Biccotest Model T535 Cable Fault Locator

Model T535 Cable Fault Locator

Issue 1

Operating Instructions and Applications Guide

Refer to Preface before operating

00901145- 1

T535 Operating Manual_______________________________________Biccotest Limited PREFACE IMPORTANT NOTE

This instrument is supplied with the internal battery discharged. Before use, charge the battery as described in 3.4. Complete discharge of the internal battery ¡s prevented by a sensing circuit which automatically disconnects the battery when its voltage falls below a pre-determined level, thus rendering the equipment inoperative. In order to restore operation either:

1. Charge the internal battery

or 2. Operate from the a.c. supply or 3. Operate from an external 11.5 to 28 volt d.c. supply.

This document does not contain servicing information. A servicing manual is available as an accessory. ___________________________________________________________________ 00901145 – 1

Biccotest Limited T535 Operating Manual

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SAFETY PRECAUTIONS:

READ CAREFULLY THE SAFETY

PRECAUTIONS ON PAGE 5

T535 Operating Manual_______________________________________Biccotest Limited

Model T535 Operating Instructions

Biccotest Limited, Delamare Road, Cheshunt, Waltham Cross, Hertfordshire, EN8 9TG ENGLAND

Tel: (0992)629011 Int: +44992629011 Fax: (0992)636170 Int: +44 992 636170

Part No. 00901145, Issue 1 © Biccotest Limited This document is the copyright property of Biccotest Limited. ___________________________________________________________________ 00901145 – 1


SAFETY PRECAUTIONS

Please read carefully before operating.

The T535 is designed to be used by trained personnel conforming with procedures and instructions described in this Operating Manual. This is in addition to those safety rules and regulations appertaining to the industry and location in which the equipment is used.

There are minimal safety problems when operating the T535 ¡n accordance with the Instruction Manual. However, special attention should be given to the following:

Ensure that the unit is set to the correct voltage rating before connecting to an a.c. supply (see Section 3.2).

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T535 Operating Manual_______________________________________Biccotest Limitedl Although the T535 is protected against voltages up to 400V PK, in the interest of operator safety:

• do not connect the output of the T535 to energized conductors. • make a separate voltage test on the conductors to be tested before connecting them to the T535 (note that the T535 is not grounded). • take precautions to avoid any impact on the cathode ray tube. Impact could cause implosion.

Internal work on the T535 shall only be performed by those acquainted with the possible shock hazard of cathode ray oscilloscope circuits and with the routine precautions to be taken to avoid such accidents.

Within the T535 there are voltages as high as 2 kV during operation, and such voltages can exist even after the T535 has been switched off.

Do not operate the T535 with the case removed except when following the procedures of the Service Manual. ___________________________________________________________________ Page 4 00901145 – 1

Biccotest Limited T535 Operating Manual LIST OF CONTENTS

Page

Safety Precautions 5

1. Introduction 11 2. Description of controls 14 3. Preparation for use 20 3.1 Introduction 20 3.2 Operation from an a.c. supply 20 3.3 Operation from an external 11 .5-28 V d.c. supply 21 3.4 Operation from the internal battery 22 3.5 Re-initialising the T535 23

List of propagation velocity f actors 24 4. Operating Procedure 25 4.1 Initialising the Control Settings 25 4.2 Single Line Testing 26

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T535 Operating Manual Biccotest Limited

Page

4.3 Comparison of Two Lines 28

4.4 Difference between Two Lines 29 4.5 Location of Crosstalk (Splits and Resplits) 29 4.6 Use of the Memory 30 4.7 X - Y, Y - T Recording 32 4.8 Printing via RS232/V24 Compatible Interface 33 4.8.1 Interface Connections 34 4.8.2 Operation with an Epsom P40 Printer 36

5. Application Guide 38 5.1 General Hints on Fault Locating 38 5.2 To Determine the (DIELECTRIC) Velocity Factor 41 5.2.1 Velocity of Propagation Known 42 5.2.2 Dielectric Constant Known 42 5.2.3 Using Short Length Cable 43 5.2.4 Route Length Known 44

