Measuring Time of Propagation in a Circuit

Hear is one way:

Al

Your main limitation is going to be in your initial transducers. What kind of signal is it that you're propagating, and in what kind of medium?

Cheers, Pete.

this guy specialises in precision timing _not_cheap_ but may be within your undisclosed budget.

OTOH can you compare your unknown medium with a known one? (perhaps by measuring the index of refraction)

Thanks for all of the replies everyone. I was trying to generalize my question, but maybe it's best if I just explain it in more detail.

What I'm really trying to do is to basically measure the length of a wire. I know the dialectric constant of the material so I figured the best way to do this would be to measure the amount of time that an electrical signal takes to propagate through the wire. Al's suggestion of the time-domain reflectometer led me to a lot of relevant information and circuits online. Most of the applications of TDR seem to be aimed at long distance (>>1m) while I would really like to be dealing with lengths less than a meter and measuring with a precision of less than a couple cm.

I'm pretty new to electronics (I'm more of a programmer) and I still have to do some reading before figuring out exactly what I need to do. One idea I had was that if I had reference lengths of wire I could send simultaneous pulses down the wire and a reference and then have them join. Maybe it would be easier to tell if they constructively interfere than to do precise timing?

Sorry I'm so unfamiliar with electronics, but I really appreciate how welcoming and helpful your comments were. Rob

If the geometry of the wire is know it may be easier to measure its capacitance.

snipped-for-privacy@gmail.com Inscribed thus:

With respect to TDR the pulse rise time determines the shortest length that you can measure. ie the time for the pulse voltage to go from zero to max has to be shorter than the time taken for its echo to return to the measurement point.

Measurement to a few mm is not an easy task and becomes more difficult as the measured length gets smaller.