GB2191364A - Fault testing telephones - Google Patents

Abstract

The microphone (41), earpiece (42) and/or tone caller (11) of a telephone instrument are tested automatically, preferably each time a call is received, by sounding the earpiece and/or tone caller and using the microphone (41) to receive the emitted sound. The signal level produced by the microphone (41) is analysed in a measuring unit (21), and optionally is correlated (50) with the signal supplied to the earpiece or tone caller originating the emitted sound. Any degradation of the performance of the microphone and/or earpiece and/or the tone caller is detected and may be indicated visually (14). <IMAGE>

Description

SPECIFICATION Fault testing telephones The present invention relates to apparatus for testing telephone apparatusfor a fault, including degradation in its acoustic performance, for example duetothe deterioration ofthe microphone, earpiece ortone caller.

Previous methods oftesting for any such fault have been undertaken by human operators applying their subjective judgement. Accordingly, minor degradationsin acoustic performances are rarely noticed by the telephone subscriber, and it is onlywhen a major fault is apparentthatthe operator is alerted.

The invention, in one aspect, provides telephone apparatus comprising a microphone and an audiofre quency emitter (for example an earpiece) coupled via an acoustic path to the microphone, means for generating a first signal to produce an audible output at the emitter, means for detecting a second signal generated bythe microphone in response to the said audible output, and means responsive to the second signal to produce an output signal indicative ofthe degree of correspondence between the first and second signals.

Telephone apparatus according to the invention is capable of operating automatically to indicate a fault, which may be a degradation in the acoustic performance ofthe microphone orthe emitter, independently of any human operator.

The microphone transmitter is preferably the microphone in the mouthpiece of a telephone instrument.

The emitter may then be the corresponding earpiece, a loudspeaker unitorthe so-called "tone caller", ofthe telephone instrument i.e. the audio transducer used to make the audible "ringing" noise.

In an alternative embodiment however, the microphone may be the earpiece of a telephone instrument, of which the tone caller constitutes the emitter.

Where the microphone forms part of a telephone mouthpiece, and the emitter isthe corresponding ea rpiece or loudspeaker unit, the telephone apparatus preferablyfurthercomprises a tone caller, and the detecting means is further responsive to a third signal, generated bythe microphone is response to an audibleoutputofthetonecaller,the processing means also responding to the third signal, and the said output signal being indicative ofthe degree of correspodence between the third signal and the first signal.

In such telephone apparatus, the said processing means responsive to the second signal preferably compares the signal level of the second signal with a predetermined level to producetheoutputsignal which is depdendent on the difference therebetween.

Where a third signal is produced, originating from the tone caller, the processing means preferably also compares the third signal level with a predetermined level to produce the output signal which is also dependent on the difference therebetween.

The means for generating the first signal is preferably adapted to generate the calling tone in the tone caller. In such apparatus, an attenuator is preferably provided between the first signal generating means and the emitter so that the signal level at the emitter is lower than the corresponding signal level atthe tone caller. This protects the ear, in the case thatthe emitter is the earpiece, in the event of a malfunction.

The said processing means preferably comprises meanscontrollingtheapplicationofthefirstsignal alternately to the tone caller and to the emitterto cause respectivelythethird and second signals to be generated in the microphone.

The effect of extraneous noise may be reduced substantially by the audio filtering ofthe second andlorthird signalsforexample using a high pass filter. Alternatively, or in addition, the telephone apparatus comprises means for correlating the first signalwiththesecond and/orthirdsignalswhenthey are compared by the said processing means, the said correlation being effective to minimise the effect of extraneous noise.

The degree of correspondence between the various signals may be ascertained simplyby determining whether or not a given signal on the earpiece or tone caller gives rise to a coincident signal at the mic rophone.The amplitude and/orfrequency of the signal at the tone caller and/or earpiece may be varied continuouslyorotherwisea more complex correlation maybe utilised.

In one form of the appartus, the telephone apparatusforms part of a telephone instrumentfor connec tion through an analogue line to an exchange, the said processing means being responsive to the presence of a call on the line to connectthefirstsignal generating means to the tone caller and to connect the microphone to the detecting means to produce the third signal, and subsequently to connectthefirst signal generating means instead to the audio frequency emittertherebyto produce the second signal.

