CA2073764A1 - Telecommunications line test system - Google Patents
Telecommunications line test systemInfo
- Publication number
- CA2073764A1 CA2073764A1 CA002073764A CA2073764A CA2073764A1 CA 2073764 A1 CA2073764 A1 CA 2073764A1 CA 002073764 A CA002073764 A CA 002073764A CA 2073764 A CA2073764 A CA 2073764A CA 2073764 A1 CA2073764 A1 CA 2073764A1
- Authority
- CA
- Canada
- Prior art keywords
- line
- component
- circuit
- volts
- threshold voltage
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M3/00—Automatic or semi-automatic exchanges
- H04M3/22—Arrangements for supervision, monitoring or testing
- H04M3/26—Arrangements for supervision, monitoring or testing with means for applying test signals or for measuring
- H04M3/28—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor
- H04M3/30—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor for subscriber's lines, for the local loop
- H04M3/301—Circuit arrangements at the subscriber's side of the line
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M3/00—Automatic or semi-automatic exchanges
- H04M3/22—Arrangements for supervision, monitoring or testing
- H04M3/26—Arrangements for supervision, monitoring or testing with means for applying test signals or for measuring
- H04M3/28—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor
- H04M3/30—Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor for subscriber's lines, for the local loop
Landscapes
- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Monitoring And Testing Of Exchanges (AREA)
- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
Abstract
A device capable for use in investigating a fault in a telecommunications system comprising a first and second part interconnected by a lines which device comprises: (a) a first circuit that can be connected in series with the line and comprising a first capacitor and a first component, such that an alternating current can pass along the line via the capacitor and a direct current can pass along the line via the first component in at least one direction with a threshold voltage; and (b) a second circuit that can be connected in parallel across the line and comprising a second component having a threshold voltage of greater than 48 volts and/or being able to pass direct current only in one direction.
Description
~r~ g1111~7x P'~'/G~91/~129 20~~7~4 Tel.eco~municati~ras lime test system The present invention relates to a device capable of investigating a fault in a telecom~uniaations system, par.
ticularly slang a telecommunications line between an exchange and a subscriber.
It is clearly desirable that a fault be quickly located in order that it be quickly put right. In addition to determining location, by which we mean determining the general area of a fault, it is also desirable to deteranine the type of fault since this knowledge will help one to locate the fault more precisely. Thus it is desirable to be able to determine whether a fault is a short circuit, for e~ta~ple between tip and ring (to use USA terminology) telephone conductors, an open circuit or an earthed conduc-.
tor.
The increasing use by subscribers of their own equip~
ment, which is simply plugged into the telephone co~pany~s system by the subscriber, has made it desirable that one can determine on which side of the plug a fault lies. The reason is that a fault on the exchange side of the plug and socket is the responsibility of the telephone company, and a fault the other side may be the responsibility of the subscriber. A fault on the subscriber's side may be due to faulty subscriber equipment or to faulty connection, and in either case location of the fault can save time and the telephone company's expense by avoiding unnecessary line testing.
Thus, devices have been proposed for incorporation at the boundary between the telephone company's and the subscriber°s responsibility. In particular such devices may be part of the socket into which a subscriber plugs his telephone or other equipment.
~ ~T'~~~'~
1~C191/11g72 Pf'f1G~91/4, 9 _ ~ _ Japanese patent specifiation A 58-.b3~60 for e~:ample describes a fault detector far communications equipment which ena tiles precise determination of the nature of a fault and the place of its occurence to be made from the telephone exchange, and so makes rapid repair possible.
This prior art fault detector is said to comprise a control part and a deteetor part, the control part comprising diodes inserted in series between the pair of conductors of a telephone~lane and the subscriber, and a varistor con-nected across the two canductors. The varistor must have a threshold value higher than the threshold values of the diodese 'The~detector part comprises a variable voltage power unit, a current detector which can detect the eurrent flowing in the conductors as a function of the variable voltage applied, and a voltage detector.
~Te haae found however that the circuitry of the control part of the prior art fault detector has some significant disadvantages. Firstly, the voltage required to be applied to the telephone line has to be higher than is preferred for saf~ty reasons (more than 100 volts is required), a sharp current-voltage curve cannot be relied on, and the detec-tor s performance is likely to fluctuate with temperature.
An alternative device has now been designed that can overcome these problems.
Thus, the present invention provides a device capable for use in investigating a fault in a telecommunications system comprising a first and a second part interconnected by a line, which device comprises:
(a) a first circuit that can be connected in series with the line and comprising a first capacitor and a first component, such that an alternating current can pass along the line via the capacitor and a direct current can pass Vf~ 91/11g'Y2 P~'1~119110~1~9 20~~'~~4 along the line via the first component in at least one direction with a threshold valtage; and (b) a second circuit that can be connected in parallel across the line and comprising a second component having a threshold voltage of greater than ~t8 volts and/or being able to pass direct current only in one direction, The invention also pravides a device capable for use in investigating a fault in a telecommunications system comprising~a first and a second part interconnected by a line, which devise comprises:
(a) a first circuit that can be connected in series with the line and comprising a first component, such that an alternating current can pass along the line and a direct current can pass along the line via the first component in at least one direction with a threshold voltageg and (b) a second circuit that can be connected in parallel across the line and comprising a second compcanent~comprising at least one zener diode and having a threshold voltage of greater than 48 volts and/or being able to pass direct current only in one directions The invention further provides a device capable for use in investigating a fault in a telecommunications system c~mprising a first and a second part interconnected by a line, which device comprises:
(a) a first circuit that can be connected in series with the line and comprising a first component comprising a zener diode, such that an alternating current can pass along the line via the capacitor and a direct current can pass along the line via the first component in at least one direction with a threshold voltage; and (b) a second circuit that can be connected in parallel across the line and comprising a second component having a threshold voltage of greater than ~d8 volts and/or being able to pass direct current only in one direction.
VU~ 91/~R~y2 ~'~:'T/G~91/a. :19 ~O~~fi4 _u_ A telecommunications line generally comprises a pair of conductors from the first part (such as an exchange) to the second part (such as subscriber equipment?, the single pair carrying information, such as speech, in both directions.
In this case the second component referred to above is con-nected across those tcao conductors. A line may however comprise four conductors, in two pairs, each pair carrying information in a single direction. In that case a device of the invention may be provided for each pair.
We prefer that the first circuit campr.ises a capacitor and a first component in series with each of the conductors of a pair. In this case, we will refer to a first capacitor and a first component in series with one conductor and a second capacitor and third component in series with the second,conductor. This terminology is used because the pre-cise characteristics (such us capacitance and threshold voltage) of the two capacitors and of the first and third components may differ, althau~h they will Function as defined above.
