[SOLVED] Please Guide me for designing the circuit

hello friends i want to measure the distance of cable fault .i found this link useful.can anybody show me how they have designed resistors and switches. Please help me. Check this video

https://www.youtube.com/watch?v=2a-VCVpF3uM

im not completely sure but there are two possibilities:
1. for eg. dividing 100m of cable into 2m and at every 2m adding a transformer or some kind of seperator. Then connecting devices between two pf such nodes to find continuity fault.
2. Or finding all parameters of a 100m cable like resistivity, cross section area, length (of course) etc and making an equivalent RLC circuit to find a time constant. Now input a step signal and waiting for it to return. If it takes less than calculated time constant, there is cut. If it takes more, i think it may be bcoz of characteristic changes in wire over time.

This is very theoretical so i cannot guarantee if its the correct one. Hope that helps.

they have simply used 1k resistors and switches in series or parallel .and measured the voltage drop throuogh adc it seems

It seems to measure cable resistance and scale the reading into distance according to the conductivity of the cable material. Measuring from one end it could only tell how far away a short circuit was and only then if the short was 'perfect'. Any resistance across the fault would make the distance seem further away than it really was and a break would return nothing. Looks like a school project to experiment with ADC rather than a practical instrument.

The method used commercially is quite different. A system called TDR (Time Domain Reflectometry) is used. A fast edged pulse is sent from one end and the return time taken for the 'echo' to come back is measured. From the velocity factor of the cable the exact distance can be determined. It works whenever there is a mismatch of cable impedance so it can detect shorts, opens and to some extent things like kinks in the cable.

Brian.

aameer said:

hello friends i want to measure the distance of cable fault

Click to expand...

If you want to measure the distance of cable fault from Power Systems perspective, then you have to use a Distance Relay. A simple Google search for Distance Relays gives you an idea of how a distance relay works.

This design assumes a certain conductor resistance per km length to use Ohm's Law to measure distance. It ignores EMI induced into long transmission lines, ignores inductance and requires that no transformers be connected when the fault is detected which would cause measurement error.

Most line fault detectors use a pulse with TDR method to locate an open or short circuit.

thanks for providing valid information .i am also to do school project for my brother. Can you tell me how they connected resistance and switches . Whether they have connected resistance in series or parallel

I would guess they wired them in series and use the switches to short out individual resistors to change the total resistance of the chain. To be honest, it wouldn't make much difference which way it was wired as long as pressing a switch changed the overall value.

As a cable fault detector it would be useless, it is nothing more than a complicated Ohm meter and probably less accurate than a cheap DVM.

My guess would be they wire a resistor of say 100K from the ADC input to ground then use the chain of resistors/switches to the 5V supply rail. It would make a potential divider with the ratio of 100K to the resistor chain deciding what voltage was measured at their junction. I'm not even sure why the second IC was used, most MCUs have a built in ADC these days.

Brian.

they have used AT89c52 in which there is no built in ADC so they have interfaced externally

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Please will u provide me the circuit of resistors and switches that is to be given to ADC

@betwixt
please provide me the circuit