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Biccotest Limited___________________________________________T535 Operating Manual

1

Page 5.2.5 Route Length Known with both ends accessible 45

5.2.6 Route Length Unknown with both ends accessible 46

(Three Stake Method) 5.3 Practical Examples 48 (1 ) Open Conductors 48

(2) Shorted Conductors 48

(3) Joints/Splices 49

(4) Capacitor Networks 49

(5) Loading Coils 50

(6) Open Sheath 50

(7) Grounded Sheath 51

(8) Wet Section (Water Ingress) 52

(9) Crossed or Split Pairs 53

(10)Taps 53

(11) Change of Cable Insulation 54 5.4 Ghost Reflections 56 6. Specification 57 0901145 - 1

T535 Operating Manual________________________________ _______Biccotest Limited The T535 has been designed primarily for testing telephone pairs. Ranges are from 30 meters, 100ft and O.S^s to 15km, 50,000ft and Measurement accuracy is ±1% of selected range setting. Examples of Displayed Waveforms

Transmitted Pulse Reflected Pulse (Fault) 1. Open Circuit or Series Fault 2. Short Circuit or Shunt Fault 3. Inductive Mismatch 4. Capacitive Mismatch Practical examples are given in Section 5. ___________________________________________________________________ 00901145 – 1


1. INTRODUCTION

The T535 is a pulse-reflection (radar) cable test set, which provides a visual indication of cable faults. The principle of operation is that a pulse transmitted into a cable travels with a velocity determined by the dielectric, or insulating medium, and is reflected by discontinuities or mismatches in the cable. The transmitted and reflected pulses are displayed on a cathode ray tube, the time between them being proportional to the distance to the point of reflection. The type of fault can be determined by analysis of the displayed waveform (see examples on page 10).

The T535 provides for:

a) Examination of a single line.

b) Comparison between a good pair and a faulty pair.

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T535 Operating Manual________________________________ _______Biccotest Limited

c) Difference between a good pair and a faulty pair, so that reflections from common features such as joints and change of wire gauge or insulation, cancel; this permits obscure faults to be more readily identified.

d) Location of crosstalk points i.e. splits and resplits, by

transmitting on one pair and receiving on the other.

e) "Before and after" comparison using the memory facility.

This manual provides sufficient information for successful operation of the T535. In order to obtain maximum benefit from the T535 read through this manual before attempting to locate a cable fault. ___________________________________________________________________ 00901145 – 1


Cable Fault Locator T535

Cable Fault Locator T535

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T535 Operating Manual________________________________ _______Biccotest Limited

2. DESCRIPTION OF CONTROLS

The controls consist of pressure operated membrane switches which are either single operation (SINGLE) only or single operation with auto repeat if maintained in the depressed condition (AUTO).

POWER SINGLE Equipment power ON – OFF

INTENSITY AUTO Varies the brightness of the CRT display.

FOCUS AUTO Varies the definition of the CRT display.

UNITS SINGLE Selects units of measurement METRES,

FEET or MICROSECONDS.

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Biccotest Limited___________________________________________T535 Operating Manual RANGE AUTO Selects the displayed range.

CURSOR AUTO Adjusts the position of the vertical line cursor.

SHIFT AUTO Adjusts the vertical position of the CRT display.

AMP AUTO Adjusts the vertical amplitude of the CRT display.

PULSE WIDTH SINGLE Selects the narrow or wide pulse available on

each range.

DIELECTRIC AUTO Selects the appropriate propagation velocity

factor for the line under test.

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PLOT SINGLE Initiates either analogue output to an external XY, YT plotter or RS232/V24 output to a printer.

SET AUTO Provides either the full scale output to the

analogue plotter or outputs a line feed to the printer.

RESET SINGLE Resets the plot output to 0V, terminates plotting, terminates output to the printer.

L1 SINGLE Trace from line connected to L1 sockets

displayed.

L1 &L2 SINGLE Traces from lines connected to both the L1

and L2 sockets displayed.

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Biccotest Limited___________________________________________T535 Operating Manual L1 - L2 SINGLE Difference between the traces of the lines

connected lo the L1 and L2 sockets displayed.

