GB2226642A - Cable testers - Google Patents

Abstract

To test a multi-conductor cable 13, a test signal from a shift register (51) of a transmitter (11) is transmitted (53) in turn along each of the wires (14) to be tested and it passively returns along all the other wires (14). LED indictors (15) of the transmitter (11) show which wire (14) is being tested and indicators (16) show whether the loop resistance is higher than it should be. The receiver (12) includes corresponding LED indicators and diodes for the return current paths. The equipment is switchable with regard to the number of connector wires (14) it is to test, and capable when that number has been tested of automatically finishing (52) the test and readying itself for a new test. <IMAGE>

Description

Cable Testers This invention concerns cable testers, and relates in particular to apparatus for testing multi-conductor cable in order to identify and locate wiring errors and faults.

It is nowadays very common, particularly in the computer field, to employ signal-carrying cables that are composed of a plurality of individual wires within a single protective sheath or casing. In a computer network, for example, individual terminals may be connected each by such a multi-core cable into a network with a controlling computer (or perhaps a file server).

The actual physical configuration of the network may take many forms - star, bus or ring, for instance - but as an example a bus network will employ what is effectively a single length of multi-core cable having spaced connection points therealong for each terminal, whereas a star network will provide a separate set of conductors for each terminal but for convenience all the sets may be gathered together into a single cable. This latter type of installation is commonly found in the networks used in supermarkets; a single multi-core cable runs the length of the line of checkouts, with connectors for its various component wires being taken off in turn and led to the individual cash registers, bar code readers and so on at each checkout point.

Whenever such a multi-connector cable is installed, and regularly during the life of the network it serves, it will be desirable to test the wires to ensure that they are indeed properly connected to the relevant input /output plug/socket (to which the "terminal equipment" is attached). The test should indicate whether each wire within the cable is unbroken, is properly insulated from (and so not shorted to) any of the other wires, and is connected between the expected points (to the correct pin of a socket, for example) rather than "crossed" with some other wire.Until relatively recently this type of test has only been possible using test equipment that can actually connect up both "ends" of the relevant length of cable - thus, for instance, the end attachable to a computer network's controlling computer and one or other of the "ends" representing the terminal attachment points. It will immediately be apparent that this requirement will only easily be met if the relevant pair of ends are physically adjacent, otherwise the test equipment must invtlv, scme additional "connection" means (such as its own cabling) long enough to extend between the two furthest apart ends to be tested.

Recently, however, there has been introduced a new, and very much improved, method of testing a length of multi-core cable, which merely requires two separate pieces of test equipment to be connected one to each of the pair of "ends" under test, and does not require the two pieces themselves to be independently connected. In brief, this new method involves sending a test signal in turn along each of the cable-contained connector wires to be tested, and passively returning the signal along all the other wires under test. The transmitter, or scanner, unit, which scans the wires at a rate of about one per second, includes indicators both to show which wire is presently being scanned ("polled") and to show whether the out-and-return loop resistance is higher than it should be (denoting either a poor connection or an actual break - an open circuit).The receiver, or terminator, unit also includes corresponding indicators to show which wire is presently being polled (if the wires are crossed the relevant pair of indicators will be actuated in the wrong order, out of the known, predetermined sequence), to show whether a line is broken (the indicator is then not activated when it should be), and to show whether two (or more) wires are shorted together (all the relevant indicators will be activated).

The equipment presently in use with this new method works quite satisfactorily, but is at the moment limited to testing a maximum of eight wires at a time. Whilst this does not mean that the equipment cannot be employed to test multi-core cables containing more than eight connector wires, it does mean that the testing of these bigger cables necessitates physically plugging (unplugging) the transmitter into the "main" end of the cable several times (each time connecting (disconnecting) it to a different set of eight wires, which can be rather a nuisance. Accordingly, it has now been proposed that the equipment be re-designed so as to test many more wires (say, up to 64) at a time - and the invention is concerned with this re-designed equipment.