We prefer that the first, second and third components each comprises a zener diode. In any case, each of said com-.
ponents may comprise two or more physically separate electrical or electronic components in electrical connection.
The second component preferably has a threshold voltage of greater than 48 volts, more preferably greater than 55 volts, especially from 6Q-75 volts. Where the threshold voltage is less than 4~ volts, the usual operating voltage of a line, some means should be provided to ensure that the subscriber apparatus is not shorted out at the normal operating voltage. This may be achieved by employing means, such as a diode, for preventing current passage through the second component in a direction opposite to that at which it W~ 91/R1A7~ ~~'1G1191J(9012~
- ~~~~7 exhibits its threshold voltage. Thus, the system is nor-mally operated using a source of direct current such that the second circuit is non-conductive. The polarity is reversed for at least part of the test,. under which con-.
ditions the threshold.voltage may be exhibited. The threshold voltage of the second component is preferably greater than that of ~he first circuit (generally the sum of that of the first and third components) unless said means for preventing the opposite passage of current is-employed.
The rbason is that otherwise the second circuit will not come into play. ~,~here the threshold. voltage of the second component is greater than ~8 volts (the normal as opposed to the test voltage) this problem need not arise and the device will be operable with either polarity of normal operating voltages between the conductors of the line. This is desirable because in many countries the polarity that is established on mating a telephone call is random.
The general principle of operation of the device can now be seen. What is required is a unique voltage-current curve corresponding to each of the fault conditions in the line to be tested. ~ voltage is applied, either between the two conductors of the line or between one of them and earth, depending on the test; and the current flowing in the line is measured. This is done for selected different voltages or continuously over 3 range of voltages. The current voltage curves will differ ,,~aepending on where a fault lies, because the different faults will cause current to follow different paths. For example the current may flow through the first circuit, through ~he seCOnd circuit, through part of one or both circuits, or not at all. The voltage is preferably applied, and the current and voltage measured at the telephone exchange. Thus the device of the invention may be used for remote investigation.
fV~ 91/11g7x ~'~"f/~~91/C u9 .
ticularly slang a telecommunications line between an exchange and a subscriber.
It is clearly desirable that a fault be quickly located in order that it be quickly put right. In addition to determining location, by which we mean determining the general area of a fault, it is also desirable to deteranine the type of fault since this knowledge will help one to locate the fault more precisely. Thus it is desirable to be able to determine whether a fault is a short circuit, for e~ta~ple between tip and ring (to use USA terminology) telephone conductors, an open circuit or an earthed conduc-.
tor.
The increasing use by subscribers of their own equip~
ment, which is simply plugged into the telephone co~pany~s system by the subscriber, has made it desirable that one can determine on which side of the plug a fault lies. The reason is that a fault on the exchange side of the plug and socket is the responsibility of the telephone company, and a fault the other side may be the responsibility of the subscriber. A fault on the subscriber's side may be due to faulty subscriber equipment or to faulty connection, and in either case location of the fault can save time and the telephone company's expense by avoiding unnecessary line testing.
Thus, devices have been proposed for incorporation at the boundary between the telephone company's and the subscriber°s responsibility. In particular such devices may be part of the socket into which a subscriber plugs his telephone or other equipment.
~ ~T'~~~'~
1~C191/11g72 Pf'f1G~91/4, 9 _ ~ _ Japanese patent specifiation A 58-.b3~60 for e~:ample describes a fault detector far communications equipment which ena tiles precise determination of the nature of a fault and the place of its occurence to be made from the telephone exchange, and so makes rapid repair possible.
This prior art fault detector is said to comprise a control part and a deteetor part, the control part comprising diodes inserted in series between the pair of conductors of a telephone~lane and the subscriber, and a varistor con-nected across the two canductors. The varistor must have a threshold value higher than the threshold values of the diodese 'The~detector part comprises a variable voltage power unit, a current detector which can detect the eurrent flowing in the conductors as a function of the variable voltage applied, and a voltage detector.
~Te haae found however that the circuitry of the control part of the prior art fault detector has some significant disadvantages. Firstly, the voltage required to be applied to the telephone line has to be higher than is preferred for saf~ty reasons (more than 100 volts is required), a sharp current-voltage curve cannot be relied on, and the detec-tor s performance is likely to fluctuate with temperature.
An alternative device has now been designed that can overcome these problems.
Thus, the present invention provides a device capable for use in investigating a fault in a telecommunications system comprising a first and a second part interconnected by a line, which device comprises:
(a) a first circuit that can be connected in series with the line and comprising a first capacitor and a first component, such that an alternating current can pass along the line via the capacitor and a direct current can pass Vf~ 91/11g'Y2 P~'1~119110~1~9 20~~'~~4 along the line via the first component in at least one direction with a threshold valtage; and (b) a second circuit that can be connected in parallel across the line and comprising a second component having a threshold voltage of greater than ~t8 volts and/or being able to pass direct current only in one direction, The invention also pravides a device capable for use in investigating a fault in a telecommunications system comprising~a first and a second part interconnected by a line, which devise comprises:
(a) a first circuit that can be connected in series with the line and comprising a first component, such that an alternating current can pass along the line and a direct current can pass along the line via the first component in at least one direction with a threshold voltageg and (b) a second circuit that can be connected in parallel across the line and comprising a second compcanent~comprising at least one zener diode and having a threshold voltage of greater than 48 volts and/or being able to pass direct current only in one directions The invention further provides a device capable for use in investigating a fault in a telecommunications system c~mprising a first and a second part interconnected by a line, which device comprises:
(a) a first circuit that can be connected in series with the line and comprising a first component comprising a zener diode, such that an alternating current can pass along the line via the capacitor and a direct current can pass along the line via the first component in at least one direction with a threshold voltage; and (b) a second circuit that can be connected in parallel across the line and comprising a second component having a threshold voltage of greater than ~d8 volts and/or being able to pass direct current only in one direction.
VU~ 91/~R~y2 ~'~:'T/G~91/a. :19 ~O~~fi4 _u_ A telecommunications line generally comprises a pair of conductors from the first part (such as an exchange) to the second part (such as subscriber equipment?, the single pair carrying information, such as speech, in both directions.
In this case the second component referred to above is con-nected across those tcao conductors. A line may however comprise four conductors, in two pairs, each pair carrying information in a single direction. In that case a device of the invention may be provided for each pair.
We prefer that the first circuit campr.ises a capacitor and a first component in series with each of the conductors of a pair. In this case, we will refer to a first capacitor and a first component in series with one conductor and a second capacitor and third component in series with the second,conductor. This terminology is used because the pre-cise characteristics (such us capacitance and threshold voltage) of the two capacitors and of the first and third components may differ, althau~h they will Function as defined above.
