Cable fault detector

Abstract:

Here we present a system to detect and locate the exact fault and fault location in

the cable in a network. The circuit uses discrete components along with ICs. The

faults in the network of cables can be cable open, cable short. The circuit will

check the cables in the network for the above mentioned faults. Also the exact

location of the fault can be found out using this circuit considering the

capacitance of the cable. The circuit considering the capacitance of the cable.

The circuit can be used to detect and locate the fault in the cable in the networks

like telephone network, cable television distribution system or any cable network.

Introduction:

For understanding the overall functioning, refer to the block diagram of the cable

fault locator shown in fig.In a network, three cases may exist: cable open, short or

it can be in the ideal condition.

In the configuration, two possibilities are considered. The cable

open, cable short. If the cable is open, it shows high impedance which causes the

output to be high. If the cable is shorted, the output is. In the second

configuration, resistance parameter is considered to be important. Depending

upon the cable resistance the location of the fault can be detected.

In the third configuration, the capacitance of the cable plays a very important

role. If the cable length is more, the capacitance is more. This capacitance can be

taken in astable mode configuration of IC 555. The output frequency which varies

depending upon the capacitance value is given to F/V converter. The output D. C.

Voltage form IC 2917 F/V converter is taken as output the output voltage for

specific cable length is reference for cable fault detection.

Block diagram of Cable fault detector :

Technical Specification:

1.Power supply

2.ADC7107

3.Wheatstone resistor bridge

4.IC2907

5.IC555

6.Cable

CIRCUIT 1:-

The circuit is based on the simple principle of

V = I x R

For the open circuit and ideal conditions we have to take the

resistance offered by the cable into account.

From the above equation it is clear that if the current (I)

flowing through the cable is kept constant then according to the variation in the

resistance (R), there will be the variation in the voltage (V) at the output of the

circuit.

CIRCUIT 2:-

For The Measurement of the Distance of Fault from the Circuit:-

For location of the fault, the capacitance of the cable is taken into

account i.e. capacitance of the cable varies with the distance.

For this purpose the timer IC 555 is operated in the astable

multivibrator configuration. The cable will be connected in parallel with the

capacitor connected between pin 2 and ground. Now as a capacitance of the

cable changes with distance, the frequency of astable multivibrator changes

accordingly. This frequency change is converted into voltage for the

measurement purpose by the frequency to voltage converter IC LM 2917.

LM2907/LM2917Frequency to Voltage Converter

The LM2907, LM2917 series are monolithic frequency tovoltage converters with a high gain op amp/comparator designedto operate a relay, lamp, or other load when the inputfrequency reaches or exceeds a selected rate. The tachometeruses a charge pump technique and offers frequencydoubling for low ripple, full input protection in two versions(LM2907-8, LM2917-8) and its output swings to ground for azero frequency input.The op amp/comparator is fully compatible with the tachometerand has a floating transistor as its output. This featureallows either a ground or supply referred load of up to 50 mA.The collector may be taken above VCC up to a maximum VCEof 28V.The two basic configurations offered include an 8-pin devicewith a ground referenced tachometer input and an internalconnection between the tachometer output and the op ampnon-inverting input. This version is well suited for singlespeed or frequency switching or fully buffered frequency tovoltage conversion applications.The more versatile configurations provide differential tachometerinput and uncommitted op amp inputs. With thisversion the tachometer input may be floated and the op ampbecomes suitable for active filter conditioning of the tachometeroutput.Both of these configurations are available with an activeshunt regulator connected across the power leads. Theregulator clamps the supply such that stable frequency tovoltage and frequency to current operations are possiblewith any supply voltage and a suitable resistor.

