GB2330421A

GB2330421A - A cable testing system

Info

Publication number: GB2330421A
Application number: GB9721760A
Authority: GB
Inventors: Jeremiah Reid
Original assignee: MENTINC ENTERPRISES Ltd
Current assignee: MENTINC ENTERPRISES Ltd
Priority date: 1997-10-09
Filing date: 1997-10-14
Publication date: 1999-04-21
Anticipated expiration: 2017-10-14
Also published as: GB2330421B; IES970737A2; GB9721760D0; IES79035B2

Abstract

A cable testing system (1) has a test instrument (2) which generates Category 5 test signals for cables. A central switch unit (3) connected to a crossconnect frame (10) causes the test instrument (2) to be connected in succession to each of a set of eight cables and the switching is synchronised with switching of a remote switch unit 15 so that it is connected in turn to the same cables at the outlets (12). Integrity of tests is ensured by use of tone generators and detectors for transmission of signals via cable for synchronisation of the central and remote switch units and a separate independent conductor is used for enabling and disabling the instrument (2) for the testing cycles. A malfunction timer (41) in a simple way detects malfunction in any parts of these circuits. The cable may then be tested by time domain reflectometry and for crosstalk, continuity, impedance and a printed report issued by the microprocessor control.

Description

"A Cable Testing System" The invention relates to a testing system for testing network cables for computer, security, multi-media, video, television, and building integrated control systems generally. These are generally referred to as structured cabling systems.

The industry standards for performance of structured cabling systems (Category 5) calls for speeds in the region of 155 MHz and to ensure that there will be satisfactory operation for up to fifteen years a complex set of tests must be carried out. These include time domain reflectometry (TDR), continuity, crosstalk, impedance, and various combined tests in a suitably controlled manner. Accordingly, testing has become a very time-consuming and specialised part of the cable installation work and it is necessary to produce a report with results of the tests for each outlet installed.

Generally, if the installation passes all of the tests the installer will offer a conformance and performance warranty for up to fifteen years.

To perform these tests, it is necessary to connect equipment to each end of each cable and to transmit test signals between the units and monitor the output. Such test equipment is described, for example in WO 89/11106, GB1298350, and US4703497. While such systems operate quite satisfactorily there is unfortunately a need for a highly skilled workforce to perform the tests, and they are very time-consuming. For example, it has been found that testing time can take an average of fifteen minutes for two engineers for each outlet installed. In a building such as an office block having many hundreds of outlets, it will be readily apparent that the labour costs can be very high. It is necessary for one engineer to move from outlet to outlet with a remote portion of the test equipment, while another engineer carries out the tests at the wiring closet or crossconnect frame. There must be excellent coordination between the two installers and generally two-way radios are required.

There is therefore a need for a cable testing system which provides comprehensive testing of cables with a lower installer time requirement. The invention is directed towards providing such a system.

According to the invention, there is provided a cable testing system comprising a test instrument comprising: a test instrument for generation of cable test and analysis signals and operating at least 100 MHz; a central switch unit having a port connected to the test instrument on one side and a plurality of ports for connection to a cable crossconnect on the other side; a remote switch unit having a plurality of ports for connection to cable outlets located remotely from the cable crossconnect; a cable switch mounted between each crossconnect port and the test instrument port of the central switch; a controller in the central switch unit comprising: a counter, means for incrementing the counter through a set of discrete values, one associated with each crossconnect port, and means for closing the associated switch for each value in succession to connect a particular cable under test; means for transmitting a test initialisation signal on a cable under test to the remote switch unit; means for receiving a confirmation signal back from the remote switch unit on the cable under test indicating that it has connected to the cable under test; means for starting a testing cycle if a confirmation signal has been received and the counter value is correct by activating a timer and enabling the test instrument; means for disabling the test instrument after the testing cycle, as determined by a timeout signal from the timer; and means in the remote switch unit for connecting to the cable under test upon receipt of an initialisation signal from the central switch, and for transmitting a confirmation signal.

In one embodiment, the controller is connected to the test instrument by an auxiliary connector independent of the port for transmission of test instrument enable and disable signals.

