminating si nals at the right or the left group selector are arranged. The signal lamps, for instance VSL, are arranged in a parabolic reflector 104. the radiance opening of which is covered with a disc 105. Said disc is provided with ten holes each hole corresponding to one of the group fire alarm boxes 110. Thus, each such hole represents a partial loop, the hole marked with 5 corresponding to the partial loop S5 etc. The stationary disc 105 is made of an uncoloured, transparent material, for instance plastic, while the holes are entirely open or covered with uncoloured protective glasses whi"h are provided with the respective group numbers 1-10. The group selector knob 101 is rigidly connected to a semi-transparent dial 106 which is coloured, for instance red. A dial of red plastic is preferably used. In said dial a single hole 107 is provided in such a position that when the knob is turned,

' the hole 107 will successively and one at a time expose the underlying holes in the disc 105. A colorless protective glass may be inserted in the hole 107.

By this it is attained hat. when the signal lamps VSL are put on, the whole dial 106 is illuminated and indicates a red signal. By turning the knob 101 the group from which the signal has been given is selected and the group number is shown in white light against the red background. Selection is thus facilitated and mistakes are avoided.

According to the invention the system is of such a nature that electrical balance is effected. For this purpose the several resistors in the ladder or chain in the re spective group selector VGS and HSS are each m ld? equal to the correspondingly located a lead resistor R2 R10, plus the wire resistance to the center thermo contact of the loop following the resistor. The resistor Rut is made as big as the resistor VSR in the left-hand group selector, the line resistor out to the resistor R111 being taken into consideration. In analogous manner the resistors HSR and Rii are made equal to each other, the line resistance being taken into consideration. The condensers are also balanced in analogous manner, so that the condensers C2-C1o, as supplemented by the distributed capacity of leads a, b out to the center of the following loop, have the same values as the correspondingly located condensers in the group selectors VGS and H68.

The system is also provided with line switches, fire sig nals, alarm apparatus, group fuses, fault indicators etc. in the usual manner but which have not been included sine they are not essential to an understanding of the present invention.

When an alarm or fault signal is given, the corresponding signal lamp is switched on which indicates that the group selector switch 680 is to be shifted optionally to the right or the left. If, for example, the switch is shifted to the right, the right-hand group selector is turned until the group number 1-10 for one of the groups is illuminated. The alarm signal then has been released from said group. In order to make a check on the indicated point of the fault, the switch GSO is shifted to the left whereafter the knob of the left-hand group selector VGS is turned until a group number is illuminated which number is to be the same as that shown by the right-hand group selector. In case these numbers differ it means that thermo-contacts have been fused so that two diiferent partial loops have been formed, that is, that the fire has spread substantially. All balancing is to begin at the thermo-contact which is located in the centre of the respective partial loop, for example S5. Balancing of the whole impedance, the capacitance as well as the resistance, therefore takes place to the centre of the respective partial loop whereby the sensitiveness and the control are increased.

The following facts should be particularly pointed out:

Owing to the fact that balancing takes place to the centre of each partial loop the unbalance will be the least possible through wire impedance (capacitance and resistance). The system therefore will to a great extent be independent of the fact whether disconnection takes place at the first or at the last thermocontact of the partial loop.

As the group by means of the cam 103 disconnects the base condenser Luc and Lie respectively in certain positions, for example for the groups 6-10 in the embodiment shown, apercentagewise greater increase in the unbalance is obtained for the higher groups and above all for the highest group. This involves an increased security.

The starting condensers Luci and Lic respectively are substantially smaller than the base condensers Luc and Lie respectively and are so fitted that a determined and equal capacity value is obtained from the central apparatus to the centre of the first and the last partial loop respectively.

If more shunted series loops (each containing a number of partial loops connected in series) are arranged the balancing onthe right side of all the loops must be 0 mutually equal as must also be the balancing on the left side of all the loops. The balancing on the left side preferably equals the balancing on the right side of the same loop. that is, the balance impedance are equal at the ends of the loop.

The neutral wire or instrument Wire of the bridge with the dim glowing lamps VGL and HGL (and their transformers VTF, HTF) and also the relays VBR, HBR are normally current carrying owing to the normal unbalance in the zero position of the group selector (VGS or HGS), but become current free when, upon an occurrence of an alarm, the group selector has been turned to the respective group and on account thereof balance has been ob tained between one, for example the left part of the loop and the corresponding part of the resistor-condenserchain in the (left) group selector. Then the lamp is extinguished and the relay VBR is disconnected. The dim glowing lamp VGL or HGL thus gives a continuous indication and glows fainter the more the group selector approaches the alarm-giving group. The relay VBR or HBR indicatesthe alarm-giving group directly.

As an example of dimensioning it can be mentioned that the condensers C2C1o ought to be mutually equal with regard to size. The condensers Luc and Lie, VSfi and HSC and also the condenser connected to the con tact 1 of the left-hand group selector VGS are three times as large as C2, while the balance condenser in the chain connected to the contact 0 of the right-hand group selector is one third as large as C2. The maximum variation of the wire capacity in the loop leads then can be kept below a suitable allowed value, for example 2.5% oi the whole capacity.