Features:Ground referenced tachometer input interfaces directlywith variable reluctance magnetic pickups Op amp/comparator has floating transistor output 50 mA sink or source to operate relays, solenoids,meters, or LEDs Frequency doubling for low ripple

Tachometer has built-in hysteresis with either differentialinput or ground referenced input Built-in zener on LM2917 ±0.3% linearity typical Ground referenced tachometer is fully protected fromdamage due to swings above VCC and below ground

Wheatstone bridge:A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Its operation is similar to the original potentiometer. It was invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. One of the Wheatstone bridge's initial uses was for the purpose of soils analysis and comparison

In the figure, is the unknown resistance to be measured; , and are resistors of known resistance and the resistance of is adjustable. If the ratio of the two resistances in the known leg is equal to the ratio of the two in the unknown leg , then the voltage between the two midpoints (B and D) will be zero and no current will flow through the galvanometer . If the bridge is unbalanced, the direction of the current indicates whether is too high or too low. is varied until there is no current through the galvanometer, which then reads zero.

Detecting zero current with a galvanometer can be done to extremely high accuracy. Therefore, if , and are known to high precision, then can be measured to high precision. Very small changes in disrupt the balance and are readily detected.

At the point of balance, the ratio of

Alternatively, if , , and are known, but is not adjustable, the voltage difference across or current flow through the meter can be used to calculate the value of , using Kirchhoff's circuit laws (also known as Kirchhoff's rules). This setup is frequently used in strain gauge and resistance thermometer measurements, as it is usually faster to read a voltage level off a meter than to adjust a resistance to zero the voltage.

ADC 7107 :

The Maxim IC7107/7106 are monolithic analog-to-digital converters (ADCs). They have very high input impedances and require no external display drive circuitry. On-board active components include polarity and digit drivers, segment decoders, voltage reference and a clock circuit. The ICL7106 will directly drive a nonmultiplexed liquid crystal display (LCD), whereas the ICL7107 will directly drive a common anode light emitting diode (LED) display.

Versatility and accuracy are inherent features of these converters. The dual-slope conversion technique automatically rejects interference signals common in industrial environments. The true differential input and reference are particularly useful when making ratiometric measurements (ohms or bridge transducers). Maxim has added a zero-integrator phase to the ICL7106 and ICL7107, eliminating overrange hangover and hysteresis effects. Finally, these devices offer high accuracy by lowering rollover error to less than one count and zero reading drift to less than 1µV/°C.

IC555

These devices are used in a wide range of digital panel meter applications. Most applications, however, involve the measurement and display of analog data.

IC 555 working :

Vcc

(5 to 15 v)

4 RESET 8 Vcc

RA 7 3 Output

Discharge

RB

2 5

Threshold Control

Voltage 0.01µf

2 Trigger 1 GND

IC 555 ASTABLE TIMER CIRCUIT

IC 555 ASTABLE TIMER CIRCUIT DIAGRAM

FUNCTIONAL BLOCK DIAGRAM

PIN DAIGRAM OF IC 555 DIAGRAMS

IC 555 AS AN ASTABLE MULTIVIBRATOR:-

The type 555 timer connected for free running or astable operation is

as shown in figure.

During the charging up period, transistor T1 is held open by the flip-

flop and the capacitor charges through the series of resistance Ra and Rb. When

the voltage across the capacitor reaches the reference level of the upper

comparator (2Vcc/3), the comparator changes the state of the flip-flop and this

turns the transistor T1 ON. The capacitor discharges through the resistor Rb, until

its voltage reaches the reference level of the comparator (Vcc/3). This

comparator changes the state of the flip-flop again, which in turn makes the

transistor T1 OFF and the cycle repeats itself.

Form the above description, the charging time is determined by the

equation:-

T1 = C (Ra + Rb) loge Vcc – Vcc/3

Vcc – 2Vcc/3

The above equation immediately follows form the fact that the charging of

the capacitor starts from Vcc/3 instead of 0. Further the charging continues up to

2Vcc/3 after which the upper comparator changes state. The above equation

simplifies to:

T1 = C (Ra + Rb) loge ^ 2

T2 = 0.7 (Ra + Rb) C

The capacitor discharges form 2Vcc/3 towards 0V at which the lower

comparator changes the state. Hence, the discharge period T2 is determined by

the equation:

T2 = C Rb loge 0 – 0Vcc/3

0 – Vcc/3

T2 = C Rb loge^2

Rectifier Filter3 TerminalVtg. Regulator

T2 = 0.7 Rb C.