L1 -»L2 SINGLE Crosstalk between the lines connected to L1

and L2 displayed.

L1 to M SINGLE Trace obtained on L1 transferred to memory.

M SINGLE The trace stored in memory will be displayed.

M & L1 SINGLE Trace from the line connected to L1 and the

trace stored in memory displayed simultaneously.

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M-L1 SINGLE Difference between the trace from the line connected to L1 and the trace stored in memory displayed.

FILTER SINGLE Switches in a high pass filter to reject low frequency components from the received

signal.

BALANCE Continuously variable control used to minimise the amplitude of the transmitted pulse

appearing at the start of the CRT trace.

INTERFACE 15 Way D type socket for interfacing with

external accessories.

11.5-28V 2 Pin socket for d.c. supply. Associated lamp indicates presence of supply.

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Biccotest Limited___________________________________________T535 Operating Manual LCD - The LCD provides the following information.

BATTERY RANGE LOW CURSOR

DISPLAY PULSE FILTER DIELECTRIC MODE WIDTH IN/OUT VELOCITY

FACTOR

The background is illuminated to facilitate use in low ambient light. __________________________________________________________________ 00901145 – 1

T535 Operating Manual_______________________________ ______________Biccotest Limited

3. PREPARATION FOR USE

3.1. Introduction The front panel cover houses the a.c. power unit and provides stowage for the power supply leads, two 3 metre (10ft) connecting leads, the instruction manual and a 2 pin d.c. input lead.

The cover also acts as a tilt stand, by releasing the two retaining clips and folding under the unit.

The unit will operate from the internal battery in the absence of any other supply.

3.2. Operation from an a.c. supply

Ensure that the voltage selector on the power supply unit is set to suit the local a.c. supply.

The d.c. supply lead to the unit is contained ¡n the middle compartment of the front cover. Release the catch and feed the d.c.

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Biccotest Limited___________________________________________T535 Operating Manual lead through the slot provided and plug into the 11.5 - 28V socket observing the polarity key.

Connect the a.c. power lead to the local supply. The 11.5-28V indicator lamp will light to indicate the presence of the d.c. supply to the unit.

3.3. Operation from an external 11.5 - 28V d.c. supply

A 2 pin d.c. input lead is supplied with the T535. When making connections observe the polarity.

Positive BROWN

Negative BLUE

Neither side is connected to ground.

Connect to a d.c. supply in the range 11.5 to 28 Volts, insert the plug into the unit and observe that the 11.5-28V indicator lamp is lit.

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T535 Operating Manual Biccotest Limited 3.4. Operation from the internal battery

The T535 will operate from the internal battery in the absence of any other supply.

Complete discharge of the battery is prevented by a sensing circuit which switches off the T535 when the battery voltage falls below a predetermined value. If this should happen ¡n use, operation can be restored for a short time by switching off for 5 minutes, allowing the battery to recover, and then switching back on.

The battery can be recharged either from a.c. or external d.c., i.e. vehicle supply.

Recharging from a.c. Connect the unit as for a.c. operation, with the unit switched OFF and allow to stand for 14 hours.

Recharging from d.c. Connect the unit to operate from external d.c., with the unit switched ___________________________________________________________________ 00901145 – 1

Biccotest Limited___________________________________________7535 Operating Manual

off. The battery will charge providing the supply exceeds 12.5 volts i.e. with the vehicle engine running. Full recharge will take 14 hours.

