Want to measure cable length

Projects Programming
1

Hi All,

Any guidance regarding any way to measure cable length between 0 to 150 meter?

How can do it with Arduino?

Thanks,

2

Are both ends of the cable in the same location ?

3

yes on the same location it's like LAN cable.

5

Propagation rate of a pulse\signal down a cable is about 198m/us.

So to get 1m accuracy to would need to measure the pulse to circa +-10nS, if you detecting the reflection from the remote end. Not straightfoward with Arduino at all.

Get a proper LAN cable TDR.

6

@srnet Thanks bro!

Any suggestion diagram connection and how to achieve it with idea?

7

Hi,
Google

Time-domain reflectometer arduino

This should give you an idea of the technicalities.

Tom... :grinning: :+1: :coffee: :australia:

1 Like
8

No ideas.

I would not bother to try, so much easier to buy one of the basic ready built ones.

And easy to do TDR measurements with a simple pulse generator and a Scope if you must, is it not ?

9

I can do the 0 meter part …

1 Like
10

Thanks guys I will try to figure it our using TDR.

11

Ohh Really!

12

Hi,
I happened to watch this video recently and thought it may be of interest, it is not Arduino based but shows the concept of building a TDR

13

Physical length, or electrical length? You need to know the velocity factor if you need to convert between the two. Cables do not pass signals at the speed of light, it's some percentage slower.

14

For co-ax LAN cables the velocity factor is around 69% and for Cat5\6 65%.

You do need to check the spec for the actual cable or calibrate.

15

  1. Many LAN cables have length marks. The spool I have they are every foot. Could you possibly have markings on yours?

  2. See if you can borrow an LAN analyzer.

16

you can get a TDR off eBay for $15. it requires a scope, but not a fantastic scope. I would get a 4 channel scope so you can see time relationships between sensors and outputs.

edit - $20, and out of stock

17

Yes. Use a tape measure.

I suppose you could also use something like this:

What makes you think that Arduino would be useful here?

18

I want electrical length not physical length

19

Electrical length - do you want cable parameters such as capacitance and resistance ? That’s a different issue and measure my technique , or is about reflections which you may be able to model .

Why do you want to know ?

Cable parameters are usually in the specification , running a cable near “its “limits for your application is not good .

20

Why? What kind of signals are you using it for? How is it terminated?

21

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