In the above equation Ra is not present because the capacitor discharges

through Rb only. This equation further is simplified to:

T2 = 0.7 Rb C

The total period is, therefore,

T = T1 + T2

T = 0.7 (Ra + Rb) C

Thus, it can be seen that charging and discharging intervals are different by

0.7 Ra C.

POWER SUPPLY

Power supply is the first and the most important part of our project.For our project we require +5v regulated power supply with maximum current rating 500 mA

Following basic building blocks are required to generated power supply.

230vac Reg.o/p

STEP DOWN TRANSFORMER :

Step down transformer is the first part or regulated power supply . To step down the mains 230V A.C. we require step down transformer. Following are the main characteristic of electronic transformer.

I) Power transformer are usually designed to operate from source of low impedance at a single freq.

II) It is required to construct with sufficient insulation of necessary dielectric strength.

III) Transformer rating are expressed in volt-amp. The volt-amp of each secondary winding or windings is added for the total secondary VA. To this are added the load losses.

IV) Temperature rise of a transformer is decided on two well known factors i.e. losses on transformer and heat dissipating or cooling facility provided unit.

RECTIFIER UNIT:

Rectifier unit is a ckt. Which converts A.C. into pulsating D.C. Generally semi-conducting diode is used as rectifying element due to its property of conducting current in one direction only Generally there are two types of rectifier.

1. Half wave rectifier2. Full wave rectifier.

In half wave rectifier only half cycle of mains A.C. rectified so its efficiency is very poor. So we use full wave bridge type rectifier, in which four diodes are used. In each half cycle, two diodes conduct at a time and we get maximum efficiency at o/p.

Following are the main advantages and is advantages of a full-wave bridge type rectifier ckt.

ADVANTAGES :

1. The need of center tapped transformer is eliminated.2. The o/p is twice that of center tap circuit for the same secondary

voltage.3. The PIV rating of diode is half of the center taps circuit.

DISADVANTAGES :

1. It requires four diodes.2. As during each half cycle of A.C. input, two diodes are

conducting therefore voltage drop in internal resistance of rectifying unit will be twice as compared to center tap circuit

Filter circuit :

Generally a rectifier is required to produce pure D.C. supply for using at

various places in the electronic circuit, However, the o/p of rectifier has pulsating

character i.e. if such a D.C. is applied to electronic circuit it will produce a hum

i.e. it will contain A.C. and D.C. components. The A.C. components are

undesirable and must be kept away from the load. To do so a filter circuit is used

which removes (or filter out) the A.C. components reaching the load. Obviously a

filter circuit is installed between rectifier and voltage regulator. In our project we

use capacitor filter because of his low cost, small size and litile weight and good

characteristic. Capacitors are connected in parallel to the rectifier o/p because it

passes A.C. but does not pass D.C. at all.

Three terminal voltage regulators :

A voltage regulator is a ckt. That supplies constant voltage regardless of change in load current. IC voltage regulators are versatile and relatively cheaper. The 7800 series consists of three terminal positive voltage regulators. these ICs are designed as fixed voltage regulator and with adequate heat sink, can deliver o/p current in excess of 1A. These devices do not require external component. This IC also has internal thermal overload protection and internal short circuit and current limiting protection for our project we use 7805 voltage regulator IC.

D3T3 D1

+5V

1GNDD2

2GND

0-10 , 500 mA

230VAC@50HZ

+C1

D4

+C3

7805

1 3VIN VOUT

Design to step down transformer :

The following information must be available to the designer before the commences for the design of transformer.

1. Power output2. operating voltage.

7812

3. Frequency Range4. Efficiency and Regulation

Size of core :

Size of core is one of the first consideration in regard of core and winding configuration used. Generally following formula is used to find area or size of core.

