FR2681208A1 - INTERCOM INSTALLATION WITH A DOOR STATION AND WITH AT LEAST ONE INTERIOR VOICE STATION. - Google Patents

Abstract

The invention relates to an intercom installation with a door station (TS) and with at least one internal voice station (ISp1 .... ISpn). The call signal is produced in a central unit (ZG) and can be transmitted individually to the indoor telephone sets (ISp1 .... ISpn), without hindering the occupation of the installation by an indoor telephone set combined with the locking of other indoor telephones or obstructing the transmission of a door opener signal from the indoor telephones. The installation has the particular advantage residing in the fact that a network comprising n + 1 conductors to the indoor stations is sufficient, n denoting the number of indoor stations.

Description

The present invention relates to an intercom installation with a

  door station and with at least one internal voice station, in which the door station is connected by individual call and conversation conductors to the internal telephone sets, in which the door station and the internal telephone sets are common reference conductor to which the acoustic circuits of the door station and the unipolar internal telephone sets are connected in which the door station and the telephones are supplied by a common DC supply voltage, one of which is connected to the reference conductor, in which, for the purpose of calling an internal telephone set, a call generator generates a call bell when a corresponding call button is operated on the door station, call signal which can be transmitted to the called indoor station, in which in the idle state, the conversation circuits of the stations t internal telephone are disconnected, in which the internal telephone sets have a means of circuiting which reacts during the maneuver of the corresponding call button of the door station and comes to occupy this internal telephone, intercom installation in which each The internal telephone has an interlocking button, the operation of which reacts the switching means, connects the internal telephone and locks the other internal telephone sets which can not then be connected, in which each internal telephone has a button. door opener, for transmitting a signal to reach the opener, the various signals that can be generated by the change in potential in the corresponding call and talk conductor, the interphone sets having a high impedance in the state of rest, a the average impedance when the interlock button is pressed and a

  low impedance when the operation button is pressed

  door, intercom installation in which the individual call and conversation conductors are each connected via a diode of

  uncoupling to a common line.

  An intercom installation of this nature has been disclosed in German patent document DE 40 15 466 C. In this known intercom installation it is necessary to provide expensive equipment for calling internal telephone sets, since each telephone set interior includes a call generator, which through a threshold voltage circuit is for a precisely defined voltage connected to the individual call and voice conductor Call generators of this nature are of complicated construction and are When the door station is equipped with numerous electronic circuits, which when the door station is located outside are subjected to the influence of The present invention aims to create an intercom installation of the aforementioned nature, in which the the expenditure on equipment for calling domestic telephones is, in the case of a large number of domestic posts, substantially reduced and in which, moreover, the door station may be

very simple construction.

  According to the invention this result is achieved by the fact that at each uncoupling diode there is connected in parallel a shunt capacitor, in that the DC supply voltage is fed to a common line via a voltage transformer and a cut-off device, in that during operation of the switch-on button in an internal telephone set, the means for switching on this station can be connected, via a first zener diode having a breaking voltage lower than the DC supply voltage, the individual call and voice conductor, an operation in which the switching means is responsive and can be connected directly to the conductor; call and individual voice, in that the voltage at the output of the voltage transformer is controlled by means of the control circuit and is, when occupying an internal telephone, voltage voltage transformer at a load voltage, in that the breaking voltage of the first Zener diodes is greater than the occupancy voltage which is established in the common line, in that at the same time the operation of the door opener button in an indoor telephone, the voltage at the output of the voltage transformer is reduced to a door opener voltage and the control circuit contacts the opener, thereby that the individual lead-drivers and voice-3 are the second Zener diode intermediate having a breaking voltage corresponding to the DC supply voltage connected to the switching means, by the was that when maneuvering a call button in the door station, an additional DC voltage can be coupled in series with the DC supply voltage and can be transmitted to the individual call and telephone conversation i called lower part, the switching means reacting via the second Zener diode and occupying the internal telephone set, in that the closing of this call circuit transmits a call signal to the common line , and by the fact that the circuit of conversation of the station of the door is, side

  alternating current, connected to the common line.