Preferably, the initialisation signal includes a frame for initialisation followed by a frame identifying the cable under test.

Preferably, the confirmation signal has the same frames as the initialisation signal.

In one embodiment, the initialisation and confirmation signals are transmitted by DTMF tone generators connected to binary encoders.

In another embodiment, the controller comprises means for disconnecting the tone generators from the cable under test during the testing cycle.

In a further embodiment the controller comprises means for outputting an error signal if a confirmation signal does not correspond to the counter value.

Ideally, the controller comprises a malfunction timer, means for activating said timer at the start of a testing cycle, and means in said timer for outputting an error signal if the timeout period passes without ending of the testing cycle.

In a still further embodiment, the controller comprises means for displaying the current counter value.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which: Fig. 1 is an overview diagram illustrating a cable testing system of the invention connected to cables; Fig. 2 is circuit diagram of a central switch unit of the system; and Fig. 3 is a circuit diagram of a remote switch unit of the system.

Referring initially to Fig. 1 a cable testing system 1 of the invention is described. The system 1 comprises a test instrument 2 which complies with Category 5 standards. It operates at a speed of up to 155 MHz and has an intelligent test port. The circuits of the instrument 2 generate TDR, continuity, crosstalk, and impedance tests on the wires in a particular cable.

The test instrument 2 is connected to a central switch 3 by a cable 4 connected to the intelligent test port of the instrument 2. The cable 4 connects with eight ports of the central switch 3 at a tester port.

The central switch 3 is in turn connected by an "octopus" cable providing a RJ45 serial link to cable ports in a crossconnect frame 10. The frame 10 is connected to several hundred cable outlets. In the drawing of Fig. 1, the only outlets shown are a set 12 of eight outlets connected by eight cables 11 to the crossconnect frame 10.

All of the eight outlets are connected by an "octopus" cable 16 providing an RJ45 link to a remote switch unit 15 of the system 1. For clarity, the system 1 comprises the test instrument 2, the central switch 3, the remote switch 15 and the interfaces which connect these units to the structured cabling system 10, 11 and 12.

Referring now to Fig. 2, the central switch unit 3 is now described in more detail. The unit 3 comprises a set of eight ports 20 which link it with cables in the crossconnect frame 10 and for each of the ports 20 there is a corresponding port 21 on the other side which links the unit 3 with the test instrument 2. This is achieved by setting an automatic switching timer to sequentially switch the corresponding complimentary lines to the tester port link. Each line is then tested in sequence according to the time allocated for the line tests.

The unit 3 also comprises a cable counter 22 which may be reset by a master reset circuit 23 which is operated when the unit 3 is powered-up. The unit 3 also has a "start" switch 26 which is operated by a user and which activates a monostable circuit 25 which supplies pulses to the counter 22 to cause it to increment through the nine values 0 to 8. The eight output value lines are indicated generally by the numeral 26 and they are all connected to a display 27 which displays the current output of the counter 22.

The counter 22 forms part of a controller of the unit 3 and the controller also comprises a timing circuit indicated generally by the numeral 30. There is one timing circuit 30 for each output line 26 of the counter 22. The link between each line and the timing circuit 30 is also connected to a relay for an associated switch 20.

In Fig. 2, only the timing circuit 30 and the switch for line 1 are illustrated. The relay for the switch 20 associated with the cable 1 and output 1 of the counter 22 is indicated by RL1.

The timing circuit 30 comprises an AND gate 31 which receives an input from the output 26 of the counter 22.

The other inputs are received from a DTMF detector 32 connected to the port 20. A zero-level output of the detector 32 is connected to a set/reset circuit 33, the Q output of which is inputted to the AND gate 31. The third input to the AND gate 31 is the positive output of the detector 32.

