Megger CFL510F User manual

CABLE FAULT LOCATOR
MEGGER®CFL510F (TDR1000/2)
User Guide
MEGGER®
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SAFETY WARNINGS
Although this tester does not generate any hazardous voltages, circuits to which it can be connected could be dangerous
due to electric shock hazard or due to arcing (initiated by short circuit). While every effort has been made by the
manufacturer to reduce the hazard, the user must assume responsibility for ensuring his, or her own safety.
For use on energised systems rated up to 300V Installation Category III* the fused clip set AVO Part
Number 6111-218, must be used.
* Relates to the transient over voltages likely to be met in fixed wiring installations.
4mm plug to BNC Adaptor:
This 4mm plug to BNC adapter is intended for use with telecomm network cables only, it is not designed or intended for
direct connection to an energised mains supply. However, in normal use it may be subject to telecom network voltages
(TNV) as defined by IEC 60950 3rd edition (1999-04).
The BNC plug and socket are, by necessity, accessible. The outer sheath for this connector is normally at SELV levels,
however under single fault conditions it may carry hazardous voltages. The operator must therefore verify that the
accessible plug or socket is at SELV levels prior to touching, or alternatively wear appropriate insulated gloves.
•The instrument should not be used if any part of it is damaged.
•Test leads, probes and crocodile clips must be in good order, clean and with no broken or cracked insulation.
•Check that all lead connections are correct before making a test.
•A Fused Lead Set must be used to connect to energised live systems. Refer to the accessories section for options.
•Disconnect the test leads before accessing the battery compartment.
•Refer to operating instructions for further explanation and precautions.
•Safety Warnings and Precautions must be read and understood before the instrument is used.
They must be observed during use.
3
NOTE
THE INSTRUMENTS MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS.
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Contents
Safety Warnings 3
Introduction 5
General description
Battery replacement
User Controls and Display 8
Layout and functions
Operation 10
General Testing procedure
Line Feed
Connection to cable under test
Measuring distance to fault
Menu
TX Null
Velocity Factor
Pulse widths
Techniques to improve accuracy
Care and Maintenance 15
Specifications 16
Symbols used on the instrument are:
Caution:Referto accompanying notes.
Equipment protected throughout by
double or reinforced nsulation.
Instrument flash tested to 3.7kV rms.
Equipment complies with current
EU directives.
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Introduction
Thank you for purchasing the CFL510F cable fault
locator. Before attempting use of your new
instrument please take the time to read this user
guide, ultimately this will save you time, advise you of
any precautions you need to take and could prevent
damage to yourself and the instrument.
The CFL510F is an advanced instrument capable of
identifying a wide range of cable faults. The
instrument uses a technique called Pulse Echo (also
known as Time Domain Reflectometry or TDR). A
pulse is launched into a cable from one end. This can
be on either a pair of conductors, or a conductor and
the screen. The pulse travels down the cable at a
velocity determined by the insulation between the
conductors and this resistance to the flow of the
pulse is characterised as impedance for the cable.
Any changes in cable impedance will cause a
proportion of the pulse to be reflected.
The pulse velocity is normally described as a fraction
of the speed of light and is called the Velocity Factor.
By measuring the time between the transmitted pulse
and the reception of the reflected pulse, and
multiplying this by the speed of light and the velocity
factor, the actual distance to the reflection point can
be established.
Reflections are caused by changes in the cables
characteristic impedance, such as poor joints or
discontinuities. Faults showing an impedance higher
than that of the cables normal impedance will cause
a reflection of the same polarity, i.e.positive, whilst
faults with an impedance lower than that of the cable
will cause an inverse negative going reflection.
Matched cable terminations absorb all the pulse
hence no “end of cable” reflection will occur, the
cable appearing endless. Open or short circuits will
reflect all the pulse and a large reflection will be
displayed. At an open or short circuit all the
transmitted energy is reflected and the TDR will not
‘see’ the cable beyond that fault.
As a pulse travels down a cable, the size and shape
of that pulse is gradually attenuated by the cable. The
pulse reduces in amplitude and becomes more
elongated or stretched. The level of attenuation (or
losses) is determined by the cable type, the condition
of the cable and any connections along its length.
The limit of how far you can see is determined by the
point beyond which you will not be able to see or
distinguish a reflection. To help identify small
reflections, especially at greater distance the
CFL510F has an adjustable gain setting. By
increasing the gain small reflections become more
obvious.
The CFL510F can be used on any cable consisting of
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Introduction
at least two insulated metallic elements, one of which
may be the armouring or screen of the cable. The
CFL510F has internal matching networks to allow
testing of 25, 50, 75 and 100 cables. (These typically
correspond to power, coaxial data and data/telecoms
cable). By selecting the TDR impedance closest to
that of the cable under test, maximum power can be
transmitted into the cable allowing long cables to be
tested.
The velocity factor of the TDR must be adjusted to
match that of the cable under test, allowing an
accurate distance measurement to be read directly
from the instrument. Where the VF of a cable is not
known, but the length is, the cursor can be set to the
end of the cable and the VF on the TDR adjusted until
the correct cable length is displayed.
Other configuration settings include changing the
distance units between metres and feet, changing the
propagation velocity units between a ratio and a
distance per microsecond. Display contrast is fully
adjustable to compensate for all viewing conditions.
A backlight aids viewing in low ambient light
conditions.