Preferably such a telephone instrument comprises a user operable switch adapted to indicate whether a telephone call is being answered: the said processing means responding to the presenceof a call on the line, and to the said switch indicatingthatthe call is unanswered, first to connectthefirst signal generating means to the tone caller and to connectthe transmitter to the detecting means to produce the third signal, and subsequently to connect the first signal generating means instead to the audio frequency emittertherebyto produce the second signal: the said processing means being further responsive to the said switch indicating thatthe call is being answered to disconnectthe tone caller and to connect the emitter and the microphone instead to the analogue line.

The telephone instrumentpreferablyfurthercom- prises indicator means, preferably a visual indicator, responsive to the output signal to provide an indication of a fault.

In an alternative form of the invention, the telephone apparatus comprises a digital telephone instrument comprising the microphone and the emitter connected by way of a digital telephone line to a digital telephone exchange. Preferably, the first signal generating means forms part ofthe exchange. Preferably also the said detecting means, and preferably further the processing means, also form part of the exchange.

Indicator means are preferably provided, either at the telephone exchange oron the telephone instrument, to provide an indication, preferably a visual indication, ofthe presence of a fault, in response to the said output signal.

Such a telephone instrument preferably comprises a control unit responsive to the presence of a call firstly to connect the first signal generating means to thetonecallerandthe microphone means to the detecting means to produce the third signal, and subsequently to connectthe first signal generating means instead to the emitter with the microphone still connected to the detecting means, to produce the second signal. Preferably, the telephone instrument comprises a user-operable switch for indicating whether a telephone call is being answered, and the control means responds to the said switch indicating that the call is being answered to disconnectthetone caller and to connectthe emitter and the microphone instead to the digital telephone line.

In orderthatthe invention may be better under stood,two preferred embodiments ofthe invention will now be described, byway of example only, with reference to the accompanying diagrammatic drawings, wherein: Figure 1 shows an analogue telephone instrument according to a first embodiment of the invention; Figures2 shows a digital telephone instrument connected to a digital telephone exchange, according to a second embodiment ofthe invention; and Figure 3 is a graph indicating the measured output ofthe microphones of the telephone instruments of Figure 1 and Figure 2.

With reference first to Figure 1, an analogue telephone instrument comprises a base unit 10 and a handset 40 which contains a microphone 41 and an earpiece 42 which comprises a transducer. A useroperable handset switch 43 opens and closes according to the position of the handset 40, which depends on whether a telephone call is being answered.

The base unit 10, which is connected in a conventional mannerto a telephone line 30, comprises a tone caller 11 operable via afirsttwo-wayswitch 19 buy a signal generator 20, and earpiece and microphone amplifiers 12 and 13 respectively. A hybrid unit 16 connects the microphone amplifier 13, and the earpiece microphone 12 by way of a second two-way switch 17, to transmit and receive signals to and from the telephone line 30.

A measuring unit 21 is also connected to the output of the microphone amplifier 13, and provides an output to a control unit 18.

The signal generator 20 is also connected, via the firsttwo-way switch 19, by way of an attenuator 15 to the second two-way switch 17 and thus to the input of the earpiece amplifier 12.

A signalling detector 22 which receives the signal from the telephone line 30 provides an output to the control unit 18 indicating whether a call is on the line.

A power extraction unit 23, also connected to the telephone line 30to receive power, supplies operating powerto each of the units in the base unit 10.

In addition to the connections to the handset switch 43,the measuring unit 21 andthesignalling detector 22, the control unit 18 is also connected to control the two two-way switches 19, 17, and is connected to provide an output signal to an indicator lamp 14 for indicating a fault in acoustic performance.