The AND gate 31 is connected to an S/Q gate 34, in turn connected to a timer counter 35. The E port of the timer 35 is connected to an OR gate 36 which is connected by an auxiliary, independent conductor to the test instrument 2. A reset output of the timer 35 is connected to an OR gate 38 which is connected to provide a reset for the flip-flop 34 and the detector 32. The other input to the OR gate 35 which can trigger a reset is from the master reset circuit 23. The timer 35 is also connected to the input of a NAND gate 39, in turn connected to a beeper 40. Another input to the NAND gate 39 is from a malfunction timer 41, which is reset by the start switch 24. This reset also causes reset via a gate 42 of a tone generation circuit. There is a tone generation circuit for each of the eight ports 20, that for cable 1 only being illustrated. Each tone generation circuit comprises a binary decoder 50 connected to a DTMF generator 51, in turn connected via a transformer T1 and a relay 52 to the cable which passes through the unit 3 between the ports 20 and 21. The switch 51 is operated by a relay RLll connected to the output of the timer 35.

Referring now to Fig. 3 the remote switch unit 15 is now described in detail. The unit 15 comprises eight ports 60 and an associated circuit. In Fig. 3, only one port 60 and associated circuit is illustrated.

The port 60 is connected to a DTMF detector 61, in turn connected to a decoder 62, there being only one of the items 61 and 62 in the unit 15. The decoder 62 has nine outputs, much like the counter 22 of the central switch unit 3. The zero output of the decoder 62 is connected to a set/reset gate 63, in turn connected to an AND gate 64, the other input of which is the first of the eight outputs of the decoder 62.

The output of the gate 64 is connected to a monostable circuit 65 which transmits a zero output to a decoder 67 and which activates a second monostable circuit 66, which in turn provides the cable number or identifier input to a decoder 67, in turn connected to a DTMF generator 68.

A monostable circuit 69 is also connected to the decoder 67 for the DTMF generator to generate a transmit DTMF tone.

A reset circuit 70 is provided by a third monostable circuit which generates a master reset until addressed again by a "01" set of DTMF tones.

The output of the DTMF generator 68 is connected to a transformer 71, in turn connected to the port 60.

In operation, the system 1 may be connected by a single engineer to a structured cabling system by connecting the central switch 3 to a first set of eight ports in the crossconnect frame 10 and by connecting the remote switch unit 15 to eight outlets. Generally, connection to the eight remote outlets is quite simple as they are located together in a typical situation.

The engineer then switches on the central switch unit 3 to power it up. This causes the master reset circuit 23 to reset the counter 22 and cause it to output a zero, which is in turn displayed on the display 27. The engineer then presses the start button 24, causing the monostable circuit 25 to transmit a pulse to the counter 26 causing it to increment to a value 1. Again, the display captures the output value and displays 1. This output value also causes the relay RL1 to close the switch 20 associated with the first cable so that the cable which passes through the crossconnect frame 10 and out to the set of outlets 12 is effectively connected to the test instrument 2 via the port 21.

The value 1 at the output of the counter 22 causes the binary decoder 50 to cause the DTMF generator 51 to transmit a 0 followed by 1 on the cable (the switch 52 being closed). The 0 is an initialisation signal and the 1 is a cable identifier. These signals are received at the remote switch unit 15 which recognises them by use of the decoder 62 and as a result connects itself to the port 60 for cable 1 by the switch 20.

The remote switch unit 15 also transmits a confirmation signal to the central switch unit, the confirmation signal being the very same as the frames of the initialisation and cable identifier signals transmitted by the DTMF generator 51.

The confirmation signal is received at the DTMF detector 32. Therefore, the AND gate 31 receives three positive inputs, one from the first output line of the counter 22, the second from the positive output of the detector 32, and the third via the invertor 33. This causes a positive signal from the gate 31 to set the gate 34 transmitting a positive signal to the OR gate 36. The second input to the gate 36 is controlled by the timer to automatically reset and restart the tester to lines 2-8.

The signal from the OR gate 36 is very important as it is transmitted on an auxiliary, independent conductor to the test instrument 2 and causes it to be enabled. This is the start of a testing cycle. This positive signal also causes the relay RL11 to open the switch 52, thus disconnecting the DTMF generator 51 from the cable.

Another important operation at the start of the testing cycle is initialisation of the timer 36, which counts to a timeout period of two minutes. This line also provides an input to the NAND gate circuit 39, the second input of which is from the malfunction timer 41.

