CABLE FAULT LOCATOR Handheld Graphical

CABLE FAULT LOCATOR Handheld Graphical
TDR Model TDR-44
Operation Manual
Contents
page
1. Introduction
1
2. Batteries
1
3. Safety Rules
2
4. Operating Instructions
2
5. Type of cable fault
5
6. Specification
8
7. Accessories
9
8. Repair and servicing
9
9. Warranty
9
WARNING:
The safety condition is not to connect Fault locator to the energised
cable, even this equipment does not generate any hazardous voltage
to other circuit.
1. Introduction
The Fault Locator is a pulse-echo cable test set which provides a visual indication of
cable faults such as open circuits, shorts and bad connections up to 3000m (9500 ft.) on
metallic cables. The principle of operation is that a pulse transmitted into a cable is reflected by any
imperfection.
The speed at which the pulse travels down the cable is depend upon the dielectric (insulation) of the cable
and the Fault Locator can be set to suit any type of cable dielectric. A list of typical propagation velocity factor
values is given in table A. and a type of cable fault can be determined as section 5. of this manual.
The Fault Locator is available with 120 ohm output impedance and 0.67 defaults PVF
2. Batteries
The unit operate from 6 AA size batteries. Instruction for place / replace batteries are as follows
1) Unscrew the two screws which secure the battery cover on rear side of unit case
2) Lift off the cover
3) Remove old batteries or place new batteries by following polarity mark on the battery pocket
4) Replace battery cover and secure two screws by not over-tightening it
1.1.
3. SAFETY RULES
Though this tester does not generate any hazardous voltages, to circuits to which it can be connected
could not be dangerous. Always check that the circuit to be tested is de- energised before connecting the
tester. Electrical circuits can be dangerous if there is a lack of caution and /or safety practices. Do not use
leads, probes or clips that are damaged or in need of repair with the tester.
Double check the lead connections before making a test.
4. OPERATING INSTRUCTIONS
The display module consists of a 128 X 64 pixel, liquid crystal graphics display with LED back-lighting. A visual
representation of the reflected pulse is provided on a single trace. The break point can be aligned with the
cursor by using the arrow keys when in locate mode and the distance to fault is displayed in meters or feet.
The instrument powers up in the locate mode with 3000 meters range selected, and the propagation
velocity factor set at the optimum for each cable fault locator. In this mode the arrow keys control the
cursor line. The Displayed Range can be altered by selecting Range mode with the menu select key. There
are four ranges and an auto-range, on auto-range the cursor will scroll to the next range when a
predetermined point on the display is reached.
LCD DISPLAY
POWER ON/OFF KEY
BACKLIGHT KEY
UP-DOWN KEY
MENU SELECT KEY
2.
Operates key
Power on/off key
Switch on and off the unit. The unit have auto
powering down If the key is not depressed 5 minutes
Menu select key
This allows the setting up of the Propagation Velocity Factor, Cursor
Control, Range select and Measure unit via the up-down arrow keys.
Backlight key
This illuminates backlight to the display when depressed.
Down key
The down key reduces the Propagation Velocity
Factor, scrolls the cursor left, scrolls down through the
Ranges and toggles measure unit between Metres
and Feet with the appropriate menu selected.
When the Locate Mode is selected and the key pressed twice and then held the
cursor scrolls at a faster rate than normal in the direction indicated.
Up key
The Up key increases the Propagation Velocity Factor, scrolls the
Cursor right, scrolls up through the Ranges and toggles measure unit
between Metres and Feet with the appropriate mode selected.
When the Locate Mode is selected and the key pressed twice and then held the
cursor scrolls at a faster rate than normal in the direction indicated.
4.1 FAULT LOCATION
The following general points should be observed when checking a faulty cable:
(1)
(2)
(3)
(4)
Carry out the safety checks listed under the SAFETY RULES.
The instrument measures the length of cable, not the length of the cable path.
Buried cable loops, snaking cables and other irregularities need to be taken into account.
Measurements will be greater on wet cables.
Do not connect the instrument to a cable pair that is to be ‘burned’ with a breakdown test set.
3.
4.2 FAULT LOCATION ON CABLES WITH KNOWN PROPAGATION VELOCITY FACTOR
In many cases, the cable layout and characteristics are known and the fault location and
analysis should be simple and quick. Under these conditions, the procedure is as follows:
(1) Disconnect the faulty pair from service if possible.
(2) Connect the faulty pair to the line terminals of the tester. (3) Press the 'ON’ key to power up the tester.
(4) After the initialisation period set the required propagation velocity factor by means of the arrow keys
when in PVF Mode. Listed in Table A. are typical values of propagation velocity factor for various cable
dielectrics. Use the menu select key to select metres or feet for the cursor value.
(5) Inspect the trace for a fault pulse and reduce to the minimum Range where the fault
pulse is clearly visible.
(6) Change to locate mode and operate the cursor keys to position the cursor line at
the start of the break point of the fault pulse , for example trace as shown in Fig.1
(7) The distance to the fault may now be read directly from the cursor value, which is at the bottom centre
of the LCD display. This reading can be in meters or feet depending on the parameter selected.
NOTE: The test lead length is automatically removed to give a direct reading of the cable length, therefore
the test leads supplied with the instruments must always be used.
Dielectric Type Typical PVF
Paper Oil filled ( PILC)
2Cross linked poly ( XPLE)
Jelly filled poly
Polyethylene ( PIC)
PTFE ( Teflon)
Paper (Pulp 0.083 uf/mile)
Paper (Pulp 0.072 uf/mile)
Foam Poly
Air space Coaxial
Air
0.50 to 0.56
0.52 to 0.58
0.64
0.67
0.71
0.72
0.88
0.82
0.94
0.98
Table A
4.