The telephone apparatus works as follows. When a telephone call is present on the telephone line 30, and the handset is placed on the base unit 10 indicating thatthe call is not being answered, the signalling detector 22 and the handset switch 43 supply corres ponding signals to the control unit 18. The control unit 18 first operates the two two-way switches 19, 17 to connect the signal generator 20 via thefirsttwo-way switch 19 to the tone caller 1 and also to connectthe attenuator 15 to the earpiece amplifier input 12. Thus the earpiece 42 in inactive, but the tone caller 11 generates an audible calling tone.Thecallingtone is received by the microphone 41 in the handset 40, and is amplified in the microphone amplifier 13 and transmitted to the measuring unit 21.The signal produced in the measuring unit 21 is represented as signal a in the graph of Figure 3.

After a predetermind interval, the control unitthen changes the state of the first two-way switch 1 9to connectthe signal generator 20 through the atte nuator 15to the earpiece amplifier 12, to produce an audible tone in the earpiece transducer 42. The sound produced in the earpiece is received in the microphone 41 through an acoustic path between the earpiece and microphone, and a corresponding signal is amplified in the microphone amplifier 13 and transmitted to the measuring unit 21, which registers a corresponding signal b (Figure 3).

There follows next an interval c (Figure 3) during which the signal generated by the signal generator 20 is at a low level, and the only sound detected by the microphone 41 is due to extraneous noise. Attheend of the next interval, the cycle is repeated by first reactivating the tone caller 11, to produce a further sequence of signals (a', b', c', Figure 3).

The control unit 18 responds to the signal levels a, b, produced by the microphone 41 in response to signals from the tone caller 11 and the earpiece 42 respective ly, to determine the differences between those signal levels and respective predetermined signal levels representative of a properly-functioning microphone earpiece and tone caller. It will be appreciated that the signal levels a, b, produced by the microphone are continuously variable over a wide range in response to the audible sound emitted by the earpiece and tone caller. The variations are indicative of the proper functioning ofthe microphone, earpiece and tone caller.In this embodiment, the control unit 18 meausres the difference in signal level between the extraneous noice c and the signal produced by the microphone 41 in response to signalsfrom the tone caller 11 and from the earpiece 42, i.e. the differences in level between signals a and c, and between signals band c (Figure 3), and comparesthese differences respectively with the predetermined signal levels.

If the level of output at the microphone due to the tone caller alone (i.e. signal level a minus signal level c) is below the corresponding predetermined signal level, or is below that predetermined signal level by more than a predetermined amount, then it is assumed thatthetone caller 11 is at fault, and the indicator lamp 14 is actuated accordingly. Similarly, if the level at the microphone due to a sound atthe earpiece alone, i.e. signal level b minus signal level c is below another predetermined level, or is below that level by more than a predertermined amount, then it is assumed that the earpiece is at fault, and the indicator lamp 14 is actuated accordingly.If the level of output from the microphone from both sources is too low, then it isassumed thatthe microphone is fault, and the indicator lamp 14 is actuated accordingly.

The indicator lamp 14 may be controlled to indicate which element of the telephone instrument is at fault, orto indicatethat anyone ofthe elements is atfau It, and the indicator lamp 14 may instead be an array of lamps or, for example, a liquid crystal display. The indication of a fault may alternatively be provided in another manner, for example by sending a signal to the signal generator20 to modify audibly the tone produced bythetone caller 11.

Substantial background noise may affectthe reliability of the fault indication, and accordingly means may be provided to avoid the effect of extraneous noise.

In one form, an audio filter,forexample a high pass or band pass filter, may be provided between the microphone amplifier 73andthe measuring unit 21, so thatthe measuring unit21 is made to consider signals only within a given waveband, corresponding to that ofthe signal generator 20.

The degree of correspondence between thevarious signals may, however, be ascertained simply, in a way which excludes much ofthe extraneous noise, by determining whether or not a given signal on the earpiece ortone caller gives rise to a coincident signal at the microphone. The amplitude and/orfrequency of thesignal atthetonecallerandiorearpiecemaybe varied continuously or otherwise a more complex correlation may be utilised.