Of course, it will often be that the cable to be tested contains less than the maximum number of wires thus, it may contain only eight wires, or it may contain 15, 25, 35, 40 or 50 wires (such cables are all quite common in the Art). In those circumstances, the invention proposes, therefore, that the equipment be further re-designed firstly so as to be switchable with regard to the number of connector wires it is to test, and secondly so that when in use that number has been tested the equipment finishes the test and readies itself for a new test.

In one aspect, therefore, the invention provides a method of testing the component connector wires of a length of multi-connector cable, in which at one end of the length of cable a test signal is applied in turn to each wire of a selected subset of the wires in the cable, whereafter the test is concluded, and the test equipment is readied for another test.

In a second aspect the invention provides equipment for testing the component connector wires of a length of multi-connector cable, which equipment includes a test signal transmitter connectable to one end of the length of cable and adapted to apply that test signal in turn to c-acl wire in the cable, which transmitter includes: wire subset selector means, for selecting for test either the whole set of wires or one of a group of predetermined subsets thereof; and test ending means, for concluding the test when the selected subset of wires has been tested, and for then readying the equipment for another test.

The invention relates to the testing of multiconnector (multi-core; multi-wire) cable, and at one end of the cable transmits a test signal to each wire in turn. Though no doubt it could be implemented some other way, this is most conveniently achieved in the same manner as is presently used in the 8-wire system described hereinbefore - that is, with separate transmitter (scanner) and receiver (terminator) units, indicator means, and so on. This is discussed in more detail hereinafter.

It is one feature of the invention that the equipment include subset selector means by which there may be selected for test either the whole set of wires or one subset from a group of predetermined subsets thereof, the test signal then being applied in turn to each wire in that subset. If the whole set of wires can be regarded as being in a sequence starting with a particular wire, the chosen subset will most conveniently be a shortened version of that sequence ie, it will start with the same start wire, and continue with all the wires in the same order, but end before it reaches the whole set's final wire. Thus, instances of possible subsets of 64 wires might be the first 8, the first 15, the first 25 . .. and so on (it is indeed quite possible to select all 64 such sequences - the first I, tne first 2, the first 3, 4, 5, . . . 63, 64).

The "mechanical" method of making the subset selection is by a switch - conveniently a conventional wiper switch - while the "electronic" method of making the connection (of determining what happens electrically when the subset is thus defined) is most conveniently to have the switch select for connection thereto the last wire in the defined subset sequence, and then use the test signal input to that wire - and thus, now, to the switch - to initiate whatever test-concluding action is required.

In the invention the test is concluded, and the equipment readied for another test, using the test ending means, when the selected subset of wires has been tested. Just how this is done depends upon the details of the equipment employed. For example, if the choosing of each wire in turn were controlled by a counter, then the testing of the final wire in the subset could be used as a signal to re-set the counter - and so to re-select the first wire (thus readying the equipment for another test). In the preferred form of the equipment of the invention, however, the sequential selection of each wire in turn is controlled by a clockdriven shift register (in one actual embodiment there are employed two 32-bit shift registers in series, making what is in effect a single 64-bit shift register).Each register location is operatively connected to the input of an operational amplifier whose output is connected to the relevant wire within the cable under test; a single pulse is passed along the register(s), and as it passes in turn from one shift register location to the next it conditions the correct one of the corresponding series of amplifiers to output the test signal to the wire connected thereto.

Witn the subset selector means suitably connected to the last wire in the chosen subset, this same test signal can then be used to enable a shift register reset - and thus both to end the test and to ready the equipment for another test. An alternative, and preferred, way to conclude the test (and ready the equipment for another) once the chosen number of wires has been polled is to poll the remaining wires at a much higher rate. This has certain advantages over a straight re-set. Thus, it can be effected with somewhat simpler electronics, and it can be arranged to give a visual indication that the remainder of the transmitter's circuitry (the amplifiers, indicators and so on) are still working.Accordingly, it is particularly preferred if, when all the wires in the chosen subset have been tested in turn, the remaining transmitter outputs be polled in turn (and in sequence) but at a higher rate (so as to reach the final output in a relatively short time), whereupon the equipment is readied for another test. By way of example, the chosen subset might be polled at a rate of one per second, whilst the remainder might be run through at the higher rate of five, or even ten, per second. In one particular embodiment of this a shift-registercontrolled system has two driving clocks, one faster than the other; the slow one is selected (either its output is enabled, or the other's is inhibited) for the test proper, whilst the fast one is similarly selected to run through the remainder after those in the chosen subset have been polled.

