DE3332893C2 - Device for loop current detection in telecommunications networks - Google Patents

Description

a) Type St, which is used to determine the operating status of the telephone set is used, and

b) Type S2, which is the detection of direct current signaling serves on the telephone line.

The loop current detection must work independent of polarity.

The connected microphone unit must reliably detect the loop current or the lack of loop current within 2 seconds. Food chicks, namely switching-related failures of the supply current for a time of <1 second, must not be evaluated.

The loop current detection of type S1 evaluates whether the handset is lifted or not. Of the The loop line to be recognized is in the operating state of the microphone unit > 0.6 mA (stimulus state).

The loop current detection of type S2 evaluates whether

a) when the connection is established, feed current from the connection line forth is present;

b) the telephone connection to the remote station exists when the intercom system is in operation or not (direct current signaling of the exchange).

The invention relates to a device for loop current detection in telecommunications networks, in particular for additional devices and connection devices, with a low resistance at which a voltage drop when the loop current flows in the network is generated, an optoelectronic coupler and an isolating transformer.

According to the definitions of the German Federal Post Office (FTZ 18Rl), additional devices belong to the call station devices and are those facilities that are directly or indirectly via other additional facilities be electrically connected to main or auxiliary units or to additional speech sets, without that they belong to their standard execution. Other call station facilities are facilities that can be connected via connection devices, such as 7. B. telecopier. Image sending devices. Playback devices For main connections with multiple access, automatic dialing machines. Answering machines and sound recorders. Additional devices are circuitry in front of the telephone or the dialing device in accordance with the guidelines of the Federal Post Office or the responsible operator.

In order to ensure the various functions of the intercom equipment connected, Loop current detection provided, which the various criteria leading to the intercom Capture telecommunication line. Special requirements are placed on such loop current detections; They are allowed to use the new type of speech. A loop current of > 15mA can be reliably recognized. On the other hand, a syrup may be of <5 mA no longer become crkanni.

The stringent requirements for insertion loss within the transfer area - including the frequency of 16 kHz for the pulse / counting - oppose the use of highly sensitive relays of, for example, 20 Ω for 15 mA for type S2. In contrast, the loop current detection must have a significantly lower internal resistance. A loop current detection with as small an internal resistance as it is for the types SI and S2 is required in accordance with the above, can only be implemented with electronic means. on the other hand the guidelines of the German Federal Post Office require that the loop current detection is galvanic must be separated from the connection line. The safe electrical separation in the sense of the VDF regulations requires hicr / u to withstand a test voltage of 4000 volts.

The object of the invention is accordingly to use clcktro niche means a device for grinding tool identification to create the one with full galvanic isolation compared to the specified test voltage has so little internal resistance that the Types Sl and S2 required loop currentc safe

bo can be recognized.

To solve this problem, a Device of the type mentioned is proposed (DE-OS 31 15 756), in which both types of loop current detection S1 and S2 are cleaned in one circuit. In this known device is the the largest part of the electronic components, in particular of the circuit part serving the type S2 on the Side of the connection line and is

The right high-performance isolating transformer with electrical Energy supplied by which the light-emitting Diode of an optoelectronic coupler for each loop detection type is fed, its galvanic Phototransistor separated from it, the additional device or switch-on device with direct current controls from another electrical energy source. In addition, for the part of the circuit that corresponds to the identification glyph Sl is used, a special closing contact is required in the telephone set in the telephone sets is not provided anywhere in the Federal Republic of Germany.

In contrast, the invention solves the above problem with a device of the type mentioned at the outset in that that the voltage drop that occurs across the low-resistance resistor is caused by the optoelectronic Coupler clocked with high frequency, can be applied to the primary winding of the isolating transformer, to which Secondary winding one or more switching elements via a frequency-determining, tuned to the clock frequency Capacities and resistances equipped selective active filter, an amplifier, a rectifier device and a bistable sound circuit are connected.

The device according to the invention is both for loop current detection according to type 1 and according to Type 2, depending on the dimensioning of its components, can be used and has compared to the known older Proposal a number of advantages on:

- Almost all electronic components except the low resistance and the light emitting The diodes of the optoelectronic coupler are galvanically isolated from the line network, as a result of which incorrect triggering of the loop signal detection due to unavoidable voltage peaks in the network, as experienced by lightning strikes and radiation from neighboring high-frequency sources / .. B. tyristorgcstcuertcr rail drives are avoided.

- The isolating transformer only needs the clocked one To transmit voltage drop at the nclzseiligen nicaerohmigen resistor and can therefore extremely can be made small and inexpensive.

- In many cases there is only one type of key recognition is required, the circuitry required is considerably lower, and the individual device is> cheaper.

- The device according to the invention works independently of the polarity, without two separate operational amplifiers for the two as with the older proposal possible polarity? u need.

- Only one auxiliary energy source is required.

- In the event of malfunctions in the facility, there are repercussions on the telephone network because of the galvanic separation in between.

- The device according to the invention needed to their Function no contacts in the telephone.

According to a first feature for the advantageous embodiment of the invention is between that of the loop current through which the low-ohmic resistance flows and the optoelectronic coupler or the primary winding the isolating transformer arranged a low-pass filter.