4.3 DETERMINING UNKNOW PVF
If the cable dielectric / propagation velocity factor is not known, the PVF setting can be determined from using a
known length of the same type of cable or distance to a known point in the same cable
a) Measure the apparent distance to end or known point with any PVF value, using the normal
procedure as section 4.2 above
b) Press Menu Select Key to PVF mode
c) Adjust Up-down key until the measured distance is agreed with the known distance
d) The PVF shown will be determined as for this type of cable
5. Type of cable fault
The Fault Locator instruments are suitable for locating a variety of faults and cable
conditions. A selection of these is outlined below:
5.1 SHORT CIRCUITS
(1) Shorts between two conductors of a cable pair. The reflection has the downward
Polarity pulse, Fig.1
(2) Sheath shorts are caused when a conductor in a cable makes contact with the
metallic sheath of the cable. To locate a sheath short, first disconnecting the
sheath from earth, connect one terminal to the sheath, the other to the conductor.
(3)
Crosses occur when conductors in the different pairs are crossed at a junction box. Crosses
produce waveforms similar to shorts, but with reduced amplitude. Crosses can be located with the
tester connected to one pair, but a more distinctive fault pulse is obtained if it is connected to the
crossed conductors.
Fig. 1
5.
5.2 OPEN CIRCUITS
(1)
Opens are caused when one or both. Conductors of a pair are disconnected or broken.
The reflection is upward polarity pulse, Fig.2
(2)
Open sheaths are caused by a break in the cable sheath. To locate such faults,
connect the line terminals to the sheath and to as many cable conductors as possible to reduce the
clutter on the screen. This fault produces a fault pulse whose amplitude depends on the resistance of
the break.
Fig. 2
5.3 High Resistive joint / splice
Joints or splices are caused by poor connections when the cables are connected at a junction box. The
reflection is similar to that for an open conductor, its amplitude being dependent upon the quality of
the joint or effective resistance. Fig 3. Besides, A transition from low impedance to high impedance
cable also cause same reflection.
Fig. 3
5.4 Split
Splits occur in cables when the pair is untwisted. This normally occurs at cable junction points, and as
such they are not really faults. They are, however, one of the main causes of clutter on the trace. The
split, when the pair is untwisted, causes an upward fault pulse and the re-split, when the pair becomes
twisted, causes a downward fault pulse Fig 4. As the split and re-split are normally close together, i.e. in
the junction box, the two fault pulses almost coincide, so that they appear on the fault trace as a weak
agitation.
Fig. 4
6.
5.5 Low insulation and Water ingress
These faults are due to contamination of the insulation medium by moisture ingress through a cable.
This gives a reflection like short conductor fault pulse, where the moisture starts, followed by a small
open-type fault pulse where the moisture ends. In some cases, where the moisture increases gradually
with distance, these fault pulses broaden out into a gentle shell or dip in the horizontal trace, Fig 5.
Caused the amplitude of next event curve in display right-side of this water ingress point become
lower. Water in jelly-filled cable may produce only very small fault pulses due to the restricted volume
of water. Besides, a transition from low impedance to high impedance cable also cause same
reflection.
Fig. 5
5.6 Low /Water at Cable joint
This fault is similar to item 5.5 but happen at Cable joint which contaminated by wet environment.
Fault trace is as Fig. 6 which after splice be followed by small sine or square that decreasing gradually.
Fig. 6
5.7 Bridge tap
Bridge taps occur when another pair of conductors is connected to a pair in the main cable to form a branch or
party line. At the branch or bridge junction, a short conductor downward reflection will occur due to the
characteristic impedance haft sharing at that point and follow by upward reflection caused by end of the tap as
shown in Fig 7.
Fig. 7
5.8 Load coils
Load coil are used on telephone lines to increase the line inductance, so improving the transmission
characteristics of long lines. TDR generally will not test pass load coil so the inductive load coils appear
as open circuits to the cable fault locator, so the upward reflection will be displayed as Fig 8.
7.
Fig. 8
6. Specification
6.1 Technical specification
Measure Range:
100, 300, 1000, 3000m and Auto range
Accuracy:
0.9% of Range
Resolution:
Gain:
1% of range
Auto Set across screen
Output Pulse:
PVF:
5V nominal in open circuit
Variable from 0.01 to 0.99
Output impedance:
120 Ohm
Pulse Width:
Connectors:
Automatically varied
Two 4mm safety terminals
LCD Display:
Update Rate:
No touch shutdown:
Display view area:
Power supply:
128x64 graphic LCD with backlight
Once per second
5 minutes
44x62 mm
Batteries 6 AA alkaline or nickel- cadmium cells
Battery Low indicator:
6.5V nominal
6.2 Environment
Operating temp:
Storage temp:
Humidity:
-20 to +60’C
-30 to +70’C
93%
6.3 Physical
Case Dimensions:
Case Material:
Weight:
Leads:
210 X 100 X 50 mm
Fiberglass Nylon 6/6
550g (with batteries)
2 metres safety plug and Alligator clip
8.
7. Accessories
7.1 2 meters test lead Safety Plug 3 mm to Alligator Clip
7.2 Soft vinyl carry case
7.3 Operation manual
8. Repair and servicing
This instrument is not a user serviceable item other than the replacement of batteries. In
the unlikely event of failure please return to the nearest distributor or Manufacturer
Manufacturer address:
Pantong Technologies Co.,Ltd
99/213 Moo 10, Bangkrang, Muangnonthaburi
Nonthaburi 11000, THAILAND
9.