We prefer that the first, second and third components each comprises a zener diode. In any case, each of said com-.
ponents may comprise two or more physically separate electrical or electronic components in electrical connection.
The second component preferably has a threshold voltage of greater than 48 volts, more preferably greater than 55 volts, especially from 6Q-75 volts. Where the threshold voltage is less than 4~ volts, the usual operating voltage of a line, some means should be provided to ensure that the subscriber apparatus is not shorted out at the normal operating voltage. This may be achieved by employing means, such as a diode, for preventing current passage through the second component in a direction opposite to that at which it W~ 91/R1A7~ ~~'1G1191J(9012~
- ~~~~7 exhibits its threshold voltage. Thus, the system is nor-mally operated using a source of direct current such that the second circuit is non-conductive. The polarity is reversed for at least part of the test,. under which con-.
ditions the threshold.voltage may be exhibited. The threshold voltage of the second component is preferably greater than that of ~he first circuit (generally the sum of that of the first and third components) unless said means for preventing the opposite passage of current is-employed.
The rbason is that otherwise the second circuit will not come into play. ~,~here the threshold. voltage of the second component is greater than ~8 volts (the normal as opposed to the test voltage) this problem need not arise and the device will be operable with either polarity of normal operating voltages between the conductors of the line. This is desirable because in many countries the polarity that is established on mating a telephone call is random.
The general principle of operation of the device can now be seen. What is required is a unique voltage-current curve corresponding to each of the fault conditions in the line to be tested. ~ voltage is applied, either between the two conductors of the line or between one of them and earth, depending on the test; and the current flowing in the line is measured. This is done for selected different voltages or continuously over 3 range of voltages. The current voltage curves will differ ,,~aepending on where a fault lies, because the different faults will cause current to follow different paths. For example the current may flow through the first circuit, through ~he seCOnd circuit, through part of one or both circuits, or not at all. The voltage is preferably applied, and the current and voltage measured at the telephone exchange. Thus the device of the invention may be used for remote investigation.
fV~ 91/11g7x ~'~"f/~~91/C u9 .
2~37~4 The first, second and third components will give rise to characteristic sudden increases in current at their threshold voltages, V1,UZ and V3 respectively and at those voltages prefers bly become substantially conducting. For example the total circuit may then have a resistance of less than 2000, prefers bly less than 1100 ohms. A threshold voltage is therefore a predetermined voltage or voltage range at,or over which a component or d circuit exhibits a sharp change in resistivity. If the current-voltage curve shows a sudden increase in current at about Vl, then one may conclude ttaat the current is flowing through the_ first com-ponent. ~ Similarly, if an increase oocur~s at V2 + V3, then current is flowing through the second and third components, but not through the first (at least not in the direction in ~rhich the threshold voltage is exhibited). We prefer that the threshold voltage of the second circuit is greater than, particularly by at lease 15 volts, especially by at least 30 volts, that of the first circuit.
As an example, normal operation of the telecom-munications system may involve current flooring through the first circuit. The capacitors are preferably provided in order that an alternating signal may pass substantially unrestricted to allow a ringing tone (generally an AC signal superimposed on a ~?C bias of usually ~t8 volts) and that a DC
audio signal or other signal may to be passed between the first part and the second part. If the threshold voltage of the first and third (where provided) components together is much less than the operating voltage of the system, the direct current for normal operation may be applied at either polarity. .If the total of the threshold voltages is higher, then normal operation will require connection such that current flows in the opposite direction to that at which the threshold voltages are exhibited. In that ease the polarity has to be reversed for at least part of the test.
~ Wf~ 91i11g'7~ P~"9G~~~/~~.25~
203?6~
_7_ It may be possible that the first and third components exhibit their threshold voltages at opposite polarities, ie they are connected in series back-to-back. In this case the normal operating voltage will need to~be higher than only one of the threshold voltages.
We prefer that the device be able to distinguish between two or more of the following conditions:
1. A short circuit within the first part of" the system (for example the telephone company°s property) 2. An open circuit within the first part A short within the second part tfor example the Subscriber°s property) 4. An open circuit within the second part 5. An earthed conductor within the second part An earthed ring conductor within the first part.
?. An earthed tip conductor within the first part, (The terms °~ring°° and~~tip'~ are standard terms used to distinguish between the two conductors of a line. In a non-symmetrical system, for example as used is the USA, the tip is generally at 0 volts and the ring at -~.$ volts. In Europe and elsewhere, the system is symmetrical and the polarity applied is random.) The device should also be substantially transparent, preferably exhibiting a voltage drop of less than 15 pre_ ferably less than 10 volts, during normal direct current operation of the line. It should also be substantially transparent to alternating current in order that a ringing tone may be transmitted.
The invention is further illustrated with reference to the accompanying drawings, in which:
1J S°t'1'~llTHE°~
~V~ ~l/~187~ P~'4~~9~~( ~9 .
~0~3~4 - g -Figure 1 shows a telecommunications system;
Figure 2 shows a prior art device;
Figures 3 and a show devices of the invention;
Figure 5-7 show various faults in a telecommunications system;
Figures 8 and g show current-voltage relationships obtained from devices of the invention; and Figures 10 and 11 show a preferred device and related current-voltage relationship. __ A telecommunications system is represented schemati-cally in Figure~t. An exchange 1 is connected to a subscriber ~ by a line 3 comprising tip and ring conductors and 5 respectively. The dotted line shows a possible division between the telephone company's responsibility and a subscriber°s responsibility. A device of the invention may be planed in the line 3 at the position of the dotted line in order that one can deter~aine whether a fault is the respon-sibility of the telephone company or the subscriber.
Preferably the devioe of the invention is incorporated in a connection block which also comprises a housing and a telephone socket. The block may be mounted on a wall of a building, The invention may be used at other positions in a telecommunications system and "1°' may be regarded as a first part of a system (as referred to above ) and ~~~°° as a second part.
A prior art device for locating a fault is shown in Figure 2. This device comprises an electrical circuit of two pairs of diodes b, the pairs being in series with the tip ~J and ring 5 conductors respectively. A varistor 7 is connected across the tip and ring conductors. The diodes of each pair are connected in opposite fashion. We have found that this circuit is somewhat susceptible to temperature variation and the current_voltage relationships for the w~ 9,~~i~~~ ~crec~meoo~~g _ g various different faults to be investigated are not suf-ficiently distinct. We have also found that ~he circuit causes some attenuation to a signal during normal use of the line, and requires unacceptably high test voltages.' The present invention adopts a different approach, as is ill ustrated in Figures 3-g.
In,Figure 3 capacitors 9 and zener diodes 10 in parallel are together connected in series with respective conductors of the line. For some investigations a capacitorlzener diode pair may be required in only one of the lines. A zener diode 10 and ordinary diode 11 (ie a diode that is substantially nonconductive in one direction over the voltage range at which it is to be used, preferably up to 80 volts) are connected in opposite fashion between the tip conductor ~i and ring conductor 5. In a modification of this design, component 11 is also a zener diode.
