CH661163A5 - CIRCUITIVE PROVISION FOR THE TRANSMISSION OF CRITERIA FOR THE CHARACTERIZATION OF THE USERS OF PUBLIC TELEPHONE CENTERS. - Google Patents

Description

The present invention allows to overcome this drawback since it is based on an impedance measurement on wire z. For this purpose, instead of a constant polarity as in the known circuit solution, it provides that a sequence V of very narrow pulses is applied to the current probe, as will be illustrated with reference to Figure 2, where diagram a) shows the trend in the time of the impedance of a counter in response to a step signal, diagram b) shows one of the pulses V used (according to the invention) for the transmission of the criteria and diagram c) shows a counting pulse.

As indicated in diagram a), upon arrival of a step signal (and obviously also upon the arrival of a pulse) the internal impedance of the user counter initially presents a value Zi due to the inductance of the counter and then decreases -

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go down more or less slowly until you return to the z2 value of the internal resistance of the meter; the duration of the initial transient phase in which the internal impedance of the meter does not differ significantly (for example by less than 10%) from the value zi is correlated to the time constant of the series circuit consisting of the inductance and the internal resistance of the counter itself.

By applying a voltage impulse on wire z, such as that indicated in diagram b), so short as to be exhausted in the initial transient phase, the impedance of the meter is very high in comparison with that of the generator G and the current that passes through the counter is almost null; the probe is therefore able to detect the presence on wire z of the mass criteria issued by the generator Gì. If the voltage pulse is long enough, such as the tax pulse shown as an example in diagram c), to allow the meter impedance to return to the rest value Z2, the current flowing through the meter it can take on a value that activates it.

In the circuit shown in figure 1, the polarity of the pulses V is therefore irrelevant: only the fact that they are sufficiently narrow not to circulate current on a user counter C. 20 matters.

The generator of criteria Gì can be constituted, as schematically shown in the figure, by a resistance and an impedance switch lower than that presented by the user counter in response to the initial edge of the pulse V if you want to transmit on the counting wire z a constant criterion; without departing from the scope of the invention, the block Gj can represent even a complex circuit, such as for example a circuit for identifying and / or classifying users, which generates a message consisting of a sequence of bits.

661 163

In this case, to ensure good transmission, each bit of the message should be sampled several times, that is, the pulses of the sequence V have a multiple frequency (for example triple 0 quintuple) of the bit frequency of the message generated by GI.

Multiple sampling makes it possible not to synchronize the timing circuits of the message generator with each other and the circuit (not explicitly indicated in the figure because it is known per se) that generates the V pulses.

Figure 3 shows a circuit arrangement in which the criteria issued by the two generators Gì and G2 are transmitted through the same counting wire z and revealed by the current probes Si, respectively S2. For this purpose the generators Gì and G2 are decoupled from each other by the diodes D3 and D4, mounted in opposition, while to the current probes Si and S2 are applied two sequences of pulses having opposite polarity. In the figure these pulse sequences have been assumed to be the same (except for polarity) and indicated with + V and -V; without departing from the scope of the invention it is possible to use sequences having the most advantageous characteristics (for example frequency and / or amplitude) in relation to the characteristics of the criteria issued by the corresponding generator G (G ,, G2).

Without departing from the scope of the invention, it is possible for the technician to make obvious or suggested variants to the schemes illustrated here, such as, for example, used in the scheme of figure 3 a single current probe to which the pulse sequence is applied having the polarity suitable to allow the reception of the criteria issued by the generator from which you want to receive the criteria from time to time.

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1 sheet of drawings

Claims (4)