  Thanks to this embodiment of the internal telephone sets and the door station, the occupation of an internal telephone can be produced by the operation of the interlocking button or by the operation of the corresponding call button in the station. Due to the voltages acting on the common line, a listening lock is achieved for the other internal telephone sets and the call signal can be generated centrally and be transmitted punctually to the internal telephone set called In this embodiment there is is offered the possibility that the sector devices for the production of DC supply voltage and additional DC voltage, the voltage transformer, the control circuit, the inrush current control, the call generator, the amplifier and the delay circuit are housed in a common control unit In this case the door station does not more than the call buttons and the conversation circuit, which just like the internal telephone

électroaccoustique.

  According to one embodiment of the invention, the circuit of the internal telephone sets is designed in such a way that the second Zener diode is followed, in series by a decoupling diode, with the series circuit of the first one. Zener diode is connected in parallel, with the contact of the switching means, a series circuit constituted by the contact of the switching means and by a light diode, the series circuit constituted by the second Zener diode and by the uncoupling diode being connected in parallel to the contact with the switching-on means The light-emitting diode signals the state of occupancy of the

internal telephone.

  According to one embodiment of the invention, the design and connection of the voice circuits are such that the voice circuits of the door station and the posts

  each have an electronic transformer

  acoustic, transformers which are both unipolarly connected to the reference conductor, that the other terminal of the voice circuit of the door station is, on the AC side, connected to the common line, and that the voice circuits of the internal telephone sets are, on the AC side, connected to the individual call conductors and

corresponding voices.

  According to another development it is expected that during the operation of the interlocking button of the internal telephone, a resistor is coupled in parallel to this station, so that the voltage of the common line is lowered to a maximum of inverting voltage, which is lower than the breaking voltage of the first Zener diodes, and when the interlocking button in an internal telephone is not operated, the common line voltage rises to the voltage of Reduced occupancy by the voltage transformer, and in this case the interlocking button of the indoor telephone may, after occupancy, be used as a talk button, to obtain a well-defined voice communication in both directions using amplifiers In this case the control of a common amplifier can be executed from

  such as during the presence of the voltage-.

  in the common line, the control circuit connects an amplifier acting as a hearing amplifier between the voice circuit of the door station and the common line, while in the presence of the inverting voltage of the the common line, the control circuit connects the amplifier, as a speech amplifier, between the common line and the voice circuit of the door station. When separate amplifiers are provided for both directions of transmission, the adopted embodiment may be such that between the common line and the cocal or conversation circuit of the gate station is coupled in parallel a circuit consisting of a speech amplifier. and a hearing amplifier, and that when the occupying voltage in the common line is present, it is the auditory amplifier that is turned on, whereas in case of voltage df ' inversion is the amplifier of

speech that is put in circuit.

  According to one embodiment, the transmission of the call signal takes place in such a way that during the operation of a call button in the door station, a contact of a call current control separates the common line of the voltage transformer and the control circuit and connects it to a call generator, and that during the duration of the call button maneuver it

activity the call generator.

  For the production of a gong signal as a calling signal, one embodiment is advantageous, which is characterized in that when operating a call button in the door station, a contact of a inrush current control activates a delayed circuit, which for a determined period of time separates the common line of the voltage transformer and the circuit

  control and connects it to a call generator, being-

  given that the duration of the call signal is independent of the

  duration of the operation of the call button.

  When it is provided according to another embodiment that the parallel circuits, consisting of decoupling diodes and shunt capacitors, parallel circuits which connect the individual call and conversation conductors to the common line, are combined in a decoupling unit, the intercom system may comprise the single decoupling unit and a door station comprising an appropriate number of call buttons corresponding to a number chosen at will.

internal telephone sets.

  The invention is now described in more detail with reference to an embodiment shown further in

  detail by drawing that takes the form of a block diagram.

  The electrical circuits of the door station and the indoor telephones are shown in detail. As shown in the drawing, the intercom installation according to the invention comprises the TS gate station modules, a number N of I Spl, I Sp 2 Ispn internal telephone sets, a ZG central control unit and

an EK decoupling unit.