As has been noted hereinbefore, the invention conveniently involves the use of separate transmitter (scanner) and receiver (terminator) units, each with indicators to show when each wire is being scanned (polled > , the receiver being a "passive" device that simply accepts the test signal along one wire and connects it, for "output", to be fed back to the transmitter along all the other wires. Though this necessitates the actual transmitter devices (normally operational amplifiers) within the transmitter unit being both source and sink devices, it has the very considerable advantage that no extra, "external" wires are needed, and the receiver unit can be an unpowered one.

Various embodiments of the invention are now described, though by way of illustration only, with reference to the accompanying Drawings in which Figure 1 shows in diagrammatic form the use of the equipment of the invention to test a length of multi-core cable; Figure 2 shows a circuit (block) diagram of a transmitter/receiver pair of the invent ion; Figure 3 shows a timing diagram for the circuit of Figure 2; and Figure 4 shows a detail of the circuit of Figure 2.

Figure 1 shows a general view of the use of equipment according to the invention to test a multicore cable. The equipment is in two parts, namely a battery-powered scanner (transmitter) unit (11) and an unpowered terminator (receiver) unit (12). The scanner unit 11 when connected to an installed data cable (13) to be tested sequentially applies a test signal to each conductor (as 14) in turn (as shown in Figure 2 hereinafter, it actually raises the potential of each conductor 14 in turn relative to all the remaining conductors in the group being tested). The scanner 11 is fitted with a grouped display of 64 red LEDs (as 15), one LED for each scan step (64 in the case of this unit), thus indicating the conductor selected for test in the scan program. Two further LEDs (16, 17) are fitted to the scanner unit 11, both green.LED 16 glows in conjunction with each LED in the scan if the out-andback "loop" resistance of the selected conductor 14 exceeds a preset value. LED 17 is used in conjunction with a flying lead (18) having an earthing clip fitted to it. This lead is intended to be attached to a convenient "earth" point (19), and will cause the LED to glow in conjunction with any scan-selected conductor 14 which has a full or partial conduction to earth.

The terminator unit 12 is designed to be plugged into an outlet (20) at the end of each segment 13 of the data cable installation, with the scanner unit 11 connected to a socket (21) at the start of the cable "run". This terminator unit 12 provides indication, via a group of 64 red LEDs (as 22; the display matches that on the scanner unit), of which conductor 14 in the cable is presently selected and being scanned. If the wiring order between the scanner and the terminator is correct - ie, true point to point - the terminator LEDs will glow in strict sequential order (in correspondence with the scanner LEDs).

Wiring fault determination is then given by the order - the incorrect order - in which the terminator's LEDs glow. Wires crossed or interchanged with each other will be indicated by their assigned LEDs 22 being illuminated in their interchanged order. Wires broken, or with their connections not made, will be indicated by their respective LEDs 22 not glowing at all. Wires which are shorted together (two or more) will be indicated by their respective LEDs 22 glowing together as they are scanned.

As is explained hereinafter, the circuit arrangement in the terminator unit 12 together with that of the scanner unit 11 completely negates the need for any one of the group of conductors 14 under.test to be a "common" return connector. This arrangement has the advantage that it additionally makes possible the identification of each conductor 14 even within a group of unidentified conductors. The procedure is as follows.

a) Select any two conductors 14 of the group.

b) Connect them to any two inputs to the terminator, and note their LEDs' position and time relationship with each other. This enables determination of their actual termination positions, and they may then be terminated correctly relative to the scanner unit.

c) Pick any other connector, and connect it at random, noting its associated LED' s relevant time of glow, which will determine its true connection. Re-connect it correctly.

d) Repeat the last step for all the other conductors.

The particular embodiment described has the capacity to check up to 64 conductors. However, this number has only be chosen for commercial reasons, and the circuit design (see below), being modular, may be extended to "infinity", only limited by the physical number of LEDs required.