3.5. Re-initialising the T535 when the battery has been disconnected and/or replaced

When the battery is disconnected the FOCUS and INTENSITY settings in the internal memory are lost and will need to be reset when the battery is reconnected. To do so use the following procedure:

a) Press the (-) negative intensity button for 3 seconds. This will reset the unit.

b) If the trace is not visible, press the (+) positive intensity button until the trace appears. This might take several seconds.

c) The trace can now be focused. Press the (-) negative focus button for 10 seconds. Then press the (+) positive focus button until the trace comes into focus.

d) The unit should now operate normally

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T535 Operating Manual______________________________________________Biccotest Limited LIST OF PROPAGATION VELOCITY FACTORS DIELECTRIC SETTING FOR TYPICAL CABLES Air 0.980 Air Spaced Coaxial 0.940 RG 58U Coaxial 0.780 RG 59U Coaxial 0.660 RG High Temperature Coaxial 0.695 Foam Poly 0.820 PTFE(Teflon) 0.710 Polyethene (PIC) 0.667 Jelly Filled Poly 0.640 Paper (Pulp .083 uF/Mile 0.720 Paper (Pulp .072 uF/Mile 0.880 Paper, oil filled (PILC) 0.500-0.560 Cross Linked Poly (XLPE) 0.520-0.580 HMW 0.560-0.620 ___________________________________________________________________ 00901145 – 1


4. OPERATING PROCEDURE

4.1. Initialising the Control Settings - (refer to Section 3.5 if the battery has been disconnected) Connect the unit to the required power source.

Switch the unit ON by depressing the POWER switch once. Check that the LCD indicates.

The following parameters are automatically set each time the unit is switched on.

Display Mode L1 Amplitude Minimum Pulse Width Narrow

The settings of the INTENSlTY, FOCUS, CURSOR, SHIFT, RANGE, UNITS, FILTER, DIELECTRIC and the contents of the memory will be retained from the equipments previous operation.

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T535 Operating Manual___________________________________________Biccotest Limited Allow 10 seconds for the CRT trace to appear.

Adjust INTENSITY and FOCUS ¡f required to obtain a well defined trace. Select Feet, Metres or Microseconds by depressing the Units Control as required.

Adjust SHIFT to position the trace ¡n the middle of the CRT screen. 4.2. Single Line Testing

Note: The fault distance displayed includes the length of the connecting lead used which should be subtracted from the reading obtained. The FILTER ¡s used to filter out low frequency components. This has the effect of sharpening up the reflection from long cables. For short cables the filter should be switched out.

1. Plug the test lead into the L1 sockets.

2. Sel the DIELECTRIC velocity factor to suit the cable type under test. A list is provided on page 24.

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Biccotest Limited___________________________________________7535 Operating Manual 3. If the cable type or the velocity factor is not known refer to Para. 5.2.

and then continue with this procedure as appropriate. Select the RANGE to cover the full cable length.

Note: The range can be incremented in single steps by separate operations of the RANGE control or progressively by applying continuous pressure to the control. Each time the RANGE control ¡s released, the CRT display is blanked out for a few seconds, whilst the range selected is automatically calibrated.

Increase the AMPLITUDE until the fault reflection is observed. Select the wide pulse if preferred.

Adjust the BALANCE control to minimise the transmitted pulse at the start of the trace.

Move the CURSOR either in single steps or progressively until it coincides with the point, at which the start of the transmitted pulse just leaves the horizontal as shown.

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T535 Operating Manual___________________________________________Biccotest Limited The distance to the fault (cursor position) is displayed in trie top right hand corner of the LCD.

4.3. Comparison of Two Lines

Using both connecting leads, connect one line to L1 and the other to L2. Select L1 & L2. Both L1 and L2 traces are displayed overlapping on the CRT. Adjust the controls as for Single Line Testing ¡n Para 4.2. Select L1 if required to assist in discriminating between L1 and L2.

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Biccotest Limited______________________________________________7535 Operating Manual 4.4. Difference between Two Lines

Using both connecting leads, connect one line to L1 and the other line toL2.

Select L1 - l_2, the trace displayed on the CRT is the difference between L1 and L2.

Select L1 & L2 or L1 to assist in identifying on which line the deviation occurs.

4.5. Location of Crosstalk (Splits and Resplits)

Connect one line to L1 and the other to L2. Select L1 -> L2

Obtain a display as described ¡n Para 4.2 except that the BALANCE control is inoperative.

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T535 Operating Manual______________________________________________Biccotest Limited

TYPICAL RESPONSE

Split Resplit

Should crosstalk result from any form of resistive or capacitive coupling, the location of the fault point is determined in the same way.