When the timeout period has elapsed, the timer 35 provides an output via the OR gate 38 which resets the gate 34 and the detector 32. The output OR gate 38 also provides a trigger into the monostable circuit 25, which causes the counter 22 to increment to the next value, representing the next one of the eight cables. When this happens, a tone generator circuit exactly similar to the circuit 50, 51 and 52 for the second output of the counter 22 performs hand shaking" with the remote switch unit 15 and the timing circuit for that cable directs a testing cycle for that cable. During the two minutes of the testing cycle, the test generator proceeds with a pre-programmed set of tests and logs the results for later up-load to computer.

In this way, the central switch unit 3 directs a testing cycle for each cable in turn until all eight of the cables have been tested. Thereafter, the test engineer connects the central switch unit 3 to the next bank of eight ports and the remote unit 15 is moved to the next set of remote outlets.

During each testing cycle, the remote switch unit 15 operates in conjunction with the test instrument 2 as described above to verify that the line being tested is as indicated by standard cable markings and identifiers.

It will be appreciated that the system of the invention provides in a simple manner for automatic testing of eight cables in succession. Each cable is comprehensively tested, irrespective of the number of wires which are included within it as the system tests only one cable at any one time. The important aspect of the testing system is that it can move from one cable to the next in a quick and efficient manner, while also ensuring integrity. For example, if a malfunction occurs this will be detected by the malfunction timer 41 which will cause an error output to be emitted from the beeper 40. Further, operation of the various tone generators and detectors helps to ensure that there is correct interconnection of the test generator and the cable ports to ensure integrity of the test results.

The invention is not limited to the embodiments hereinbefore described, but may be varied in construction and detail.

Claims

CLAIMS 1. A cable testing system comprising a test instrument comprising: a test instrument for generation of cable test and analysis signals and operating at least 100 MHz; a central switch unit having a port connected to the test instrument on one side and a plurality of ports for connection to a cable crossconnect on the other side; a remote switch unit having a plurality of ports for connection to cable outlets located remotely from the cable crossconnect; a cable switch mounted between each crossconnect port and the test instrument port of the central switch; a controller in the central switch unit comprising: a counter, means for incrementing the counter through a set of discrete values, one associated with each crossconnect port, and means for closing the associated switch for each value in succession to connect a particular cable under test; means for transmitting a test initialisation signal on a cable under test to the remote switch unit; means for receiving a confirmation signal back from the remote switch unit on the cable under test indicating that it has connected to the cable under test; means for starting a testing cycle if a confirmation signal has been received and the counter value is correct by activating a timer and enabling the test instrument; means for disabling the test instrument after the testing cycle, as determined by a timeout signal from the timer; and means in the remote switch unit for connecting to the cable under test upon receipt of an initialisation signal from the central switch, and for transmitting a confirmation signal.
2. A cable testing system as claimed in claim 1, wherein the controller is connected to the test instrument by an auxiliary connector independent of the port for transmission of test instrument enable and disable signals.
3. A cable testing system as claimed in claim 1 or 2, wherein the initialisation signal includes a frame for initialisation followed by a frame identifying the cable under test.
4. A cable testing system as claimed in claim 3, wherein the confirmation signal has the same frames as the initialisation signal.
5. A cable testing system as claimed in any preceding claim, wherein the initialisation and confirmation signals are transmitted by DTMF tone generators connected to binary encoders.
6. A cable testing system as claimed in claim 5, wherein the controller comprises means for disconnecting the tone generators from the cable under test during the testing cycle.
7. A cable testing system as claimed in any preceding claim, wherein the controller comprises means for outputting an error signal if a confirmation signal does not correspond to the counter value.
8. A cable testing system as claimed in any preceding claim, wherein the controller comprises a malfunction timer, means for activating said timer at the start of a testing cycle, and means in said timer for outputting an error signal if the timeout period passes without ending of the testing cycle.
9. A cable testing system as claimed in any preceding claim, wherein the controller comprises means for displaying the current counter value.