In the event that it is required to check a lesser number of conductors, and in order to save time under those circumstances, the scanner unit 11 includes circuitry and a selector switch (25) which allows the scan to end at a selected point in the overall sequence, and then rapidly return to the start (scanning sequences are usually repetitive until the scanner is actually switched off). The pre-selected quantities of wire scanned - the subset sizes - may be "infinitely" variable throughout the overall range. Thus, for a total scan capacity of 64, a 64-position switch 25 could be fitted. However, it will generally suffice to pick a few of the more common possibilities, namely 15, 25, 35 and so forth, as mentioned hereinbefore.

The block circuit diagram of Figure 2 shows the main components of this embodiment. There is a separate scanner unit 11 and terminator unit 12, joined only by the cable under test (13; represented simply by some of the individual conductor wires 14 from which it is made).

The scanner unit 11 contains a shift register 51 driven by one or other of two clocks - a slow, scan speed clock (A) and a fast clock (B > - selected via a bistable (52). Each location in the shift register 51 has an associated operational amplifier (as 53), with both source and sink capability, and each amplifier's output is fed both to one of the conductors 14 and to an LED indicator 15. The scanner unit 11 also contains an out/back loop high resistance LED indicator 16 and an earth leakage LED indicator 17.

The terminator unit 12 contains merely the series of indicator LEDs 22, each of which is connected to a common bus, the voltage thereon being fed back past all the other LEDs 22 to their cable conductors 14 and thus to the associated amplifiers 53 (hence the need for each to have sink as well as source capability).

The circuitry of Figure 2 operates as follows: At initial switch-on, the following conditions are set up coincidentally:- a) An input (logic level 1) is applied to the shift register input for a controlled period of time.

b) The reset control line to the bistable is held to logic 0 for a controlled period of time. This ensures the clock inhibit to the fast clock (B) is applied and that there is no inhibit applied to the scan speed clock (A).

c) The first clock "on" period is arranged to be present before the shift register input is removed.

A timing diagram for the circuit is shown in Figure 3; these conditions are always re-applied at the end of the total possible scan (in this case, 64) H- "ing set the scan clock in operation, for every positive-going excursion of the clock the logic level 1 applied to the shift register 51 input is shifted along the register. The change in state of the output of each segment of the shift register causes the associated amplifiers 53 also to change their output state. There is one amplifier for each shift register stage. Since the transfer from one shift register stage to another is instantaneous upon application of a positive-going clock pulse, there is applied a "strobe" facility to all the amplifiers at the same time - this only allows the selected amplifier's output to rise during the time for which the strobe is applied.Since the clock is at Logic 1 for 50% of its total period, the strobe control is also the clock output (the reason for the 50% duty cycle is both to preserve battery life and to allow the eye more easily to follow the LED displays at both the scanner and the terminator).

The amplifiers' outputs are used directly to turn on LEDs 15 to indicate the scan step. They are also directly applied to each of the conductors 14 within the cable segment 13 under test. An important feature is the ability of the amplifier outputs to both source (LEDs turn on) and sink (LEDs off) current. It is this characteristic which makes possible the design of the "powerless" terminator 12, and negates the need for a common return conductor for the terminator LEDs 22. It is important to note that the current source ability must be greater than the current sink ability. This makes possible the indication of "shorted together" conductors 14 under test, since the drive current of the selected amplifier 51 has to overcome the current sink effect of the amplifier associated with any other conductor to which it may be shorted.

The scan speed clock A will continue until the bistable 52 changes state. This will occur when the scan step selected by the switch 25 is reached. The bistable will change state on the falling (lagging) edge of the associated amplifier output. Upon the bistable 52 changing state, its outputs now apply an inhibit to the scan speed clock (A: output held to 0 volts) and remove the inhibit from the fast clock B. The scan is now quickly moved through to the last stage, when its falling edge causes the bistable to reset and restore the original set-up conditions.

Resistor R, is required to balance the brilliance of the scanner LEDs 15 to those 22 in the terminator.