661 163 1. Circuit arrangement for the transmission of criteria for the characterization of users of public telephone exchanges, circuit arrangement in which the criteria, issued by at least one circuit generating the criteria, are transmitted on the counting wire and detected by at least one connected current probe to the counting wire itself, characterized in that the current probe (S) is activated by at least one periodic pulse signal (V) having predetermined polarity, the duration of each pulse being much less than the time constant of the series circuit constituted by the resistance internal and by the inductance of a user counter (C). 2. Circuit arrangement as in claim 1 and adapted to transmit the criteria issued by two generator circuits, characterized in that a decoupling diode is inserted between the output of each of the generator circuits and the counting wire (z). that the two diodes (D3, Di) are in opposition to each other and by the fact that the impulsive signal applied to the current probe (S), has a first polarity capable of causing the first decoupling diode (D3) to conduct, thus inhibiting the second ( D4), or a second polarity, opposite to the first and capable of causing the second decoupling diode (D4) to conduct, cutting off the first (D3). 2 Circuit arrangement as in claim 2, characterized in that it comprises a first and a second current probe (Si, S2) connected to the count wire (z) and activated by impulsive signals having, respectively, the first and second polarity. Circuit arrangement as in the preceding claims, characterized in that at least one of said criteria generating circuits generates a message comprising a plurality of bits and in that the impulsive signal has a multiple frequency than the bit frequency of the message to be received. The invention relates to a circuit arrangement which allows to transmit criteria (for example identification messages) which characterize the users connected to a public telephone exchange, and this in accordance with the preamble of claim 1. The problem of identification and / or classification or, more generally, of the characterization of the users connected to a public telephone exchange has great importance for modern electronic exchanges and for traditional ones with indirect control; in direct-control units, this problem is currently of limited importance to some auxiliary services (for example, identification and blocking of a "jammer user") but is destined to become increasingly important as the companies managing the telephone service wish to be able to to improve its management organization (for example, to charge charges to a computer that also issues invoices for users), and to offer the public at least part of the services currently offered only by private plants (for example, complete documentation of charges, classification of users and differentiated accessibility to various services based on class, etc.). Currently only electronic power plants are or can be set up to offer these additional services, while electromechanical power plants, which constitute and will constitute the vast majority of power plants in service in the next decade, are unable to do so. A possible solution is to equip the electromechanical control unit with a logic unit, suitably interfaced with the electromechanical organs, which is able to intervene on the same and / or perform additional services if and as required by the class to which each user belongs. . The insertion of the logical unit necessarily requires to modify to some extent a telephone exchange which is and must remain in operation: it is advisable that these modifications be extremely limited both as regards the possible addition of wires and as regards the modifications to be made to the control panels. A circuit solution has been proposed which envisages using the counting wire as a support to transmit characterization criteria (identification, class, etc.) of the users attested to the control unit: according to this solution, the criteria, which have the opposite polarity to that used for the taxation pulses are injected on the count wire by means of a driver and detected by a current probe; a pair of diodes, suitably polarized, prevents the criteria from activating the counter, respectively the counting pulses from influencing the driver. This solution has the advantage of requiring minimal changes to the taxation circuit (the insertion of a diode, preferably immediately before the meter), and also the driver and the current probe are connected to the counting wire by means of welds made on the contact banks selectors, having minimal influence on the normal operation of the control unit; however, it cannot be used for duplex users nor when you wish to be able to receive criteria from two distinct sources. The object of the present invention is a circuit arrangement which allows to overcome this drawback; it provides that the criteria are transmitted on the counting wire and detected by at least one current probe connected to the wire itself and is characterized by the fact that the current probe is activated by at least one periodic pulse signal having predetermined polarity, the duration of each pulse being much less than the time constant of the series circuit consisting of the internal resistance and the inductance of a user counter. The invention will be better described with reference to an example of embodiment illustrated in the attached figures where: Figure 1 schematically shows a circuit arrangement according to the invention; figure 2 shows some waveforms relating to the scheme of figure 1; Figure 3 shows another circuit arrangement according to the invention. As indicated in the circuit diagram of Figure 1, the two user counters Ci and C2 relating to a pair of duplex users are decoupled from each other by means of the diodes Di and D2 and are advanced by the taxation pulses sent by the IT generator via the wire z and having negative polarity, respectively positive. Wanting to use the counting wire z as a transmission medium for the criteria generated by the generator Gì, as provided for in the known circuit solution previously cited, the probe is no longer able to continuously discriminate the resistance presented by a counter from that of the counter and the generator Gì placed in parallel with each other (the resistance value of generator Gì must be much greater than the internal resistance of the meter in order not to appreciably alter the value of current circulating in the meter during the counting phase): it is no longer possible to detect in I continue the criteria generated by Gì.