4.6. Use of the Memory

The memory is principally provided to afford "before and after" comparison testing of the same line.

Note: Only the trace of the line connected to L1 can be stored. To store a trace, connect the line ¡n question to the L1 sockets. ___________________________________________________________________ 00901145 – 1

Biccotest Limited______________________________________________T535 Operating Manual Obtain the L1 trace as described ¡n Para 4.2. Depress the L1 to M control, the trace displayed is now transferred to memory.

To observe the trace stored in memory, depress the M control. The LCD will indicate M and will also display the parameters relating to the stored trace.

The one can now be disconnected from the T535 and subjected to external stimulation to "enhance" the fault.

Reconnect the line to the L1 sockets. Depress the M & L1 control, both the line and stored traces will now be displayed. The SHIFT control can be used to separate the traces.

If the fault is not obvious, depress the M - L1 control and the difference between the line and stored traces is displayed.

Should the RANGE, PULSE WIDTH, FILTER, UNITS, or DIELECTRIC be inadvertently changed during the exercise, thus

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rendering the comparison between the direct and stored trace invalid, the LCD will flash and indicate the parameter ¡n error. Note the indicated error, switch back to L1 and correct the error.

Comparison between the line and stored trace can now proceed as previously described.

4.7. X - Y, Y - T Recording

The output to the external plotter is via the 15 way D type interface plug. The output voltage is O to 1V d.c.

Note: Only the trace stored in memory can be plotted.

Connect the plotter observing the connections detailed above. Switch the plotter to accommodate 1 volt full scale.

To check the full scale deflection depress the SET control to obtain a 1 volt signal.

Depress RESET to reset to zero. ___________________________________________________________________ 00901145 – 1

Biccotest Limited______________________________________________T535 Operating Manual With the desired trace from L1 displayed on the CRT, depress L1 to M to transfer the trace into memory.

Depress M to check that the trace has been transferred into memory.

To initiate plotting depress the PLOT control.

The LCD will now indicate "PLOTTING".

The complete recording takes 60 seconds.

To terminate plotting at any time depress the RESET control.

4.8. Printing on Epsom P40 via RS-232/V24 Compatible Interface

Note: The Epsom P40 must be equipped with a serial RS-232C interface.

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4.8.1 Interface Connections

The output ¡s via the 15 way D type ¡nterface plug.

CONNECTIONS EXTERNAL VIEW OF PLUG PINS

Pin 2 Tx Data Pin 4 RTS Pin 5 CTS (RFS) Pin 7 OV Link on mating socket to set data

PinSSLO ) rates defined in table below.

Pin9SL1 ) Pin10SL2) Pin 11 Mode Select Link to 7 (OV) for printer. Leave open

circuit for Analogue Plotter. Data Rate Link to Set 4800 Baud 10 to 7 2400 Baud 8 and 9 to 7 1200 Baud 9 to 7

600 Baud 8 to 7 300 Baud No Links

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Biccotest Limited______________________________________________T535 Operating Manual Lead between the T535 and the Epsom P40 printer. (T535) 15 Way D Type Socket (P40) 6 Pin DIN plug Note: SLO, SL1, SL2 Set for 4800 Baud

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4.8.2 Operation with an Epsom P40 printer

The following settings of the DIP switch on the printer are required for correct operation. (These are normally the factory settings of the printer).

Switch No.

Function ON OFF Required Settings

1 Auto Line Peed Val id Invalid OFF

2 Parity Valid Invalid OFF

3 Parity Even Odd OFF

4 Word Length 7 bits 8 bits OFF

5 Bit rate 3 Settings for 4800oaud OFF 6 Bit rate 2 ON

7 Bit rate 1 OFF

8 Bit rate 0 ON

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Biccotest Limited___________________________________________T535 Operating Manual The printer should be connected to the T535 with the lead as detailed in 4.8.1. This ¡s available as an accessory, Part No. 31302402 Pressing PLOT causes the information on the screen and LCD to be printed on the printer. Depending on T535 trace selection any of the following can be printed, L1, L1 & L2, L1 - L2, L1 -> L2, M, M & L1, M-L1. When printing has finished, pressing SET will output Line Feeds to the printer, causing the paper to advance. Printing can be terminated by pressing RESET. Note: If the settings of RANGE, PULSE WIDTH, FILTER, UNITS, or DIELECTRIC differ between M and L1 then the M & L1 and M - L1 screens cannot be printed. See 4.6.