Another feature of the advantageous embodiment of the invention provides a clock whose frequency-determining capacitance has the same size and the same temperature coefficient as the capacitances in the selective active filter.
The invention is explained in more detail below with reference to an embodiment shown in the single drawing figure

The telephone line is looped into the terminals La and Lb and a low-resistance one. Resistance R 1 of example 1 Ω out with a low pass filter consisting of the ohmic resistors R 2 and /? 3 and the capacitors Ci, C2, the ringing alternating current in the telephone line (F = 22-55 Hz) of the following Schaltungsan- Order kept away.

The phototransistor PT of an optoelectronic coupler OK and the primary winding of an isolating transformer TR are connected in series to the low-pass filter. The optoelectronic coupler OK contains for driving the Phototransi:.: Rs PTferner a light emitting diode LD, via the Vd -alleischaitung an ohmic resistor R 5 and a capacitor C4 to a clock TC, such as a CMOS-purpose clock generator via the terminal 7 angescr The frequency of the clock generator TG is preferably 25-3OkHz and is determined by the combination of the resistors R 10 and R 11 with a capacitor C9. The resistor R 11 can be adjusted to adjust the clock frequency.

When a loop current flowing through the terminals La, Lb is detected, a DC voltage is applied to the capacitor C 2 of the low-pass filter, which is cyclically applied to the primary winding of the isolating transformer IR via the phototransistor PT clocked by the clock TC via the optoelectronic coupler OK and chopped up in it Direct current can flow, which induces an alternating voltage in the secondary winding of the insulating support IR , which is preferably equipped with a ferrite pot core.

The alternating voltage induced in the secondary winding of the isolating transformer TR is in the first Stu-Te F of a 4-way operational amplifier. which is connected as an active selective band filter, amplify. The frequency-determining capacitances C6 and Cl of the band filter have the same size and approximately the same low temperature coefficient as the capacitor C9 of the clock TC. This ensures that the relative frequency deviation between the clock TC and the active bandpass filter F is very small, even with greater temperature fluctuations.

In the subsequent amplifier stage V of the operational amplifier, the high-frequency alternating voltage at the output 10 of the band filter e •! »Ch-ir-end is amplified. The gain of this stage is determined by the size ratio of the resistors R Jl and R 8. By choosing an appropriate size of the resistor R 12 , the arrangement can be adjusted to the respective application as type S1 or S2.
In the subsequent third stage G, the high-frequency alternating voltage is rectified and fed to the fourth stage in the form of a bistable circuit BS , which is preferably formed by a Schmitt trigger. Finally, a switching device such as a relay R is connected to the fourth stage, between the output terminals 1, 2 of which a contact which closes when the relay is actuated is arranged
With a /? C combination, consisting of a wi-

the stand R 17 and a capacitor ClO, the release delay of the relay R is effected. It is measured for the intended application at approx. 2 seconds. As a result, gaps in the supply due to a failure of the supply current due to switching, e.g. B. when pressing the number switch of the telephone device, not evaluated.

The circuit described above is supplied with power from a direct current network N via a plus terminal and a minus terminal and is stabilized to 4.7 V, for example , by a Zener diode D 2. The usual power sources from 5 V upwards can be adapted by selecting the series resistor R 18 accordingly.

Through the above-mentioned /? C combination R 2, R 3, C 1, C2, the alternating voltage generated in the primary circuit of the isolating transformer TR by the pulsing is transmitted from the telecommunication terminal? fprngrhnjtpn. tn hate the size of the clamps La. Lb resulting radio interference voltage and interference field strength complies with the relevant VDE regulations.

The requirement for compliance with a test voltage of 4000 V is made through the appropriate choice of the optoelectronic coupler and one for the test voltage rated isolating transformer fulfilled.

The arrangement described can be installed in additional equipment if the wiring within the device complies with VDE regulations and the ohmic resistance of the supply lines meets the requirements. It can also be accommodated in a separate housing right next to the previously described junction box of the intercom. This means that additional devices or other devices that are further away can be controlled via the relay contacts 1, 2. Instead of the relay R , one or more switching transistors can also be controlled by the bistable circuit BS of the fourth stage of the operational amplifier.

1 sheet of drawings

45

60

Claims (3)

Patent claims: 1. Device for loop current detection in telecommunications networks, in particular for additional devices and connection devices, with a low-ohmic resistor at which a voltage drop is generated when the loop current is flowing in the network, an optoelectronic coupler and an isolating transformer, characterized in that the one connected to the low-ohmic resistor (R J) resulting voltage drop, ticked with high frequency by the optoelectronic coupler (OK) , can be applied to the primary winding of the isolating transformer (TR) , on whose secondary winding one or more switching elements (R) via a frequency-determining capacitance ( C6, CT) and resistors (R 4, R 6) equipped selective active filter (F), an amplifier (V), a rectifier device (C) and a bistable circuit (BS) are connected. 2. Device according to claim 1, characterized in that between the low-ohmic resistor (R 1) through which the loop current flows and the optoelectronic coupler (OK) or the primary winding of the isolating transformer (TR) a low-pass filter (R 2, R 3, Ci, C2 ) is arranged 3. Device according to claim 1 or 2, characterized by a clock generator (TG), the frequency-determining capacitance (C9) of which has the same size and the same temperature as the capacitors (C6. Cl) in the selective active filter (F) . Control devices do not impair the transmission quality cause. The German Federal Post Office distinguishes between two different types of loop current detection, namely