The first and second circuits can now be seen. The first circuit comprises the wen diode Z1 (the first component referred to above) the telephone 8 (or rather a connections therefor since the telephone is not part of the circuit per se) the zener diode Z3, and the two capacitors 9. The second circuit comprises the zener diode Z2 (the second component referred to above) and the ordinary diode 11.
For nornual operation of the telephone a voltage of generally 48 volts is applied between the tip and ring con doctors. (Tip and ring is terminology used in the USA where the line is non-symetric, but it will be used here also to refer to symetric lines although designation of each line will be arbitiary.) The telephone company will first have sent a ringing tone (where the telephone 8 is receiving a Ball) by means of an alternating current, and this can flow ~~ 91/1172 PC.'I°/G1391/0 :9 2~~~3'~~~
in the first circuit through the capacitors 9 with little or no attenuation. The capacitors preferably are substantially transparent to audio frequencies, and preferably have a capacitance of at least 5 microfarads~,especially at least 10 microfarads. The second circuit will not be in use because the threshold value of Z2 is 70 volts, ie greater than the 48 volts operating voltage, and because of the diode 11, In the embodiment illustrated, the zener diodes Z1 and Z3 have threshold voltages of 20 and 30 volts respectively, Since the voltage applied for normal use (48U) is less than the total voltage drop for reverse operation of these diodes (ie the total threshold voltage of the circuit) the circuit will only work at signal frequencies at which the capacitors are substantially transparent. Thus, the capacitors may be chosen.to allow passage of normal audio frequencies.
Preferably the capacitors have a capacitance of at least 10 micrafarads. 4Jhere polarity is predeterztined, preferred values for Z1 and Z3 are 5-40 especially 1S-25 volts for Z1, and 15-~5 especially 25-35 volts for Z2. The total threshold voltage of the first circuit is preferably less than 70 volts, especially 40-60 volts.
A test is made by reversing the polarity so that the tip conductor 4 is negative with respect to the ring conduc-tor 5. The voltage is then increased from 0, up to a value somewhat above the greater of the threshold voltages of the first and second circuits, in this case 70 volts.
The current flowing is measured as a function of voltage.
The current-voltage relationship may be determined continuously over, say, the range 0-75 volts, or it may be sampled at values for example slightly below and above each of the threshold voltages, ie 18,22,28,32,48,52,68 and 72 volts. Ldhat is desired is a different current-voltage rela-tionship for each fault. The path the current takes, and '~'~ ~l/1i~72 PCf/~~9~/~129 therefore the zener diode or diodes whose threshold value or values must be reached, will depend on the location of the fault. Examples are given for various faults in Figures 8 and 9.
The device shown in Figure 4 is a modification of that of Figure 3, designed for normal telephone operation under either polarity. Again, component 11 may be a zener diode thus making the device completely symetric. __ Since the telephone 8. must work under either polarity, zener diodes 21 arid Z3 must not provide an excessive voltage drop for either direction of current flow in this ease we prefer that each has a threshold voltage of 15 volts or less, preferably less than 10 volts, more preferably less than ?,volts, and that their combined threshold voltage is less than 2p volts. It is also desirable that their threshold voltages be different (to be explained below) and we prefer values of 1.5~4, especially 2.5.3.5 volts, and 4-7 especially 4.5 to 5.5 volts.
Again, since current may flow in either direction during normal telephone operation, the threshold voltage of Z2 must be greater than the normal operating voltage, usually 48 volts. If this were not so, the telephone would be short circuited by the second circuit during normal operation under one of the two polarities.
In Figure 4 a telephone or other equipment 8 is repre-sented by its resistance, and the resistances of the lines are shown as 12. A reverse polarity switch 13 connects the line to a source of variable voltage power 14 for testing, During testing the applied voltage is measured at X and the current flowing is measured at Y, for example by measuring the voltage drop across a known resistor. 'The outputs from voltmeter X and ammeter Y may be plotted as the X and Y axes of a graph, as shown in Figures $ and 9.
~ S7°'i~°U°~'H1°
iW~ 91/11g'~Z ~G°fAGI;Il/~" '9 20~3~64 Figure 4 therefore shows a control unit C, a line (and exchange etc) L a device of the invention D and a subscribe rs telephone S. The device D will determine whether a fault falls in region G or region S and whether that fault is a short. circuit, an open circuit or an earth.
Figure 5 shows an open circuit 1~ at the subscriber.
On application of a voltage for testing, any current must flow thr~ugh the second circuit, and this will be_indicated by a current-voltage above showing, if line 5 is made posi_ tine, the threshold voltage of the second component, ie zener diode Z2. If line 4 is made positive, no current will flow due to diode 11. An open circuit on the exchange side, ie region L of Figure ~d, would prevent current flowing completely, Figure 6 shows a short 16 on the exchange side, The current-voltage curve will. now show no threshold voltage since the current path involves neither the first nor second circuit. The slope of the curve will be substantially constant, and will give the resistance of the line (together with that of the short itself). The same result will be obtained for either polarity.
In Figure 7 the fault is an earth connection 17 at the subscriber. This is revealed by applying the test voltage between one of the conductors 4 and 5, and earth. In general it will be necessary only to apply the voltage bet-ween one of the conductors and earth, but the test may be continued using the other conductor. The current will now flow through part of the first curcuit, ie through the zener diode Z1, but not through the zoner diode Z3~ The current-voltage curve will therefore exhibit the threshold voltage of Z1 when conductor 5 is positive and no threshold voltage when conductor ~ is negative with respect to earth. If the ~~ ~~>xi~az ~~o~~~~»i~~
~ ~3 _ voltage were applied between the other conductor and earth, the theshold voltage of Z3 would be exhibited. It will not always be necessary to extend the test over both polari-ties since this will depend on the amount of information required, and on the ahreshold values of the circuits. An earth fault on the exchange side will mean no current will flow through the first or second circuits, and the current-voltage,curve will not show a threshold voltage. This fault is however distinguishable from the fault of Figure 6 because different tests are required to produce the similar current-voltage curves. Also, the curves will be slightly different since the resistances of the two resulting current paths are likely to be different.
Figure 8 shows the current-voltage curves produced from the device of Figure 3 under the following faults Figure 8a short at exchange or line Figure 8b short at subscriber Figure 8c earth at exchange or tip conductor of line Figure 8d earth at exchange or ring conductor of line Figure 8e earth at subscriber Figure 8f open circuit at exchange or line Figure 8g open circuit at subscriber.