  The station of the door TS contains N call buttons KR, K 2 Kn and an electroacoustic transformer in the form of a conversation circuit L Sa, which is connected by a capacitor to the conductors leading to the central control unit ZG and to the reference conductor b The call buttons K 1, K 2 Kn are coupled in parallel to a terminal and are via the call conductor r connected to the central control unit ZG The other terminals of the buttons call KR, K 2, Kn are connected to the corresponding individual call and conversation conductors ai, 2 year, which end at the talk terminals of the internal telephone sets I Spl, I Sp 2 I Spn, while the other terminals of conversation of the I Spl, I Sp 2 I Spn internal telephone sets are connected to the reference conductor b The 2-year call and talk conductors are connected via parallel circuits, including a diode IEC 60050 - International Electrotechnical Vocabulary - Details for IEV number 841-02-21 Circuit technology / Analog conductors / Circuit breakers C 2 and a shunt capacitor C at a common line ax of the transmission line The parallel circuits of all the individual call and talk conductors ai, 2 years are combined in an EK decoupling unit Ax common line also leads to the control unit ZG control The opener is connected via the control driver c to

the central control unit ZG.

  The internal telephone sets I Spl, I Sp 2 I Spn have an interlocking means A, which can be a relay. This relay is connected in series with a light diode LD. This series coupling is connected in parallel with a speech circuit. L If the internal telephone I Spl, Sp I I Spn, which includes an electroacoustic transformer, which is connected in series with a separation capacitor C1 When operating the interlocking button bl, the means of A engagement is via a first zener diode ZD 1 subject to the voltage established in the individual call and conversation conductor, as will be further described below The contact has a firm engagement means A a holding circuit for the engagement means A, since it shunts the contact of the engagement button bl and the first

  Zener diode ZD 1 with inclusion of the LD light-emitting diode.

  Another contact of the switch-on button bi connects the resistor R1 in parallel with the internal telephone set I Spl, Sp I I Spn, which leads to a change in the voltage in the common line ax, as will be described more With the aid of the door opener button b 2, the resistor R 2 can be connected in parallel in the internal telephone set I Spl, I Sp 2 - I Spn This resistance R 2 is of lower resistance than the resistor R1, which leads to a further reduction of the voltage in the common line ax In contact with the engagement means A is connected in parallel a series circuit comprising a

  second zener diode ZD 2 and a decoupling diode bl, -

  which is part of the circuit of call, as will be described

also further.

  The central control unit ZG is powered by the AC mains voltage and comprises two power supply units NG 1 and NG 2. The power supply unit NG 1 produces the DC supply current C = 24 V, while the power supply unit NG 2 provides the additional direct current U 2 = 12 V The supply DC voltage C is connected by the negative pole to the reference conductor b The positive potential is via a voltage transformer SU, of a circuit-breaker AB and of the resting side of a switch contact S of a call current control S injected at the common line ax At the output of the voltage transformer SU, the voltage is evaluated by means of a circuit control circuit UW, circuit which for a voltage of ut = 15 V, a voltage u 2 = 9 V and a voltage u 3 = 3 V transmits the control signals respectively to sut, su 2 or su 3 At the output of voltage transformer SU and circuit breaker AS, the additional DC voltage u 2 = 12 V is connected via the inrush current control S in series with the output voltage of the voltage transformer SU. In this way, a continuous dc voltage is established in the call conductor. ur = 36 V The inrush current control S by contacts S the call generator TG, cuts the common line ax of the control circuit UW and connects the call signal of the call generator TG to the common line ax By the control signal su 3, which during the operation of a door opener button bl in an internal telephone I Spl, I Sp 2 Ispn and for the voltage u 3 = 3 V which s' establishes in the common line ax, the TU opener is operated by

through the driver c.

  The control signals sut and su 2, which are established in an internal telephone set I Spi, I Sp 2 Ispn, when the switch-on button bi is not actuated and is actuated, that is to say for voltages ut = X 9 V in the common line ax, connect the auditory amplifier HV or the speech amplifier SV, which are coupled in parallel in the corresponding transmission directions and which are connected to the common line ax by the intermediate of a separation capacitor as well as via the conductor a 'to the conversation circuit L Sa of the station of

the door.

  In Fig 1, the intercom system is shown in the home position. The operation of the intercom system is now described in more detail.

  detail with reference to an operational diagram.

  In the idle state, the DC supply voltage Ul = 24 V is connected via the voltage transformer SU, the switch-off unit AB and the control of the call signal S in series with the additional DC voltage U 2 = 12 V and is therefore injected as a continuous call voltage ur = 36 V to the calling conductor r When in the station of the door TS is actuated a call button, for example the button K 1 is a closed circuit circuit, which circuit via the second Zener diode ZD 2, the diode of decoupling Di, the light diode LD and the

  interlocking means A leads to the reference conductor b.

