World's Largest Wheatstone Bridge [Physics]

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From: Bret Cahill on 3 May 2010 14:38

> >String a wire back and forth across / along a fault line to measure
> >very small displacements in the earth's surface. If the resistance
> >and/or tensile strength needs to be higher than a common single alloy
> >wire then structural steel cable could be wrapped around a insulated
> >wire with a higher resistivity. It could be temperature compensated
> >as usual, with another wire of the same length loosely supported
> >nearby in another leg of the bridge.
>
> >An abandoned power line may be good to go if it is properly located.
>
> >Good info sometimes comes in small displacements.
>
> >Bret Cahill
>
> You cannot get a good enought temperature (and other factors)
> compensation with such a setup.

Compensation for temp. and other factors is easy: Just loosely wrap
another identical wire around the taught wire and shield and insulate
it for another leg of the bridge.

> A bird sitting on the wire

They may have to use fake owls or bury it underground.

> would trigger a massive earthquake alarm, and the evacuation of San Francisco and Los Angeles and every
> clay hut in between, for example.

The data wouldn't be made available to the general public until after
it was studied and determined to be useful in predicting earthquakes.

Supposing 95% of a certain kind of fault line gives some kind of micro
displacement warning an hour or so in advance of an M 8.0?

Wouldn't that be worth an investigation?

The World's Largest Strain Gage might turn out to be pretty cost
effective at saving lives and property.

Bret Cahill

From: Sjouke Burry on 3 May 2010 15:14

Bret Cahill wrote:
>>> String a wire back and forth across / along a fault line to measure
>>> very small displacements in the earth's surface. If the resistance
>>> and/or tensile strength needs to be higher than a common single alloy
>>> wire then structural steel cable could be wrapped around a insulated
>>> wire with a higher resistivity. It could be temperature compensated
>>> as usual, with another wire of the same length loosely supported
>>> nearby in another leg of the bridge.
>>> An abandoned power line may be good to go if it is properly located.
>>> Good info sometimes comes in small displacements.
>>> Bret Cahill
>> Two gps stations on both sides do the same trick
>
> What's the smallest displacement -- not movement but actual change in
> _distance_ between two points -- they can measure?
>
>
> Bret Cahill
>
They measure continental drift with them in cm's per year....

From: jimp on 3 May 2010 15:01

In sci.physics Bret Cahill <BretCahill(a)peoplepc.com> wrote:
>> >String a wire back and forth across / along a fault line to measure
>> >very small displacements in the earth's surface. If the resistance
>> >and/or tensile strength needs to be higher than a common single alloy
>> >wire then structural steel cable could be wrapped around a insulated
>> >wire with a higher resistivity. It could be temperature compensated
>> >as usual, with another wire of the same length loosely supported
>> >nearby in another leg of the bridge.
>>
>> >An abandoned power line may be good to go if it is properly located.
>>
>> >Good info sometimes comes in small displacements.
>>
>> >Bret Cahill
>>
>> You cannot get a good enought temperature (and other factors)
>> compensation with such a setup.
>
> Compensation for temp. and other factors is easy: Just loosely wrap
> another identical wire around the taught wire and shield and insulate
> it for another leg of the bridge.

Wind.

Yet more silly, comic book engineering to solve a problem solved a long
time ago.

The challenge to monitoring such stuff isn't an engineering problem, it is
an economic problem.

--
Jim Pennino

Remove .spam.sux to reply.

From: Cwatters on 3 May 2010 15:44

From: Bob Eld on 3 May 2010 19:42

"Bret Cahill" <BretCahill(a)peoplepc.com> wrote in message
news:dc103c5f-bec3-4b24-afcf-5a02c8eb89ff(a)g5g2000pre.googlegroups.com...
> String a wire back and forth across / along a fault line to measure
> very small displacements in the earth's surface. If the resistance
> and/or tensile strength needs to be higher than a common single alloy
> wire then structural steel cable could be wrapped around a insulated
> wire with a higher resistivity. It could be temperature compensated
> as usual, with another wire of the same length loosely supported
> nearby in another leg of the bridge.
>
> An abandoned power line may be good to go if it is properly located.
>
> Good info sometimes comes in small displacements.
>
>
> Bret Cahill

What you are trying to make is a strain gauge. This scheme wont work because
the gauge has to be attached to the substrate along it's whole length not
just strung up like a power line. But attaching it to the earth in any
meaningful way over distance would be next to impossible. Yes, you can
compensate for the temperature coefficient of resistance but how do you
compensate for the change in length due to temperature, coefficient of
expansion, a very different animal. I can't see a strain gauge being a
solution for seismic motions.

The best way is a laser interferometer for small displacements and GPS or
gross measurements. Only two points need to be attached to the earth with
these schemes.

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