CN1961566A - Method for testing line equipment provided with an off-hook sensor, and line equipment for implementing said method - Google Patents

Abstract

The invention relates to a method for testing analogue telephone line equipment, in particular to a method for detecting failure of a filter (312) of a disconnection/reconnection detection circuit (112). The method includes isolating (103) a telephone line device from the line, applying a normal battery signal to the device (108), and adding a test signal to one of the terminals connecting a hybrid circuit (107) to a detection circuit (112). On line (202), the test signal is capable of reversing the polarity of the input to the detection circuit. In order to be able to control the operation of the filter (312), for frequencies lower than the cut-off frequency and for frequencies higher than the cut-off frequency, it is only necessary to perform two steps in succession, first sending the test signal (206) with a low repetition rate, and then with A test signal is sent (206) at a high repetition rate and vice versa.

Description

Test method for line equipment with disconnection detector and line equipment for implementing the method

technical field

This invention relates to methods of testing analog telephone line equipment, and more particularly to methods of testing line equipment comprising a disconnect detector using a voltage comparator and a filter which prevents the detector from ringing Signal works. The invention also relates to a circuit arrangement for carrying out the method.

Background technique

Document EP 0,808,053 describes a method for testing disconnect/reconnect detection circuits in analogue telephone line equipment, said detection circuits comprising amplifiers and comparators. The comparator has two inputs connected to the output of the amplifier and to a reference voltage. The amplifier has two inputs connected to the two inputs of a mixed resistor network connected to the telephone line. The detection circuit sends an off/on logic signal. The test method for this circuit first places the output of the amplifier in a high-impedance state to isolate the comparator, and then applies a test signal that reverses the polarity between the two inputs to one of the comparator's inputs. Toggling of the off/reclose logic signal in response to the test signal indicates that the off/reclose detection comparator is functioning well.

In some analog telephone line equipment, the disconnection/reconnection detection circuit includes a prior comparator for low pass filtering to prevent ringing signals from acting on the comparator. It is therefore desirable to be able to test this filter in a simple manner.

Fig. 1 shows a kind of conventional line equipment connected to the base telephone office by a telephone line 101 (with two conductors L1/L2), that is to say that the equipment is different from ISDN or ADSL type systems, for example, in common analog lines to operate. The circuits and components used to transmit and receive speech signals between the device and the automatic transmitter are well known and are not described for the sake of simplicity, since they do not belong to the scope of the present invention.

The line equipment includes:

- overvoltage protection device 102,

- said line test relay 103,

- said device test relay 105, and

- Subsystem 115 comprising hybrid resistor network 107 and disconnection/reconnection detection circuit 112 .

The telephone line is connected to a known overvoltage protection device 102 . The device 102 is connected to a line test relay 103 . The relay 103 isolates the line equipment from the telephone line and connects the line to a line test bus 104 which provides a line test signal. This relay is connected to the device test relay 105 .

The equipment test relay 105 can test the operation of the line equipment. A relay 105 may isolate the input of the hybrid resistor network 107 from the line and may connect it to an equipment test bus 106 which provides test signals for testing various components of the line equipment. Outside of test times, relay 105 connects line 101 to the input of hybrid resistor network 107 via protection device 102 and relay 103 .

The hybrid resistor network 107 is connected to the power supply circuit 109 or the ringing circuit 111 through the ringing relay 108 . In this example, the power supply circuit 109 includes two poles switched by the relay 108 and the ringing circuit 111 includes two poles switched by the relay 108 . The control of these various relays is well known and therefore not shown in the figure.

The two inlets of the hybrid resistor network 107 are respectively connected to the two inputs of the disconnection/reconnection detection circuit 112 . A supply voltage Vcc applied to circuit 112 by connector 114 enables the circuit to operate. Circuitry 112 provides a logic signal to output connector 113 when a disconnection is detected. The circuit may emit a supplemental logic signal upon detection of reactivation.

The use of relays 105 to test the individual components of the line arrangement entails additional costs for the same number of relays 105 as the line arrangement and the number of telephone exchanges connected. It would therefore be desirable to be able to test line equipment, particularly components of the disconnect/reclose detection circuit, without the use of such relays.