  The inrush current control S and the switch-on means A react, since the second zener diode ZD 2 has a breaking voltage of 24 V. The internal telephone set I Spl is thus occupied and the contacts S The common line ax is cut off from the control circuit UW and is connected to the output of the call generator TG. In the embodiment shown, call signal is transmitted as long as the call button Kl is activated In the case where the call generator TG actuates a gong signal, the inrush current control S can act on the call generator TG by through a timed circuit, which independently of the duration

  depressing the call button Kl transmits a call signal.

  of a predetermined duration When the duration for which the call button Kl is pressed is greater than this predetermined duration, the programmed transmission of the call signal

  is repeated until the call button K1 is released.

  After the calling operation, the common line ax is again connected to the control circuit UW When the telephone set called I Spl is switched on, the control circuit UW emits the control signal sub, by which the transformer voltage SU is switched to the occupancy voltage ul = 15 V Other internal telephone sets I Sp 2 I Spn can not be connected, since during the operation of the interlock button bl, the reaction circuit for the switching means A passes through the first zener diode ZDI, which has a breaking voltage equal to or greater than 15 V, but less than 24 V. Therefore, the interlocking means A of this internal telephone set I Sp 2 I Spn can not react and it is ensured that these internal telephone sets I Sp 2 Ispn do not

do not participate in listening.

  h When establishing the occupancy voltage ut = V in the common line ax, the control circuit UW transmits the control signal sui, which connects the auditory amplifier HV. The direction of the conversation therefore goes to the station from the TS gate to the busy indoor telephone I Spl When in the internal telephone set I Spl is actuated the interlock button bl, this button acts as a talk button With the parallel connection of the resistor RI, the voltage at the common line ax is reduced to u 2 = 9 V The control circuit UW then transmits the control signal su 2, which connects the speech amplifier SV and therefore establishes the direction of the conversation from the occupied internal telephone set I Spl to the TS gate station The control signals sui and su 2 can also be used for the switching of a single amplifier, which in this case, depending on the actuation or the non-actuation activation of the interlock button = talk button in the occupied indoor telephone set I Spl, is connected as a speech amplifier or as a hearing amplifier When occupying an internal telephone I Sp I, I Sp 2 I Spn, the control circuit Ut W transmits the control signal suo to the power-off unit AB This power-off unit AB contains a delayed circuit, which after a determined period of time from example t at 2 minutes disconnects from the common line ax the occupancy voltage ut = 15 V supplied by the voltage transformer SU and then opens the holding circuit for the engagement means A within the occupied internal telephone set I Spl The internal telephone I Spt is disconnected by the contact a of the switching means A. When the switching off unit AB reestablishes the connection with the common line, there is no current flowing to the link The UW control circuit records this situation as an unoccupied state, and as a result of the absence of a control signal sub, the voltage transformer SU again supplies the DC supply voltage C = 24 V, such that the intercom installation is available for a new call. Disconnection of the occupied internal telephone set I Spl can already take place when the opener button b 2 is actuated. Thanks to the parallel connection of the resistor R 2, the voltage applied to the common line is lowered to ue = 3 V The control circuit UW emits the control signal su 3, which can directly control the door opener TU The resistor R 2 is practically equivalent, with regard to the switching means A, to a short-circuit, of so that means A falls back and releases the post

internal telephone I Spl.

  The individual call and conversation conductors a, a 2 year are connected individually by the call buttons KR, K 2 Kn To obtain the common line ax, the individual call and conversation conductors al, a 2 year are mutually disconnected via the decoupling diodes D 2 and are connected on the AC side by the shunt capacitors C connected in parallel with the uncoupling diodes D 2.

  parallel are combined in a decoupling unit EK.

  The occupancy of the intercom system can also take place from an internal telephone, eg I Spl, when the interlock button bl is activated. Therefore, the first zener diode ZD 1 closes a circuit. As the common line ax is subjected to the DC supply voltage U1 = 24 V and the first zener diode ZDI has a breaking voltage of, for example, 15 V, current is established and the engagement means A reacts In the central control unit ZG is produced the reduction of the voltage of the common line ax, which is reduced to the occupation voltage ul = 15 V. All others operations are similar to those which are valid for the occupation of an internal telephone set by the actuation of the corresponding call button

in the TS gate station.