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T535 Operating Manual___________________________________________Biccotest Limited 5. APPLICATION CUIDE

5.1. General Hints on Fault Locating

The position on the trace to which the cursor is set is the point at which the reflected pulse just leaves the horizontal.

The amplitude of the reflected pulse decreases with increased distance because of signal loss in the cable, and the AMP control should be adjusted accordingly. Multiple faults may or may not be observed. If the first fault encountered is severe, most or all of the pulse energy will be reflected, disguising other possible faults. After clearing the indicated fault, check again to ensure that no other faults are present.

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Biccotest Limited______________________________________________T535 Operating Manual

Telephone cables by the nature of their construction produce displays not a 'clean' as for a coaxial cable or power cable. This is why the T535 has the facility for comparing two lines or displaying the difference between two lines so that common reflections cancel.

Whenever possible obtain a second location of the fault from another access point.

Experience has shown that most faults occur at joints, pillars, splices, cabinets, or where the cable has been damaged.

1. Check in the area of the indicated fault position for any disturbance of the ground.

2. If the T535 shows the fault position to be close to a splice (joint), the chances are that the fault is at the splice (joint).

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T535 Operating Manual___________________________________________Biccotest Limited Insulation faults with resistance above a few kilohms are more likely to be located by using a high-resistance bridge; unless water is present, when the T535 will locate the change in capacitance caused by the water ingress.

The T535 will not 'see' through load coils, which appear as high-impedance series faults.

The transmitted pulse is subject to high attenuation (loss of signal) in telephone pairs because of the small-diameter conductors used. The smaller the conductor the higher the attenuation and the less the effective range. It may be necessary to go to the next higher range and wide pulse width to be more effective.

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Biccotest Limited___________________________________________T535 Operating Manual 5.2. To determine the DIELECTRIC (Velocity Factor)

If the propagation velocity factor is not known, it can be calculated from a), b), and c) below, or alternative methods of measurement can be used as in d) and e) below. These calculations and measurement methods are described in sub-paras 5.2.1 to 5.2.5 below. Refer to Para. 4.2 for the general operating procedure.

a) Velocity of propagation for the cable known.

b) Dielectric constant for the cable insulation known.

c) Short length of the same type of cable available.

d) Route length known of a good pair in the same cable.

e) Route length known with both ends accessible.

f) Route length unknown with both ends accessible (Three Stake Method).

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T535 Operating Manual___________________________________________Biccotest Limited 5.2.1 Velocity of Propagation Known

Calculate propagation velocity factor

Where v= velocity of propagation for the cable in m/μs or ft/ μs. c = velocity in free space 300 m/ μs or 984 ft/ μs.

5.2.2 Dielectric constant known

Propagation velocity factor = where e = dielectric constant for the cable

Set DIELECTRIC control to 0.667 ___________________________________________________________________ 00901145 – 1


5.2.3 Using Short length same type of cable

1. Measure the physical length of the sample cable.

2. Set the DIELECTRIC control to any value in the range 0.400 to 0.999.

3. Obtain a reading for the apparent distance to the end of the cable indicated by the first reflection after the transmitted pulse.

4. Keep the bright-up cursor at the point of reflection, and re-adjust the DIELECTRIC setting until the distance on the readout is the same as the physical length measured in (1). Note the reading of the DIELECTRIC setting, which should be recorded for later reference. This setting can be applied to ANY T535, not just the one on which the measurement was made.

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5.2.4 Route length known of a good pair in the same cable

Method 1 1. Connect the T535 to a good pair.

2. Determine the propagation velocity factor as previously described for a sample length and set the DIELECTRIC control.

3. Connect to the faulty pair and measure the distance to the fault.

Method 2

1. Connect the T535 to a good pair with any DIELECTRIC setting in the range 0.400 to 0.999 and measure the apparent distance (d1) to the end of the cable.

