How to measure stress/tension on a rope?

T

Tony Limson

Guest
(a) Imagine an 5-100kg (we do not know exact weight) object is hanged with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the string?
 
(c) How can we measure, electronically,em the stress/tension on the string?
Click to expand...
Study catenary curves. Apply some high school physics and algebra.
 
"Tony Limson" <tl@abcde.com> wrote in message
news:43203573$0$21677$afc38c87@news.optusnet.com.au...
(a) Imagine an 5-100kg (we do not know exact weight) object is hanged with
a piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the
string?
Click to expand...

** PISS OFF YOU DOPEY TROLL !!




............ Phil
 
"Tony Limson" <tl@abcde.com> writes:

(a) Imagine an 5-100kg (we do not know exact weight) object is hanged with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the string?
Click to expand...
I think you need to say if you are allowed to cut the rope in order to
insert a transducer (load cell etc).

Also the question appears a bit homework-like! So if it isn't, perhaps
you should tell us a bit more about the application so that people are
not put off replying.


--

John Devereux
 
In comp.arch.embedded Tony Limson <tl@abcde.com> wrote:

(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the string?
Click to expand...
Without access to the string, it can't be done in any way that could
justifiably be called "electronically". You're talking about doing
some serious physics here. Like: shoot a lot of x-ray intensity at it
and have an expert interpret the diffraction pattern for you to
determine the lattice length of the string, from that (assuming you at
least know the material) the deformation and from that, in turn, the
tension. Or shoot acoustic energy at it over a wide spectrum and try
to find its resonance frequency.

--
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.
 
"Hans-Bernhard Broeker"

Or shoot acoustic energy at it over a wide spectrum and try
to find its resonance frequency.
Click to expand...

** That is the key.

You need to know about the string/wire/rope ( ie mass per unit length ) to
relate resonant frequency to tension.

Then just pluck the string and measure the frequency of vibration - many
ways to do that.





........... Phil
 
Tony Limson wrote:
(a) Imagine an 5-100kg (we do not know exact weight) object is hanged
with a piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the
string?
Click to expand...
Make a loop in the middle of the string and put an electronic scale or load
cell in there.

Mitch
 
Tony Limson wrote:
(a) Imagine an 5-100kg (we do not know exact weight) object is hanged with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the string?
Click to expand...

You have described a "pendulum" : oscillation frequency is
proportional to pendulum length and weight on the end.

If you know the time for one oscillation, the gravitational
acceleration, length of the rope, you should be able to
solve for the mass of the pendulum (weight + rope).

Once you have the mass at the end and the velocity of it you
should be able to calculate the force exerted on the rope
through centrifugal force.

Sounds like a lot of mucking around.
 
On Thu, 08 Sep 2005 23:52:52 +1000, Mark Harriss <billy@blartco.co.uk>
wrote:

Tony Limson wrote:
(a) Imagine an 5-100kg (we do not know exact weight) object is hanged with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the string?





You have described a "pendulum" : oscillation frequency is
Click to expand...
Yes.

proportional to pendulum length and weight on the end.
Click to expand...
Umm, no. But thanks for playing.

Hint: where is the "weight" in 2*pi*sqrt(L/g)?

Regards,

-=Dave
--
Change is inevitable, progress is not.
 
"Mark Harriss" <billy@blartco.co.uk> wrote in message
news:43204229$0$22631$61c65585@uq-127creek-reader-03.brisbane.pipenetworks.com.au...
Tony Limson wrote:
(a) Imagine an 5-100kg (we do not know exact weight) object is hanged
with a piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the
string?


You have described a "pendulum" : oscillation frequency is
proportional to pendulum length and weight on the end.
Click to expand...
Pendulum, yes.

But length only, not weight. Therefore, probably no help here.

Perhaps if you knew the length and weight of the string, you
could calculate the center of mass by the period of the swing,
then from that the mass of the object.

But my last Physics class was about 30 years ago...

Rufus
 
(a) Imagine an 5-100kg (we do not know exact weight) object is hanged
with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the
string?

I think you need to say if you are allowed to cut the rope in order to
insert a transducer (load cell etc).

Also the question appears a bit homework-like! So if it isn't, perhaps
you should tell us a bit more about the application so that people are
not put off replying.
John Devereux
Click to expand...

No, this is not homework, and I'm not a student.

Imagine a parachute. How can you measure stress/tension on a parachute line?
You can not access the either end of the string/line. (One end connectected
to parachute, the other is connected to carabiner.)
 