  As shown in the drawing, the TS door station with the electroacoustic transformer of the speech and hearing circuit L Sa and the call buttons Ki, K 2 Kn is very simple in construction and does not have any electronic circuits. I Spl, Isp 2 I Spn are also of simple design, since the call requires only one central call generator TG and for this purpose only the second zener diode ZD 2 is required in telephone sets

I Spl, I Sp 2 I Spn.

  All other control circuits can be

  gathered and housed in a central control unit.

Claims (11)

claims   1 Intercom installation with a door station and with at least one internal voice station, in which the door station is connected by individual call and conversation conductors to the internal telephone sets, in which the door station and the internal telephone sets have a common reference conductor to which the acoustic circuitry of the door station and the unipolar internal telephone sets are connected in which the door station and the telephone sets are supplied with a direct voltage d common power supply, one pole of which is connected to the reference conductor, in which, for the purpose of calling an internal telephone set, a call generator produces a call signal when a call button is operated corresponding door station, call signal that can be transmitted to the called indoor station, in which in the state of rest of ci Conversions of the internal telephone sets are disconnected, in which the internal telephone sets have a means of circuiting which responds when the corresponding call button of the door station is operated and takes up the position of the internal telephone set. an intercom in which each internal telephone has an interlocking button, the operation of which reacts a switching means, connects the internal telephone and locks other internal telephone sets which can not then be connected, wherein each telephone set interior has a door opener button, for transmitting a signal to reach the opener, the various signals that can be produced by the change of potential in the corresponding call and individual conversation conductor, the telephone sets interiors with an impedance raised in the idle state, a mean impedance when actuating the latch button and a low impedance when actuating the opener button, intercom installation in which the individual drivers of call and conversation are each connected by means of a decoupling diode to a common line, characterized in that at each uncoupling diode (D 2) there is connected in parallel a shunt capacitor (C), in that the DC supply voltage (U1 = 24 V) is fed to a common line (ax) via a voltage transformer (SU) and a breaking device (AB), by the fact that during operation of the interlocking button (bi) in an internal telephone set (I Spl, I Sp 2 - I Spn), the switching means (A) of this station can be connected by the a first zener diode (ZD 1) having a breaking voltage lower than the continuous supply voltage (UI) to the individual call and voice conductor (ai, a 2-year), operation in which the switching means (A) reacts and can be connected directly using a holding contact (a) to the call and voice conductor (al, a 2-year), in that the voltage at the output of the voltage transformer (SU) is controlled by means of the control circuit (UW) and when occupying an internal telephone set (I Spi, I Sp 2 Ispn), reduced by the voltage transformer (SU) to a voltage of occupation (ul = 15 V),   in that the breaking voltage of the first diodes of   Zener (ZD 1) is larger than the occupancy voltage (ut -   V) which is established in the common line,   by the fact that during the operation of the operation button   door (b 2) in an internal telephone set (I Spl, I Sp 2 Ispn), the voltage at the output of the voltage transformer (SU) is reduced to a door opener voltage (u 3 = 3 V) and that the control circuit (UW) contacts the opener (TU), in that the individual call and voice conductors (al, a 2 year) are via a second Zener diode ( ZD 2) having a breaking voltage corresponding to the DC supply voltage (U1) connected to the switching means (A), in that when operating a call button (K1, K2) Kn) in the gate station (TS), an additional DC voltage (U 2) can be coupled in series with the DC supply voltage and can be transmitted to the individual call and conversation conductor (ai, a 2 an) of the internal telephone set (I Spl, I Sp 2 Ispn) called, the switching means (A) reacting via the second Zener diode (ZD 2) and coming off uper the internal telephone set (I Spl, I Sp 2 Ispn), in that the closing of this call circuit transmits a call signal to the common line (ax), and in that the circuit of conversation (L Sa) of the door station (TS) is, on the AC side, connected to the common line (ax).   Intercom installation according to Claim 1, characterized in that the second Zener diode (ZD 2) is followed, in series, by an uncoupling diode (D1), and that at the series circuit of the first zener diode (ZD 1) with the contact of the switch-on button (bl) is connected in parallel a series circuit consisting of the contact (a) of the switching means (A) and a light diode (LD), the series circuit constituted by the second Zener diode (ZD 2) and the uncoupling diode (D1) being connected in parallel with the contact (a) of the setting means circuit (A).   