In a more complex form, a furthersignal path 50 is provided between the signal generator20 andthe measuring unit 21, and the measuring unit21 comprises a correlation ci rcuit for correlating the signal from the signal generator20 (i.e. thatsentto the tone caller 11 or the earpiece 421with the signal from the microphone amplifier 13.Since the extraneous noise does not correlate with the signal generator output, it is excludedfrom the signal output by the measuring unit 21.Thecorrnlation circuit may take any conventional forrn,for example a double balanced modulator circuit In such a double balanced modulatorcircuft,a pair of balanced modulators both receivethesignal from the microphone and provide a corresponding modulation of a carrier signal from the signal generator20.One balanced modulator receives its carrier signal from the signal generator 20 direct; the other balanced modulator receives its carrier signal from the signal generator 20 shifted by 90" in phase. The-o.utputs from the two balanced modulators araboth squared and are then summed to produce an output indicative ofthe strength ofthe portion of the signal from the microphone amplifier 13 which eorrelateswith the signal from the signal generator 20.

Whenthe telephone call is answered, the handset switch 43 sends a corresponding signal to the control unit 18, which ensures that the switches 17, 19 are in the positions shown in Figure 1, connecting the microphone 41 and earpiece 42 through their respec tive amplifiersto the hybrid 16 and thus to the telephone line 30, for operation in the normal manner.

Thesignal provided bytheindicatorl4maybe maintained,for example by means of a latch, to provide a permanent indication of a fault.

In the preferred form ofthe invention, the telephone instrument is configured to enhance the acoustic coupling between the microphone 41 and the earpiece 42, and between the microphone41 and the tone caller 1 1,withthe hand set 40 resting on the base unit 10, and so asto exclude as far as possible any extraneous noise from the microphone.

The testing operation has been described above as being initiated every time that the telephone instrument receives a call on the telephone line 30. An alternative would beto activate the control unit 18 to gothroughthetest routine only in response to a specific command, e.g. on the operation of a button (not shown) on the telephone instrument. Further, the testing could be limited to a measurement ofthe signal a (Figure 3) or signal b (Figure 3), i.e. involving a measurement of the signal produced in the microphone 41 as a result of signal produced only by the earpiece42, or only by the tone caller 11.Itwill be appreciated thatthe testing routine would be equally effective with a loudspeaker unit instead of, or in addition to, the earpiece 42; the telephone instrument could even be tested by applying the signal from the signal generator 20 to the microphone 41 operating as a loudspeaker, and detecting the corresponding signal produced in the earpiece acting temporarily as a microphone, or even the signal reflected backtothe microphone 41 using a "sonar" technique.

A second embodiment ofthe invention will now be described with reference to Figures 2 and 3.

A digital telephone instrument comprises a base unit 110 and a handset140which contains a microphone 141 and an earpiece 142. The base unit 110 comprises a tone caller 111 with an input amplifier 112 connected to oneterminal of a two-way switch 151 operated by a control unit 118. An otherterminai of the two-way switch 151 is connected to the earpiece 142.

The two-way switch 151 operates to connectthe output of a pulse code modulation (PCM) decoder 152 alternatively to the tone caller 111 orto the earpiece 142.The microphone 141 isconnectedtotheinputofa PCM encoder 153 whose output is connected to a muitiplexer/de-multiplexer unit 154. The input of the PCM decoder 152 is also connected to the multiplexer/ de-multiplexer unit 154. The control unit 118 is connected to operate a display device such as an indicatorlamp 114, and communicateswiththe multiplexer/de-multiplexer unit 154.

The telephone instrument is connected through a digital link 1 30to a digital telephone exchange 200 which has a corresponding mutliplexer/de-multiplexer unit 155. The telephone exchange 200 comprises a signal generator 120 whose output is connected to the multiplexer/de-multiplexer unit 155, a measuring unit 121 whose input is connected to the multiplexer/demultiplexer unit 155, and a signalling control unit 156 connected to the multiplexer/de-multiplexer unit 155.

The telephone apparatus of Figure 2 operates as follows.

Acall signal from the signalling control unit 156 in the telephone exchange 200 transmits a call signal from the multiplexer/de-multiplexer unit 155, in digital form to the corresponding multiplexer/de-multiplexer unit 154 in the telephone instrument base unit 110.