The effective voltage drop across this resistor is the difference between the battery 0 volts and the low voltage level of the drive amplifiers plus the voltage "drop" across one diode (0. 6V). The voltage varies according to the resistance in the selected conductor under test. This fall is used to indicate, by the "resistance high" LED 16 and its amplifier (54), any conductor 14 which, for any reason - poor solder joints etc. - has a resistance greater than a preset level.

This level is set by pre-setting the "set trip level" potentiometer (55) shown in the diagram. A similar circuit arrangement (LED 17, amplifier 56, potentiometer 57) is used to indicate any conductor which may be partially or fully connected to earth. Both the amplifiers 54, 56 used for these two facilities are configured as Schmitt triggers - ie, a hysteresis characteristic is added.

Figure 4, which is "part" of Figure 2, helps to provide an understanding of how the Figure 2 circuit works. Imagine that it is scan step 1, and line 1 is under test. The conductor A voltage is higher than that of conductor B (scan step 2 is not yet selected, therefore the voltage is still low), and current flows from A through LED E which glows, and returns via diode K to B the current sink (voltage low point) at the output of scan amplifier 2 (if the wires A and B were reversed at a connector, for scan step 1 LED F at the terminator would glow, not E).

As the scan steps from 1 to 2, the current flow is reversed, and LED F in the terminator glows.

As will be clear from the Figures and the associated description, the total circuit of the multiconduct or test equipment is contained within two physical parts - viz, the scanner 11 and the terminator 12. The purpose of both parts of the circuit when connected together via the cable 13 to be tested is to provide information about each conductor 14 regarding a) non connection, b) connections made incorrectly (wrong destination of conductor), c) conductors having interchanged positions within a connector, d) conductors "short circuited" to each other or in groups, e) conductors poorly connected producing an effective "high resistance" conductor, and f) partial or full connection to earth. These checks are performed by sequentially sampling each conductor in turn as determined by the scanner. Items a) to d) are indicated by the terminator unit.Items d) to f) are indicated by the scanner unit (item d) is indicated by both units).

Should the scan (step) capacity of the scanner be excessive compared with the number of conductors to be checked, provision is made to speed up the scan rate beyond that required and to return the scanner to the start of the next cycle quickly. This saves testing time.

Three other important aspects are achieved with the preferred circuit. They are: 1) no one conductor within the group is relied upon as a common return conductor; 2) no extra conductors are needed between the scanner and the terminator; 3) no power source is required at the terminator (the equipment is totally powered at the scanner).

It is an important feature of the preferred form of circuit (as in Figure 2) that the amplifier devices 53 directly connected to the conductors 14 to be checked (at the scanner) must be able to both source and sink current. Furthermore, the sink capability must be less than the source capability.

Claims (9)

1. Equipment for testing the component connector wires of a length of multi-connector multi-core cable, which equipment includes a test signal transmitter connectable to one end of the length of cable and adapted to apply that test signal in turn to each wire in the cable, which transmitter includes: wire subset selector means, for selecting for test either the whole set of wires or one of a group of predetermired subsets thereof; and test ending means, for concluding the test when the selected subset of wires has been tested, and for then readying the equipment for another test.

2. Test equipment as claimed in Claim 1, which includes separate transmitter (scanner) and receiver (terminator) units, which units are unconnected save by the cable under test, and wherein the receiver unit passively returns the test signal, received along one wire, along all the other wires.

3. Test equipment as claimed in either of the preceding Claims, which includes subset selector means by which there may be selected for test a subset of wires from a group of predetermined subsets thereof, and each subset is a shortened version of the sequence of the whole set of wires, starting with the same wire and continuing with all the wir-es in the same order, but ending before it reaches the whole set's final wire.

4. Test equipment as claimed in any of the preceding Claims, wherein the "mechanical" method of making the subset selection is by a wiper switch, while tne "electronic" method of making the connection is to have the switch select for connection thereto the last wire in the defined subset sequence, and then to use the test signal input to that wire - and thus, now, to the switch - to initiate whatever test-concluding action is required.