3 Intercom installation according to one or the other claims 1 and 2,   characterized in that the conversation circuits (L Sa) of the door station (TS) and the internal telephone sets (I Spl, I Sp 2 I Spn) each have an electroacoustic transformer, transformers both of which are connected unipolar to the reference conductor (b), in that the other terminal of the conversation circuit (L Sa) of the gate station (TS) is on the AC side (for example capacitor) connected to the common line (ax ), and that the speech circuits (L Si) of the internal telephone sets (I Spl, I Sp 2 I Spn) are AC-side, connected to the individual conductors   call and conversation (ai, a year).   4 Intercom installation according to any one claims from 1 to 3,   characterized in that in the case of actuation of the interlocking button (bl) of the internal telephone set (i Spl, Sp I I Spn), a resistor (Rl) is connected in parallel, so that the voltage (u 2) in the common line (ax) is lowered to an inverting voltage (e.g. 9 V), which is lower than the breaking voltage of the first Zener electrodes (ZD 1), and in that when the switch-on button (bi) in a busy internal telephone set (I Spl, I Sp 2 I Spn) is not actuated, the voltage (ul) in the common line (ax) goes back to the occupancy voltage (for example 15 V)   reduced by the voltage transformer (SU).   Intercom installation according to Claim 4, characterized in that when an occupancy voltage (ul = 15 V) is applied to the common line (ax), the control circuit (UW) connects a function amplifier of an auditory amplifier between the conversation circuit (L Sa) of the door station (TS) and the common line (ax), whereas when the inversion voltage (u 2 = 9 V) is applied to the common line (ax), the control circuit (UW) connects the amplifier acting as speech amplifier between the common line (ax) and the conversation circuit (L Sa) of the door station (TS).  Intercom installation according to Claim 4, characterized in that between the common line (ax) and the conversation circuit (L Sa) of the door station (TS) is connected a parallel circuit consisting of the speech amplifier (SV) and the auditory amplifier (HV), and in that when the occupancy voltage (ul = 15 V) is applied to the common line (ax), the control circuit (UW) plugs the auditory amplifier (HV), while when the inverting voltage (u 2 = 9 V) is applied to the common line, the control circuit (UW) connects the amplifier Speech (SV).   7 Intercom installation according to any one of claims from 1 to 6,   characterized by the fact that when a call button (K1, K2 Kn) is actuated in the door station (TS), a contact (s) of an inrush current control (S ) cuts the common line (ax) of the voltage transformer (SU) and the control circuit (UW) and connects it to a call generator (TG), and that for the duration of the actuation of the call button (Kl, K 2 Kn) the inrush control   (S) plugs the call generator (TG).   8 Intercom installation according to any one of claims from 1 to 6,   characterized by the fact that during the actuation of a call button (K 1, K 2 Kn) in the door station (TS), a contact (s) of an inrush current control ( S) connects a timed circuit, which for a specified time intersects the common line (ax) of the voltage transformer (SU) and the control circuit (UW) and connects it to the call generator (TG). 9 Intercom installation according to any one claims from t to 8,   characterized in that the mains units (NG 1, NG 2) for the production of the DC supply voltage (UI) and the additional DC voltage (U 2), the voltage transformers (SU), the control (UW), the inrush current control (S), the call generator (TG), the amplifiers and the delay circuit are housed in a central control unit (ZG).   Intercom installation according to any one claims from 1 to 9,   characterized in that the parallel circuits connecting the individual call and talk conductors (ai, a 2-year) to the common line (ax) and composed of uncoupling diodes (D 2) and shunt capacitors (C ) are   gathered in a decoupling unit (EK).   11 Intercom installation according to any one of claims from 1 to 9, characterized   by the fact that when the operation button is pressed   door (b) in an indoor telephone set (I Spl, I Sp 2 Ispn) occupied, the connecting or switching means (A) drops as a result of the parallel connection of resistance (R 2).   12 Intercom installation according to any one of claims from 1 to 11,   characterized in that when a busy voltage (ul = 15 V) is applied to the common line (ax), the control circuit (UW) transmits a control signal (suo) to a breaking device (AB). ), which after a holding period   predetermined separates the conductor from the common line (ax).   13 Intercom installation according to any one of claims from 1 to 12,   characterized in that when the interlocking button (bl) is actuated in an internal telephone set (I Spl, Sp I I Spn), the control circuit (UW) transmits a control signal (sub) to the voltage transformer (SU) and switches it in such a way that it produces the voltage occupancy (ul = 15 V).