Simultaneoulsy, a tone signal is generated by the signal generator 120 and istransmittedtothe multiplexer/de-multiplexer unit 154 in the telephone instrument. The control unit 118 respondsto the control signal originating from the signalling control unit 1 56to move the two-way switch 151 so as to connectthetonesignalfromthesignal generator 120 through the PCM decoder 152 and the input amplifier 1 12 to the tone caller 11 1,which generates an audible tone.This tone is picked up bythe microphone 141, which transmits a signal to the PCM encoder 153 and, by way of the multiplexer/de-multiplexerunits 154, 155to the measuring unit 121 atthetelephone exchange 200. The measuring unit 121 registers a signal level a (Figure 3), representative ofthe acoustic coupling between the tone caller 111 and the microphone 141,which signal level is degraded whenever eitherof these components is faulty.

After a predetermined interval, a control unit 118 then changes the position ofthetwo-way switch 151 so as to connect the PCM decoder 152 instead to the ea rpiece 142, which receives the tone signal originating from the signal generator 120. The microphone 141 picks up the audible signal from the earpiece 141, and produces a signal which is received by the measuring unit 121 in a similar manner. The signal level nowcorrespondsto level b (Figure 3), representative of the acoustic coupling between the earpiece 142 and the microphone 141 which is degraded when either of these elements is faulty.

After a predetermined interval, the outputfrom the signal generator 120 falls to zero, and the measuring unit 121 receives a signal from the microphone 141 at a level c (Figure 3) corresponding to any extraneous noise.

The affect of extraneous noise can be reduced or eliminated using the techniques described above with reference to Figure 1.

The measuring unit 121 transmits signals representing the signal levels a, b, and c of Figure 3 to the control unit 118 in the telephone instrument, which then analysesthe relative levels ina mannersimilartothat described above with reference to control unit 118 of Figure 1. The control unit 118 actuates the indicator lamp 114 in a similarmannertothe actuation ofthe indicator lamp 14 of Figure 1.

The alternative arrangements discussed above with reference to the embodiment of Figure 1 are applicable also to the digital apparatus described with reference to Figure 2. In addition, the indication of a fault condition may be supplied along the digital link 130 to the telephone exchange 200, instead of, or in addition to, the indication provided by the indicator lamp 1 on the telephone instrument.

Claims (1)

1. Telephone apparatus comprising a microphone and an audio frequency emitter coupled via an acoustic path to the microphone, means for generating a first signal to produce an audible output at the emitter, meansfordetecting a second signal gener ated by the microphone in response to the said audible output, and means responsive to the second signal to produce an output signal indicative of the degree of correspodence between the first and second signals.

2. Apparatus according to Claim 1, wherein the emitter is a tone caller.

3. Apparatus according to Claim 1, wherein the microphone forms part of a telephone mouthpiece.

4. Apparatus according to Claim 1 or3,wherein the emitterforms part of a telephone earpiece.

5. Apparatus according to Claim 7 or3, wherein the emitter is a telephone loudspeaker unit,

6. Apparatus according to any of Claims3 to5, comprising a tone caller.

7. Apparatus according to Claim 6, wherein the means for generating the first signal is adapted to generatethe calling tone in thetone call

8. Apparatus according to Claim 6 or 7, wherein an attenuator is provided between the first signal generating means and the emitter so that the signal level at the emitte is lowerthan the corresponding signal level atthetone caller.

9. Apparatus according to Claim 6,7 or 8, wherein the detecting means is further responsive to a third signal, generated by the microphone in response to an audible output ofthe tone caller, the processing means also responding to the third signal, and the said output signal being indicative ofthe degree of correspodence between the third signal and the first signal.

10. Apparatus according to Claim 9, wherein the processing means compares the third signal level with a predetermined level to produce the output signal which is depedenent on the difference therebetween.

11. Apparatus according to Claim 10, wherein the processing means is adapted to compare the first and third signals, the output signal being dependent upon the result ofthe said comparison.

12. Apparatus according to Claim 11, wherein the said comparison of the first and third signals is a correlation,thesignal level of the portion ofthethird signal which correlates with the first signal being compared with the said predetermined level to produce the output signal.

