Measuring Time of Propagation in a Circuit

[[email protected]]

Hello,

I'm new here but I have a question that hopefully somebody will help
me out with. I'm interested in measuring the amount of time it takes
for a signal to propagate through a medium. Ideally, I would like to
measure times on the order of 200 to 2000 picoseconds with a
resolution of 10 picoseconds or better. My worry is that these numbers
are unrealistic (taking budget and complexity into account). I figured
it was worth asking though. Maybe there are highspeed ICs that could
facilitate this?

Thanks in advance for any helpful comments; I'm just trying to learn,
Rob

 

[alchazz]

Hello,

I'm new here but I have a question that hopefully somebody will help me
out with. I'm interested in measuring the amount of time it takes for a
signal to propagate through a medium. Ideally, I would like to measure
times on the order of 200 to 2000 picoseconds with a resolution of 10
picoseconds or better. My worry is that these numbers are unrealistic
(taking budget and complexity into account). I figured it was worth
asking though. Maybe there are highspeed ICs that could facilitate this?

Thanks in advance for any helpful comments; I'm just trying to learn,
Rob

Hear is one way:

http://en.wikipedia.org/wiki/Time-domain_reflectometer



Al

 

[Pete Wilcox]

Hello,

I'm new here but I have a question that hopefully somebody will help me
out with. I'm interested in measuring the amount of time it takes for a
signal to propagate through a medium. Ideally, I would like to measure
times on the order of 200 to 2000 picoseconds with a resolution of 10
picoseconds or better. My worry is that these numbers are unrealistic
(taking budget and complexity into account). I figured it was worth
asking though. Maybe there are highspeed ICs that could facilitate this?

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.

 

[Jasen Betts]

Hello,

I'm new here but I have a question that hopefully somebody will help
me out with. I'm interested in measuring the amount of time it takes
for a signal to propagate through a medium. Ideally, I would like to
measure times on the order of 200 to 2000 picoseconds with a
resolution of 10 picoseconds or better. My worry is that these numbers
are unrealistic (taking budget and complexity into account). I figured
it was worth asking though. Maybe there are highspeed ICs that could
facilitate this?

Thanks in advance for any helpful comments; I'm just trying to learn,
Rob

www.highlandtechnology.com

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)

 

[[email protected]]

 www.highlandtechnology.com

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

 

[Jasen Betts]

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.

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

 

[Baron]

[email protected] Inscribed thus:

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

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.