The tests were carried out as explained in relation to Figures 5-7. In each case the X-coordinate of the graph is the voltage measured as X in Figures 5_7 with positive values refering to a positive ring conductor, and the Y~coordinate is the current measured as at Y in Figures 5-7.
The graph of Figure 8b is similar to what would be obtained if the test were carried out in the absence of the fault. It will not, however, generally be necessary iden-tify a lack of a fault by means of a test, The graph may be less steep in the absence of a subscriber fault due to the added resistance of the telephone.
fyt'~91/~1g72 PCf/G~9yl~4. ,9 ~~ ~3'~64 The threshold values of Z1 + Z3 can be seen in Figures 8b and 8e, of Z1 in Figure ~e and of Z2 in Figure 8g.
Figures 9a-9g correspond to Figures 8a-8g, but apply to a modified c.ireuit of Figure 3 where the threshold voltages of Z1,ZZ and Z3 are 3,4 and 5 volts respectively, and where Z3 is reversed. This shows that Z2 need not be higher than both Z1 and Z3.
A particularly preferred device is shown in Figure 10, and the various current-voltage relationships it generates are sh~~an in Figues 11A-ilE. 'this device may be entirely symmetric. and is therefore ideal for European telephone cir-cuits where the imposed polarity is random. The circuit of Figure 10 includes four zener diodes 10, namely Z1,Z2,Z3 and Z4. A short circuit during normal telephone operation and during the ringing tone is avoided by the threshold voltages for Z~ and Z4 being greater than the operating voltage, far example greater than 46 volts which is the DC voltage on which an AG ringing signal is often impressed. The threshold voltages of Z2 and Z4 may conveniently be 100-130 volts. The z~ner diodes Z1 and Z3 may if desired have low threshold voltages, for example in the range of a few volts, for example less than 10 volts, preferably less than 5 volts, especially less than 3 volts. This avoids an unaccep-table DC voltage drip across one of them (across which will depend on the operating plarity) of the DC bias voltage during normal operation. The zener diodes 21 and Z3 may have the same threshold voltage, during but they may nave different voltage in which case earthing at the subscriber of respective lines will be distinguisliable.
The capacitors 9 preferably each have a capacitance of Greater than 5, especially greater than 10 microfarads. The pairs of diodes Z1, Z3 and/or Z2,Z4 may be reversed where W~ 91/11'72 h~f/~1~91/~~29 ~0~~'~~4 15 _ the device is to be used on lines of fixed polarily (as is the case in the USA) one only of the diodes Z1 and Z2 may be reversed.
Because the circuit is symetrical, the current/voltage graphs will be in principle symmetrical. E~ience in Figures 11A-.11E only the top right quadvants of the graphs have been completed, the lower left hand quadrants will be similar, although~the precise threshold voltages may be different.
Figure 11A shows the normal situation when the telephone is not being used. The threshold voltage of Z2 or Z4 (which may be different 5ut are preferably substantially equal) will be apparent.
In Figure 11B an open circuit at the exchange or line results in no current flow.
Earth leakages of two different resistance at the exchange or line is shown in Figure 11C.
The threshold voltage of identical diodes Z1 or Z3 is shown in Figure 11D where there is earth 1°akage on the subsscribers side. Again two different leattage resistances are shown. This system cannot distinguish between a leakage from line 4 and from line 5.
In Figure lltr zener diodes Z1 and Z3 have different threshold voltages allowing the position of a subscriber earth leakage to be determined. The graph shows two leakage resistanees at line a (left hand pair of curves) and at line (right hand pair of curves).
For the avoidance of doubt it is here stated that the invention provides a device for investigating a fault in a telecommunications system where a useful current voltage L! ~'!~°U°T°t°I°~' ~O~a11~872 ~'~'1"6Cg~91la. X29 - ,s relationship can be generated, particularly a threshold voltage which is distinguishable from noise often to be found in telecommunications lines. 'the device may camprise any one or more of the various components interconnected in any of the various ways described herein. nor example any one or more of the zener diodes, capacitors, switches, power souroes, and measuring devices may be selected.
As an example, normal operation of the telecom-munications system may involve current flooring through the first circuit. The capacitors are preferably provided in order that an alternating signal may pass substantially unrestricted to allow a ringing tone (generally an AC signal superimposed on a ~?C bias of usually ~t8 volts) and that a DC
audio signal or other signal may to be passed between the first part and the second part. If the threshold voltage of the first and third (where provided) components together is much less than the operating voltage of the system, the direct current for normal operation may be applied at either polarity. .If the total of the threshold voltages is higher, then normal operation will require connection such that current flows in the opposite direction to that at which the threshold voltages are exhibited. In that ease the polarity has to be reversed for at least part of the test.
~ Wf~ 91i11g'7~ P~"9G~~~/~~.25~
203?6~
_7_ It may be possible that the first and third components exhibit their threshold voltages at opposite polarities, ie they are connected in series back-to-back. In this case the normal operating voltage will need to~be higher than only one of the threshold voltages.
We prefer that the device be able to distinguish between two or more of the following conditions:
1. A short circuit within the first part of" the system (for example the telephone company°s property) 2. An open circuit within the first part A short within the second part tfor example the Subscriber°s property) 4. An open circuit within the second part 5. An earthed conductor within the second part An earthed ring conductor within the first part.
?. An earthed tip conductor within the first part, (The terms °~ring°° and~~tip'~ are standard terms used to distinguish between the two conductors of a line. In a non-symmetrical system, for example as used is the USA, the tip is generally at 0 volts and the ring at -~.$ volts. In Europe and elsewhere, the system is symmetrical and the polarity applied is random.) The device should also be substantially transparent, preferably exhibiting a voltage drop of less than 15 pre_ ferably less than 10 volts, during normal direct current operation of the line. It should also be substantially transparent to alternating current in order that a ringing tone may be transmitted.
The invention is further illustrated with reference to the accompanying drawings, in which:
1J S°t'1'~llTHE°~
~V~ ~l/~187~ P~'4~~9~~( ~9 .
~0~3~4 - g -Figure 1 shows a telecommunications system;
Figure 2 shows a prior art device;
Figures 3 and a show devices of the invention;
Figure 5-7 show various faults in a telecommunications system;
Figures 8 and g show current-voltage relationships obtained from devices of the invention; and Figures 10 and 11 show a preferred device and related current-voltage relationship. __ A telecommunications system is represented schemati-cally in Figure~t. An exchange 1 is connected to a subscriber ~ by a line 3 comprising tip and ring conductors and 5 respectively. The dotted line shows a possible division between the telephone company's responsibility and a subscriber°s responsibility. A device of the invention may be planed in the line 3 at the position of the dotted line in order that one can deter~aine whether a fault is the respon-sibility of the telephone company or the subscriber.