2. Connect the T535 to the faulty pair with the same DIELECTRIC setting and measure the apparent distance (d2 )

True distance to the fault

where ∫ = true length of the cable

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Biccotest Limited___________________________________________T535 Operating Manual 5.2.5 Route length known and both ends accessible

1. Set the DIELECTRIC to any setting between 0.400 and 0.999. 2. Measure the apparent distance (x) to the fault from end A and the apparent distance (y) to the fault from end B.

Then distance to the fault from end A where ∫ = route length of the cable.

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T535 Operating Manual______________________________________________Biccotest Limited 5.2.6 Route length unknown and both ends accessible

(Three Stake Method)

If cable dielectric ¡s unknown and cable distance ¡s unknown, the three stake method can be used. Set Dielectric Control to PIC or any insulation setting and continue using the same setting.

x = Stake or marker Df = Unknown distance to fault

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T1 = Distance in feet to the first reading.

Place first stake at this location.

T2 = Distance in feet from the far end of the cable.

Place second stake at this location.

G = Measured distance between stakes 1 and 2.

Then complete the following:

Note: If stakes T1 and T2 fall short add the correction factor,

however if they overlap subtract the correction factor. __________________________________________________________________ 00901145 – 1

T535 Operating Manual______________________________________________Biccotest Limited 5.3. Practical examples

1. Open Conductors The reflection from an open conductor is a positive or upward pulse. If only one conductor is open the amplitude of the reflection will be smaller.

Note: No reflection from the far end of the cable.

2. Shorted Conductors

The reflection from a shorted pair is a negative or downward pulse. Note: No reflection from the far end of the cable.

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3. Joints (splices) A joint (splice) produces an "S" shaped reflection.

High resistance joint (splice). A high-resistance joint produces a positive or upward pulse similar to that of an open conductor, the amplitude being dependent upon the effective resistance.

4. Capacitor Networks A capacitor network presents a low shunt impedance to the transmitted pulse and produces a negative or downward reflection followed by a small positive overshoot.

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5. Loading Coils A loading coil presents a high series impedance to the transmitted pulse and positive or upward reflection. It is not possible to 'see' beyond the first loading coil.

6. Open Sheath

An open sheath may be located where the sheath is completely open, for example, where there is a missing strap. The sheath must be isolated in the measuring direction and the lest connection made between the sheath and a shorted, twisted pair.

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Biccotest Limited___________________________________________T535 Operating Manual 7. Grounded Sheath

Grounded sheaths are difficult to locate with pulse echo equipment and may be more readily located by using a high-resistance bridge.

However, in some circumstances where the earth is moist, it may be possible to locate the fault.

Either: (a) connect between the sheath and a pair, or (b) connect between the sheath and ground.

In (a) the velocity of propagation is that of the cable. In (b) the velocity of propagation is unknown and the fault can be located by knowing the route length of the cable.

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T535 Operating Manual Biccotest Limited 8. Wet Section (water Ingress)

Water present in a cable increases the dielectric constant and hence the capacitance of the cable. The water boundary produces a 'noisy' negative reflection, of amplitude dependent upon the degree of saturation, with a positive pulse at the end. See Waveform (a). Because the velocity of propagation is slower in the wet section, for accurate location of the far end of the set section repeat the test from the other end of the cable. Faults such as open-circuits will show up in the display of the wet section. Waveform (b) shows a wet joint (splice) case.

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Biccotest Limited T535 Operating Manual 9. Crossed Or Split Pairs

The joint (splice) at which the split occurs is indicated by a positive or negative reflection. The resplit is indicated by a pulse of opposite polarity, but of small amplitude, because of the loss of pulse energy at the split. First locate and clear the split, then locate the resplit.

10. Taps

The tap appears as a negative pulse followed immediately by a positive overshoot. Because of multiple reflections it is difficult to troubleshoot circuits that contain several taps, so test progressively by moving from tap to tap.