Ai = (p1/0.87)

Where

Ai = Area of cross section in sq. cm.

P1 = Primary voltage

In Transformer P1 = P2

For our project we required +5V regulated output. So transformer secondary rating is 12V, 500 mA.

So secondary power wattage is,

P2 = 12 X 500 X 10 –3 w.

= 6w.

so ,

Ai = (6/0.87)

= 2.62

Generally 10% of area should be added to core accommodate all turns for low Iron losses and compact size.

So,

Ai = 2.88.

Turns per volt

Turns per volt of transformer are given by relation

10,000

Turns/volt = -------------------

4.44f B Ai

Here;

F is the frequency in Hz

B is flux density in Wb/m2

A is net area of cross section.

For project for 50Hz the turns per volt for 0.91 wb/m2,

Turns per volt = 50/Ai

= 50/ 2.88

= 17

Thus for primary winding = 220 X 17 = 3800.

For secondary winding = 12 X 17 = 204

Rectifier design :

R. M. S. Secondary voltage at secondary of transformer is 12V. So, maximum voltage Vm across Secondary is

= RMS voltage *1.41

= 12* 1.41

=16.97

D.C. output voltage at rectifier o/p is

Vdc = 2Vm/3.14

= 2*16.97/3.14

= 10.80 v

PIV = 2 Vm

= 2 X 16.97

= 34V

Design of filter capacitor

Formula for calculating filter capacitor is,

1

C = -----------------------------

4. 3 r f RL

r = ripple present at o/p of rectifier.

(Which is maximum 0.1 for full wave rectifier ?)

f = Frequency of mains A.C.

R = I/p impedance of voltage regulator IC.

1

C = ------------------- = 1000F

4 3 0.1*50*28

IC 7805 (Voltage regulator IC):-

Specifications :-

Available o/p D.C.voltage = + 5V Line regulation = 0.03 Load regulation = 0.5 Vin maximum = 35 V Ripple Rejection = 66-180(db)

TESTING AND TROUBLESHOOTING

Before soldering in components:

Check that component agree with the parts list (value and power of resistors, value and voltage rating of capacitor, etc.) if in any doubt double check the polarized components (diodes, capacitor, rectifiers etc)

If there is a significant time elapse between circuit, take the trouble to read the article; the information is often given in a very condensed from. Try to get most important point out of the description of the operation of the circuit, even if you don’t understand exactly what is supposed to happen.

If there is any doubt that some component may not be exact equivalent, check that they are compatible.

Only use good quality IC sockets. Check the continuity of the tracks on the PCB (and through plated holes

with double sided boards) with a resistance meter or continuity tester. Make sure that all drilling, filling and other ‘heavy’ work is done before

mounting any components. If possible keep any heat sinks well isolated from other components. Make a wiring diagram if the layout involves lots of wires spread out in all

directions. Check that the connectors used are compatible and that they are mounted

the right way round. Do not reuse wire unless it is of good quality. Cut off the ends and strip it a

new.

After mounting the component:

Inspect all soldered joints by eye or using a magnifying glass and check them with a continuity tester. Make sure there are no dry joints and no tracks are short circuited by poor soldering.

Ensure that the positions of all the component agree with the mounting diagram

Check that any links needed are present and that they are in the right positions to give the desired configuration.

Check all ICs in their sockets (see that there are no pins bent under any ICs, no near ICs are interchanged etc.)

Check all the polarized components (diodes, capacitor etc) are fitted correctly.

Check the wiring (watch for off cuts of components leads) at the same time ensure that there are no short-circuits between potentiometer, switches,

etc. and there immediate surrounding (other components or the case). Do the same with mounting hardware such as spacers, nuts and bolts etc.

Ensure that the supply transformer is located as closely as possible to the circuits (this could have a significant improvement in the case of critical signal level).

Check that the connections to the earth are there and that they are of good contact.

Make sure the circuit is working correctly before spending any time putting it into a case.