Preferably the devioe of the invention is incorporated in a connection block which also comprises a housing and a telephone socket. The block may be mounted on a wall of a building, The invention may be used at other positions in a telecommunications system and "1°' may be regarded as a first part of a system (as referred to above ) and ~~~°° as a second part.
A prior art device for locating a fault is shown in Figure 2. This device comprises an electrical circuit of two pairs of diodes b, the pairs being in series with the tip ~J and ring 5 conductors respectively. A varistor 7 is connected across the tip and ring conductors. The diodes of each pair are connected in opposite fashion. We have found that this circuit is somewhat susceptible to temperature variation and the current_voltage relationships for the w~ 9,~~i~~~ ~crec~meoo~~g _ g various different faults to be investigated are not suf-ficiently distinct. We have also found that ~he circuit causes some attenuation to a signal during normal use of the line, and requires unacceptably high test voltages.' The present invention adopts a different approach, as is ill ustrated in Figures 3-g.
In,Figure 3 capacitors 9 and zener diodes 10 in parallel are together connected in series with respective conductors of the line. For some investigations a capacitorlzener diode pair may be required in only one of the lines. A zener diode 10 and ordinary diode 11 (ie a diode that is substantially nonconductive in one direction over the voltage range at which it is to be used, preferably up to 80 volts) are connected in opposite fashion between the tip conductor ~i and ring conductor 5. In a modification of this design, component 11 is also a zener diode.
The first and second circuits can now be seen. The first circuit comprises the wen diode Z1 (the first component referred to above) the telephone 8 (or rather a connections therefor since the telephone is not part of the circuit per se) the zener diode Z3, and the two capacitors 9. The second circuit comprises the zener diode Z2 (the second component referred to above) and the ordinary diode 11.
For nornual operation of the telephone a voltage of generally 48 volts is applied between the tip and ring con doctors. (Tip and ring is terminology used in the USA where the line is non-symetric, but it will be used here also to refer to symetric lines although designation of each line will be arbitiary.) The telephone company will first have sent a ringing tone (where the telephone 8 is receiving a Ball) by means of an alternating current, and this can flow ~~ 91/1172 PC.'I°/G1391/0 :9 2~~~3'~~~
in the first circuit through the capacitors 9 with little or no attenuation. The capacitors preferably are substantially transparent to audio frequencies, and preferably have a capacitance of at least 5 microfarads~,especially at least 10 microfarads. The second circuit will not be in use because the threshold value of Z2 is 70 volts, ie greater than the 48 volts operating voltage, and because of the diode 11, In the embodiment illustrated, the zener diodes Z1 and Z3 have threshold voltages of 20 and 30 volts respectively, Since the voltage applied for normal use (48U) is less than the total voltage drop for reverse operation of these diodes (ie the total threshold voltage of the circuit) the circuit will only work at signal frequencies at which the capacitors are substantially transparent. Thus, the capacitors may be chosen.to allow passage of normal audio frequencies.
Preferably the capacitors have a capacitance of at least 10 micrafarads. 4Jhere polarity is predeterztined, preferred values for Z1 and Z3 are 5-40 especially 1S-25 volts for Z1, and 15-~5 especially 25-35 volts for Z2. The total threshold voltage of the first circuit is preferably less than 70 volts, especially 40-60 volts.
A test is made by reversing the polarity so that the tip conductor 4 is negative with respect to the ring conduc-tor 5. The voltage is then increased from 0, up to a value somewhat above the greater of the threshold voltages of the first and second circuits, in this case 70 volts.
The current flowing is measured as a function of voltage.
The current-voltage relationship may be determined continuously over, say, the range 0-75 volts, or it may be sampled at values for example slightly below and above each of the threshold voltages, ie 18,22,28,32,48,52,68 and 72 volts. Ldhat is desired is a different current-voltage rela-tionship for each fault. The path the current takes, and '~'~ ~l/1i~72 PCf/~~9~/~129 therefore the zener diode or diodes whose threshold value or values must be reached, will depend on the location of the fault. Examples are given for various faults in Figures 8 and 9.
The device shown in Figure 4 is a modification of that of Figure 3, designed for normal telephone operation under either polarity. Again, component 11 may be a zener diode thus making the device completely symetric. __ Since the telephone 8. must work under either polarity, zener diodes 21 arid Z3 must not provide an excessive voltage drop for either direction of current flow in this ease we prefer that each has a threshold voltage of 15 volts or less, preferably less than 10 volts, more preferably less than ?,volts, and that their combined threshold voltage is less than 2p volts. It is also desirable that their threshold voltages be different (to be explained below) and we prefer values of 1.5~4, especially 2.5.3.5 volts, and 4-7 especially 4.5 to 5.5 volts.
Again, since current may flow in either direction during normal telephone operation, the threshold voltage of Z2 must be greater than the normal operating voltage, usually 48 volts. If this were not so, the telephone would be short circuited by the second circuit during normal operation under one of the two polarities.
In Figure 4 a telephone or other equipment 8 is repre-sented by its resistance, and the resistances of the lines are shown as 12. A reverse polarity switch 13 connects the line to a source of variable voltage power 14 for testing, During testing the applied voltage is measured at X and the current flowing is measured at Y, for example by measuring the voltage drop across a known resistor. 'The outputs from voltmeter X and ammeter Y may be plotted as the X and Y axes of a graph, as shown in Figures $ and 9.
~ S7°'i~°U°~'H1°
iW~ 91/11g'~Z ~G°fAGI;Il/~" '9 20~3~64 Figure 4 therefore shows a control unit C, a line (and exchange etc) L a device of the invention D and a subscribe rs telephone S. The device D will determine whether a fault falls in region G or region S and whether that fault is a short. circuit, an open circuit or an earth.
Figure 5 shows an open circuit 1~ at the subscriber.
On application of a voltage for testing, any current must flow thr~ugh the second circuit, and this will be_indicated by a current-voltage above showing, if line 5 is made posi_ tine, the threshold voltage of the second component, ie zener diode Z2. If line 4 is made positive, no current will flow due to diode 11. An open circuit on the exchange side, ie region L of Figure ~d, would prevent current flowing completely, Figure 6 shows a short 16 on the exchange side, The current-voltage curve will. now show no threshold voltage since the current path involves neither the first nor second circuit. The slope of the curve will be substantially constant, and will give the resistance of the line (together with that of the short itself). The same result will be obtained for either polarity.