13. Apparatus according to Claim 8,9or 10, wherein the processing means compares the second signal level with a predetermined level to producethe output signal which is dependenton the difference therebetween.

14. Apparatus according to Claim T3,,wherein the processing means is adaptedto comparethetirst and second signals, the output signal being dependent upon the result of the said comparison.

15. Apparatus according to Claim 14, wherein the said comparison of the first and second signals is a correlation, the signal level of the portion of the second signal which correlateswiththefirstsignal being compared with the said predetermined level to produce the output signal.

16. Apparatus according to Claim 14 or 15, where- in the said predetermined level is the second signal level orthe signal level of the portion of the second signal which correlates with the first signal.

17. Apparatus according to any of Claim 9 to 16, wherein the processing means comprises means controlling the application ofthefirst signal alternate lytothetonecallerandtotheemitter,tocause respectivelythethird and second signals to be generated in the microphone.

18. Apparatus according to any of Claims 6to 17 comprising anaudiofilterforfilteringthethirdsignal.

19. Apparatus according to any preceding claim, comprising an audio filter applied to filter the second signal.

20. Apparatus according to any of Claims 6 to 18, wherein thetelephone apparatus forms part of a telephone instrument for connection through an analogue line to an exchange, the said processing means being responsive to the presence of a call on the line to connect the first signal generating means to thetonecallerandtoconnectthemicrophonetothe detecting means to produce the third signal, and subsequentlyto connect the first signal generating means instead to the audio frequency emitter thereby to produce the second signal.

21. Apparatus according to Claim 20, wherein the telephone instrument comprises a useroperable switch adapted to indicate whether a telephone call is being answered: the said processing means responding to the presence of a call on the line, and to the said switch indicating that the call is unanswered, first to connect the first signal generating means to the tone caller and to connect the transmitter to the detecting means to produce the third signal, and subsequently to connect the first signal generating means instead to the audio frequency emitter thereby to produce the second signal: the said processing means being further responsive to the said switch indicating that the call is being answered to disconnect the tone caller and to connect the emitter and the microphone insteadto the analogue line.

22. Apparatus according to Claim 21, wherein the telephone instrument further comprises indicator means responsive to the output signals to provide an indication when the result of the comparison of the second signal is indicative of a fault.

23. Apparatus according to Claim 22, wherein the indicator means provides a visual indication.

24. Apparatus according to any of Claims 1 to 20, comprising a digital telephone instrument housing the said emitter and microphone, the telephone instrument being connected by way of a digital telephone line to a digital telephone exchange.

25. Apparatus according to Claim 24 wherein the first signal generating means forms part of the exchange.

26. Apparatus according to Claim 24 or 25, wherein the detecting means forms part ofthe exchange.

27. Apparatus according to any of Claims 24to 27, wherein the processing means forms part of the exchange.

28. Apparatus according to any of Claims 24to 26, wherein the telephone apparatus comprises indicator means responsive to the output signal for providing an indication when the result ofthe comparison of the second signal is indicative of a fault.

29. Apparatus according to Claim 28, wherein the indicator means provide a visual indication.

30. Apparatus according to Claim 28 or 29, wherein the indicator means are provided at the telephone exchange.

31. Apparatus according to Claim 28 or 29, wherein the indicator means are provided on the telephone instrument.

32. Apparatus according to any of Claims 24to 31, wherein the telephone instrument comprises a control unit responsive to the presence of a call first to connect thefirstsignal generating meanstothetone caller and the microphone to the detecting means to produce the third signal, and subsequently to connectthefirst signal generating means instead to the emitter with the microphone still connected to the detecting means, to produce the second signal.

32. Apparatus according to Claim 32, wherein the telephone instrument comprises a user-operable switch for indicating whether a telephone call is being answered, and the control means responds to the said switch indicating thatthe call is being answered to disconnectthetonecallerandtoconnecttheemitter and the microphone instead to the digital telephone iine.

34. Telephone apparatus substantially as described herein with reference to Figure 1 of the accompany drawings.

35. Telephone apparatus substantially as described herein with reference to Figure2 of the accompanying drawings.