sensor for detection wire length

[asa1365]

Dear friends
I want to design a circuit to detection wire length.
please introduce a suitable sensor .

Thank you

 

[FvM]

Insufficient problem information. E.g. a wire is laying on the table, stretched free in air, coiled...

Could e.g. measure wire resistance.

 

[asa1365]

Thank you ,how measure wire resistance?
and how can i detection where wire is broken or cut?

 

[FvM]

Resistance measurement is utilizing ohms law, I = V/R. E.g. applying a voltage, measuring current, or vice versa.

To approach the other problem, you should answer the simple questions above. Under circumstances, wave travel time can be used (TDR), possibly simple capacitance measurement, may be non-electrical methods like sound/ultrasonic propagation.

 

[asa1365]

Thanks, can I use ultrasonic sensor for second problem ?

too I want to Check open, short, cross, crosstalk cable and
Locate short and breakage point accurately for cable ?
please suggest a solution ?

 

[FvM]

Now the problem has changed from wire length to cable open and short detection. An universal solution is using previously mentioned time domain reflectrometry (TDR), suggest you read about it. https://en.wikipedia.org/wiki/Time-domain_reflectometer

 

[asa1365]

thank you , exactly it is like what i need , for design its circuit should search about TDR circuit

 

[FvM]

Requirements for TDR circuits are quite different depending on intended length resolution. To demonstrate/evaluate the technique, a fast pulser with <ns rise time and a sufficient fast oscilloscope can do. Consider that 1 ns round trip resolution translates to about 10 cm length for a cable with 5 ns/m propagation delay.

 

[asa1365]

Thank you very much . can you explain how calculate rise time for for a 1 m coaxial cable ?

 

[123jack]

If you use a scope make sure it's in calibration.
I once sent a man out to dig up a waveguide and was quite a distance off where
the rat had chewed through it....
10 points if you can tell me how we knew it was a rat ......

 

[chuckey]

Bits of burnt rat hanging in the bushes?
Frank

 

[ahsan_i_h]

Thank you very much . can you explain how calculate rise time for for a 1 m coaxial cable ?

Rise time must be lower than the time delay between incident wave and reflected wave. Lower the rise time, better the accuracy. Your coaxial cable length is 1m, so the delay is 10ns. With a rise time of 2-5ns you can possibly detect the length.

 

[comparch]

Also, Resistance = rho * (length of wire/ Area of cross section of the wire), where "rho" is resistivity of wire material.

Something that can be useful.

 

[CataM]

If you use a scope make sure it's in calibration.
I once sent a man out to dig up a waveguide and was quite a distance off where
the rat had chewed through it....
10 points if you can tell me how we knew it was a rat ......

Are you going to tell us how did you know?

 

[asa1365]

can I create pulse with microcontroller for example stm32f103by timer ?

 

[c_mitra]

You need to consider several aspects before you put on your soldering iron.

1. You can certainly produce a pulse using a microcontroller. How do you apply and also detect the echo?

2. During its journey along the wire, the pulse will get integrated by local capacitances and inductances. So you must apply a reasonably strong pulse.

3. When it reaches the end, it finds no load (where to dump its energy) and decides to come back. You can consider that it is more like a wave that has hit the wall.

4. When it returns you must have your probe ready at the same place. It may not be in good shape but then...

 

[asa1365]

your opinion, , how much frequency need for a cable about 2m for work well ?

if I want to detect pulse with out probe and just display result on Lcd , how can continue?

 

[c_mitra]

You need to consider the following:

The velocity of the pulse is same as the velocity of light in vacuum but it is about 10% in metals. Light travels 30cm/nS in vacuum and as a rough estimate, the electrical pulse will travel about 3 cm/nS.

You need to follow one edge of the pulse; no need to produce extremely narrow pulses. But the pulse must be over before we settle down and look for the reflection.

Basically we see that 1 uS pulse will extend about 3 meters of the cable. So you need to use pulses in the nS range. One single pulse having 10-100ns may be sufficient.

 

[123jack]

Sorry for the delay - not been here for a few days....
10 points to chucky of course...
It fried the little bugger.

 

[asa1365]

Thank you , please explain about detect pulse echo with micro or every Ic ?