The instrument can be powered by manganese-
alkali, nickel-cadmium or nickel-metal-hydride
batteries. All cells must be of the same type.
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When the low battery symbol appears in the
display window the cells are nearly exhausted and
should be replaced as soon as possible. Use alkaline
cells IEC LR6 (AA) 1.5V or 1.2V rechargeable cells
only.
To install or replace the cells, switch the instrument
off. Disconnect the test leads, loosen the battery
cover retaining screws and remove the cover. Lift out
and disconnect the battery holder.
Replace the cells, ensuring that correct polarity is
observed (shown on the battery holder).
Incorrect battery cell polarity can cause electrolyte
leakage resulting in damage to the instrument
Refitting the battery holder is the reverse of removing
it.
7
Battery fitting and replacement
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User controls and display
8
The controls of the TDR have been arranged such that
the instrument is easy to learn and use. The instrument
controls consist of the following
Instrument Display: The display shows the user the
current settings of the instrument and the reflected
energy trace from the cable connected.
Tx Null: This rotary control allows the user to
match the internal balance circuit of the TDR to
that of the cable under test. When correctly
adjusted the majority of the displayed
transmitted pulse can be nulled out, allowing
cable features close to the start of the cable to
be identified. Refer to section TX Null for further
details.
Cursor Left: Moves the ‘distance’ cursor to the
left. Auto repeats if held down.
Cursor Right: Moves the ‘distance’ cursor to
the right. Auto repeats if held down
3000m 1780m 75
0.67R
Ω
Transmission
pulse
Range Distance to cursor Impedance
Gain
Reflection
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9
User controls and display
Find key: Automatically moves the cursor to
the first potential fault (change of impedance).
Power: Pressing this button will turn the
instrument on or off depending on its current
state.
Range: A bi-directional button allowing range
adjustment from 10m (30ft) to 3km (10 000ft)
in 6 steps. The bi-directional feature allows
ranges to be selected forward and backward,
without having to scroll through all the ranges
in one direction
Gain: This control is used to increase or
decrease the gain of the instrument. This
helps the user identify faults over the entire
cable length.
Velocity Factor: Adjusts the Velocity Factor
(VF) of the instrument to match that of the
cable under test.
IMPORTANT: The VF value must match the
VF of the cable under test to give an accurate
distance measurement.
Menu: Allows the user to change the units of
measurement for Distance, Velocity Factor,
Impedance and Test Rate. Refer to menu
section later in this text.
Backlight: Pressing this button will toggle the
backlight on and off. The backlight will
automatically switch off after 1 minute
Contrast: Allows the user to manually correct
the display contrast to suit local ambient
lighting conditions.
Output Sockets: 4mm shrouded sockets designed to
accept the leads supplied with the instrument.
Battery cover: Located on the back of the instrument
and provides the user with access to the battery
compartment. The cover must not be removed while
the instrument is switched on or connected to a cable.
The instrument must not be operated with the cover
open.
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Operation
10
General Testing procedure
Ensure the correct test leads are firmly fitted into the
sockets of the instrument.
Switch on the instrument. The CFL510F will display
the start screen for a couple of seconds, followed by
a trace. The instrument will be set to the range and
velocity factor last used. If these settings are different
for the cable under test (C.U.T) then use the RANGE
and VF keys to set the correct values. Refer also to
‘Velocity factor’ later in this text.
Connection to Cable Under Test
Connect the test lead to the cable under test.
Connection may be made to a live system with a
voltage to earth (ground) less than 300V with an
installation (over voltage) category of III or lower. This
means that the instrument may be connected to any
fixed wiring of a building installation, but not to
primary supply circuits such as overhead cables.
A Fused Lead Set must be used to connect to
energised live systems. Refer to the accessories
section for options.
When selecting 25 cable impedance, an internal
50Hz/60Hz filter is automatically switched in.
Measuring distance to fault
Ensure that the whole length of the cable can be seen
on the display, and that the range selected is correct.
Find key
The Find key searches for the furthest major
change of impedance. This may be a fault or the end
of the cable if this is a short or open circuit.
When found the event is displayed and the cursor
placed on the leading edge. The gain, zoom and
cursor position may need to be adjusted for accurate
measurement. Note that Find does not adjust the
TxNull or Velocity Factor.
To enable ‘difficult to see’ faults to be identified, the
gain of the instrument can be adjusted. With the gain
at minimum small changes of cable impedance may
be overlooked. By increasing the gain the fault
becomes more obvious.
If no faults are obvious, adjust the gain until any major
reflections appear. Open and short circuits should
easily be identified. Partial faults can be less obvious.
If no significant reflections can be seen use the “TX
Null” to minimise the effect of the output pulse on any
potential “near end” faults (refer to section on TX
Null).
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Operation
11
In the event of no reflections being visible, increase
gain until any reflection can be easily identified.
(If no reflections can be seen, try shorting or earthing
the far end of the cable to ensure that you are
“seeing” the whole length of the cable).
The cursor can also be moved using the LEFT and
RIGHT cursor keys. Move the cursor to the beginning
of the reflection. The distance to the fault can then be
directly read from the display.
NOTE: The distance calculation is performed using
the velocity factor set in the TDR. If this velocity
factor is not correct for the circuit under test, the
displayed distance will be incorrect.
Opposite are shown two typical trace displays. The
top shows an open circuit at 2000m away; the
second a short circuit at 2000m away.
0.67R
3000m 2000m
100Ω
0.67R
3000m 2000m
100Ω
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