In Figure 7 the fault is an earth connection 17 at the subscriber. This is revealed by applying the test voltage between one of the conductors 4 and 5, and earth. In general it will be necessary only to apply the voltage bet-ween one of the conductors and earth, but the test may be continued using the other conductor. The current will now flow through part of the first curcuit, ie through the zener diode Z1, but not through the zoner diode Z3~ The current-voltage curve will therefore exhibit the threshold voltage of Z1 when conductor 5 is positive and no threshold voltage when conductor ~ is negative with respect to earth. If the ~~ ~~>xi~az ~~o~~~~»i~~
~ ~3 _ voltage were applied between the other conductor and earth, the theshold voltage of Z3 would be exhibited. It will not always be necessary to extend the test over both polari-ties since this will depend on the amount of information required, and on the ahreshold values of the circuits. An earth fault on the exchange side will mean no current will flow through the first or second circuits, and the current-voltage,curve will not show a threshold voltage. This fault is however distinguishable from the fault of Figure 6 because different tests are required to produce the similar current-voltage curves. Also, the curves will be slightly different since the resistances of the two resulting current paths are likely to be different.
Figure 8 shows the current-voltage curves produced from the device of Figure 3 under the following faults Figure 8a short at exchange or line Figure 8b short at subscriber Figure 8c earth at exchange or tip conductor of line Figure 8d earth at exchange or ring conductor of line Figure 8e earth at subscriber Figure 8f open circuit at exchange or line Figure 8g open circuit at subscriber.
The tests were carried out as explained in relation to Figures 5-7. In each case the X-coordinate of the graph is the voltage measured as X in Figures 5_7 with positive values refering to a positive ring conductor, and the Y~coordinate is the current measured as at Y in Figures 5-7.
The graph of Figure 8b is similar to what would be obtained if the test were carried out in the absence of the fault. It will not, however, generally be necessary iden-tify a lack of a fault by means of a test, The graph may be less steep in the absence of a subscriber fault due to the added resistance of the telephone.
fyt'~91/~1g72 PCf/G~9yl~4. ,9 ~~ ~3'~64 The threshold values of Z1 + Z3 can be seen in Figures 8b and 8e, of Z1 in Figure ~e and of Z2 in Figure 8g.
Figures 9a-9g correspond to Figures 8a-8g, but apply to a modified c.ireuit of Figure 3 where the threshold voltages of Z1,ZZ and Z3 are 3,4 and 5 volts respectively, and where Z3 is reversed. This shows that Z2 need not be higher than both Z1 and Z3.
A particularly preferred device is shown in Figure 10, and the various current-voltage relationships it generates are sh~~an in Figues 11A-ilE. 'this device may be entirely symmetric. and is therefore ideal for European telephone cir-cuits where the imposed polarity is random. The circuit of Figure 10 includes four zener diodes 10, namely Z1,Z2,Z3 and Z4. A short circuit during normal telephone operation and during the ringing tone is avoided by the threshold voltages for Z~ and Z4 being greater than the operating voltage, far example greater than 46 volts which is the DC voltage on which an AG ringing signal is often impressed. The threshold voltages of Z2 and Z4 may conveniently be 100-130 volts. The z~ner diodes Z1 and Z3 may if desired have low threshold voltages, for example in the range of a few volts, for example less than 10 volts, preferably less than 5 volts, especially less than 3 volts. This avoids an unaccep-table DC voltage drip across one of them (across which will depend on the operating plarity) of the DC bias voltage during normal operation. The zener diodes 21 and Z3 may have the same threshold voltage, during but they may nave different voltage in which case earthing at the subscriber of respective lines will be distinguisliable.
The capacitors 9 preferably each have a capacitance of Greater than 5, especially greater than 10 microfarads. The pairs of diodes Z1, Z3 and/or Z2,Z4 may be reversed where W~ 91/11'72 h~f/~1~91/~~29 ~0~~'~~4 15 _ the device is to be used on lines of fixed polarily (as is the case in the USA) one only of the diodes Z1 and Z2 may be reversed.
Because the circuit is symetrical, the current/voltage graphs will be in principle symmetrical. E~ience in Figures 11A-.11E only the top right quadvants of the graphs have been completed, the lower left hand quadrants will be similar, although~the precise threshold voltages may be different.
Figure 11A shows the normal situation when the telephone is not being used. The threshold voltage of Z2 or Z4 (which may be different 5ut are preferably substantially equal) will be apparent.
In Figure 11B an open circuit at the exchange or line results in no current flow.
Earth leakages of two different resistance at the exchange or line is shown in Figure 11C.
The threshold voltage of identical diodes Z1 or Z3 is shown in Figure 11D where there is earth 1°akage on the subsscribers side. Again two different leattage resistances are shown. This system cannot distinguish between a leakage from line 4 and from line 5.
In Figure lltr zener diodes Z1 and Z3 have different threshold voltages allowing the position of a subscriber earth leakage to be determined. The graph shows two leakage resistanees at line a (left hand pair of curves) and at line (right hand pair of curves).
For the avoidance of doubt it is here stated that the invention provides a device for investigating a fault in a telecommunications system where a useful current voltage L! ~'!~°U°T°t°I°~' ~O~a11~872 ~'~'1"6Cg~91la. X29 - ,s relationship can be generated, particularly a threshold voltage which is distinguishable from noise often to be found in telecommunications lines. 'the device may camprise any one or more of the various components interconnected in any of the various ways described herein. nor example any one or more of the zener diodes, capacitors, switches, power souroes, and measuring devices may be selected.
Claims (18)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A device capable for use in investigating a fault in a telecommunications system comprising a first and a second part interconnected by a line, which device comprises:
(a) a first circuit that can be connected in series with the line and comprising a first capacitor and a first component, such that an alternating current can pass along the line via the capacitor and a direct current can pass along the line via the first component in at least one direction with a threshold voltage; and (b) a second circuit that can be connected in parallel across the line and comprising a second component having a threshold voltage of greater than 48 volts and/or being able to pass direct current only in one direction.
(a) a first circuit that can be connected in series with the line and comprising a first capacitor and a first component, such that an alternating current can pass along the line via the capacitor and a direct current can pass along the line via the first component in at least one direction with a threshold voltage; and (b) a second circuit that can be connected in parallel across the line and comprising a second component having a threshold voltage of greater than 48 volts and/or being able to pass direct current only in one direction.
2. A device according to claim 1, which additionally comprises a second capacitor and a third component exhi-biting a threshold voltage (as herein defined), the first capacitor and first component being connected in parallel with each other and being each connectable in series with a first conductor of the line; and the second capacitor and third component being connected in parallel with each other and being each connectable with a second conductor of the line.
3. A device according to claim 1 or 2, in which the first capacitor, and where present the second capacitor, has a capacitance of at least 10 microfarads.
4. A device according to any preceding claim, in which the first circuit has a threshold voltage of less than 20 volts and the second component has a threshold voltage greater than 48 volts and the second circuit can pass direct current in only one direction.