Contents of the invention

The object of the invention is a method of testing an analogue telephone line device comprising a resistor network, which device is connected on the one hand to the telephone line and on the other hand to a disconnection/reconnection detection circuit, which disconnection/reconnection detection The circuit includes a low-pass filter followed by a comparator providing an off/on logic signal;

It is characterized in that a test signal is added to a voltage supplied by a resistive network with a filter having an alternating component whose repetition frequency is less than the cut-off frequency of the filter and whose amplitude is sufficient such that the voltage resulting from the addition causes the comparator to be trigger; immediately followed or preceded by another identical test signal, but with a repetition rate higher than the cutoff frequency; and

In the first case, the control off/on logic signal changes state in the rhythm of the test signal, and in the second case, the control logic signal does not change state.

The method is therefore also characterized in allowing testing of filters, and additionally testing of comparators, without the use of relays, since no transformation is required to apply the test voltage, forcing the voltage by means of a circuit which adds alternating voltages to static voltages Applied to the input of the filter.

The invention also relates to a device simulating a telephone line implementing the method.

Description of drawings

Other features and advantages of the invention will become more clearly understood in the following description with reference to the accompanying drawings in which:

Fig. 1 is a simplified schematic diagram of known line equipment;

Figure 2 is a schematic diagram of Figure 1 modified according to the present invention; and

FIG. 3 is a schematic diagram of components within the range of the dotted box 115 in FIG. 2 .

Detailed ways

FIG. 2 shows a line arrangement capable of carrying out the method according to the invention. It is determined that the difference between this line device and the device shown in FIG. 1 is that the running test relay 105 is canceled, and a test device composed of some components is added within the range of the dotted line frame 115 .

3 shows a detailed schematic diagram of the elements within the area of the dotted box 115 to illustrate the functioning of the method according to the invention for testing the disconnection/reconnection detection circuit, in particular the filter it comprises.

The two inlets of the hybrid resistor network 107 are connected to the two inputs of the circuit 112 through two connection lines 201 and 202 with voltages VA and VB respectively. In this embodiment, the above-mentioned test device is connected to the line 202, but it can also be connected to the line 201 by adjusting the polarity as necessary. The device is formed by a resistor 203 connected at one end to a line 202 and at the other end by a transistor 204 to provide a voltage source Vcc. A test signal is applied via resistor 205 to the base of the transistor. In this example, the transistor is a bipolar transistor, but any other technology would work. The resistance values of the resistors 203 and 205 are calculated by known methods according to other parameter values and the mode of operation described below.

The disconnection/reconnection detection circuit 112 mainly includes a voltage comparator 212 and a low-pass filter 312 whose cutoff frequency is lower than the frequency of the ringing signal. The active filter in this exemplary embodiment can be activated or deactivated by an activation signal applied via connection 313 . The filter receives the signal from the mixing circuit 107 to substantially eliminate the ringing signal. With the filter 312, the comparator 212 is not triggered during the transmission of the ring signal.

It is well known that the voltage between VA and VB is reversed when the telephone exchange connected to the line equipment is disconnected. This inversion is detected by a comparator 212 emitting at its output a logic signal VS indicative of disconnection. During switch-on, reverse operation. When a logic signal is established, the signal is a stable signal with no transitions.

The operational tests of the disconnect/reclose detection circuit 112 include:

- disconnecting the line device by activating the relay 103,

- apply the battery voltage Vbat to the hybrid resistor network 107 by activating the relay 108,

- Sending a test logic signal 206 formed by an alternation of 0s and 1s corresponding to ground and voltage Vcc respectively to the base of transistor 204 .

First, a first test signal 206 is used whose repetition frequency is much smaller than the cut-off frequency of the filter 212 . This signal 206 is obtained by a simple program of the control computer of the automatic transmitter connected to the line equipment. If the filter 212 works well, the first test signal 206 is passed without attenuation, since this is a low pass filter.

When transistor 204 is turned off by test signal 206, voltage VB is not changed by the test circuit and the voltage difference VA-VB is positive because the line is not connected to the device, which corresponds to the connected state. The logic signal VS on the output of the comparator 212 thus indicates the state of the connection to the calculator.

When transistor 204 is turned on after changing the state of the test signal, the transistor saturates and resistor 203 connects line 202 to voltage Vcc. The net 107 and the resistor 203 form an adder which adds the test signal to the voltage VB supplied through the resistive network 107 . The resulting voltage VB is a function of the voltage Vbat, the value of the network resistor 107, the value of the resistor 203, and the voltage Vcc. These values are chosen so that the resulting voltage VB becomes greater than the voltage VA. Voltage VA-VB becomes negative. The value of Vcc and resistor 203 is calculated by known methods to obtain the inversion of the sign of voltage VA-VB. The voltage VA-VB is forced to be negative to simulate the disconnected state. The logic signal VS is therefore toggled, indicating this off state to the calculator.