And if it breaks down:

Recheck everything suggested so far. Re-read the article carefully and carefully anything about which you are

doubtful. Check the supply voltage or voltages carefully and make sure that they

reach the appropriate components especially pins of the ICs (test the pins of ICs and not the soldered joints).

Check currents (generally they are stated on the circuit diagram or in the text). Don’t be too quick to suspect the ICs of overheating.

If possible check the operation of the circuit in the separate stages as a general rule follow the course of the signal.

While checking voltages, currents, frequencies or testing the circuits with an oscilloscope work systematically and take notes.

And don’t forget to switch the power on and check the fuses. PCB DESIGN

Designing of PCB :

I) After selection of electronic circuit, make a block diagram of various circuits to know various inter-connections required, which will help in reducing the number of wires.

II) The designer should have the complete idea of the circuit regarding the function and signal flows through.

III) Keep each and very component you need, while starting the designing.

IV) Use of templates is essential if you are new designer, if the design is manual i.e. hand made and not with software such as Orcas, Auto CAD, Pads, Ideas, Circuit maker, etc.

V) Standard PCB size should be decided in the beginning only.VI) Preferably, layout ands artwork should be in 1:2 scales.VII) Sequential stage after PCB size is decided.VIII) Component placement.IX) Track routing i.e. layout.X) Artwork making with ink or ready made tapes and pads.XI) While routing the tracks, carrying AC mains voltage, consider the

safety rules ands regulations.XII) In analog and digital systems together, care should be taken that

analog and digital ground will not mix each other affecting the stability ands fluctuations in the display.

XIII) In power system i.e. high current, the track width and the track spacing should be as maximum as possible.

XIV) While placing the components on the PCB preferably the load on PCB, should be evenly distributed to avoid the problems at completion stage during wave-soldering i.e. warping of PCB etc.

XV) To avoid weakening of the pup tool, the perforation length should be kept minimum i.e.<40 mm.

XVI) For the manually shouldered components vent i.e. cut pads should be provided to avoid the blocking of the holes during shouldering

COMPOMENT PLACEMENT :

I) Preferably, place the component in X-Y direction subjected to mechanical construction.

II) All components should be flat mounted i.e. flat placed to avoid of leads and for easy requirements. However in case of space limitation the components such as resistors, diodes, etc. may be mounted vertically which doesn’t affect the performance.

III) In case separate analog and digital ground.

IV) Orientation of multi-lead components(e.g. switches, Ics) should be connected in between the analog and digital ground .

V) Sufficient clearance is provided around component so that inversion or replacement ands repair is easy.

VI) The design should such that minimum jumpers are allowed.VII) It is preferable that, components like present, coils, and trim

pots, etc. which alignment of calibration are placed in such that, they are accessible after the assembly of the PCB on cabinet also.

VIII) If the components are not flush mounted, provide the sleeve for leads.

APPLICATIONS:-

1. In Cable Networks

A) In Telephone Cable Network

B) In Cable Tv Distribution System

2. In Any Type of System Having Large Hardware Section.

For the systems containing enormous amount of hardware, if any fault

persists in the cable then it is very difficult to detect and locate the fault.

In such cases this system is employed for the purpose of fault detection

and location of fault. In such cases a lookup table for all the cables in the

circuit is prepared and the corresponding action is taken.

Component List:

No. Component Qty.1 Power supply 12 Wheatstone bridge 13 LED display 14 ADC 7107 1

5 IC 2907 16 Cable 17 IC 555 1

8

Costing :

No. Component Cost per item1 Power supply2 Wheatstone bridge3 LED display4 ADC 71075 IC 29076 Cable7 IC5558910

Time management :

No. Nature of the activity Time study1 Servey and searching of project 15 days 2 Finalization of project title 15 days 3 Selection of components 8

4 Fabrication of basic structure 105 Machining and assembly of sub assemblies 106 Assembly of the main project 157 Testing and trials to be taken. 48 Result preparation 29 Documentation 810 Report preperation 8