DE928353C - Circuit arrangement for telephone systems with two-way connections - Google Patents

Description

Circuit arrangement for telephone systems with two-way connections one The basic requirement for shared lines is to maintain telephony secrecy, combined with the stipulation, also the possibility of mutual interference of community participants largely excluded.

Due to the circuit technology with two-way connections, a certain phase of connection establishment and termination in the exchange facilities a switching criterion, which - if the other community participant a Initiate a connection, answer a call or end a call - at the unused call station expresses itself in the form of an alarm clock. This effect in the Participant has its cause as a balancing process in its alarm bridge on the official side, z. B. in the transition from the area code to the group selection, and is according to its course can be seen from the circuit diagram. A known switch circuit is shown for the two-way connection in connection with the circuit extract of a preselector as Call unit and group dial level, all for understanding the following The operations described are not necessary elements are neglected and the Blocking cells Spi and Spe are initially assessed as a short circuit.

In the idle state there is negative potential across the windings R = and RII of the stimulus relay in the preselector on both wires of the common subscriber line TL. As a result, the capacitor in the alarm clock bridge of the subscriber microphone units Tü i and Tn 2 is given a charge with the indicated polarity and a curve in the direction of the arrow x +, (SP), ui, Tn r (alarm clock capacitor), u2, relay UIl, TLd, il, Relay RI, Wi, -or. -E-, (SP), u2, Tn 2 (alarm clock capacitor), u1, relay U12, TLb, t2, relay RII, Wi, -.

If a calling subscriber of the common line picks up his handset, he seizes the common selection by closing the loop. This starts up in a known manner, is thereby blocked against occupancy by the line selection level and checks its outputs in a free choice on a group selector. It occupies the connected stage via the first free output, blocks it by shifting potential against occupancy from other preselectors and is shut down itself. Simultaneously with the response of the isolating relay T, not shown, the stimulus relay R is de-energized when the subscriber Tn z has initiated a connection, while it remains energized for Tn 2 on the path +, y3, Wi, t3, winding R11, Wi, - and the speech wires exchanged by means of its contacts v1 and v2. The a / b line is switched through to the group dialing stage, which now takes over the supply of the caller via the windings A_, and AI, of the A relay. This reverses the polarity of the potential on the speech cores which, in the stimulation phase, carried negative potential across the windings of the high-resistance R relay. Now the plus potential comes into effect on the unactuated call station, namely from +, winding A, ', VW either via the contacts yi, t1 to the subscriber Vn z or the contacts y2, t2 to Vn 2. This change in potential the capacitor in the alarm bridge is short-circuited and is able to balance its charge in the direction of arrow y via the reacting alarm clock to earth if the blocking cell SP1, Spe shown is initially considered to be short-circuited. This happens before the point relay Ur, carrying fault current. or UI, Minus now picks up in series with the low-resistance feed relay winding AI and switches off the unused call station with its contacts u1 or u2, connects the calling call station and completes the feed circuit via the pull-through winding UIIl or Uli, of the switch relay. After the conversation has ended, the corresponding count is made; the outgoing test wire becomes free. This triggers the connection, the preselector turns to the rest position and can be assigned again. In the subscriber switch the U relay of the person hanging up is de-energized, its contacts return to the rest position and establish the circuits for connection monitoring. Via the windings of the stimulus relay R, the capacitor in the alarm bridge of the previously unactuated intercom station is recharged, which must again be expressed in the form of an alarm stop, since the charging current runs through the alarm clock in the opposite direction. If a line selector checks for the two-way connection in incoming traffic, the common preselector is blocked. The ringing current for subscriber Tn z is sent over the a-wire, that for Tn 2 over the b-wire. The switching through of the voice wires to the feeder relay of the line selector in turn causes a potential change, which leads to the described charge equalization in the alarm bridge for the subscriber who is not called. At the end of the call, the onset of charging acts on the alarm clock in the direction of the arrow x.

Hitting the alarm clock has the disadvantage that a participant of the Two-way connection is always oriented about the operation of its partner station. this allows misuse z. B. the registering community participant, on the part deliberately blocking a long-distance call from the other intercom, if over this the common connection line is occupied before the remote connection arrives or is deliberately blocked by simply picking up the handset for a long time (case of injury of telephony secrecy).

It is known that such faults in circuit arrangements for two-way connections, in which both cores of the connection line are the same when the system is idle Potential lead to be excluded by adding one in the course of the connection establishment one wire of the common line changes the direction of the current in stages carried out and thus an influence on the calling organ who is not connected to the call participating intercom is prevented. The conversion required for this and Expansion of the official facilities is in an unfavorable proportion in terms of expenditure to the solution according to the invention, which also has the advantage of the possibility offers to use your funds retrospectively in any turnout circuit.

The invention prevents the alarm clock from stopping by adding a rectifier blocking cell Sp switches on as dormant switching means in the stimulus circuit, which occurs during the unintentional discharge of the capacitor in the alarm bridge as a locking means becomes fully effective. The one that occurs due to a change in the potential on the speech veins Discharge surge can now due to the resistance of the lying in the reverse direction Cell does not suddenly overbalance and affect the alarm clock; the undesirable The participant does not hit the alarm clock.

The charging of the alarm clock capacitor runs in the forward direction of the cell and polarizes the alarm clock system of both microphone units accordingly Idle state of the office facilities. When recharging after completing a During the conversation, the anchor of the alarm clock retains its pre-polarized position unaffected the interception of the equalization process at and is from that in the forward direction again incipient charge current is only tightened more firmly.

Since the blocking cell is at the same time in the ringing current discharge, it is dimensioned according to a further feature of the invention so that it is overdriven by the ringing current half-wave in the reverse direction and is heavily loaded by the half-wave in the through-conduction direction, so that it forms an ohmic resistance for the ringing current, which causes a maximum voltage reduction of about 5%. The short-term overload caused by the call and further call is acceptable for the blocking cell without causing damage. The cell is enough. in the circuit it is therefore advantageous to have a second, fundamentally different function, which uses its behavior outside the blocking range.

According to a further development of the invention, excessive voltage amplitudes can be used of the ringing current through a glow lamp connected in parallel to the rectifier cell are intercepted, which - appropriately sized - bridges the cell when ignited and protects them from damage by short-circuiting both half-waves.

The drawing illustrates the creation of the capacitive equalization in the alarm bridge using the current flow excerpt; it also represents an exemplary embodiment according to the invention for its suppression, with the rectifier cell Sp in the switch circuit for subscriber Tn i and the variation from the parallel circuit for Tn 2 of blocking cell Spe and glow lamp GI is used.

The idea of the invention is based on the illustrated embodiment not restricted, rather it advantageously relates to all circuit arrangements, in those without significant technical effort and subject to a passive Switching element similar phenomena are to be made ineffective.

Claims (3)

PATENT CLAIMS: i. Circuit arrangement for several over a common Subscriber stations connected to the office, especially for two-way connections in telephone systems, characterized in that in the subscriber switch for prevention of the alarm clock a rectifier cell with reverse direction to earth in the stimulus circuit is switched on. 2. Circuit arrangement according to claim i, characterized in that that the rectifier cell is so overdriven by the ringing current in the reverse direction becomes that it acts as an insignificant ohmic resistance in the ringing current discharge. 3. Circuit arrangement according to claims i and 2, characterized in that a voltage limitation of the ringing current caused by the blocking cell equal to or is less than 5 ° / o. q .. circuit arrangement according to claims i to 3, characterized in that a glow lamp is connected in parallel to the blocking cell, whose ignition voltage is dimensioned according to the ringing current amplitude. Referred publications: German patent specification No. 666 q.38.