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T535 Operating Manual Biccolest Limited 11. Change of Cable Insulation POLYTHENE PAPER

The point at which a change of cable insulation occurs results in a positive or negative reflection. Polyethylene to Paper - Negative Paper to Polyethylene – Positive Since the velocity of propagation is different for each cable type, care should be taken to ensure that the correct value is used. In the case illustrated, first select 0.670 for Polyethylene for accurate location in the Polyethylene section, and if the fault occurs in the dry paper section select 0.710 (or the appropriate number for the particular type of paper insulation).

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Obtain a reading (d1) for the apparent distance to the point of change. Then measure the apparent distance (d2) lo the fault. The accurate distance-to-fault (D) from the point of change is given by:

D= d2 - d1

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T535 Operating Manual Biccotest Limited 5.4. Ghost reflections

It is sometimes convenient to select a range shorter than that necessary to cover full cable length. Under these circumstances ¡t ¡s possible for a reflection resulting from a point beyond the range selected to appear on the display, giving a false indication of a fault. This ¡s referred to as a "ghost reflection". It is caused by a reflection resulting from one transmitted pulse occurring during the trace period of the second or a subsequent transmitted pulse.

To identify possible ghost reflections:

NOTE ALL SIGNIFICANT REFLECTIONS ON A RANGE THAT COVERS THE FULL CABLE LENGTH. WHEN SWITCHING TO A SHORTER RANGE, ANY APPARENT REFLECTION, OTHER THAN THOSE PREVIOUSLY IDENTIFIED, IS A GHOST REFLECTION.

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6. SPECIFICATION Displayed Ranges 10 ranges, nominal full scale based on

a velocity factor of 0.667. 30m-15Km 100ft - 50,000 ft 0.3ns -150 μs

Resolution 0.4% of selected range

Accuracy Better than 1% of range selected

Dielectric Velocity Factor 0.400 to 0.999

Fault Location Set by means of a vertical line cursor.

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Transmitted Pulse Characteristics Waveform sine squared approx. Amplitude 20v peak in to 100 ohms Output Impedance 100 ohms Half Height Width ± 20% Range Wide Narrow 1 30ns 30ns 2 30ns 30ns 3 80ns 30ns 4 80ns 30ns 5 210ns 80ns 6 210ns 80ns 7 560ns 210ns 8 560ns 210ns 9 1.8 μs 560ns 10 1.8 μs 560ns

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Biccotest Limited T535 Operating Manual Sensitivity 3mV/cm Balance Up to 2K ohms. Line Connections 4mm banana sockets 19mm (3/4 inch) spacing Input Protection 400 V (d.c. plus peak a.c.) Filter High Pass cut off frequency 150 kHz Display Modes Direct L1 Single Line

L1 and L2 Two Lines L1 - L2 Difference between two lines L1 -> L2 Transmit on L1

Receive on L2

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L1 to M Transfer L1 to Memory. M Memory trace displayed. M & L1 Memory and L1 direct displayed.

M - L1 Difference between Memory and L1 direct traces displayed.

XY. YT X and Y axis outputs 0-1V nominal into at least 5K ohms.

Plotting time 60 seconds. Displays CRT 7 x 5 cm display area.

LCD Alpha numeric, two rows of 16 characters. RS232/V24 Interface to EPSOM P40 (RS232 Serial Interface version). Printer Normally set to 9600 baud. ___________________________________________________________________ 00901145 – 1

Biccotest Limited T535 Operating Manual Power a.c. single phase: 93 - 130V requirements 45 – 440 Hz 186-260V

d.c. Operating: 11.5V to 28V Charging: 12.5V to 28V Neither side is connected to ground. Internal Battery: 4hrs continuous operation. Recharge in 14 hours.

Dimensions 140 x 290 x 260 mm

Weight 7.5 Kg approx, including battery

Safety IEC 348 Class 2

Environmental IEC 68 for field portable test equipment.

Ambient Operating -25°C to + 55°C -13° Fto + 131°F

Temperature Non Operating -40°C lo + 70°C -40°F to +158°F

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Biccotest Model T535 Cable Fault Locator

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