If the signal VS does not toggle when the test signal changes state, it indicates that the disconnection/reclosing detection system 112 has failed. Typically this defect refers to the comparator 212 , but could also be the hybrid circuit 107 or the filter 312 .

To test the operation of the filter 312 at frequencies below the cutoff frequency, in fact only one state change of the test signal is sufficient, but it is preferred to use repeated state changes with a slow rhythm, significantly below the cutoff frequency of the filter 312.

Therefore, when it is detected that the output signal VS does not respond to the test signal, the control calculator of the automatic transmitter connected to the line equipment can easily determine whether the filter 312 or the disconnection/reconnection detection circuit 112 of the line equipment is incorrect. qualified. This detection can also be performed here with a simple calculator program.

Conversely, a positive result of the first test is not sufficient to conclude that the filter 312 is functioning well, since this is only a test of its frequency when it is well below the cutoff frequency.

A second test signal 206 is therefore used next, the repetition frequency of which is much higher than the cut-off frequency of the filter. For example, the repetition frequency of the test signal 206 used is 10 times the filter cutoff frequency. This second test signal 206 is obtained using a simple program of the control computer of the automatic transmitter connected to the line equipment.

The voltage difference VA-VB has a sign that changes to this repetition frequency. If filter 212 works well, it attenuates alternating components of voltage VA-VB, the attenuation is deterministic. The output of filter 312 provides a signal with a DC component and a very weak alternating component for the repetition frequency. The remaining test signal cannot trigger the comparator 212, and the output signal VS remains constant. The control calculator detects this lack of response and interprets it as the filter is functioning properly in relation to its specified repetition rate. Conversely, output signal VS triggering in the rhythm of the test signal indicates that the filter is operating abnormally. This detection can also be realized by a simple program of a calculator.

In order to be able to control the operation of the filter 312, for frequencies lower than the cut-off frequency and for frequencies higher than the cut-off frequency, it is only necessary to use two consecutive subsequent steps, first sending the logic signal 206 at a low repetition rate, and then at High repetition rates send logic signals 206 and vice versa.

This method does not require specific relays to introduce the test signal. The present invention therefore allows the omission of the test relay 105 as well as the bus and associated electronics for each line device at the expense of several low cost components added for each device and a calculator program added to the automatic transmitter In several programs, the automatic transmitter is connected with all line equipment.

The invention also applies to circuit arrangements in which relays, in particular relay 108 , are replaced by semiconductor components.

Claims (3)

1. A method of testing an analog telephone line device comprising a resistor network (107), which device is connected to the telephone line on the one hand and to a disconnection/reconnection detection circuit (112) on the other hand, the disconnection/reconnection detection circuit (112) being connected The reclosing detection circuit includes a low pass filter (312) followed by a comparator (212) providing an off/reclosing logic signal (VS); It is characterized in that a test signal is added to the voltage (VA-VB) supplied to the filter (312) by the resistor network (107) with an alternating component whose repetition frequency is less than the cut-off frequency of the filter (312) and whose the amplitude is sufficient so that the voltage resulting from the addition causes the comparator (212) to be triggered; immediately followed or preceded by another identical test signal, but with a repetition rate higher than the cut-off frequency; and In the first case, the off/on logic signal (VS) is controlled to change state in the rhythm of the test signal, and in the second case, the logic signal is controlled not to change state. 2. An analog telephone line device comprising a resistive network (107), which device is connected on the one hand to the telephone line and on the other hand to a disconnection/reconnection detection circuit (112), the disconnection/reconnection The detection circuit includes a low pass filter (312) followed by a comparator (212) providing an off/on logic signal (VS); It is characterized in that the device comprises means (203-205) for adding a test signal having alternating components to the voltage (VA-VB) supplied by the resistor network (107) to the input of the filter (312) (203-205) The repetition frequency is less than the cutoff frequency of the filter, followed or preceded by another identical test signal, but with a repetition frequency higher than the cutoff frequency. 3. The analog telephone line device according to claim 2, wherein said adding means comprises: A resistor (203) whose first end is connected to the input of a filter (312) connected to the output of the resistor network (107) and whose second end is connected to the DC voltage (Vcc) through an electronic transmitter (204) generator, the transmitter is controllable by a binary test signal (206).

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