5. A device according to claim 4, in which the threshold value of the second component is from 55.90 volts.
6. A device according to claim 5, in which the threshold value of the second component is from 65-75 volts.
7. A device according to any of claims 4,5 and 6 in which the threshold voltage of the first component is less than 7 volts.
8. A device according to claim 7, in which the threshold voltage of the first component is from 4-7 volts and that of the second component where present is from 1.5-4 volts,
9. A device according to any of claims 1-3, in which the first circuit has a threshold voltage of 20-70 volts.
10. A device according to any preceding claim, in which the threshold voltage of the second circuit is greater than that of the first circuit.
11. A device according to claim 10, in which the threshold value of the second circuit is at least 15 volts greater than that of the first circuit.
12. A device according to any preceding claim in which the second circuit has a diode by means of which it is able to pass current in only one direction.
13. A device according to any preceding claims in which one or more of the first, second and where provided third com-ponents is a zener diode.
14. A device capable for use in investigating a fault in a telecommunications system comprising a first and a second part interconnected by a line, which device comprises:
(a) a first circuit that can be connected in series with the line and comprising a first component, such that an alternating current can pass along the line and a direct current can pass along the line via the first component in at least one direction with a threshold voltage; and (b) a second circuit that can be connected in parallel across the line and comprising a second component comprising at least one zener diode and having a threshold voltage of greater than 48 volts and/or being able to pass direct current only in one direction.
(a) a first circuit that can be connected in series with the line and comprising a first component, such that an alternating current can pass along the line and a direct current can pass along the line via the first component in at least one direction with a threshold voltage; and (b) a second circuit that can be connected in parallel across the line and comprising a second component comprising at least one zener diode and having a threshold voltage of greater than 48 volts and/or being able to pass direct current only in one direction.
15. A device according to claim 14 in which the second com-ponent comprisess two zener diodes back-to-back.
16. A device capable for use in investigating a fault in a telecommunications system comprising a first and a second part interconnected by a line, which device comprises:
(a) a first circuit that can be connected in series with the line and comprising a first component, comprising a zener diode, such that an alternating current can pass along the line via the capacitor and a direct current can pass along the line via the first component in at least one direction with a threshold voltage; and (b) a second circuit that can be connected in parallel across the line and comprising a second component having a threshold voltage of greater than 48 volts and/or being able to pass direct current only in one direction.
(a) a first circuit that can be connected in series with the line and comprising a first component, comprising a zener diode, such that an alternating current can pass along the line via the capacitor and a direct current can pass along the line via the first component in at least one direction with a threshold voltage; and (b) a second circuit that can be connected in parallel across the line and comprising a second component having a threshold voltage of greater than 48 volts and/or being able to pass direct current only in one direction.
17. A connection black for a telephone, comprising a housing, a telephone socket and a device according to any preceding claim.
18. A method of remote investigation of a telecom-munications system having a device according to any of claims 1-16 connected between (a) a first part and a line thereof and (b) a second part thereof, which comprises applying selected voltages to the line from the first part and measuring the current flowing at the first part.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB909002171A GB9002171D0 (en) | 1990-01-31 | 1990-01-31 | Maintenance telecommunications unit |
| GB9002171.8 | 1990-01-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2073764A1 true CA2073764A1 (en) | 1991-08-01 |
Family
ID=10670198
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002073764A Abandoned CA2073764A1 (en) | 1990-01-31 | 1991-01-30 | Telecommunications line test system |
Country Status (10)
| Country | Link |
|---|---|
| EP (1) | EP0513101A1 (en) |
| JP (1) | JPH05504452A (en) |
| KR (1) | KR920704487A (en) |
| AU (1) | AU7189591A (en) |
| BR (1) | BR9105973A (en) |
| CA (1) | CA2073764A1 (en) |
| FI (1) | FI923435A0 (en) |
| GB (1) | GB9002171D0 (en) |
| LV (1) | LV10552B (en) |
| WO (1) | WO1991011872A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6895081B1 (en) | 1999-04-20 | 2005-05-17 | Teradyne, Inc. | Predicting performance of telephone lines for data services |
| GB2355361B (en) | 1999-06-23 | 2004-04-14 | Teradyne Inc | Qualifying telephone lines for data transmission |
| EP1260085A2 (en) * | 2000-02-24 | 2002-11-27 | Teradyne, Inc. | Method and apparatus for termination detection in an adsl environment |
| GB0005227D0 (en) | 2000-03-03 | 2000-04-26 | Teradyne Inc | Technique for estimatio of insertion loss |
| GB2365253B (en) | 2000-07-19 | 2004-06-16 | Teradyne Inc | Method of performing insertion loss estimation |
| US7042983B2 (en) | 2000-10-19 | 2006-05-09 | Teradyne, Inc. | Method and apparatus for bridged tap impact analysis |
| US7386039B2 (en) | 2003-09-26 | 2008-06-10 | Tollgrade Communications, Inc. | Method and apparatus for identifying faults in a broadband network |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4415779A (en) * | 1981-06-15 | 1983-11-15 | Western Electric Company, Inc. | Methods of and apparatus for testing telephone subscriber loop to locate a fault relative to a reference point |
| DE3148740C2 (en) * | 1981-12-05 | 1985-04-11 | Fritz Kuke Kg, 1000 Berlin | Termination for telephone lines |
-
1990
- 1990-01-31 GB GB909002171A patent/GB9002171D0/en active Pending
-
1991
- 1991-01-30 BR BR919105973A patent/BR9105973A/en not_active Application Discontinuation
- 1991-01-30 EP EP91903294A patent/EP0513101A1/en not_active Ceased
- 1991-01-30 AU AU71895/91A patent/AU7189591A/en not_active Abandoned
- 1991-01-30 CA CA002073764A patent/CA2073764A1/en not_active Abandoned
- 1991-01-30 WO PCT/GB1991/000129 patent/WO1991011872A1/en not_active Application Discontinuation
- 1991-01-30 KR KR1019920701812A patent/KR920704487A/en not_active Application Discontinuation
- 1991-01-30 JP JP3503794A patent/JPH05504452A/en active Pending
-
1992
- 1992-07-30 FI FI923435A patent/FI923435A0/en not_active Application Discontinuation
- 1992-12-30 LV LVP-92-631A patent/LV10552B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| LV10552A (en) | 1995-02-20 |
| FI923435A (en) | 1992-07-30 |
| GB9002171D0 (en) | 1990-03-28 |
| BR9105973A (en) | 1992-11-03 |
| AU7189591A (en) | 1991-08-21 |
| KR920704487A (en) | 1992-12-19 |
| EP0513101A1 (en) | 1992-11-19 |
| FI923435A0 (en) | 1992-07-30 |
| LV10552B (en) | 1995-04-20 |
| WO1991011872A1 (en) | 1991-08-08 |
| JPH05504452A (en) | 1993-07-08 |
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