It should be observed that the condenser VSC is disconnected by the contact 102 simultaneously with condenser Luc. In analogous manner condenser I-iSC is disconnected simultaneously with condenser lie. The current path for the left-hand bridge relay passes through a normally open make contact on the generator start relay GSR, so that the lamp VSL normally is extinguished. The same is the case as far as the right side is concerned.

The balance condenser of the condenser chain of the group selector, which is connected to the contact 1 of the left-hand group selector VGS and also the balance condenser of the condenser chain of the right-hand group selector, which is connected to the contact 0 of said group selector have the function to efiect as great unbalance in the zero position of the respective group selector, that alarm is not indicated in said position (the resting position)..

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a switch or alarm circuit, the combination with a pair of leads extending adjacent each other through the area to be protected, a current source at a central station to which the input and the output ends of both leads are normally connected, alarm stations along said leads and dividing the two-wire loop circuit thereof into a plurality of serially connected partial loops, manually operable means at each alarm station for opening said leads to initiate an alarm at said central station, a plurality of thermal switches in each partial loop for opening said leads when exposed to excessive temperatures, impedance means individual to each of said partial loops, and switch means at said central station for connecting one end of said two-wire loop circuit as one arm of a Wheatstone bridge network upon an opening of said loop circuit, of base impedances insaid leads at the input end and the output end of said two-wire loop circuit; said base impedances each having a magnitude substantially greater than that of the impedance means individual to said partial loops.

2. In a control or alarm circuit, the invention as recited in claim 1, wherein said impedance means individual to each partial loop comprises a series resistor and a shunt capacitor.

3. In a control or alarm circuit, the invention as recited in claim 1, wherein said Wheatstone bridge network includes as an adjustable balance arm a group of balance impedances, and a selector switch adjustable to connect said balance impedances step-by-step into said balance arm; said balance impedances having values such that the step-by-step accumulated values correspond respectively to that of said leads from the central station out to the centers of the correspondingly located partial loops.

4. In an electric control or alarm circuit, the combination with a loop circuit comprising a pair of leads extending adjacent each other through the area to be controlled or protected, a current source at a central station to which the input and the output ends of both leads are normally connected, section indicator stations along said leads and dividing the two-wire loop circuit thereof into a plurality of serially connected partial loop sections, a plurality of thermal switches in each. partial loop section for opening said leads when exposed to excessive temperatures, impedance means in said section indicator stations and individual to each of said section indicator stations, manually operable electrical measuring means at said central station for measuring and indicating the number of section indicator impedance means connected in parallel between a station end of said leads and the point at which they are opened, and switch means at said central station for connecting one end of said two-wire loop circuit to said electrical measuring means upon an opening of said circuit.

5. In an electric control and alarm circuit, the combination with a pair of leads extending adjacent each other through the area to be controlled and protected, a current source at a central station to which the input ends and the output ends of both leads are normally connected to form a two-wire loop circuit, section indicator stations along said leads and dividing the two-wire loop circuit thereof into a plurality of serially connected partial loop sections, switches in each partial loop section responsive to the feature to be controlled, said switches being operable to open said leads when exposed to an excessive deviation of said feature from normal, section indicator impedances connected between said leads at said section indicator stations and individual to each of said section indicator stations, at least one base impedance at said central station, and means at said central station for determining the point in said loop circuit at which said leads are opened by measuring the impedance across that portion of the loop circuit between a station end thereof and the opening of said leads, said measuring means including switch means for disconnecting said base impedance when less than a preselected number of section indicator impedances are connected in parallel upon an opening of said two-wire loop circuit.

6. In an electric control or alarm circuit, the combination with a pair of leads extending adjacent each other through the area to be controlled or protected, a current source at a central station to which the input and the output ends of both leads are normally connected, section indicator stations along said leads and dividing the twowire loop circuit thereof into a plurality of serially connected partial loop sections, a plurality of thermal switches in each partial loop section for opening said leads when exposed to excessive temperatures, impedance means in said section indicator stations and individual to each of said section indicator stations, measuring means at said central station responsive to and indicating the number of section indicator impedance means connected in parallel up to an opened partial loop section, and switch means at said central station for connecting one end of said two-wire loop circuit to said measuring means upon an opening of said circuit; said measuring means including duplicate networks for selective connection respectively to the opposite station ends of said two-wire loop circuit, and said switch means comprising a common shaft operable in opposite directions by one single handle in accordance with the measuring network to be connected to the opened loop circuit.

References Cited in the file of this patent UNITED STATES PATENTS 1,977,121 Ekman Oct. 16, 1934 2,003,443 Henneberger June 4, 1935 2,028,653 Ekman Jan. 21, 1936 2,071,283 Grant Feb. 16, 1937 2,422,542 Gustafsson June 17, 1947 2,428,290 Peck Sept. 30, 1947 2,556,363 Lord et al. June 12, 1951

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