Tony Limson wrote:
(a) Imagine an 5-100kg (we do not know exact weight) object is hanged with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the string?
Click to expand...
Maybe you're trying to design the ultimate way to hang people? :D
 
"Tony Limson" <tl@abcde.com> wrote in message
news:43205daa$0$22808$afc38c87@news.optusnet.com.au...
(a) Imagine an 5-100kg (we do not know exact weight) object is hanged
with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the
string?

I think you need to say if you are allowed to cut the rope in order to
insert a transducer (load cell etc).

Also the question appears a bit homework-like! So if it isn't, perhaps
you should tell us a bit more about the application so that people are
not put off replying.
John Devereux


No, this is not homework, and I'm not a student.

Imagine a parachute. How can you measure stress/tension on a parachute
line?
You can not access the either end of the string/line. (One end
connectected to parachute, the other is connected to carabiner.)
Click to expand...
Can we contact the string/line at all? Do we know what it is made of?

If so we could potentially measure stretch over a small sample if we can
access it before the load is applied and can previously know the stretch
characteristics.
 
Dave Hansen wrote:
On Thu, 08 Sep 2005 23:52:52 +1000, Mark Harriss <billy@blartco.co.uk
wrote:


Tony Limson wrote:

(a) Imagine an 5-100kg (we do not know exact weight) object is hanged with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the string?





You have described a "pendulum" : oscillation frequency is


Yes.


proportional to pendulum length and weight on the end.


Umm, no. But thanks for playing.

Hint: where is the "weight" in 2*pi*sqrt(L/g)?

Regards,

-=Dave
Click to expand...
Unless the rope is infinitely rigid (wonderful first year physics assumption),
the period and the swing itself will vary with the mass, because the rope will
stretch with the angular acceleration. I don't want to do the math, even if I
could.

Not that this applies to this case, but just to be complete.
 
Tony Limson wrote:
(a) Imagine an 5-100kg (we do not know exact weight) object is hanged with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the string?
Click to expand...
I'm sure Gary Peek would know. He's an
occasional poster on this group and has
used our controllers to measure tension
on parachute shrouds.
 
On Fri, 9 Sep 2005 01:56:11 +1000, "Tony Limson" <tl@abcde.com> put
finger to keyboard and composed:

(a) Imagine an 5-100kg (we do not know exact weight) object is hanged
with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the
string?

I think you need to say if you are allowed to cut the rope in order to
insert a transducer (load cell etc).

Also the question appears a bit homework-like! So if it isn't, perhaps
you should tell us a bit more about the application so that people are
not put off replying.
John Devereux


No, this is not homework, and I'm not a student.

Imagine a parachute. How can you measure stress/tension on a parachute line?
You can not access the either end of the string/line. (One end connectected
to parachute, the other is connected to carabiner.)
Click to expand...
Would it be acceptable to fit a sensor to the harness and assume the
load is equally distributed amongst the risers?

Otherwise, is this what you are looking for?

Collecting Parachute Test Drop Data:
http://www.industrologic.com/cptdd.htm

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.
 
In article <43203573$0$21677$afc38c87@news.optusnet.com.au>,
tl@abcde.com says...
(a) Imagine an 5-100kg (we do not know exact weight) object is hanged with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the string?




Lots of people make load cells designed to measure tension on lines.
Click to expand...
One compact version---albeit for higher loads, is shown at:

http://www.atairaerospace.com/das/sensors/

Mark Borgerson
 
On Fri, 9 Sep 2005 01:56:11 +1000, "Tony Limson" <tl@abcde.com>
wrote:

(a) Imagine an 5-100kg (we do not know exact weight) object is hanged
with a
piece of string/rope/wire and swings randomly.
(b) We do not have access to either end of this string.
(c) How can we measure, electronically,em the stress/tension on the
string?

I think you need to say if you are allowed to cut the rope in order to
insert a transducer (load cell etc).

Also the question appears a bit homework-like! So if it isn't, perhaps
you should tell us a bit more about the application so that people are
not put off replying.
John Devereux


No, this is not homework, and I'm not a student.

Imagine a parachute. How can you measure stress/tension on a parachute line?
You can not access the either end of the string/line. (One end connectected
to parachute, the other is connected to carabiner.)
Click to expand...
You probably could make a simple gizmo to measure the strain
using inexpensive force sensors like below (search
www.digikey.com for force sensors). You would just slip the
parachute line in the gizmo sideways and when the string is
pulled tight the gizmo flexes pinching the sensor in preportion
to the pull on the line.

http://tinyurl.com/96srw
 
Dave Hansen wrote:
Umm, no. But thanks for playing.

Hint: where is the "weight" in 2*pi*sqrt(L/g)?
Click to expand...

Try 2*pi*sqrt(L/g)= 2*pi*sqrt(m/k)

where m = mass

Regards,

-=Dave
Click to expand...


thanks for playing.

Regards,

-=Mark
 
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