5. Test equipment as claimed in any of the preceding Claims, wherein the sequential selection of each wire in turn is controlled by a clock-driven shift register; each register location is operatively connected to the input of an operational & plifier whose output is connected to the relevant wire within the cable under test; and a single pulse is passed along the register(s), and as it passes in turn from one shift register location to the next it conditions the correct one of the corresponding series of amplifiers to output the test signal to the wire connected thereto.

6. Test equipment as claimed in any of the preceding Claims, wherein with the subset selector means suitably connected to the last wire in the chosen subset, the test signal is used to trigger polling of the remaining wires at a much higher rate than that employed when polling the chosen subset.

7. Test equipment as claimed in Claim 6, wherein there is employed a shift-register-controlled system with two driving clocks, one faster than the other; the slow one is selected for the test proper, whilst the fast one is similarly selected to run through the remainder after those wires in the chosen subset have been polled.

8. Multi-connector multi-core cable test equipment as claimed in any of the preceding Claims and substantially as described hereinbefore.

9. A multi-connector multi-core cable test method as claimed in Claim 8 and substantially as described hereinbefore.

9. A method of testing the component wires of a length of multi-connector multi-core cable, in which at one end of the length of cable a test signal is applied in turn to each wire of a selected subset of the wires in the cable, whereafter the test is concluded, and the test equipment is readied for another test.

10. A method as claimed in Claim 9 and using equipment as defined in any of Claims 1 to 8.

11. A multi-connector multi-core cable test method as claimed in either of Claims 9 and 10 and substantially as described hereinbefore.

Amendments to the claims have been filed as follows 1. Equipment for testing the component connector wires of a length of multi-connector multi-core cable, which equipment includes: a test signal transmitter connectable to one end of the length of cable and adapted to apply that test signal in turn to each wire in the cable; and a test signal receiver connectable to the other end of the length of cable, the transmitter and receiver being in operation unconnected save by the cable under test, and the receiver passively returning the test signal, received along one wire, along all the other wires; and wherein the transmitter includes wire subset selector means, for selecting for test either the whole set of wires or one of a group of predetermined subsets thereof, and test ending means, for concluding the test when the selected subset of wires has been tested, and for then readying the equipment for another test.

2. Test equipment as claimed in Claim 1, which includes subset selector means by which there may be selected for test a subset of wires from a group of predetermined subsets thereof, and each subset is a shortened version of the sequence of the whole set of wires, starting with the same wire and continuing with all the wires in the same order, but ending before it reaches the whole set's final wire.

3. Test equipment as claimed in either of the preceding Claims, wherein the "mechanical" method of making the subset selection is by a wiper switch, while the "electronic" method of making the connection is to have the switch select for connection thereto the last wire in the defined subset sequence, and then to use the test signal input to that wire - and thus, now, to the switch - to initiate whatever test-concluding action is required.

4. Test equipment as claimed in any of the preceding Claims, wherein the sequential selection of each wire in turn is controlled by a clock-driven shift register; each register location is operatively connected to the input of an operational amplifier whose output is connected to the relevant wire within the cable under test; and a single pulse is passed along the register(s), and as it passes in turn from one shift register location to the next it conditions the correct one of the corresponding series of amplifiers to output the test signal to the wire connected thereto.

5. Test equipment as claimed in any of the preceding Claims, wherein with the subset selector means suitably connected to the last wire in the chosen subset, the test signal is used to trigger polling of the remaining wires at a much higher rate than that employed when polling the chosen subset.

6. Test equipment as claimed in Claim 5, wherein there is employed a shift-register-controlled system with two driving clocks, one faster than the other; the slow one is selected for the test proper, whilst the fast one is similarly selected to run through the remainder after those wires in the chosen subset have been polled.

7. Multi-connector multi-core cable test equipment as claimed in any of the preceding Claims and substantially as described hereinbefore.

8. A method of testing the component wires of a length of multi-connector multi-core cable, in which, using equipment as defined in any of the preceding Claims, at one end of the length of cable a test signal is applied in turn to each wire of a selected subset of the wires in the cable, whereafter the test is concluded, and the test equipment is readied for another test.

using equipment as defined in any of Claims 1 to 8.